Brotli Compression

The Brotli module provides high-ratio compression services for HTTP content encoding.

Overview

Brotli is a modern compression algorithm that typically achieves better compression ratios than gzip/deflate, especially for text content. It’s widely supported for HTTP Content-Encoding: br.

Basic Usage

#include <boost/http/brotli.hpp>

namespace brotli = boost::http::brotli;

// Create context and install services
boost::capy::polystore ctx;
auto& encoder = brotli::install_encode_service(ctx);
auto& decoder = brotli::install_decode_service(ctx);

Compression

// Compress data
std::vector<char> input = /* ... */;
std::vector<char> output(brotli::encodeBound(input.size()));

brotli::encode_result result = encoder.encode(
    input.data(), input.size(),
    output.data(), output.size()
);

output.resize(result.bytes_written);

Quality Levels

Brotli quality ranges from 0 (fastest) to 11 (best compression):

// Set quality (0-11)
encoder.set_quality(6);  // Balanced

// Quality guidelines:
// 0-4:  Fast compression, larger output
// 5-6:  Balanced (good for real-time)
// 7-9:  Slower, better compression
// 10-11: Very slow, best compression (static content)

Decompression

// Decompress data
std::vector<char> compressed = /* ... */;
std::vector<char> output(expected_size);

brotli::decode_result result = decoder.decode(
    compressed.data(), compressed.size(),
    output.data(), output.size()
);

output.resize(result.bytes_written);

Shared Dictionary

Brotli supports shared dictionaries for improved compression of similar content:

// Load custom dictionary
brotli::shared_dictionary dict = load_dictionary();

// Install services with dictionary
auto& encoder = brotli::install_encode_service(ctx, dict);
auto& decoder = brotli::install_decode_service(ctx, dict);

Error Handling

brotli::encode_result result = encoder.encode(input, output);

if (result.ec == brotli::error::invalid_input)
{
    // Malformed input
}

Integration with HTTP

The brotli services integrate with HTTP parser and serializer through content encoding:

// Parser automatically decompresses Content-Encoding: br
http::response_parser::config cfg;
cfg.apply_brotli_decoder = true;

// Serializer automatically compresses when Content-Encoding is set
http::serializer::config ser_cfg;
ser_cfg.apply_brotli_encoder = true;

Performance Considerations

Quality	Speed	Ratio	Use Case
0-4	Fast	Lower	Real-time compression
5-6	Medium	Good	General purpose
7-9	Slow	Better	Offline compression
10-11	Very slow	Best	Static assets

Quality

Speed

Ratio

Use Case

0-4

Fast

Lower

Real-time compression

5-6

Medium

Good

General purpose

7-9

Slow

Better

Offline compression

10-11

Very slow

Best

Static assets

Reference

Functions

Function Description

Function	Description
`brotli::install_encode_service`	Install compression service
`brotli::install_decode_service`	Install decompression service

brotli::install_encode_service

Install compression service

brotli::install_decode_service

Install decompression service

Types

Type Description

Type	Description
`brotli::shared_dictionary`	Shared dictionary for improved compression

brotli::shared_dictionary

Shared dictionary for improved compression