mpack

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The Write API

The Write API encodes structured data to MessagePack.

// encode to memory buffer
char* data;
size_t size;
mpack_writer_t writer;
mpack_writer_init_growable(&writer, &data, &size);

// write the example on the msgpack homepage
mpack_build_map(&writer);
mpack_write_cstr(&writer, "compact");
mpack_write_bool(&writer, true);
mpack_write_cstr(&writer, "schema");
mpack_write_uint(&writer, 0);
mpack_complete_map(&writer);

// finish writing
if (mpack_writer_destroy(&writer) != mpack_ok) {
    fprintf(stderr, "An error occurred encoding the data!\n");
    return;
}

// use the data
do_something_with_data(data, size);
free(data);

In the above example, we encode to a growable memory buffer. The writer can instead write to a pre-allocated or stack-allocated buffer (with up-front sizes for compound types), avoiding the need for memory allocation. The writer can also be provided with a flush function (such as a file or socket write function) to call when the buffer is full or when writing is done.

If any error occurs, the writer is placed in an error state. The writer will flag an error if too much data is written, if the wrong number of elements are written, if an allocation failure occurs, if the data could not be flushed, etc. No additional error handling is needed in the above code; any subsequent writes are ignored when the writer is in an error state, so you don’t need to check every write for errors.

The above example uses mpack_build_map() to automatically determine the number of key-value pairs contained. If you know up-front the number of elements needed, you can pass it to mpack_start_map() instead. In that case the corresponding mpack_finish_map() will assert in debug mode that the expected number of elements were actually written, which is something that other MessagePack C/C++ libraries may not do.

Comparison With Other Parsers

MPack is rich in features while maintaining very high performance and a small code footprint. Here’s a short feature table comparing it to other C parsers:

	MPack (v1.1)	msgpack-c (v3.3.0)	CMP (v19)	CWPack (v1.3.1)
No libc requirement	✓		✓	✓
Growable memory writer	✓	✓		✓*
File I/O helpers	✓	✓		✓*
Stateful error handling	✓		✓
Incremental parser	✓		✓	✓
Tree stream parser	✓	✓
Compound size tracking	✓
Automatic compound size	✓

A larger feature comparison table is available here which includes descriptions of the various entries in the table.

This benchmarking suite compares the performance of MPack to other implementations of schemaless serialization formats. MPack outperforms all JSON and MessagePack libraries (except CWPack), and in some tests MPack is several times faster than RapidJSON for equivalent data.

Testing MPack

The MPack build process does not build MPack into a library; it is used to build and run the unit tests. You do not need to build MPack or the unit testing suite to use MPack.

See test/README.md for information on how to test MPack.