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rust-rocksdb/src/ffi_util.rs

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// Copyright 2016 Alex Regueiro
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
use crate::Error;
use libc::{self, c_char, c_void};
use std::ffi::{CStr, CString};
use std::path::Path;
use std::ptr;
pub(crate) unsafe fn from_cstr(ptr: *const c_char) -> String {
let cstr = CStr::from_ptr(ptr as *const _);
String::from_utf8_lossy(cstr.to_bytes()).into_owned()
}
pub(crate) unsafe fn raw_data(ptr: *const c_char, size: usize) -> Option<Vec<u8>> {
if ptr.is_null() {
None
} else {
let mut dst = vec![0; size];
ptr::copy_nonoverlapping(ptr as *const u8, dst.as_mut_ptr(), size);
Some(dst)
}
}
pub fn error_message(ptr: *const c_char) -> String {
unsafe {
let s = from_cstr(ptr);
libc::free(ptr as *mut c_void);
s
}
}
pub fn opt_bytes_to_ptr<T: AsRef<[u8]>>(opt: Option<T>) -> *const c_char {
match opt {
Some(v) => v.as_ref().as_ptr() as *const c_char,
None => ptr::null(),
}
}
pub(crate) fn to_cpath<P: AsRef<Path>>(path: P) -> Result<CString, Error> {
match CString::new(path.as_ref().to_string_lossy().as_bytes()) {
Ok(c) => Ok(c),
Err(e) => Err(Error::new(format!(
"Failed to convert path to CString: {}",
e,
))),
}
}
macro_rules! ffi_try {
( $($function:ident)::*() ) => {
ffi_try_impl!($($function)::*())
};
( $($function:ident)::*( $arg1:expr $(, $arg:expr)* $(,)? ) ) => {
ffi_try_impl!($($function)::*($arg1 $(, $arg)* ,))
};
}
macro_rules! ffi_try_impl {
( $($function:ident)::*( $($arg:expr,)*) ) => {{
let mut err: *mut ::libc::c_char = ::std::ptr::null_mut();
let result = $($function)::*($($arg,)* &mut err);
if !err.is_null() {
return Err(Error::new($crate::ffi_util::error_message(err)));
}
result
}};
}
/// Value which can be converted into a C string.
///
/// The trait is used as argument to functions which wish to accept either
/// [`&str`] or [`&CStr`] arguments while internally need to interact with
/// C APIs. Accepting [`&str`] may be more convenient for users but requires
/// conversion into [`CString`] internally which requires allocation. With this
/// trait, latency-conscious users may choose to prepare `CStr` in advance and
/// then pass it directly without having to incur the conversion cost.
///
/// To use the trait, function should accept `impl CStrLike` and after baking
/// the argument (with [`CStrLike::bake`] method) it can use it as a `&CStr`
/// (since the baked result dereferences into `CStr`).
///
/// # Example
///
/// ```
/// use std::ffi::{CStr, CString};
/// use rocksdb::CStrLike;
///
/// fn strlen(arg: impl CStrLike) -> std::result::Result<usize, String> {
/// let baked = arg.bake().map_err(|err| err.to_string())?;
/// Ok(unsafe { libc::strlen(baked.as_ptr()) })
/// }
///
/// const FOO: &str = "foo";
/// const BAR: &CStr = unsafe { CStr::from_bytes_with_nul_unchecked(b"bar\0") };
///
/// assert_eq!(Ok(3), strlen(FOO));
/// assert_eq!(Ok(3), strlen(BAR));
/// ```
pub trait CStrLike {
type Baked: std::ops::Deref<Target = CStr>;
type Error: std::fmt::Debug + std::fmt::Display;
/// Bakes self into value which can be freely converted into [`&CStr`].
///
/// This may require allocation and may fail if `self` has invalid value.
fn bake(self) -> Result<Self::Baked, Self::Error>;
/// Consumers and converts value into an owned [`CString`].
///
/// If `Self` is already a `CString` simply returns it; if it’s a reference
/// to a `CString` then the value is cloned. In other cases this may
/// require allocation and may fail if `self` has invalid value.
fn into_c_string(self) -> Result<CString, Self::Error>;
}
impl CStrLike for &str {
type Baked = CString;
type Error = std::ffi::NulError;
fn bake(self) -> Result<Self::Baked, Self::Error> {
CString::new(self)
}
fn into_c_string(self) -> Result<CString, Self::Error> {
CString::new(self)
}
}
// This is redundant for the most part and exists so that `foo(&string)` (where
// `string: String` works just as if `foo` took `arg: &str` argument.
impl CStrLike for &String {
type Baked = CString;
type Error = std::ffi::NulError;
fn bake(self) -> Result<Self::Baked, Self::Error> {
CString::new(self.as_bytes())
}
fn into_c_string(self) -> Result<CString, Self::Error> {
CString::new(self.as_bytes())
}
}
impl CStrLike for &CStr {
type Baked = Self;
type Error = std::convert::Infallible;
fn bake(self) -> Result<Self::Baked, Self::Error> {
Ok(self)
}
fn into_c_string(self) -> Result<CString, Self::Error> {
Ok(self.to_owned())
}
}
// This exists so that if caller constructs a `CString` they can pass it into
// the function accepting `CStrLike` argument. Some of such functions may take
// the argument whereas otherwise they would need to allocated a new owned
// object.
impl CStrLike for CString {
type Baked = CString;
type Error = std::convert::Infallible;
fn bake(self) -> Result<Self::Baked, Self::Error> {
Ok(self)
}
fn into_c_string(self) -> Result<CString, Self::Error> {
Ok(self)
}
}
// This is redundant for the most part and exists so that `foo(&cstring)` (where
// `string: CString` works just as if `foo` took `arg: &CStr` argument.
impl<'a> CStrLike for &'a CString {
type Baked = &'a CStr;
type Error = std::convert::Infallible;
fn bake(self) -> Result<Self::Baked, Self::Error> {
Ok(self)
}
fn into_c_string(self) -> Result<CString, Self::Error> {
Ok(self.clone())
}
}
#[test]
fn test_c_str_like_bake() {
fn test<S: CStrLike>(value: S) -> Result<usize, S::Error> {
value
.bake()
.map(|value| unsafe { libc::strlen(value.as_ptr()) })
}
assert_eq!(Ok(3), test("foo")); // &str
assert_eq!(Ok(3), test(&String::from("foo"))); // String
assert_eq!(Ok(3), test(CString::new("foo").unwrap().as_ref())); // &CStr
assert_eq!(Ok(3), test(&CString::new("foo").unwrap())); // &CString
assert_eq!(Ok(3), test(CString::new("foo").unwrap())); // CString
assert_eq!(3, test("foo\0bar").err().unwrap().nul_position());
}
#[test]
fn test_c_str_like_into() {
fn test<S: CStrLike>(value: S) -> Result<CString, S::Error> {
value.into_c_string()
}
let want = CString::new("foo").unwrap();
assert_eq!(Ok(want.clone()), test("foo")); // &str
assert_eq!(Ok(want.clone()), test(&String::from("foo"))); // &String
assert_eq!(
Ok(want.clone()),
test(CString::new("foo").unwrap().as_ref())
); // &CStr
assert_eq!(Ok(want.clone()), test(&CString::new("foo").unwrap())); // &CString
assert_eq!(Ok(want), test(CString::new("foo").unwrap())); // CString
assert_eq!(3, test("foo\0bar").err().unwrap().nul_position());
}