From c664cfddd1c256a990269cd53c0a2038d55d2205 Mon Sep 17 00:00:00 2001
From: Alex Crichton <alex@alexcrichton.com>
Date: Fri, 2 Nov 2018 10:54:00 -0700
Subject: [PATCH] Use a global cache for all downloaded binaries

This commit switches wasm-pack to using a global cache for all download
binaries, living typically in a user's home directory. The intention
here is to aovid creating a `bin` folder in all wasm-pack projects and
additionally share downloads between projects to ensure that you're
downloading a minimal number of binaries from the network.

Along the way the downloading code was restructured to support a global
cache, but everything should largely be as it was before!

Closes #292
---
 Cargo.lock                 | 191 +++++++++++++----
 Cargo.toml                 |   3 +
 src/binaries.rs            | 422 +++++++++++++++++++------------------
 src/bindgen.rs             | 208 +++++++++---------
 src/command/build.rs       |  19 +-
 src/command/test.rs        |  29 +--
 src/lib.rs                 |   3 +
 src/test/webdriver.rs      | 137 +++++-------
 tests/all/bindgen.rs       |  31 ++-
 tests/all/build.rs         |  13 +-
 tests/all/test.rs          |  63 +++---
 tests/all/utils/fixture.rs | 144 +++++--------
 tests/all/webdriver.rs     |   7 +-
 13 files changed, 670 insertions(+), 600 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 7b20a0f..6804bd0 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -5,10 +5,10 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "aho-corasick"
-version = "0.6.8"
+version = "0.6.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "memchr 2.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "memchr 2.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -19,6 +19,23 @@ dependencies = [
  "winapi 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "argon2rs"
+version = "0.2.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "blake2-rfc 0.2.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "scoped_threadpool 0.1.9 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "arrayvec"
+version = "0.4.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "nodrop 0.1.12 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "atty"
 version = "0.2.11"
@@ -55,6 +72,15 @@ name = "bitflags"
 version = "1.0.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "blake2-rfc"
+version = "0.2.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "arrayvec 0.4.7 (registry+https://github.com/rust-lang/crates.io-index)",
+ "constant_time_eq 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "build_const"
 version = "0.2.1"
@@ -62,7 +88,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "byteorder"
-version = "1.2.6"
+version = "1.2.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
@@ -164,6 +190,11 @@ dependencies = [
  "winapi 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "constant_time_eq"
+version = "0.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "crc"
 version = "1.8.1"
@@ -194,13 +225,23 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "cc 1.0.25 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.43 (registry+https://github.com/rust-lang/crates.io-index)",
- "libz-sys 1.0.24 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libz-sys 1.0.25 (registry+https://github.com/rust-lang/crates.io-index)",
  "openssl-sys 0.9.39 (registry+https://github.com/rust-lang/crates.io-index)",
  "pkg-config 0.3.14 (registry+https://github.com/rust-lang/crates.io-index)",
  "vcpkg 0.2.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "winapi 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "dirs"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "libc 0.2.43 (registry+https://github.com/rust-lang/crates.io-index)",
+ "redox_users 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "error-chain"
 version = "0.12.0"
@@ -224,9 +265,9 @@ version = "0.1.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "proc-macro2 0.4.20 (registry+https://github.com/rust-lang/crates.io-index)",
- "quote 0.6.8 (registry+https://github.com/rust-lang/crates.io-index)",
- "syn 0.15.13 (registry+https://github.com/rust-lang/crates.io-index)",
- "synstructure 0.10.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quote 0.6.9 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 0.15.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "synstructure 0.10.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -276,6 +317,19 @@ name = "fuchsia-zircon-sys"
 version = "0.3.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "heck"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "unicode-segmentation 1.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "hex"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "human-panic"
 version = "1.0.1"
@@ -348,7 +402,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "libz-sys"
-version = "1.0.24"
+version = "1.0.25"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "cc 1.0.25 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -368,7 +422,7 @@ dependencies = [
 
 [[package]]
 name = "memchr"
-version = "2.1.0"
+version = "2.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "cfg-if 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -413,6 +467,11 @@ dependencies = [
  "winapi 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "nodrop"
+version = "0.1.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "num-integer"
 version = "0.1.39"
@@ -521,7 +580,7 @@ dependencies = [
 
 [[package]]
 name = "quote"
-version = "0.6.8"
+version = "0.6.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "proc-macro2 0.4.20 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -575,16 +634,27 @@ dependencies = [
  "redox_syscall 0.1.40 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "redox_users"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "argon2rs 0.2.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "failure 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "redox_syscall 0.1.40 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "regex"
 version = "0.2.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "aho-corasick 0.6.8 (registry+https://github.com/rust-lang/crates.io-index)",
- "memchr 2.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "aho-corasick 0.6.9 (registry+https://github.com/rust-lang/crates.io-index)",
+ "memchr 2.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "regex-syntax 0.5.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "thread_local 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
- "utf8-ranges 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "utf8-ranges 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -592,11 +662,11 @@ name = "regex"
 version = "1.0.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "aho-corasick 0.6.8 (registry+https://github.com/rust-lang/crates.io-index)",
- "memchr 2.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "aho-corasick 0.6.9 (registry+https://github.com/rust-lang/crates.io-index)",
+ "memchr 2.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "regex-syntax 0.6.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "thread_local 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
- "utf8-ranges 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "utf8-ranges 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -604,7 +674,7 @@ name = "regex-syntax"
 version = "0.5.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "ucd-util 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "ucd-util 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -612,7 +682,7 @@ name = "regex-syntax"
 version = "0.6.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "ucd-util 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "ucd-util 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -650,6 +720,11 @@ dependencies = [
  "winapi 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "scoped_threadpool"
+version = "0.1.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "scopeguard"
 version = "0.3.3"
@@ -680,8 +755,8 @@ version = "1.0.80"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "proc-macro2 0.4.20 (registry+https://github.com/rust-lang/crates.io-index)",
- "quote 0.6.8 (registry+https://github.com/rust-lang/crates.io-index)",
- "syn 0.15.13 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quote 0.6.9 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 0.15.18 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -694,6 +769,11 @@ dependencies = [
  "serde 1.0.80 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "siphasher"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "slog"
 version = "2.4.1"
@@ -752,41 +832,42 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "structopt"
-version = "0.2.12"
+version = "0.2.13"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "clap 2.32.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "structopt-derive 0.2.12 (registry+https://github.com/rust-lang/crates.io-index)",
+ "structopt-derive 0.2.13 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "structopt-derive"
-version = "0.2.12"
+version = "0.2.13"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
+ "heck 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "proc-macro2 0.4.20 (registry+https://github.com/rust-lang/crates.io-index)",
- "quote 0.6.8 (registry+https://github.com/rust-lang/crates.io-index)",
- "syn 0.15.13 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quote 0.6.9 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 0.15.18 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "syn"
-version = "0.15.13"
+version = "0.15.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "proc-macro2 0.4.20 (registry+https://github.com/rust-lang/crates.io-index)",
- "quote 0.6.8 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quote 0.6.9 (registry+https://github.com/rust-lang/crates.io-index)",
  "unicode-xid 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "synstructure"
-version = "0.10.0"
+version = "0.10.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "proc-macro2 0.4.20 (registry+https://github.com/rust-lang/crates.io-index)",
- "quote 0.6.8 (registry+https://github.com/rust-lang/crates.io-index)",
- "syn 0.15.13 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quote 0.6.9 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 0.15.18 (registry+https://github.com/rust-lang/crates.io-index)",
  "unicode-xid 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -833,7 +914,7 @@ name = "term"
 version = "0.5.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "byteorder 1.2.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "byteorder 1.2.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "winapi 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -899,7 +980,12 @@ dependencies = [
 
 [[package]]
 name = "ucd-util"
-version = "0.1.1"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "unicode-segmentation"
+version = "1.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
@@ -922,7 +1008,7 @@ dependencies = [
 
 [[package]]
 name = "utf8-ranges"
-version = "1.0.1"
+version = "1.0.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
@@ -962,8 +1048,10 @@ dependencies = [
  "cargo_metadata 0.6.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "console 0.6.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "curl 0.4.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "dirs 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "failure 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "flate2 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "hex 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "human-panic 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "indicatif 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "lazy_static 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -972,10 +1060,11 @@ dependencies = [
  "serde 1.0.80 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 1.0.80 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_json 1.0.32 (registry+https://github.com/rust-lang/crates.io-index)",
+ "siphasher 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "slog 2.4.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "slog-async 2.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "slog-term 2.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "structopt 0.2.12 (registry+https://github.com/rust-lang/crates.io-index)",
+ "structopt 0.2.13 (registry+https://github.com/rust-lang/crates.io-index)",
  "tar 0.4.17 (registry+https://github.com/rust-lang/crates.io-index)",
  "tempfile 3.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "toml 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1051,14 +1140,17 @@ dependencies = [
 
 [metadata]
 "checksum adler32 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)" = "7e522997b529f05601e05166c07ed17789691f562762c7f3b987263d2dedee5c"
-"checksum aho-corasick 0.6.8 (registry+https://github.com/rust-lang/crates.io-index)" = "68f56c7353e5a9547cbd76ed90f7bb5ffc3ba09d4ea9bd1d8c06c8b1142eeb5a"
+"checksum aho-corasick 0.6.9 (registry+https://github.com/rust-lang/crates.io-index)" = "1e9a933f4e58658d7b12defcf96dc5c720f20832deebe3e0a19efd3b6aaeeb9e"
 "checksum ansi_term 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ee49baf6cb617b853aa8d93bf420db2383fab46d314482ca2803b40d5fde979b"
+"checksum argon2rs 0.2.5 (registry+https://github.com/rust-lang/crates.io-index)" = "3f67b0b6a86dae6e67ff4ca2b6201396074996379fba2b92ff649126f37cb392"
+"checksum arrayvec 0.4.7 (registry+https://github.com/rust-lang/crates.io-index)" = "a1e964f9e24d588183fcb43503abda40d288c8657dfc27311516ce2f05675aef"
 "checksum atty 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)" = "9a7d5b8723950951411ee34d271d99dddcc2035a16ab25310ea2c8cfd4369652"
 "checksum backtrace 0.3.9 (registry+https://github.com/rust-lang/crates.io-index)" = "89a47830402e9981c5c41223151efcced65a0510c13097c769cede7efb34782a"
 "checksum backtrace-sys 0.1.24 (registry+https://github.com/rust-lang/crates.io-index)" = "c66d56ac8dabd07f6aacdaf633f4b8262f5b3601a810a0dcddffd5c22c69daa0"
 "checksum bitflags 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)" = "228047a76f468627ca71776ecdebd732a3423081fcf5125585bcd7c49886ce12"
+"checksum blake2-rfc 0.2.18 (registry+https://github.com/rust-lang/crates.io-index)" = "5d6d530bdd2d52966a6d03b7a964add7ae1a288d25214066fd4b600f0f796400"
 "checksum build_const 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "39092a32794787acd8525ee150305ff051b0aa6cc2abaf193924f5ab05425f39"
-"checksum byteorder 1.2.6 (registry+https://github.com/rust-lang/crates.io-index)" = "90492c5858dd7d2e78691cfb89f90d273a2800fc11d98f60786e5d87e2f83781"
+"checksum byteorder 1.2.7 (registry+https://github.com/rust-lang/crates.io-index)" = "94f88df23a25417badc922ab0f5716cc1330e87f71ddd9203b3a3ccd9cedf75d"
 "checksum bzip2 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "42b7c3cbf0fa9c1b82308d57191728ca0256cb821220f4e2fd410a72ade26e3b"
 "checksum bzip2-sys 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)" = "2c5162604199bbb17690ede847eaa6120a3f33d5ab4dcc8e7c25b16d849ae79b"
 "checksum cargo_metadata 0.6.1 (registry+https://github.com/rust-lang/crates.io-index)" = "1aaa1a9856ae2d188340526d0986feb6899c9ad11c5dfd73453c784fed6e373d"
@@ -1069,9 +1161,11 @@ dependencies = [
 "checksum clicolors-control 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "1f84dec9bc083ce2503908cd305af98bd363da6f54bf8d4bf0ac14ee749ad5d1"
 "checksum cloudabi 0.0.3 (registry+https://github.com/rust-lang/crates.io-index)" = "ddfc5b9aa5d4507acaf872de71051dfd0e309860e88966e1051e462a077aac4f"
 "checksum console 0.6.2 (registry+https://github.com/rust-lang/crates.io-index)" = "ecd48adf136733979b49e15bc3b4c43cc0d3c85ece7bd08e6daa414c6fcb13e6"
+"checksum constant_time_eq 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)" = "8ff012e225ce166d4422e0e78419d901719760f62ae2b7969ca6b564d1b54a9e"
 "checksum crc 1.8.1 (registry+https://github.com/rust-lang/crates.io-index)" = "d663548de7f5cca343f1e0a48d14dcfb0e9eb4e079ec58883b7251539fa10aeb"
 "checksum curl 0.4.18 (registry+https://github.com/rust-lang/crates.io-index)" = "a9e5285b49b44401518c947d3b808d14d99a538a6c9ffb3ec0205c11f9fc4389"
 "checksum curl-sys 0.4.13 (registry+https://github.com/rust-lang/crates.io-index)" = "08459503c415173da1ce6b41036a37b8bfdd86af46d45abb9964d4c61fe670ef"
+"checksum dirs 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)" = "88972de891f6118092b643d85a0b28e0678e0f948d7f879aa32f2d5aafe97d2a"
 "checksum error-chain 0.12.0 (registry+https://github.com/rust-lang/crates.io-index)" = "07e791d3be96241c77c43846b665ef1384606da2cd2a48730abe606a12906e02"
 "checksum failure 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)" = "6dd377bcc1b1b7ce911967e3ec24fa19c3224394ec05b54aa7b083d498341ac7"
 "checksum failure_derive 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)" = "64c2d913fe8ed3b6c6518eedf4538255b989945c14c2a7d5cbff62a5e2120596"
@@ -1081,6 +1175,8 @@ dependencies = [
 "checksum foreign-types-shared 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "00b0228411908ca8685dba7fc2cdd70ec9990a6e753e89b6ac91a84c40fbaf4b"
 "checksum fuchsia-zircon 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "2e9763c69ebaae630ba35f74888db465e49e259ba1bc0eda7d06f4a067615d82"
 "checksum fuchsia-zircon-sys 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "3dcaa9ae7725d12cdb85b3ad99a434db70b468c09ded17e012d86b5c1010f7a7"
+"checksum heck 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ea04fa3ead4e05e51a7c806fc07271fdbde4e246a6c6d1efd52e72230b771b82"
+"checksum hex 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)" = "805026a5d0141ffc30abb3be3173848ad46a1b1664fe632428479619a3644d77"
 "checksum human-panic 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "21638c5955a6daf3ecc42cae702335fc37a72a4abcc6959ce457b31a7d43bbdd"
 "checksum indicatif 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "a29b2fa6f00010c268bface64c18bb0310aaa70d46a195d5382d288c477fb016"
 "checksum isatty 0.1.9 (registry+https://github.com/rust-lang/crates.io-index)" = "e31a8281fc93ec9693494da65fbf28c0c2aa60a2eaec25dc58e2f31952e95edc"
@@ -1089,13 +1185,14 @@ dependencies = [
 "checksum lazy_static 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)" = "76f033c7ad61445c5b347c7382dd1237847eb1bce590fe50365dcb33d546be73"
 "checksum lazy_static 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ca488b89a5657b0a2ecd45b95609b3e848cf1755da332a0da46e2b2b1cb371a7"
 "checksum libc 0.2.43 (registry+https://github.com/rust-lang/crates.io-index)" = "76e3a3ef172f1a0b9a9ff0dd1491ae5e6c948b94479a3021819ba7d860c8645d"
-"checksum libz-sys 1.0.24 (registry+https://github.com/rust-lang/crates.io-index)" = "4401fe74560a0d46fce3464625ac8aa7a79d291dd28cee021d18852d5191c280"
+"checksum libz-sys 1.0.25 (registry+https://github.com/rust-lang/crates.io-index)" = "2eb5e43362e38e2bca2fd5f5134c4d4564a23a5c28e9b95411652021a8675ebe"
 "checksum lock_api 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)" = "775751a3e69bde4df9b38dd00a1b5d6ac13791e4223d4a0506577f0dd27cfb7a"
-"checksum memchr 2.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "4b3629fe9fdbff6daa6c33b90f7c08355c1aca05a3d01fa8063b822fcf185f3b"
+"checksum memchr 2.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "0a3eb002f0535929f1199681417029ebea04aadc0c7a4224b46be99c7f5d6a16"
 "checksum miniz-sys 0.1.11 (registry+https://github.com/rust-lang/crates.io-index)" = "0300eafb20369952951699b68243ab4334f4b10a88f411c221d444b36c40e649"
 "checksum miniz_oxide 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "5ad30a47319c16cde58d0314f5d98202a80c9083b5f61178457403dfb14e509c"
 "checksum miniz_oxide_c_api 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "28edaef377517fd9fe3e085c37d892ce7acd1fbeab9239c5a36eec352d8a8b7e"
 "checksum msdos_time 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)" = "aad9dfe950c057b1bfe9c1f2aa51583a8468ef2a5baba2ebbe06d775efeb7729"
+"checksum nodrop 0.1.12 (registry+https://github.com/rust-lang/crates.io-index)" = "9a2228dca57108069a5262f2ed8bd2e82496d2e074a06d1ccc7ce1687b6ae0a2"
 "checksum num-integer 0.1.39 (registry+https://github.com/rust-lang/crates.io-index)" = "e83d528d2677f0518c570baf2b7abdcf0cd2d248860b68507bdcb3e91d4c0cea"
 "checksum num-traits 0.2.6 (registry+https://github.com/rust-lang/crates.io-index)" = "0b3a5d7cc97d6d30d8b9bc8fa19bf45349ffe46241e8816f50f62f6d6aaabee1"
 "checksum openssl 0.10.15 (registry+https://github.com/rust-lang/crates.io-index)" = "5e1309181cdcbdb51bc3b6bedb33dfac2a83b3d585033d3f6d9e22e8c1928613"
@@ -1109,13 +1206,14 @@ dependencies = [
 "checksum pkg-config 0.3.14 (registry+https://github.com/rust-lang/crates.io-index)" = "676e8eb2b1b4c9043511a9b7bea0915320d7e502b0a079fb03f9635a5252b18c"
 "checksum podio 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)" = "780fb4b6698bbf9cf2444ea5d22411cef2953f0824b98f33cf454ec5615645bd"
 "checksum proc-macro2 0.4.20 (registry+https://github.com/rust-lang/crates.io-index)" = "3d7b7eaaa90b4a90a932a9ea6666c95a389e424eff347f0f793979289429feee"
-"checksum quote 0.6.8 (registry+https://github.com/rust-lang/crates.io-index)" = "dd636425967c33af890042c483632d33fa7a18f19ad1d7ea72e8998c6ef8dea5"
+"checksum quote 0.6.9 (registry+https://github.com/rust-lang/crates.io-index)" = "63b5829244f52738cfee93b3a165c1911388675be000c888d2fae620dee8fa5b"
 "checksum rand 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)" = "8356f47b32624fef5b3301c1be97e5944ecdd595409cc5da11d05f211db6cfbd"
 "checksum rand 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)" = "e464cd887e869cddcae8792a4ee31d23c7edd516700695608f5b98c67ee0131c"
 "checksum rand_core 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "1961a422c4d189dfb50ffa9320bf1f2a9bd54ecb92792fb9477f99a1045f3372"
 "checksum rand_core 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "0905b6b7079ec73b314d4c748701f6931eb79fd97c668caa3f1899b22b32c6db"
 "checksum redox_syscall 0.1.40 (registry+https://github.com/rust-lang/crates.io-index)" = "c214e91d3ecf43e9a4e41e578973adeb14b474f2bee858742d127af75a0112b1"
 "checksum redox_termios 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "7e891cfe48e9100a70a3b6eb652fef28920c117d366339687bd5576160db0f76"
+"checksum redox_users 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "214a97e49be64fd2c86f568dd0cb2c757d2cc53de95b273b6ad0a1c908482f26"
 "checksum regex 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)" = "9329abc99e39129fcceabd24cf5d85b4671ef7c29c50e972bc5afe32438ec384"
 "checksum regex 1.0.5 (registry+https://github.com/rust-lang/crates.io-index)" = "2069749032ea3ec200ca51e4a31df41759190a88edca0d2d86ee8bedf7073341"
 "checksum regex-syntax 0.5.6 (registry+https://github.com/rust-lang/crates.io-index)" = "7d707a4fa2637f2dca2ef9fd02225ec7661fe01a53623c1e6515b6916511f7a7"
@@ -1125,12 +1223,14 @@ dependencies = [
 "checksum rustc_version 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "138e3e0acb6c9fb258b19b67cb8abd63c00679d2851805ea151465464fe9030a"
 "checksum ryu 0.2.6 (registry+https://github.com/rust-lang/crates.io-index)" = "7153dd96dade874ab973e098cb62fcdbb89a03682e46b144fd09550998d4a4a7"
 "checksum schannel 0.1.14 (registry+https://github.com/rust-lang/crates.io-index)" = "0e1a231dc10abf6749cfa5d7767f25888d484201accbd919b66ab5413c502d56"
+"checksum scoped_threadpool 0.1.9 (registry+https://github.com/rust-lang/crates.io-index)" = "1d51f5df5af43ab3f1360b429fa5e0152ac5ce8c0bd6485cae490332e96846a8"
 "checksum scopeguard 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "94258f53601af11e6a49f722422f6e3425c52b06245a5cf9bc09908b174f5e27"
 "checksum semver 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "1d7eb9ef2c18661902cc47e535f9bc51b78acd254da71d375c2f6720d9a40403"
 "checksum semver-parser 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "388a1df253eca08550bef6c72392cfe7c30914bf41df5269b68cbd6ff8f570a3"
 "checksum serde 1.0.80 (registry+https://github.com/rust-lang/crates.io-index)" = "15c141fc7027dd265a47c090bf864cf62b42c4d228bbcf4e51a0c9e2b0d3f7ef"
 "checksum serde_derive 1.0.80 (registry+https://github.com/rust-lang/crates.io-index)" = "225de307c6302bec3898c51ca302fc94a7a1697ef0845fcee6448f33c032249c"
 "checksum serde_json 1.0.32 (registry+https://github.com/rust-lang/crates.io-index)" = "43344e7ce05d0d8280c5940cabb4964bea626aa58b1ec0e8c73fa2a8512a38ce"
+"checksum siphasher 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "0b8de496cf83d4ed58b6be86c3a275b8602f6ffe98d3024a869e124147a9a3ac"
 "checksum slog 2.4.1 (registry+https://github.com/rust-lang/crates.io-index)" = "1e1a2eec401952cd7b12a84ea120e2d57281329940c3f93c2bf04f462539508e"
 "checksum slog-async 2.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "e544d16c6b230d84c866662fe55e31aacfca6ae71e6fc49ae9a311cb379bfc2f"
 "checksum slog-term 2.4.0 (registry+https://github.com/rust-lang/crates.io-index)" = "5951a808c40f419922ee014c15b6ae1cd34d963538b57d8a4778b9ca3fff1e0b"
@@ -1138,10 +1238,10 @@ dependencies = [
 "checksum socket2 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)" = "c4d11a52082057d87cb5caa31ad812f4504b97ab44732cd8359df2e9ff9f48e7"
 "checksum stable_deref_trait 1.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "dba1a27d3efae4351c8051072d619e3ade2820635c3958d826bfea39d59b54c8"
 "checksum strsim 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "bb4f380125926a99e52bc279241539c018323fab05ad6368b56f93d9369ff550"
-"checksum structopt 0.2.12 (registry+https://github.com/rust-lang/crates.io-index)" = "d77af7242f18c40fd19cb270985930f239ee1646cfb482050bbae9da1d18743b"
-"checksum structopt-derive 0.2.12 (registry+https://github.com/rust-lang/crates.io-index)" = "17ff01fe96de9d16e7372ae5f19dd7ece2c703b51043c3db9ea27f9e393ea311"
-"checksum syn 0.15.13 (registry+https://github.com/rust-lang/crates.io-index)" = "7b4439ee8325b4e4b57e59309c3724c9a4478eaeb4eb094b6f3fac180a3b2876"
-"checksum synstructure 0.10.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ec37f4fab4bafaf6b5621c1d54e6aa5d4d059a8f84929e87abfdd7f9f04c6db2"
+"checksum structopt 0.2.13 (registry+https://github.com/rust-lang/crates.io-index)" = "41c4a2479a078509940d82773d90ff824a8c89533ab3b59cd3ce8b0c0e369c02"
+"checksum structopt-derive 0.2.13 (registry+https://github.com/rust-lang/crates.io-index)" = "5352090cfae7a2c85e1a31146268b53396106c88ca5d6ccee2e3fae83b6e35c2"
+"checksum syn 0.15.18 (registry+https://github.com/rust-lang/crates.io-index)" = "90c39a061e2f412a9f869540471ab679e85e50c6b05604daf28bc3060f75c430"
+"checksum synstructure 0.10.1 (registry+https://github.com/rust-lang/crates.io-index)" = "73687139bf99285483c96ac0add482c3776528beac1d97d444f6e91f203a2015"
 "checksum take_mut 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "f764005d11ee5f36500a149ace24e00e3da98b0158b3e2d53a7495660d3f4d60"
 "checksum tar 0.4.17 (registry+https://github.com/rust-lang/crates.io-index)" = "83b0d14b53dbfd62681933fadd651e815f99e6084b649e049ab99296e05ab3de"
 "checksum tempdir 0.3.7 (registry+https://github.com/rust-lang/crates.io-index)" = "15f2b5fb00ccdf689e0149d1b1b3c03fead81c2b37735d812fa8bddbbf41b6d8"
@@ -1154,11 +1254,12 @@ dependencies = [
 "checksum thread_local 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)" = "c6b53e329000edc2b34dbe8545fd20e55a333362d0a321909685a19bd28c3f1b"
 "checksum time 0.1.40 (registry+https://github.com/rust-lang/crates.io-index)" = "d825be0eb33fda1a7e68012d51e9c7f451dc1a69391e7fdc197060bb8c56667b"
 "checksum toml 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)" = "4a2ecc31b0351ea18b3fe11274b8db6e4d82bce861bbb22e6dbed40417902c65"
-"checksum ucd-util 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "fd2be2d6639d0f8fe6cdda291ad456e23629558d466e2789d2c3e9892bda285d"
+"checksum ucd-util 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "d0f8bfa9ff0cadcd210129ad9d2c5f145c13e9ced3d3e5d948a6213487d52444"
+"checksum unicode-segmentation 1.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "aa6024fc12ddfd1c6dbc14a80fa2324d4568849869b779f6bd37e5e4c03344d1"
 "checksum unicode-width 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)" = "882386231c45df4700b275c7ff55b6f3698780a650026380e72dabe76fa46526"
 "checksum unicode-xid 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "fc72304796d0818e357ead4e000d19c9c174ab23dc11093ac919054d20a6a7fc"
 "checksum unreachable 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "382810877fe448991dfc7f0dd6e3ae5d58088fd0ea5e35189655f84e6814fa56"
-"checksum utf8-ranges 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "fd70f467df6810094968e2fce0ee1bd0e87157aceb026a8c083bcf5e25b9efe4"
+"checksum utf8-ranges 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)" = "796f7e48bef87609f7ade7e06495a87d5cd06c7866e6a5cbfceffc558a243737"
 "checksum uuid 0.6.5 (registry+https://github.com/rust-lang/crates.io-index)" = "e1436e58182935dcd9ce0add9ea0b558e8a87befe01c1a301e6020aeb0876363"
 "checksum vcpkg 0.2.6 (registry+https://github.com/rust-lang/crates.io-index)" = "def296d3eb3b12371b2c7d0e83bfe1403e4db2d7a0bba324a12b21c4ee13143d"
 "checksum vec_map 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)" = "05c78687fb1a80548ae3250346c3db86a80a7cdd77bda190189f2d0a0987c81a"
diff --git a/Cargo.toml b/Cargo.toml
index 56392cf..b486071 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -14,8 +14,10 @@ atty = "0.2.11"
 cargo_metadata = "0.6.0"
 console = "0.6.1"
 curl = "0.4.13"
+dirs = "1.0.4"
 failure = "0.1.2"
 flate2 = "1.0.2"
+hex = "0.3"
 human-panic = "1.0.1"
 indicatif = "0.9.0"
 lazy_static = "1.1.0"
@@ -24,6 +26,7 @@ parking_lot = "0.6"
 serde = "1.0.74"
 serde_derive = "1.0.74"
 serde_json = "1.0.26"
+siphasher = "0.2.3"
 slog = "2.3"
 slog-term = "2.4"
 slog-async = "2.3"
diff --git a/src/binaries.rs b/src/binaries.rs
index ba7a1ec..a34c872 100644
--- a/src/binaries.rs
+++ b/src/binaries.rs
@@ -1,247 +1,257 @@
 //! Utilities for finding and installing binaries that we depend on.
 
 use curl;
-use error::Error;
-use failure;
+use dirs;
+use failure::{Error, ResultExt};
 use flate2;
-use slog::Logger;
+use hex;
+use siphasher::sip::SipHasher13;
 use std::collections::HashSet;
+use std::env;
 use std::ffi;
 use std::fs;
+use std::hash::{Hash, Hasher};
 use std::io;
 use std::path::{Path, PathBuf};
 use tar;
-use target;
-use which::which;
 use zip;
 
-/// Get the path for a crate's directory of locally-installed binaries.
-///
-/// This does not check whether or ensure that the directory exists.
-pub fn local_bin_dir(crate_path: &Path) -> PathBuf {
-    crate_path.join("bin")
+/// Global cache for wasm-pack, currently containing binaries downloaded from
+/// urls like wasm-bindgen and such.
+pub struct Cache {
+    destination: PathBuf,
 }
 
-/// Ensure that the crate's directory for locally-installed binaries exists.
-pub fn ensure_local_bin_dir(crate_path: &Path) -> io::Result<()> {
-    fs::create_dir_all(local_bin_dir(crate_path))
+/// Representation of a downloaded tarball/zip
+pub struct Download {
+    root: PathBuf,
 }
 
-/// Get the path for where `bin` would be if we have a crate-local install for
-/// it.
-///
-/// This does *not* check whether there is a file at that path or not.
-///
-/// This will automatically add the `.exe` extension for windows.
-pub fn local_bin_path(crate_path: &Path, bin: &str) -> PathBuf {
-    let mut p = local_bin_dir(crate_path).join(bin);
-    if target::WINDOWS {
-        p.set_extension("exe");
+impl Cache {
+    /// Returns the global cache directory, as inferred from env vars and such.
+    ///
+    /// This function may return an error if a cache directory cannot be
+    /// determined.
+    pub fn new() -> Result<Cache, Error> {
+        let destination = dirs::cache_dir()
+            .map(|p| p.join("wasm-pack"))
+            .or_else(|| {
+                let home = dirs::home_dir()?;
+                Some(home.join(".wasm-pack"))
+            })
+            .ok_or_else(|| format_err!("couldn't find your home directory, is $HOME not set?"))?;
+        Ok(Cache::at(&destination))
     }
-    p
-}
 
-/// Get the local (at `$CRATE/bin/$BIN`; preferred) or global (on `$PATH`) path
-/// for the given binary.
-///
-/// If this function returns `Some(path)`, then a file at that path exists (or
-/// at least existed when we checked! In general, we aren't really worried about
-/// racing with an uninstall of a tool that we rely on.)
-pub fn bin_path(log: &Logger, crate_path: &Path, bin: &str) -> Option<PathBuf> {
-    assert!(!bin.ends_with(".exe"));
-    debug!(log, "Searching for {} binary...", bin);
-
-    // Return the path to the local binary, if it exists.
-    let local_path = |crate_path: &Path| -> Option<PathBuf> {
-        let p = local_bin_path(crate_path, bin);
-        debug!(log, "Checking for local {} binary at {}", bin, p.display());
-        if p.is_file() {
-            Some(p)
-        } else {
-            None
+    /// Creates a new cache specifically at a particular directory, useful in
+    /// testing and such.
+    pub fn at(path: &Path) -> Cache {
+        Cache {
+            destination: path.to_path_buf(),
         }
-    };
+    }
 
-    // Return the path to the global binary, if it exists.
-    let global_path = || -> Option<PathBuf> {
-        debug!(log, "Looking for global {} binary on $PATH", bin);
-        if let Ok(p) = which(bin) {
-            Some(p)
-        } else {
-            None
+    /// Joins a path to the destination of this cache, returning the result
+    pub fn join(&self, path: &Path) -> PathBuf {
+        self.destination.join(path)
+    }
+
+    /// Downloads a tarball or zip file from the specified url, extracting it
+    /// locally and returning the directory that the contents were extracted
+    /// into.
+    ///
+    /// Note that this function requries that the contents of `url` never change
+    /// as the contents of the url are globally cached on the system and never
+    /// invalidated.
+    ///
+    /// The `name` is a human-readable name used to go into the folder name of
+    /// the destination, and `binaries` is a list of binaries expected to be at
+    /// the url. If the URL's extraction doesn't contain all the binaries this
+    /// function will return an error.
+    pub fn download(
+        &self,
+        install_permitted: bool,
+        name: &str,
+        binaries: &[&str],
+        url: &str,
+    ) -> Result<Option<Download>, Error> {
+        let mut hasher = SipHasher13::new();
+        url.hash(&mut hasher);
+        let result = hasher.finish();
+        let hex = hex::encode(&[
+            (result >> 0) as u8,
+            (result >> 8) as u8,
+            (result >> 16) as u8,
+            (result >> 24) as u8,
+            (result >> 32) as u8,
+            (result >> 40) as u8,
+            (result >> 48) as u8,
+            (result >> 56) as u8,
+        ]);
+        let dirname = format!("{}-{}", name, hex);
+
+        let destination = self.destination.join(&dirname);
+        if destination.exists() {
+            return Ok(Some(Download { root: destination }));
         }
-    };
-
-    local_path(crate_path)
-        .or_else(global_path)
-        .map(|p| {
-            let p = p.canonicalize().unwrap_or(p);
-            debug!(log, "Using {} binary at {}", bin, p.display());
-            p
-        })
-        .or_else(|| {
-            debug!(log, "Could not find {} binary.", bin);
-            None
-        })
-}
 
-fn with_url_context<T, E>(url: &str, r: Result<T, E>) -> Result<T, impl failure::Fail>
-where
-    Result<T, E>: failure::ResultExt<T, E>,
-{
-    use failure::ResultExt;
-    r.with_context(|_| format!("when requesting {}", url))
-}
+        if !install_permitted {
+            return Ok(None);
+        }
 
-fn transfer(
-    url: &str,
-    easy: &mut curl::easy::Easy,
-    data: &mut Vec<u8>,
-) -> Result<(), failure::Error> {
-    let mut transfer = easy.transfer();
-    with_url_context(
-        url,
-        transfer.write_function(|part| {
-            data.extend_from_slice(part);
-            Ok(part.len())
-        }),
-    )?;
-    with_url_context(url, transfer.perform())?;
-    Ok(())
-}
+        let data = curl(&url).with_context(|_| format!("failed to download from {}", url))?;
 
-fn curl(url: &str) -> Result<Vec<u8>, failure::Error> {
-    let mut data = Vec::new();
+        // Extract everything in a temporary directory in case we're ctrl-c'd.
+        // Don't want to leave around corrupted data!
+        let temp = self.destination.join(&format!(".{}", dirname));
+        drop(fs::remove_dir_all(&temp));
+        fs::create_dir_all(&temp)?;
 
-    let mut easy = curl::easy::Easy::new();
-    with_url_context(url, easy.follow_location(true))?;
-    with_url_context(url, easy.url(url))?;
-    transfer(url, &mut easy, &mut data)?;
+        if url.ends_with(".tar.gz") {
+            self.extract_tarball(&data, &temp, binaries)
+                .with_context(|_| format!("failed to extract tarball from {}", url))?;
+        } else if url.ends_with(".zip") {
+            self.extract_zip(&data, &temp, binaries)
+                .with_context(|_| format!("failed to extract zip from {}", url))?;
+        } else {
+            // panic instead of runtime error as it's a static violation to
+            // download a different kind of url, all urls should be encoded into
+            // the binary anyway
+            panic!("don't know how to extract {}", url)
+        }
 
-    let status_code = with_url_context(url, easy.response_code())?;
-    if 200 <= status_code && status_code < 300 {
-        Ok(data)
-    } else {
-        Err(Error::http(&format!(
-            "received a bad HTTP status code ({}) when requesting {}",
-            status_code, url
-        ))
-        .into())
+        // Now that everything is ready move this over to our destination and
+        // we're good to go.
+        fs::rename(&temp, &destination)?;
+        Ok(Some(Download { root: destination }))
     }
-}
 
-/// Download the `.tar.gz` file at the given URL and unpack the given binaries
-/// from it into the given crate.
-///
-/// Upon success, every `$BIN` in `binaries` will be at `$CRATE/bin/$BIN`.
-pub fn install_binaries_from_targz_at_url<'a, I>(
-    crate_path: &Path,
-    url: &str,
-    binaries: I,
-) -> Result<(), failure::Error>
-where
-    I: IntoIterator<Item = &'a str>,
-{
-    let mut binaries: HashSet<_> = binaries.into_iter().map(ffi::OsStr::new).collect();
-
-    let tarball = curl(&url).map_err(|e| Error::http(&e.to_string()))?;
-    let mut archive = tar::Archive::new(flate2::read::GzDecoder::new(&tarball[..]));
-
-    ensure_local_bin_dir(crate_path)?;
-    let bin = local_bin_dir(crate_path);
-
-    for entry in archive.entries()? {
-        let mut entry = entry?;
-
-        let dest = match entry.path()?.file_stem() {
-            Some(f) if binaries.contains(f) => {
-                binaries.remove(f);
-                bin.join(entry.path()?.file_name().unwrap())
-            }
-            _ => continue,
-        };
-
-        entry.unpack(dest)?;
-    }
+    fn extract_tarball(&self, tarball: &[u8], dst: &Path, binaries: &[&str]) -> Result<(), Error> {
+        let mut binaries: HashSet<_> = binaries.into_iter().map(ffi::OsStr::new).collect();
+        let mut archive = tar::Archive::new(flate2::read::GzDecoder::new(tarball));
+
+        for entry in archive.entries()? {
+            let mut entry = entry?;
+
+            let dest = match entry.path()?.file_stem() {
+                Some(f) if binaries.contains(f) => {
+                    binaries.remove(f);
+                    dst.join(entry.path()?.file_name().unwrap())
+                }
+                _ => continue,
+            };
+
+            entry.unpack(dest)?;
+        }
+
+        if !binaries.is_empty() {
+            bail!(
+                "the tarball was missing expected executables: {}",
+                binaries
+                    .into_iter()
+                    .map(|s| s.to_string_lossy())
+                    .collect::<Vec<_>>()
+                    .join(", "),
+            )
+        }
 
-    if binaries.is_empty() {
         Ok(())
-    } else {
-        Err(Error::archive(&format!(
-            "the tarball at {} was missing expected executables: {}",
-            url,
-            binaries
-                .into_iter()
-                .map(|s| s.to_string_lossy())
-                .collect::<Vec<_>>()
-                .join(", "),
-        ))
-        .into())
+    }
+
+    fn extract_zip(&self, zip: &[u8], dst: &Path, binaries: &[&str]) -> Result<(), Error> {
+        let mut binaries: HashSet<_> = binaries.into_iter().map(ffi::OsStr::new).collect();
+
+        let data = io::Cursor::new(zip);
+        let mut zip = zip::ZipArchive::new(data)?;
+
+        for i in 0..zip.len() {
+            let mut entry = zip.by_index(i).unwrap();
+            let entry_path = entry.sanitized_name();
+            match entry_path.file_stem() {
+                Some(f) if binaries.contains(f) => {
+                    binaries.remove(f);
+                    let mut dest = bin_open_options()
+                        .write(true)
+                        .create_new(true)
+                        .open(dst.join(entry_path.file_name().unwrap()))?;
+                    io::copy(&mut entry, &mut dest)?;
+                }
+                _ => continue,
+            };
+        }
+
+        if !binaries.is_empty() {
+            bail!(
+                "the zip was missing expected executables: {}",
+                binaries
+                    .into_iter()
+                    .map(|s| s.to_string_lossy())
+                    .collect::<Vec<_>>()
+                    .join(", "),
+            )
+        }
+
+        return Ok(());
+
+        #[cfg(unix)]
+        fn bin_open_options() -> fs::OpenOptions {
+            use std::os::unix::fs::OpenOptionsExt;
+
+            let mut opts = fs::OpenOptions::new();
+            opts.mode(0o755);
+            opts
+        }
+
+        #[cfg(not(unix))]
+        fn bin_open_options() -> fs::OpenOptions {
+            fs::OpenOptions::new()
+        }
     }
 }
 
-/// Install binaries from within the given zip at the given URL.
-///
-/// Upon success, the binaries will be at the `$CRATE/bin/$BIN` path.
-pub fn install_binaries_from_zip_at_url<'a, I>(
-    crate_path: &Path,
-    url: &str,
-    binaries: I,
-) -> Result<(), failure::Error>
-where
-    I: IntoIterator<Item = &'a str>,
-{
-    let mut binaries: HashSet<_> = binaries.into_iter().map(ffi::OsStr::new).collect();
-
-    let data = curl(&url).map_err(|e| Error::http(&e.to_string()))?;
-    let data = io::Cursor::new(data);
-    let mut zip = zip::ZipArchive::new(data)?;
-
-    ensure_local_bin_dir(crate_path)?;
-    let bin = local_bin_dir(crate_path);
-
-    for i in 0..zip.len() {
-        let mut entry = zip.by_index(i).unwrap();
-        let entry_path = entry.sanitized_name();
-        match entry_path.file_stem() {
-            Some(f) if binaries.contains(f) => {
-                binaries.remove(f);
-                let mut dest = bin_open_options()
-                    .write(true)
-                    .create_new(true)
-                    .open(bin.join(entry_path.file_name().unwrap()))?;
-                io::copy(&mut entry, &mut dest)?;
-            }
-            _ => continue,
-        };
+impl Download {
+    /// Manually constructs a download at the specified path
+    pub fn at(path: &Path) -> Download {
+        Download {
+            root: path.to_path_buf(),
+        }
     }
 
-    if binaries.is_empty() {
-        Ok(())
-    } else {
-        Err(Error::archive(&format!(
-            "the zip at {} was missing expected executables: {}",
-            url,
-            binaries
-                .into_iter()
-                .map(|s| s.to_string_lossy())
-                .collect::<Vec<_>>()
-                .join(", "),
-        ))
-        .into())
+    /// Returns the path to the binary `name` within this download
+    pub fn binary(&self, name: &str) -> PathBuf {
+        let ret = self
+            .root
+            .join(name)
+            .with_extension(env::consts::EXE_EXTENSION);
+        assert!(ret.exists(), "binary {} doesn't exist", ret.display());
+        return ret;
     }
 }
 
-#[cfg(unix)]
-fn bin_open_options() -> fs::OpenOptions {
-    use std::os::unix::fs::OpenOptionsExt;
+fn curl(url: &str) -> Result<Vec<u8>, Error> {
+    let mut data = Vec::new();
 
-    let mut opts = fs::OpenOptions::new();
-    opts.mode(0o755);
-    opts
-}
+    let mut easy = curl::easy::Easy::new();
+    easy.follow_location(true)?;
+    easy.url(url)?;
+    easy.get(true)?;
+    {
+        let mut transfer = easy.transfer();
+        transfer.write_function(|part| {
+            data.extend_from_slice(part);
+            Ok(part.len())
+        })?;
+        transfer.perform()?;
+    }
 
-#[cfg(not(unix))]
-fn bin_open_options() -> fs::OpenOptions {
-    fs::OpenOptions::new()
+    let status_code = easy.response_code()?;
+    if 200 <= status_code && status_code < 300 {
+        Ok(data)
+    } else {
+        bail!(
+            "received a bad HTTP status code ({}) when requesting {}",
+            status_code,
+            url
+        )
+    }
 }
diff --git a/src/bindgen.rs b/src/bindgen.rs
index 296e4ab..46ce8a4 100644
--- a/src/bindgen.rs
+++ b/src/bindgen.rs
@@ -1,16 +1,17 @@
 //! Functionality related to installing and running `wasm-bindgen`.
 
-use binaries::{self, bin_path, install_binaries_from_targz_at_url};
+use binaries::{Cache, Download};
 use cargo_metadata;
 use child;
 use emoji;
-use error::Error;
 use failure::{self, ResultExt};
 use progressbar::Step;
 use slog::Logger;
+use std::fs;
 use std::path::{Path, PathBuf};
 use std::process::Command;
 use target;
+use which::which;
 use PBAR;
 
 /// Install the `wasm-bindgen` CLI.
@@ -20,46 +21,66 @@ use PBAR;
 /// tarball from the GitHub releases page, if this target has prebuilt
 /// binaries. Finally, falls back to `cargo install`.
 pub fn install_wasm_bindgen(
-    root_path: &Path,
+    cache: &Cache,
     version: &str,
     install_permitted: bool,
     step: &Step,
     log: &Logger,
-) -> Result<(), failure::Error> {
-    // If the `wasm-bindgen` dependency is already met, print a message and return.
-    if wasm_bindgen_path(log, root_path)
-        .map(|bindgen_path| wasm_bindgen_version_check(&bindgen_path, version, log))
-        .unwrap_or(false)
-    {
-        let msg = format!("{}wasm-bindgen already installed...", emoji::DOWN_ARROW);
-        PBAR.step(step, &msg);
-        return Ok(());
-    }
-
-    // If the `wasm-bindgen` dependency was not met, and installs are not
-    // permitted, return a configuration error.
-    if !install_permitted {
-        let msg = format!("wasm-bindgen v{} is not installed!", version);
-        return Err(Error::crate_config(&msg).into());
+) -> Result<Download, failure::Error> {
+    // If `wasm-bindgen` is installed globally and it has the right version, use
+    // that. Assume that other tools are installed next to it.
+    //
+    // This situation can arise if `wasm-bindgen` is already installed via
+    // `cargo install`, for example.
+    if let Ok(path) = which("wasm-bindgen") {
+        debug!(
+            log,
+            "found global wasm-bindgen binary at: {}",
+            path.display()
+        );
+        if wasm_bindgen_version_check(&path, version, log) {
+            return Ok(Download::at(path.parent().unwrap()));
+        }
     }
 
     let msg = format!("{}Installing wasm-bindgen...", emoji::DOWN_ARROW);
     PBAR.step(step, &msg);
 
-    download_prebuilt_wasm_bindgen(root_path, version).or_else(|e| {
-        warn!(
-            log,
-            "could not download pre-built `wasm-bindgen`: {}. Falling back to `cargo install`.", e
-        );
-        cargo_install_wasm_bindgen(log, root_path, version)
-    })
+    let dl = download_prebuilt_wasm_bindgen(&cache, version, install_permitted);
+    match dl {
+        Ok(dl) => return Ok(dl),
+        Err(e) => {
+            warn!(
+                log,
+                "could not download pre-built `wasm-bindgen`: {}. Falling back to `cargo install`.",
+                e
+            );
+        }
+    }
+
+    cargo_install_wasm_bindgen(log, &cache, version, install_permitted)
 }
 
-/// Download a tarball containing a pre-built `wasm-bindgen` binary.
+/// Downloads a precompiled copy of wasm-bindgen, if available.
 pub fn download_prebuilt_wasm_bindgen(
-    root_path: &Path,
+    cache: &Cache,
     version: &str,
-) -> Result<(), failure::Error> {
+    install_permitted: bool,
+) -> Result<Download, failure::Error> {
+    let url = match prebuilt_url(version) {
+        Some(url) => url,
+        None => bail!("no prebuilt wasm-bindgen binaries are available for this platform"),
+    };
+    let binaries = &["wasm-bindgen", "wasm-bindgen-test-runner"];
+    match cache.download(install_permitted, "wasm-bindgen", binaries, &url)? {
+        Some(download) => Ok(download),
+        None => bail!("wasm-bindgen v{} is not installed!", version),
+    }
+}
+
+/// Returns the URL of a precompiled version of wasm-bindgen, if we have one
+/// available for our host platform.
+fn prebuilt_url(version: &str) -> Option<String> {
     let target = if target::LINUX && target::x86_64 {
         "x86_64-unknown-linux-musl"
     } else if target::MACOS && target::x86_64 {
@@ -67,32 +88,40 @@ pub fn download_prebuilt_wasm_bindgen(
     } else if target::WINDOWS && target::x86_64 {
         "x86_64-pc-windows-msvc"
     } else {
-        return Err(Error::unsupported(
-            "there are no pre-built `wasm-bindgen` binaries for this target",
-        )
-        .into());
+        return None;
     };
 
-    let url = format!(
+    Some(format!(
         "https://github.com/rustwasm/wasm-bindgen/releases/download/{0}/wasm-bindgen-{0}-{1}.tar.gz",
         version,
         target
-    );
-
-    install_binaries_from_targz_at_url(
-        root_path,
-        &url,
-        vec!["wasm-bindgen", "wasm-bindgen-test-runner"],
-    )
+    ))
 }
 
 /// Use `cargo install` to install the `wasm-bindgen` CLI locally into the given
 /// crate.
 pub fn cargo_install_wasm_bindgen(
     logger: &Logger,
-    crate_path: &Path,
+    cache: &Cache,
     version: &str,
-) -> Result<(), failure::Error> {
+    install_permitted: bool,
+) -> Result<Download, failure::Error> {
+    let dirname = format!("wasm-bindgen-cargo-install-{}", version);
+    let destination = cache.join(dirname.as_ref());
+    if destination.exists() {
+        return Ok(Download::at(&destination));
+    }
+
+    if !install_permitted {
+        bail!("wasm-bindgen v{} is not installed!", version)
+    }
+
+    // Run `cargo install` to a temporary location to handle ctrl-c gracefully
+    // and ensure we don't accidentally use stale files in the future
+    let tmp = cache.join(format!(".{}", dirname).as_ref());
+    drop(fs::remove_dir_all(&tmp));
+    fs::create_dir_all(&tmp)?;
+
     let mut cmd = Command::new("cargo");
     cmd.arg("install")
         .arg("--force")
@@ -100,17 +129,19 @@ pub fn cargo_install_wasm_bindgen(
         .arg("--version")
         .arg(version)
         .arg("--root")
-        .arg(crate_path);
+        .arg(&tmp);
 
     child::run(logger, cmd, "cargo install").context("Installing wasm-bindgen with cargo")?;
-    assert!(binaries::local_bin_path(crate_path, "wasm-bindgen").is_file());
-    Ok(())
+
+    fs::rename(&tmp, &destination)?;
+    Ok(Download::at(&destination))
 }
 
 /// Run the `wasm-bindgen` CLI to generate bindings for the current crate's
 /// `.wasm`.
 pub fn wasm_bindgen_build(
     path: &Path,
+    bindgen: &Download,
     out_dir: &Path,
     name: &str,
     disable_dts: bool,
@@ -127,46 +158,42 @@ pub fn wasm_bindgen_build(
 
     let out_dir = out_dir.to_str().unwrap();
 
-    if let Some(wasm_bindgen_path) = wasm_bindgen_path(log, path) {
-        let manifest = path.join("Cargo.toml");
-        let target_path = cargo_metadata::metadata(Some(&manifest))
-            .unwrap()
-            .target_directory;
-        let mut wasm_path = PathBuf::from(&target_path)
-            .join("wasm32-unknown-unknown")
-            .join(release_or_debug)
-            .join(binary_name);
-        wasm_path.set_extension("wasm");
-        let wasm_path = wasm_path.display().to_string();
-
-        let dts_arg = if disable_dts {
-            "--no-typescript"
-        } else {
-            "--typescript"
-        };
-        let target_arg = match target {
-            "nodejs" => "--nodejs",
-            "no-modules" => "--no-modules",
-            _ => "--browser",
-        };
-        let bindgen_path = Path::new(&wasm_bindgen_path);
-        let mut cmd = Command::new(bindgen_path);
-        cmd.current_dir(path)
-            .arg(&wasm_path)
-            .arg("--out-dir")
-            .arg(out_dir)
-            .arg(dts_arg)
-            .arg(target_arg);
-
-        if debug {
-            cmd.arg("--debug");
-        }
-
-        child::run(log, cmd, "wasm-bindgen").context("Running the wasm-bindgen CLI")?;
-        Ok(())
+    let manifest = path.join("Cargo.toml");
+    let target_path = cargo_metadata::metadata(Some(&manifest))
+        .unwrap()
+        .target_directory;
+    let mut wasm_path = PathBuf::from(&target_path)
+        .join("wasm32-unknown-unknown")
+        .join(release_or_debug)
+        .join(binary_name);
+    wasm_path.set_extension("wasm");
+    let wasm_path = wasm_path.display().to_string();
+
+    let dts_arg = if disable_dts {
+        "--no-typescript"
     } else {
-        Err(Error::crate_config("Could not find `wasm-bindgen`").into())
+        "--typescript"
+    };
+    let target_arg = match target {
+        "nodejs" => "--nodejs",
+        "no-modules" => "--no-modules",
+        _ => "--browser",
+    };
+    let bindgen_path = bindgen.binary("wasm-bindgen");
+    let mut cmd = Command::new(bindgen_path);
+    cmd.current_dir(path)
+        .arg(&wasm_path)
+        .arg("--out-dir")
+        .arg(out_dir)
+        .arg(dts_arg)
+        .arg(target_arg);
+
+    if debug {
+        cmd.arg("--debug");
     }
+
+    child::run(log, cmd, "wasm-bindgen").context("Running the wasm-bindgen CLI")?;
+    Ok(())
 }
 
 /// Check if the `wasm-bindgen` dependency is locally satisfied.
@@ -192,16 +219,3 @@ fn wasm_bindgen_version_check(bindgen_path: &PathBuf, dep_version: &str, log: &L
         })
         .unwrap_or(false)
 }
-
-/// Return a `PathBuf` containing the path to either the local wasm-bindgen
-/// version, or the globally installed version if there is no local version.
-fn wasm_bindgen_path(log: &Logger, crate_path: &Path) -> Option<PathBuf> {
-    bin_path(log, crate_path, "wasm-bindgen")
-}
-
-/// Return a `PathBuf` containing the path to either the local
-/// wasm-bindgen-test-runner version, or the globally installed version if there
-/// is no local version.
-pub fn wasm_bindgen_test_runner_path(log: &Logger, crate_path: &Path) -> Option<PathBuf> {
-    bin_path(log, crate_path, "wasm-bindgen-test-runner")
-}
diff --git a/src/command/build.rs b/src/command/build.rs
index 7eed1f0..12381fe 100644
--- a/src/command/build.rs
+++ b/src/command/build.rs
@@ -1,5 +1,6 @@
 //! Implementation of the `wasm-pack build` command.
 
+use binaries::{Cache, Download};
 use bindgen;
 use build;
 use command::utils::{create_pkg_dir, set_crate_path};
@@ -17,7 +18,8 @@ use std::time::Instant;
 use PBAR;
 
 /// Everything required to configure and run the `wasm-pack init` command.
-pub(crate) struct Build {
+#[allow(missing_docs)]
+pub struct Build {
     pub crate_path: PathBuf,
     pub scope: Option<String>,
     pub disable_dts: bool,
@@ -27,6 +29,8 @@ pub(crate) struct Build {
     // build_config: Option<BuildConfig>,
     pub crate_name: String,
     pub out_dir: PathBuf,
+    pub bindgen: Option<Download>,
+    pub cache: Cache,
 }
 
 /// The `BuildMode` determines which mode of initialization we are running, and
@@ -113,9 +117,16 @@ impl Build {
             // build_config,
             crate_name,
             out_dir,
+            bindgen: None,
+            cache: Cache::new()?,
         })
     }
 
+    /// Configures the global binary cache used for this build
+    pub fn set_cache(&mut self, cache: Cache) {
+        self.cache = cache;
+    }
+
     /// Execute this `Build` command.
     pub fn run(&mut self, log: &Logger) -> Result<(), failure::Error> {
         let process_steps = Build::get_process_steps(&self.mode);
@@ -276,13 +287,14 @@ impl Build {
             BuildMode::Force => true,
             BuildMode::Noinstall => false,
         };
-        bindgen::install_wasm_bindgen(
-            &self.crate_path,
+        let bindgen = bindgen::install_wasm_bindgen(
+            &self.cache,
             &bindgen_version,
             install_permitted,
             step,
             log,
         )?;
+        self.bindgen = Some(bindgen);
         info!(&log, "Installing wasm-bindgen-cli was successful.");
 
         info!(&log, "Getting the crate name from the manifest...");
@@ -300,6 +312,7 @@ impl Build {
         info!(&log, "Building the wasm bindings...");
         bindgen::wasm_bindgen_build(
             &self.crate_path,
+            self.bindgen.as_ref().unwrap(),
             &self.out_dir,
             &self.crate_name,
             self.disable_dts,
diff --git a/src/command/test.rs b/src/command/test.rs
index 507bd18..0c31dac 100644
--- a/src/command/test.rs
+++ b/src/command/test.rs
@@ -1,6 +1,7 @@
 //! Implementation of the `wasm-pack test` command.
 
 use super::build::BuildMode;
+use binaries::Cache;
 use bindgen;
 use build;
 use command::utils::set_crate_path;
@@ -81,6 +82,7 @@ pub struct TestOptions {
 /// A configured `wasm-pack test` command.
 pub struct Test {
     crate_path: PathBuf,
+    cache: Cache,
     node: bool,
     mode: BuildMode,
     firefox: bool,
@@ -139,6 +141,7 @@ impl Test {
         }
 
         Ok(Test {
+            cache: Cache::new()?,
             crate_path,
             node,
             mode,
@@ -154,6 +157,11 @@ impl Test {
         })
     }
 
+    /// Configures the cache that this test command uses
+    pub fn set_cache(&mut self, cache: Cache) {
+        self.cache = cache;
+    }
+
     /// Execute this test command.
     pub fn run(mut self, log: &Logger) -> Result<(), failure::Error> {
         let process_steps = self.get_process_steps();
@@ -303,16 +311,15 @@ impl Test {
             }
         };
 
-        bindgen::install_wasm_bindgen(
-            &self.crate_path,
+        let dl = bindgen::install_wasm_bindgen(
+            &self.cache,
             &bindgen_version,
             install_permitted,
             step,
             log,
         )?;
 
-        self.test_runner_path = Some(bindgen::wasm_bindgen_test_runner_path(log, &self.crate_path)
-            .expect("if installing wasm-bindgen succeeded, then we should have wasm-bindgen-test-runner too"));
+        self.test_runner_path = Some(dl.binary("wasm-bindgen-test-runner"));
 
         info!(&log, "Getting wasm-bindgen-cli was successful.");
         Ok(())
@@ -335,13 +342,12 @@ impl Test {
         Ok(())
     }
 
-    fn step_get_chromedriver(&mut self, step: &Step, log: &Logger) -> Result<(), failure::Error> {
+    fn step_get_chromedriver(&mut self, step: &Step, _log: &Logger) -> Result<(), failure::Error> {
         PBAR.step(step, "Getting chromedriver...");
         assert!(self.chrome && self.chromedriver.is_none());
 
         self.chromedriver = Some(webdriver::get_or_install_chromedriver(
-            log,
-            &self.crate_path,
+            &self.cache,
             self.mode,
         )?);
         Ok(())
@@ -378,13 +384,12 @@ impl Test {
         Ok(())
     }
 
-    fn step_get_geckodriver(&mut self, step: &Step, log: &Logger) -> Result<(), failure::Error> {
+    fn step_get_geckodriver(&mut self, step: &Step, _log: &Logger) -> Result<(), failure::Error> {
         PBAR.step(step, "Getting geckodriver...");
         assert!(self.firefox && self.geckodriver.is_none());
 
         self.geckodriver = Some(webdriver::get_or_install_geckodriver(
-            log,
-            &self.crate_path,
+            &self.cache,
             self.mode,
         )?);
         Ok(())
@@ -421,11 +426,11 @@ impl Test {
         Ok(())
     }
 
-    fn step_get_safaridriver(&mut self, step: &Step, log: &Logger) -> Result<(), failure::Error> {
+    fn step_get_safaridriver(&mut self, step: &Step, _log: &Logger) -> Result<(), failure::Error> {
         PBAR.step(step, "Getting safaridriver...");
         assert!(self.safari && self.safaridriver.is_none());
 
-        self.safaridriver = Some(webdriver::get_safaridriver(log, &self.crate_path)?);
+        self.safaridriver = Some(webdriver::get_safaridriver()?);
         Ok(())
     }
 
diff --git a/src/lib.rs b/src/lib.rs
index ed2e390..702fafa 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -5,9 +5,11 @@
 extern crate cargo_metadata;
 extern crate console;
 extern crate curl;
+extern crate dirs;
 #[macro_use]
 extern crate failure;
 extern crate flate2;
+extern crate hex;
 extern crate indicatif;
 #[macro_use]
 extern crate lazy_static;
@@ -15,6 +17,7 @@ extern crate parking_lot;
 #[macro_use]
 extern crate serde_derive;
 extern crate serde_json;
+extern crate siphasher;
 #[macro_use]
 extern crate structopt;
 #[macro_use]
diff --git a/src/test/webdriver.rs b/src/test/webdriver.rs
index cac6d39..4b06314 100644
--- a/src/test/webdriver.rs
+++ b/src/test/webdriver.rs
@@ -1,40 +1,32 @@
 //! Getting WebDriver client binaries.
 
-use binaries::{
-    self, bin_path, install_binaries_from_targz_at_url, install_binaries_from_zip_at_url,
-};
+use binaries::Cache;
 use command::build::BuildMode;
-use error::Error;
 use failure;
-use slog::Logger;
-use std::path::{Path, PathBuf};
+use std::path::PathBuf;
 use target;
 
 /// Get the path to an existing `chromedriver`, or install it if no existing
 /// binary is found.
 pub fn get_or_install_chromedriver(
-    log: &Logger,
-    crate_path: &Path,
+    cache: &Cache,
     mode: BuildMode,
 ) -> Result<PathBuf, failure::Error> {
-    match (mode, bin_path(log, crate_path, "chromedriver")) {
-        (_, Some(path)) => Ok(path),
-        (BuildMode::Normal, None) => install_chromedriver(crate_path),
-        (BuildMode::Force, None) => install_chromedriver(crate_path),
-        (BuildMode::Noinstall, None) => Err(Error::crate_config(
-            "No crate-local `chromedriver` binary found, and could not find a global \
-             `chromedriver` on the `$PATH`. Not installing `chromedriver` because of noinstall \
-             mode.",
-        )
-        .into()),
+    if let Ok(path) = which::which("chromedriver") {
+        return Ok(path);
     }
+    let installation_allowed = match mode {
+        BuildMode::Noinstall => false,
+        _ => true,
+    };
+    install_chromedriver(cache, installation_allowed)
 }
 
-fn get_local_chromedriver_path(crate_path: &Path) -> PathBuf {
-    binaries::local_bin_path(crate_path, "chromedriver")
-}
-
-fn get_chromedriver_url() -> Result<String, Error> {
+/// Download and install a pre-built `chromedriver` binary.
+pub fn install_chromedriver(
+    cache: &Cache,
+    installation_allowed: bool,
+) -> Result<PathBuf, failure::Error> {
     let target = if target::LINUX && target::x86_64 {
         "linux64"
     } else if target::MACOS && target::x86_64 {
@@ -42,46 +34,49 @@ fn get_chromedriver_url() -> Result<String, Error> {
     } else if target::WINDOWS && target::x86 {
         "win32"
     } else {
-        return Err(Error::unsupported(
-            "geckodriver binaries are unavailable for this target",
-        ));
+        bail!("geckodriver binaries are unavailable for this target")
     };
 
-    Ok(format!(
+    let url = format!(
         "https://chromedriver.storage.googleapis.com/2.41/chromedriver_{}.zip",
         target
-    ))
-}
-
-/// Download and install a pre-built `chromedriver` binary.
-pub fn install_chromedriver(crate_path: &Path) -> Result<PathBuf, failure::Error> {
-    let url = get_chromedriver_url()?;
-    install_binaries_from_zip_at_url(crate_path, &url, Some("chromedriver"))?;
-    let chromedriver = get_local_chromedriver_path(crate_path);
-    assert!(chromedriver.is_file());
-    Ok(chromedriver)
+    );
+    match cache.download(
+        installation_allowed,
+        "chromedriver",
+        &["chromedriver"],
+        &url,
+    )? {
+        Some(dl) => Ok(dl.binary("chromedriver")),
+        None => bail!(
+            "No cached `chromedriver` binary found, and could not find a global \
+             `chromedriver` on the `$PATH`. Not installing `chromedriver` because of noinstall \
+             mode."
+        ),
+    }
 }
 
 /// Get the path to an existing `geckodriver`, or install it if no existing
 /// binary is found.
 pub fn get_or_install_geckodriver(
-    log: &Logger,
-    crate_path: &Path,
+    cache: &Cache,
     mode: BuildMode,
 ) -> Result<PathBuf, failure::Error> {
-    match (mode, bin_path(log, crate_path, "geckodriver")) {
-        (_, Some(path)) => Ok(path),
-        (BuildMode::Normal, None) => install_geckodriver(crate_path),
-        (BuildMode::Force, None) => install_geckodriver(crate_path),
-        (BuildMode::Noinstall, None) => Err(Error::crate_config(
-            "No crate-local `geckodriver` binary found, and could not find a global `geckodriver` \
-             on the `$PATH`. Not installing `geckodriver` because of noinstall mode.",
-        )
-        .into()),
+    if let Ok(path) = which::which("geckodriver") {
+        return Ok(path);
     }
+    let installation_allowed = match mode {
+        BuildMode::Noinstall => false,
+        _ => true,
+    };
+    install_geckodriver(cache, installation_allowed)
 }
 
-fn get_geckodriver_url() -> Result<String, Error> {
+/// Download and install a pre-built `geckodriver` binary.
+pub fn install_geckodriver(
+    cache: &Cache,
+    installation_allowed: bool,
+) -> Result<PathBuf, failure::Error> {
     let (target, ext) = if target::LINUX && target::x86 {
         ("linux32", "tar.gz")
     } else if target::LINUX && target::x86_64 {
@@ -93,36 +88,21 @@ fn get_geckodriver_url() -> Result<String, Error> {
     } else if target::WINDOWS && target::x86_64 {
         ("win64", "zip")
     } else {
-        return Err(Error::unsupported(
-            "geckodriver binaries are unavailable for this target",
-        ));
+        bail!("geckodriver binaries are unavailable for this target")
     };
 
-    Ok(format!(
+    let url = format!(
         "https://github.com/mozilla/geckodriver/releases/download/v0.21.0/geckodriver-v0.21.0-{}.{}",
         target,
         ext,
-    ))
-}
-
-fn get_local_geckodriver_path(crate_path: &Path) -> PathBuf {
-    binaries::local_bin_path(crate_path, "geckodriver")
-}
-
-/// Download and install a pre-built `geckodriver` binary.
-pub fn install_geckodriver(crate_path: &Path) -> Result<PathBuf, failure::Error> {
-    let url = get_geckodriver_url()?;
-
-    if url.ends_with("tar.gz") {
-        install_binaries_from_targz_at_url(crate_path, &url, Some("geckodriver"))?;
-    } else {
-        assert!(url.ends_with("zip"));
-        install_binaries_from_zip_at_url(crate_path, &url, Some("geckodriver"))?;
+    );
+    match cache.download(installation_allowed, "geckodriver", &["geckodriver"], &url)? {
+        Some(dl) => Ok(dl.binary("geckodriver")),
+        None => bail!(
+            "No cached `geckodriver` binary found, and could not find a global `geckodriver` \
+             on the `$PATH`. Not installing `geckodriver` because of noinstall mode."
+        ),
     }
-
-    let geckodriver = get_local_geckodriver_path(crate_path);
-    assert!(geckodriver.is_file());
-    Ok(geckodriver)
 }
 
 /// Get the path to an existing `safaridriver`.
@@ -130,12 +110,9 @@ pub fn install_geckodriver(crate_path: &Path) -> Result<PathBuf, failure::Error>
 /// We can't install `safaridriver` if an existing one is not found because
 /// Apple does not provide pre-built binaries. However, `safaridriver` *should*
 /// be present by default.
-pub fn get_safaridriver(log: &Logger, crate_path: &Path) -> Result<PathBuf, Error> {
-    if let Some(p) = bin_path(log, crate_path, "safaridriver") {
-        Ok(p)
-    } else {
-        Err(Error::crate_config(
-            "could not find `safaridriver` on the `$PATH`",
-        ))
+pub fn get_safaridriver() -> Result<PathBuf, failure::Error> {
+    match which::which("safaridriver") {
+        Ok(p) => Ok(p),
+        Err(_) => bail!("could not find `safaridriver` on the `$PATH`"),
     }
 }
diff --git a/tests/all/bindgen.rs b/tests/all/bindgen.rs
index 4892019..985a4d0 100644
--- a/tests/all/bindgen.rs
+++ b/tests/all/bindgen.rs
@@ -1,4 +1,5 @@
 use tempfile;
+use wasm_pack::binaries::Cache;
 use wasm_pack::bindgen;
 
 #[test]
@@ -8,21 +9,11 @@ use wasm_pack::bindgen;
     all(windows, target_arch = "x86_64"),
 ))]
 fn can_download_prebuilt_wasm_bindgen() {
-    use std::env;
     let dir = tempfile::TempDir::new().unwrap();
-    bindgen::download_prebuilt_wasm_bindgen(dir.path(), "0.2.21").unwrap();
-    assert!(dir
-        .path()
-        .join("bin")
-        .join("wasm-bindgen")
-        .with_extension(env::consts::EXE_EXTENSION)
-        .is_file());
-    assert!(dir
-        .path()
-        .join("bin")
-        .join("wasm-bindgen-test-runner")
-        .with_extension(env::consts::EXE_EXTENSION)
-        .is_file());
+    let cache = Cache::at(dir.path());
+    let dl = bindgen::download_prebuilt_wasm_bindgen(&cache, "0.2.21", true).unwrap();
+    assert!(dl.binary("wasm-bindgen").is_file());
+    assert!(dl.binary("wasm-bindgen-test-runner").is_file())
 }
 
 #[test]
@@ -34,9 +25,13 @@ fn can_download_prebuilt_wasm_bindgen() {
 fn downloading_prebuilt_wasm_bindgen_handles_http_errors() {
     let dir = tempfile::TempDir::new().unwrap();
     let bad_version = "0.2.21-some-trailing-version-stuff-that-does-not-exist";
-    let result = bindgen::download_prebuilt_wasm_bindgen(dir.path(), bad_version);
+    let cache = Cache::at(dir.path());
+    let result = bindgen::download_prebuilt_wasm_bindgen(&cache, bad_version, true);
     assert!(result.is_err());
-    let error_msg = result.unwrap_err().to_string();
-    assert!(error_msg.contains("404"));
-    assert!(error_msg.contains(bad_version));
+    let error = result.err().unwrap();
+
+    assert!(error.iter_chain().any(|e| e.to_string().contains("404")));
+    assert!(error
+        .iter_chain()
+        .any(|e| e.to_string().contains(bad_version)));
 }
diff --git a/tests/all/build.rs b/tests/all/build.rs
index 240a1a2..295708d 100644
--- a/tests/all/build.rs
+++ b/tests/all/build.rs
@@ -1,6 +1,6 @@
 use structopt::StructOpt;
 use utils;
-use wasm_pack::{command, logger, Cli};
+use wasm_pack::Cli;
 
 #[test]
 fn build_in_non_crate_directory_doesnt_panic() {
@@ -11,14 +11,13 @@ fn build_in_non_crate_directory_doesnt_panic() {
         &fixture.path.display().to_string(),
     ])
     .unwrap();
-    let logger = logger::new(&cli.cmd, cli.verbosity).unwrap();
-    let result = command::run_wasm_pack(cli.cmd, &logger);
+    let result = fixture.run(cli.cmd);
     assert!(
         result.is_err(),
         "running wasm-pack in a non-crate directory should fail, but it should not panic"
     );
-    let err_msg = result.unwrap_err().to_string();
-    assert!(err_msg.contains("missing a `Cargo.toml`"));
+    let err = result.unwrap_err();
+    assert!(err.iter_chain().any(|e| e.to_string().contains("missing a `Cargo.toml`")));
 }
 
 #[test]
@@ -31,7 +30,5 @@ fn it_should_build_js_hello_world_example() {
         &fixture.path.display().to_string(),
     ])
     .unwrap();
-    let logger = logger::new(&cli.cmd, cli.verbosity).unwrap();
-    command::run_wasm_pack(cli.cmd, &logger)
-        .expect("running wasm-pack in a js-hello-world directory should succeed.");
+    fixture.run(cli.cmd).unwrap();
 }
diff --git a/tests/all/test.rs b/tests/all/test.rs
index 54d4131..6bad2d6 100644
--- a/tests/all/test.rs
+++ b/tests/all/test.rs
@@ -1,8 +1,5 @@
 use std::env;
-use std::fs;
-use tempfile;
 use utils::fixture;
-use wasm_pack::binaries;
 use wasm_pack::command::{self, build, test, Command};
 use wasm_pack::logger;
 
@@ -16,8 +13,7 @@ fn it_can_run_node_tests() {
         mode: build::BuildMode::Noinstall,
         ..Default::default()
     });
-    let logger = logger::new(&cmd, 3).unwrap();
-    command::run_wasm_pack(cmd, &logger).expect("should run test command OK");
+    fixture.run(cmd).unwrap();
 }
 
 #[test]
@@ -30,8 +26,7 @@ fn it_can_run_tests_with_different_wbg_test_and_wbg_versions() {
         mode: build::BuildMode::Noinstall,
         ..Default::default()
     });
-    let logger = logger::new(&cmd, 3).unwrap();
-    command::run_wasm_pack(cmd, &logger).expect("should run test command OK");
+    fixture.run(cmd).unwrap();
 }
 
 #[test]
@@ -81,8 +76,7 @@ fn it_can_run_browser_tests() {
         ..Default::default()
     });
 
-    let logger = logger::new(&cmd, 3).unwrap();
-    command::run_wasm_pack(cmd, &logger).expect("should run test command OK");
+    fixture.run(cmd).unwrap();
 }
 
 #[test]
@@ -111,34 +105,35 @@ fn it_can_run_failing_tests() {
     all(target_os = "windows", target_arch = "x86_64")
 ))]
 fn it_can_find_a_webdriver_on_path() {
+    use std::process::Command;
+
     let fixture = fixture::wbg_test_browser();
-    fixture.install_local_wasm_bindgen();
-    fixture.install_local_geckodriver();
-
-    let geckodriver_dir = tempfile::TempDir::new().unwrap();
-    let local_geckodriver = binaries::local_bin_path(&fixture.path, "geckodriver");
-    fs::copy(
-        &local_geckodriver,
-        geckodriver_dir
-            .path()
-            .join(local_geckodriver.file_name().unwrap()),
-    )
-    .unwrap();
-    fs::remove_file(&local_geckodriver).unwrap();
+    let local_geckodriver = fixture.install_local_geckodriver();
+    let local_wasm_bindgen = fixture.install_local_wasm_bindgen();
 
     let mut paths: Vec<_> = env::split_paths(&env::var("PATH").unwrap()).collect();
-    paths.insert(0, geckodriver_dir.path().into());
-    env::set_var("PATH", env::join_paths(paths).unwrap());
-
-    let cmd = Command::Test(test::TestOptions {
-        path: Some(fixture.path.clone()),
-        firefox: true,
-        headless: true,
-        mode: build::BuildMode::Noinstall,
-        ..Default::default()
-    });
-    let logger = logger::new(&cmd, 3).unwrap();
-    command::run_wasm_pack(cmd, &logger).expect("should run test command OK");
+    paths.insert(0, local_geckodriver.parent().unwrap().to_path_buf());
+    paths.insert(0, local_wasm_bindgen.parent().unwrap().to_path_buf());
+    let path = env::join_paths(paths).unwrap();
+
+    let mut me = env::current_exe().unwrap();
+    me.pop();
+    me.pop();
+    me.push("wasm-pack");
+    let output = Command::new(&me)
+        .arg("test")
+        .arg("--firefox")
+        .arg("--headless")
+        .arg("--mode")
+        .arg("no-install")
+        .env("PATH", &path)
+        .arg(&fixture.path)
+        .output()
+        .unwrap();
+    println!("stdout: {}", String::from_utf8_lossy(&output.stdout));
+    println!("stderr: {}", String::from_utf8_lossy(&output.stderr));
+    println!("status: {}", output.status);
+    assert!(output.status.success());
 }
 
 #[test]
diff --git a/tests/all/utils/fixture.rs b/tests/all/utils/fixture.rs
index dc47369..64ccbdd 100644
--- a/tests/all/utils/fixture.rs
+++ b/tests/all/utils/fixture.rs
@@ -1,7 +1,6 @@
 use super::logger::null_logger;
 use std::env;
 use std::fs;
-use std::io;
 use std::mem::ManuallyDrop;
 use std::path::{Path, PathBuf};
 use std::process::{Command, Stdio};
@@ -9,12 +8,7 @@ use std::sync::{Once, ONCE_INIT};
 use std::thread;
 use tempfile::TempDir;
 use wasm_pack;
-
-fn hard_link_or_copy<P1: AsRef<Path>, P2: AsRef<Path>>(from: P1, to: P2) -> io::Result<()> {
-    let from = from.as_ref();
-    let to = to.as_ref();
-    fs::hard_link(from, to).or_else(|_| fs::copy(from, to).map(|_| ()))
-}
+use wasm_pack::binaries::Cache;
 
 /// A test fixture in a temporary directory.
 pub struct Fixture {
@@ -134,120 +128,63 @@ impl Fixture {
     ///
     /// Takes care not to re-install for every fixture, but only the one time
     /// for the whole test suite.
-    pub fn install_local_wasm_bindgen(&self) -> &Self {
+    pub fn install_local_wasm_bindgen(&self) -> PathBuf {
         static INSTALL_WASM_BINDGEN: Once = ONCE_INIT;
+        let cache = self.cache();
+        let version = "0.2.21";
+        let log = &null_logger();
+
+        let download = || {
+            if let Ok(download) =
+                wasm_pack::bindgen::download_prebuilt_wasm_bindgen(&cache, version, true)
+            {
+                return Ok(download);
+            }
 
-        let tests = Path::new(env!("CARGO_MANIFEST_DIR")).join("tests");
-        let shared_wasm_bindgen = wasm_pack::binaries::local_bin_path(&tests, "wasm-bindgen");
-        let shared_wasm_bindgen_test_runner =
-            wasm_pack::binaries::local_bin_path(&tests, "wasm-bindgen-test-runner");
+            wasm_pack::bindgen::cargo_install_wasm_bindgen(log, &cache, version, true)
+        };
 
+        // Only one thread can perform the actual download, and then afterwards
+        // everything will hit the cache so we can run the same path.
         INSTALL_WASM_BINDGEN.call_once(|| {
-            if shared_wasm_bindgen.is_file() {
-                assert!(shared_wasm_bindgen_test_runner.is_file());
-                return;
-            }
-
-            const WASM_BINDGEN_VERSION: &str = "0.2.21";
-            wasm_pack::bindgen::download_prebuilt_wasm_bindgen(&tests, WASM_BINDGEN_VERSION)
-                .or_else(|_| {
-                    wasm_pack::bindgen::cargo_install_wasm_bindgen(
-                        &null_logger(),
-                        &tests,
-                        WASM_BINDGEN_VERSION,
-                    )
-                })
-                .unwrap();
+            download().unwrap();
         });
-
-        assert!(shared_wasm_bindgen.is_file());
-        assert!(shared_wasm_bindgen_test_runner.is_file());
-
-        wasm_pack::binaries::ensure_local_bin_dir(&self.path).unwrap();
-
-        hard_link_or_copy(
-            &shared_wasm_bindgen,
-            wasm_pack::binaries::local_bin_path(&self.path, "wasm-bindgen"),
-        )
-        .expect("could not copy `wasm-bindgen` to fixture directory");
-
-        hard_link_or_copy(
-            &shared_wasm_bindgen_test_runner,
-            wasm_pack::binaries::local_bin_path(&self.path, "wasm-bindgen-test-runner"),
-        )
-        .expect("could not copy `wasm-bindgen-test` to fixture directory");
-
-        self
+        download().unwrap().binary("wasm-bindgen")
     }
 
     /// Download `geckodriver` and return its path.
     ///
     /// Takes care to ensure that only one `geckodriver` is downloaded for the whole
     /// test suite.
-    pub fn install_local_geckodriver(&self) -> &Self {
+    pub fn install_local_geckodriver(&self) -> PathBuf {
         static FETCH_GECKODRIVER: Once = ONCE_INIT;
+        let cache = self.cache();
 
-        let tests = Path::new(env!("CARGO_MANIFEST_DIR")).join("tests");
-
-        wasm_pack::binaries::ensure_local_bin_dir(&tests)
-            .expect("could not create fixture's `bin` directory");
-
-        let geckodriver = wasm_pack::binaries::local_bin_path(&tests, "geckodriver");
-
+        // like above for synchronization
         FETCH_GECKODRIVER.call_once(|| {
-            if geckodriver.is_file() {
-                return;
-            }
-
-            wasm_pack::test::webdriver::install_geckodriver(&tests).unwrap();
-            assert!(geckodriver.is_file());
+            wasm_pack::test::webdriver::install_geckodriver(&cache, true).unwrap();
         });
-
-        wasm_pack::binaries::ensure_local_bin_dir(&self.path)
-            .expect("could not create fixture's `bin` directory");
-
-        hard_link_or_copy(
-            &geckodriver,
-            wasm_pack::binaries::local_bin_path(&self.path, "geckodriver"),
-        )
-        .expect("could not copy `geckodriver` to fixture directory");
-
-        self
+        wasm_pack::test::webdriver::install_geckodriver(&cache, true).unwrap()
     }
 
     /// Download `chromedriver` and return its path.
     ///
     /// Takes care to ensure that only one `chromedriver` is downloaded for the whole
     /// test suite.
-    pub fn install_local_chromedriver(&self) -> &Self {
+    pub fn install_local_chromedriver(&self) -> PathBuf {
         static FETCH_CHROMEDRIVER: Once = ONCE_INIT;
+        let cache = self.cache();
 
-        let tests = Path::new(env!("CARGO_MANIFEST_DIR")).join("tests");
-
-        wasm_pack::binaries::ensure_local_bin_dir(&tests)
-            .expect("could not create fixture's `bin` directory");
-
-        let chromedriver = wasm_pack::binaries::local_bin_path(&tests, "chromedriver");
-
+        // like above for synchronization
         FETCH_CHROMEDRIVER.call_once(|| {
-            if chromedriver.is_file() {
-                return;
-            }
-
-            wasm_pack::test::webdriver::install_chromedriver(&tests).unwrap();
-            assert!(chromedriver.is_file());
+            wasm_pack::test::webdriver::install_chromedriver(&cache, true).unwrap();
         });
+        wasm_pack::test::webdriver::install_chromedriver(&cache, true).unwrap()
+    }
 
-        wasm_pack::binaries::ensure_local_bin_dir(&self.path)
-            .expect("could not create fixture's `bin` directory");
-
-        hard_link_or_copy(
-            &chromedriver,
-            wasm_pack::binaries::local_bin_path(&self.path, "chromedriver"),
-        )
-        .expect("could not copy `chromedriver` to fixture directory");
-
-        self
+    pub fn cache(&self) -> Cache {
+        let target_dir = Path::new(env!("CARGO_MANIFEST_DIR")).join("target");
+        Cache::at(&target_dir.join("test_cache"))
     }
 
     /// The `step_install_wasm_bindgen` and `step_run_wasm_bindgen` steps only
@@ -266,6 +203,23 @@ impl Fixture {
             .unwrap();
         self
     }
+
+    pub fn run(&self, cmd: wasm_pack::command::Command) -> Result<(), failure::Error> {
+        let logger = wasm_pack::logger::new(&cmd, 3)?;
+        match cmd {
+            wasm_pack::command::Command::Test(cmd) => {
+                let mut test = wasm_pack::command::test::Test::try_from_opts(cmd)?;
+                test.set_cache(self.cache());
+                test.run(&logger)
+            }
+            wasm_pack::command::Command::Build(cmd) => {
+                let mut build = wasm_pack::command::build::Build::try_from_opts(cmd)?;
+                build.set_cache(self.cache());
+                build.run(&logger)
+            }
+            _ => unreachable!(),
+        }
+    }
 }
 
 impl Drop for Fixture {
diff --git a/tests/all/webdriver.rs b/tests/all/webdriver.rs
index 5e3b0cb..f57c275 100644
--- a/tests/all/webdriver.rs
+++ b/tests/all/webdriver.rs
@@ -1,4 +1,5 @@
 use utils::fixture;
+use wasm_pack::binaries::Cache;
 use wasm_pack::test::webdriver;
 
 #[test]
@@ -9,7 +10,8 @@ use wasm_pack::test::webdriver;
 ))]
 fn can_install_chromedriver() {
     let fixture = fixture::js_hello_world();
-    assert!(webdriver::install_chromedriver(&fixture.path).is_ok());
+    let cache = Cache::at(&fixture.path);
+    assert!(webdriver::install_chromedriver(&cache, true).is_ok());
 }
 
 #[test]
@@ -22,5 +24,6 @@ fn can_install_chromedriver() {
 ))]
 fn can_install_geckodriver() {
     let fixture = fixture::js_hello_world();
-    assert!(webdriver::install_geckodriver(&fixture.path).is_ok());
+    let cache = Cache::at(&fixture.path);
+    assert!(webdriver::install_geckodriver(&cache, true).is_ok());
 }