expose WAL iterator in the C API

Summary:
A minor change: I wrapped TransactionLogIterator for the C API.
I needed that for the golang binding.
Closes https://github.com/facebook/rocksdb/pull/3304

Differential Revision: D6628736

Pulled By: miasantreble

fbshipit-source-id: 3374f3c64b1d7b225696b8767090917761e2f30a

db/c.cc

@@ -102,6 +102,8 @@ using rocksdb::OptimisticTransactionDB;
 using rocksdb::OptimisticTransactionOptions;
 using rocksdb::Transaction;
 using rocksdb::Checkpoint;
+using rocksdb::TransactionLogIterator;
+using rocksdb::BatchResult;
 using rocksdb::PerfLevel;
 using rocksdb::PerfContext;
 
@@ -135,6 +137,8 @@ struct rocksdb_cuckoo_table_options_t  { CuckooTableOptions rep; };
 struct rocksdb_seqfile_t         { SequentialFile*   rep; };
 struct rocksdb_randomfile_t      { RandomAccessFile* rep; };
 struct rocksdb_writablefile_t    { WritableFile*     rep; };
+struct rocksdb_wal_iterator_t { TransactionLogIterator* rep; };
+struct rocksdb_wal_readoptions_t { TransactionLogIterator::ReadOptions rep; };
 struct rocksdb_filelock_t        { FileLock*         rep; };
 struct rocksdb_logger_t          { shared_ptr<Logger>  rep; };
 struct rocksdb_cache_t           { shared_ptr<Cache>   rep; };
@@ -930,6 +934,54 @@ rocksdb_iterator_t* rocksdb_create_iterator(
   return result;
 }
 
+rocksdb_wal_iterator_t* rocksdb_get_updates_since(
+        rocksdb_t* db, uint64_t seq_number,
+        const rocksdb_wal_readoptions_t* options,
+        char** errptr) {
+  std::unique_ptr<TransactionLogIterator> iter;
+  TransactionLogIterator::ReadOptions ro;
+  if (options!=nullptr) {
+      ro = options->rep;
+  }
+  if (SaveError(errptr, db->rep->GetUpdatesSince(seq_number, &iter, ro))) {
+    return nullptr;
+  }
+  rocksdb_wal_iterator_t* result = new rocksdb_wal_iterator_t;
+  result->rep = iter.release();
+  return result;
+}
+
+void rocksdb_wal_iter_next(rocksdb_wal_iterator_t* iter) {
+    iter->rep->Next();
+}
+
+unsigned char rocksdb_wal_iter_valid(const rocksdb_wal_iterator_t* iter) {
+    return iter->rep->Valid();
+}
+
+void rocksdb_wal_iter_status (const rocksdb_wal_iterator_t* iter, char** errptr) {
+    SaveError(errptr, iter->rep->status());
+}
+
+void rocksdb_wal_iter_destroy (const rocksdb_wal_iterator_t* iter) {
+  delete iter->rep;
+  delete iter;
+}
+
+rocksdb_writebatch_t* rocksdb_wal_iter_get_batch (const rocksdb_wal_iterator_t* iter, uint64_t* seq) {
+  rocksdb_writebatch_t* result = rocksdb_writebatch_create();
+  BatchResult wal_batch = iter->rep->GetBatch();
+  result->rep = * wal_batch.writeBatchPtr.release();
+  if (seq != nullptr) {
+    *seq = wal_batch.sequence;
+  }
+  return result;
+}
+
+uint64_t rocksdb_get_latest_sequence_number (rocksdb_t *db) {
+    return db->rep->GetLatestSequenceNumber();
+}
+
 rocksdb_iterator_t* rocksdb_create_iterator_cf(
     rocksdb_t* db,
     const rocksdb_readoptions_t* options,

include/rocksdb/c.h

@@ -124,6 +124,8 @@ typedef struct rocksdb_optimistictransaction_options_t
     rocksdb_optimistictransaction_options_t;
 typedef struct rocksdb_transaction_t rocksdb_transaction_t;
 typedef struct rocksdb_checkpoint_t rocksdb_checkpoint_t;
+typedef struct rocksdb_wal_iterator_t rocksdb_wal_iterator_t;
+typedef struct rocksdb_wal_readoptions_t rocksdb_wal_readoptions_t;
 
 /* DB operations */
 
@@ -297,6 +299,12 @@ extern ROCKSDB_LIBRARY_API void rocksdb_multi_get_cf(
 extern ROCKSDB_LIBRARY_API rocksdb_iterator_t* rocksdb_create_iterator(
     rocksdb_t* db, const rocksdb_readoptions_t* options);
 
+extern ROCKSDB_LIBRARY_API rocksdb_wal_iterator_t* rocksdb_get_updates_since(
+        rocksdb_t* db, uint64_t seq_number,
+        const rocksdb_wal_readoptions_t* options,
+        char** errptr
+);
+
 extern ROCKSDB_LIBRARY_API rocksdb_iterator_t* rocksdb_create_iterator_cf(
     rocksdb_t* db, const rocksdb_readoptions_t* options,
     rocksdb_column_family_handle_t* column_family);
@@ -400,6 +408,14 @@ extern ROCKSDB_LIBRARY_API const char* rocksdb_iter_value(
 extern ROCKSDB_LIBRARY_API void rocksdb_iter_get_error(
     const rocksdb_iterator_t*, char** errptr);
 
+extern ROCKSDB_LIBRARY_API void rocksdb_wal_iter_next(rocksdb_wal_iterator_t* iter);
+extern ROCKSDB_LIBRARY_API unsigned char rocksdb_wal_iter_valid(
+        const rocksdb_wal_iterator_t*);
+extern ROCKSDB_LIBRARY_API void rocksdb_wal_iter_status (const rocksdb_wal_iterator_t* iter, char** errptr) ;
+extern ROCKSDB_LIBRARY_API rocksdb_writebatch_t* rocksdb_wal_iter_get_batch (const rocksdb_wal_iterator_t* iter, uint64_t* seq) ;
+extern ROCKSDB_LIBRARY_API uint64_t rocksdb_get_latest_sequence_number (rocksdb_t *db);
+extern ROCKSDB_LIBRARY_API void rocksdb_wal_iter_destroy (const rocksdb_wal_iterator_t* iter) ;
+
 /* Write batch */
 
 extern ROCKSDB_LIBRARY_API rocksdb_writebatch_t* rocksdb_writebatch_create();