# rust-brotli
[](https://crates.io/crates/brotli)
[](https://travis-ci.org/dropbox/rust-brotli)
# What's new in 9.0.0
* Custom dictionaries. Depends on brotli-decompressor 6.0.0, whose dictionary
support is re-exported from this crate, so `brotli::Decompressor`,
`brotli::DecompressorWriter` and `brotli::BrotliState` all gain
`attach_dictionary` and `attach_serialized_dictionary`:
* `attach_dictionary` takes a raw LZ77 prefix dictionary and is the
equivalent of the C `BrotliDecoderAttachDictionary` with
`BROTLI_SHARED_DICTIONARY_RAW`. Up to 15 may be attached, and they must be
attached before the first read or write.
* Dictionaries now live in their own buffers (the C implementation's
"compound dictionary" scheme) rather than being copied into the ring
buffer, so they stay addressable after the ring buffer wraps. Streams where
output plus dictionary exceed the window decode correctly, and dictionaries
larger than the window are no longer truncated.
* `attach_serialized_dictionary` accepts the serialized shared dictionary
container (magic `0x91 0x00`) from
draft-vandevenne-shared-brotli-format, including embedded LZ77 prefix
dictionaries, custom word lists, custom transform lists and context-based
dictionary selection.
* Breaking: the allocator crates move a major version, to alloc-no-stdlib 3.x
and alloc-stdlib 0.3.x. alloc-no-stdlib's `Allocator`/`SliceWrapper` traits
are part of the public API of this crate and of brotli-decompressor, so a
crate that passes its own allocator to rust-brotli must move to the same
generation: with a split, an allocator built against 2.x no longer satisfies
the 3.x `Allocator` bound. The dependency ranges are pinned so that the
resolver cannot span the major.
* Breaking, FFI: `BrotliDecoderSetParameter` now returns `BROTLI_BOOL` and
takes the parameter selector as an `int`, matching the prototype in
`c/brotli/decode.h` and the C library. It returns false for an unrecognized
selector instead of forming an invalid enum discriminant at the ABI boundary.
C callers that ignored the return value are unaffected; Rust callers of
`CBrotliDecoderSetParameter` should pass `BrotliDecoderParameter::... as i32`.
* New non-default `portable-float` feature that makes encoder output
target-independent, so the same input compresses to byte-identical output on
every target. It routes the cost estimators' `log2`/`powf` onto the
table-driven implementations `no_std` builds already use, instead of the
platform libm, whose one-ULP differences could move a block-split boundary.
It is off by default because it changes the emitted bytes and costs about
0.006% of ratio.
* The `safe` feature is now declared in `Cargo.toml`. The `cfg` had been
referenced from `src/ffi` since the FFI was added but was never listed, so it
could not actually be turned on. With it, the FFI drops the two `unsafe impl
Send` lines and the encoder and multicompress entry points that rely on them;
the decoder FFI is unaffected.
* Fix #257: `SendableMemoryBlock<T>` in the FFI allocator no longer claims
`Send` for a `T` that is not itself `Send`.
* Fix #258: `BroCatli` recognizes a complete empty stream as soon as its
window, ISLAST and ISLASTEMPTY bits are buffered, rather than waiting for the
normal four- or five-byte prefix.
* The `simd` feature builds on current nightly again (`Mask::to_int` was
renamed to `Mask::to_simd`).
* The `seccomp` feature builds again: the calloc-backed allocator macros are
brought into scope in the `brotli` binary, and `alloc-no-stdlib`'s `unsafe`
feature, which gates them on 3.x, is enabled by it.
## What's new in 8.0.4
Fix: adjust versions of rust-decompressor and rust-alloc-no-stdlib and
alloc-stdlib so the Allocator<> trait is identical for all associated crates.
Return BrotliFileNotCraftedForConcatenation when a new stream header advertises more whole source bytes than have been buffered. This prevents the unsigned subtraction in shift_and_check_new_stream_header from underflowing on truncated metadata headers.
Return NULL from BrotliEncoderCreateInstance and BrotliEncoderCreateWorkPool when a caller-provided allocator returns NULL, rather than writing state through a NULL pointer.
Wrap the mutable Broccoli FFI entry points in a local catch_unwind helper, matching the encoder FFI convention so Rust panics do not unwind across extern C when std panic catching is available.
Return BrotliFileNotCraftedForConcatenation on caught panics and keep the existing pass-through behavior for no-std or pass-through-ffi-panics builds. Add regression coverage for a crafted stream input that previously panicked through BroccoliConcatStream.
Reject serialized BroCatli buffers with out-of-range live state fields before constructing the state. This keeps deserialize_from_buffer on its existing Result<BroCatli, ()> API while returning Err(()) for corrupt buffers that would otherwise panic on later use
## What's new in 8.0.3
Fix: avoid panic across Broccoli FFI boundary with BroCatLi
Fix: CompressMulti worker joins on errors
## What's new in 8.0.2
Fix for memory leak in ffi API
## What's new in 8.0.1
Compatibility for ffi builds
## What's new in 8.0.0
* Fixed LZ77 to comply with the specification
* No longer seed the context by the end of the lz77 dictionary. Instead use
zero for the seed as would happen without a dictionary. This matches the
behavior of brotli with a custom dictionary as specified in
* https://datatracker.ietf.org/doc/draft-vandevenne-shared-brotli-format/
## What's new in 7.0.0
* Fix error with short writes
* allow quality=10 for certain APIs and make it default to 9.5
## What's new in 6.0.0
* Remove unused SIMD use statements
* hide a few warnings - these are TODOs, and should be fixed in separate PRs
* do NOT build SIMD as part of MSRV -- doesn't make any sense to combine nightly with MSRV
## What's new in 5.0.0
* The FFI is no longer active by default to avoid ODR issues if multiple versions of brotli are included in several dependent crates.
## What's new in 4.0.0
Pinned to a rust-brotli-decompressor that can disable the ffi with the ffi-api
flag.
This can help avoid symbol conflicts with other brotli libs.
## What's new in 3.5
Updated SIMD support.
Better CI integration.
Cleaned up some of the clippy warnings.
## What's new in 3.4
Brotli decompressor's reader and writer has better behavior when operating upon brotli streams with extra bits at the end.
Optional features like stdsimd are now tested or disabled for now.
## What's new in 3.2
* into_inner conversions for both Reader and Writer classes
## What's new in 3.0
* A fully compatible FFI for drop-in compatibiltiy with the https://github.com/google/brotli binaries
* custom allocators fully supported
* Multithreaded compression so multiple threads can operate in unison on a single file
* Concatenatability mode to add the feature requested in https://github.com/google/brotli/issues/628
* binary tool catbrotli can accomplish this if the first file was specified with -apendable and the second with -catable
* validation mode where a file is double-checked to be able to be decompressed with the same settings; useful for benchmarking or fuzzing
* Magic Number: where the brotli file can have a useful header with a few magic bytes, concatability info and a final output size for pre-allocating memory
## What's new in 2.5
* In 2.5 The callback also passes down an allocator to make new StaticCommands and PDFs and 256 bit floating point vectors.
* In 2.4 The callback with the compression intermediate representation now passes a full metablock at a time. Also these items are mutable
in case futher optimization is desired
## What's new in 2.3
* Flush now produces output instead of calling finish on the stream. This allows you to use the writer abstraction to
get immediate output without having to resort to the CompressStream internal abstraction
## Project Requirements
Direct no-stdlib port of the C brotli compressor to Rust
no dependency on the Rust stdlib: this library would be ideal for decompressing within a rust kernel among other things.
This is useful to see how C and Rust compare in an apples-to-apples
comparison where the same algorithms and data structures and
optimizations are employed.
## Compression Usage
Rust brotli currently supports compression levels 0 - 11
They should be bitwise identical to the brotli C compression engine at compression levels 0-9
Recommended lg_window_size is between 20 and 22
### With the io::Read abstraction
```rust
let mut input = brotli::CompressorReader::new(&mut io::stdin(), 4096 /* buffer size */,
quality as u32, lg_window_size as u32);
```
then you can simply read input as you would any other io::Read class
### With the io::Write abstraction
```rust
let mut writer = brotli::Compressor::new(&mut io::stdout(), 4096 /* buffer size */,
quality as u32, lg_window_size as u32);
```
There are also methods to build Compressor Readers or Writers using the with_params static function
eg:
```rust
let params = BrotliEncoderParams::default();
// modify params to fit the application needs
let mut writer = brotli::Compressor::with_params(&mut io::stdout(), 4096 /* buffer size */,
params);
```
or for the reader
```rust
let params = BrotliEncoderParams::default();
// modify params to fit the application needs
let mut writer = brotli::CompressorReader::with_params(&mut io::stdin(), 4096 /* buffer size */,
params);
```
### With the Stream Copy abstraction
```rust
match brotli::BrotliCompress(&mut io::stdin(), &mut io::stdout(), &brotli_encoder_params) {
Ok(_) => {},
Err(e) => panic!("Error {:?}", e),
}
```
## Decompression Usage
### With the io::Read abstraction
```rust
let mut input = brotli::Decompressor::new(&mut io::stdin(), 4096 /* buffer size */);
```
then you can simply read input as you would any other io::Read class
### With the io::Write abstraction
```rust
let mut writer = brotli::DecompressorWriter::new(&mut io::stdout(), 4096 /* buffer size */);
```
### With the Stream Copy abstraction
```rust
match brotli::BrotliDecompress(&mut io::stdin(), &mut io::stdout()) {
Ok(_) => {},
Err(e) => panic!("Error {:?}", e),
}
```
### With a custom dictionary
A raw LZ77 prefix dictionary is attached before the first read (or the first
write, for `DecompressorWriter`); up to 15 may be attached. The dictionary is
handed over as the allocator's memory type, and `attach_dictionary` returns
false if it could not be attached.
```rust
use brotli::enc::StandardAlloc;
use brotli::{Allocator, Decompressor, SliceWrapperMut};
let mut alloc = StandardAlloc::default();
let mut dict = <StandardAlloc as Allocator<u8>>::alloc_cell(&mut alloc, dictionary.len());
dict.slice_mut().clone_from_slice(dictionary);
let mut input = brotli::Decompressor::new(&mut io::stdin(), 4096 /* buffer size */);
assert!(input.attach_dictionary(dict));
```
The dictionary lives in its own buffer rather than in the ring buffer, so it
stays addressable for the whole stream even when it is larger than the window or
when the output outgrows the window.
`attach_serialized_dictionary` takes the same kind of argument, but the bytes are
a serialized shared dictionary container (magic `0x91 0x00`) which may carry an
LZ77 prefix dictionary, a custom word list and a custom transform list.
The matching binary tool flag is `-customdictionary=<file>`, on both compression
and decompression:
```
brotli -c -customdictionary=dict.bin < plaintext > compressed.br
brotli -customdictionary=dict.bin < compressed.br > plaintext
```
### With manual memory management
There are 3 steps to using brotli without stdlib
1. setup the memory manager
2. setup the BrotliState
3. in a loop, call BrotliDecompressStream
in Detail
```rust
// at global scope declare a MemPool type -- in this case we'll choose the heap to
// avoid unsafe code, and avoid restrictions of the stack size
declare_stack_allocator_struct!(MemPool, heap);
// at local scope, make a heap allocated buffers to hold uint8's uint32's and huffman codes
let mut u8_buffer = define_allocator_memory_pool!(4096, u8, [0; 32 * 1024 * 1024], heap);
let mut u32_buffer = define_allocator_memory_pool!(4096, u32, [0; 1024 * 1024], heap);
let mut hc_buffer = define_allocator_memory_pool!(4096, HuffmanCode, [0; 4 * 1024 * 1024], heap);
let heap_u8_allocator = HeapPrealloc::<u8>::new_allocator(4096, &mut u8_buffer, bzero);
let heap_u32_allocator = HeapPrealloc::<u32>::new_allocator(4096, &mut u32_buffer, bzero);
let heap_hc_allocator = HeapPrealloc::<HuffmanCode>::new_allocator(4096, &mut hc_buffer, bzero);
// At this point no more syscalls are going to be needed since everything can come from the allocators.
// Feel free to activate SECCOMP jailing or other mechanisms to secure your application if you wish.
// Now it's possible to setup the decompressor state
let mut brotli_state = BrotliState::new(heap_u8_allocator, heap_u32_allocator, heap_hc_allocator);
// at this point the decompressor simply needs an input and output buffer and the ability to track
// the available data left in each buffer
loop {
result = BrotliDecompressStream(&mut available_in, &mut input_offset, &input.slice(),
&mut available_out, &mut output_offset, &mut output.slice_mut(),
&mut written, &mut brotli_state);
// just end the decompression if result is BrotliResult::ResultSuccess or BrotliResult::ResultFailure
}
```
This interface is the same interface that the C brotli decompressor uses
Also feel free to use custom allocators that invoke Box directly.
This example illustrates a mechanism to avoid subsequent syscalls after the initial allocation
## Using the C interface
rust-brotli is a drop-in replacement for the official https://github.com/google/brotli C
implementation. That means you can use it from any place that supports that library.
To build rust-brotli in this manner enter the c subdirectory and run make there
cd c && make
this should build c/target/release/libbrotli.so and should build the vanilla
command line tool in C for compressing and decompressing any brotli file.
the libbrotli.so in c/target/release should be able to replace any other libbrotli.so
file, but with all the advantages of using safe rust (except in the FFI bindings)
The code also allows a wider range of options, including forcing the prediction mode
(eg UTF8 vs signed vs MSB vs LSB) and changing the weight of the literal cost from 540
to other values.
Custom dictionaries are reachable from C as well: `brotli/decode.h` declares
`BrotliDecoderAttachDictionary`, which takes a `BrotliSharedDictionaryType` of
either `BROTLI_SHARED_DICTIONARY_RAW` or `BROTLI_SHARED_DICTIONARY_SERIALIZED`
from `brotli/shared_dictionary.h`. As in the C library, the dictionary must be
attached before decoding starts, ownership is not transferred, and the buffer
must stay alive until the decoder instance is destroyed.
```c
BrotliDecoderState *state = BrotliDecoderCreateInstance(NULL, NULL, NULL);
if (!BrotliDecoderAttachDictionary(state, BROTLI_SHARED_DICTIONARY_RAW,
dict_size, dict)) {
/* dictionary was corrupt, or the 15 dictionary limit was reached */
}
```
## Stream Concatenation
Brotli supports creating streams that can be concatenated together, useful for streaming
scenarios where you want to compress chunks independently but decompress as a single stream.
### Simple Concatenation (Fast)
Use `-bare -appendable` for the first file and `-bare -catable` for subsequent files.
These can be combined using plain byte concatenation without special tools, with a
finalization byte (`0x03`) added at the end:
```bash
# Create the base file with header but no trailer (must specify window size)
brotli -c -bare -appendable -w22 input1.txt > base.br
# Create bare-catable streams (no header, no trailer, same window size!)
brotli -c -bare -catable -w22 input2.txt > part2.br
brotli -c -bare -catable -w22 input3.txt > part3.br
# Simple concatenation with finalization byte
# Note: printf '\x03' adds the required final byte
(cat base.br part2.br part3.br; printf '\x03') > combined.br
# Decompress normally
brotli -d combined.br -o output.txt
```
**Advantages:**
- Instant concatenation (no processing)
- No special tools required
- Bare streams can be appended in any order
**Requirements:**
- All files must use the same window size (`-w22` recommended)
- First file: `-bare -appendable` (has header, no trailer)
- Subsequent files: `-bare -catable` (no header, no trailer, no dictionary refs)
- A final `0x03` byte must be appended to complete the stream
### Efficient Concatenation (Size-optimized)
Use the `catbrotli` tool with `-catable` and `-appendable` flags for better compression
at the cost of processing time:
```bash
# Create files for catbrotli tool
brotli -c -appendable input1.txt > appendable.br
brotli -c -catable input2.txt > catable1.br
brotli -c -catable input3.txt > catable2.br
# Concatenate using catbrotli tool
catbrotli appendable.br catable1.br catable2.br > combined.br
```
**Tradeoff:** `catbrotli` produces smaller output but requires CPU time to process the
streams intelligently. Use this when size matters more than concatenation speed.
### Technical Reference: Stream Parameter Interactions
**Stream Types and Their Parameters:**
| Standard | false | false | false | false | true | Normal brotli stream with header and trailer |
| First (simple concat) | true | true | true | false | true | Has header, no trailer - for simple `cat` concatenation |
| Subsequent (simple concat) | true | true | true | true | false | No header, no trailer, no dict refs - append to first |
| Appendable (catbrotli) | false | varies | true | false | true | For use with `catbrotli` tool |
| Catable (catbrotli) | false | varies | true | true | false | For use with `catbrotli` tool |
**Important Notes:**
- **Parameter dependencies are applied automatically** by the library in both CLI and API usage
- The library's `SanitizeParams` function ensures:
- `catable = true` → automatically sets `appendable = true` and `use_dictionary = false`
- `bare_stream = true` → automatically sets `byte_align = true`
- `!appendable` → automatically sets `byte_align = false`
- When using `set_parameter()`, dependencies are applied immediately
- When setting fields directly (e.g., `params.catable = true`), dependencies are applied during compression initialization
- **No manual fixups needed** - the library handles all parameter dependencies
- The `use_dictionary = false` for catable streams prevents references to bytes before the chunk boundary
- Simple concatenation requires a final `0x03` byte to complete the stream
- All concatenated streams must use the same window size
**Example API Usage:**
```rust
// First file: -bare -appendable equivalent
params.bare_stream = true; // Sets bare_stream=true, byte_align=true (automatic)
params.appendable = true; // Sets appendable=true
// Subsequent files: -bare -catable equivalent
params.bare_stream = true; // Sets bare_stream=true, byte_align=true (automatic)
params.catable = true; // Sets catable=true, appendable=true, use_dictionary=false (automatic)
// All parameter dependencies are handled automatically by the library.
// No manual fixups required - just set the primary flags you want.
```