Compression

Default Compression

When using build_connect() on a service builder, gzip compression is enabled by default:

let router = helloworldservice::HelloWorldServiceBuilder::new()
    .say_hello(say_hello)
    .build_connect();  // Includes default gzip compression

This uses MakeServiceBuilder::new() internally, which provides:

• Default gzip compression and decompression
• Standard ConnectLayer configuration

Custom Configuration

For custom compression settings, use MakeServiceBuilder directly:

use connectrpc_axum::{MakeServiceBuilder, CompressionConfig, CompressionLevel};

MakeServiceBuilder::new()
    .add_router(router)
    .compression(
        CompressionConfig::new(512)           // Compress responses >= 512 bytes
            .level(CompressionLevel::Default) // Use default compression level
    )
    .build()

Compression Level

Control the compression quality/speed tradeoff:

use connectrpc_axum::{CompressionConfig, CompressionLevel};

// Fastest compression (larger output, less CPU)
let config = CompressionConfig::default().level(CompressionLevel::Fastest);

// Best compression (smaller output, more CPU)
let config = CompressionConfig::default().level(CompressionLevel::Best);

// Algorithm default (recommended for most cases)
let config = CompressionConfig::default().level(CompressionLevel::Default);

// Precise level (algorithm-specific, clamped to max)
let config = CompressionConfig::default().level(CompressionLevel::Precise(6));

Level	Description
Fastest	Prioritize speed over compression ratio
Best	Prioritize compression ratio over speed
Default	Algorithm's default balance
Precise(n)	Exact level (clamped to algorithm's max)

TIP

The compression level applies uniformly to all enabled algorithms (gzip, deflate, br, zstd). Tower-http does not support per-algorithm level configuration.

Supported Encodings

Encoding	Feature Flag
gzip	(always enabled)
deflate	compression-deflate
br	compression-br
zstd	compression-zstd
identity	(always enabled)

Enable additional algorithms in Cargo.toml:

[dependencies]
connectrpc-axum = { version = "...", features = ["compression-br", "compression-zstd"] }

# Or enable all
connectrpc-axum = { version = "...", features = ["compression-full"] }

Configuration Options

Minimum Bytes Threshold

Only compress responses larger than a threshold:

use connectrpc_axum::CompressionConfig;

// Compress responses >= 512 bytes
let config = CompressionConfig::new(512);

// Default: 0 bytes (compress everything, matching connect-go)
let config = CompressionConfig::default();

Disabling Compression

use connectrpc_axum::MakeServiceBuilder;

MakeServiceBuilder::new()
    .add_router(router)
    .disable_compression()
    .build()

When disabled, no compression or decompression layers are added - more efficient than using a high threshold.

Request Decompression

The server automatically decompresses incoming requests. Unsupported encodings return Unimplemented error listing enabled encodings.

gRPC Compression (Tonic)

gRPC compression is configured separately using Tonic's built-in methods. See Tonic Integration → gRPC Compression.

TIP

MakeServiceBuilder::compression() only affects Connect RPCs. gRPC compression is handled by Tonic.

Implementation Notes

Architecture

• Unary RPCs: HTTP body compression via Tower's CompressionLayer (Accept-Encoding / Content-Encoding)
• Streaming RPCs: Per-envelope compression (Connect-Accept-Encoding / Connect-Content-Encoding)

Protocol Headers

RPC Type	Request	Response Negotiation
Unary	Content-Encoding	Accept-Encoding
Streaming	Connect-Content-Encoding	Connect-Accept-Encoding

Negotiation

Following connect-go: first supported encoding wins, q=0 means disabled, other q-values ignored.

Conformance with connect-go

• Default min_bytes is 0
• Streaming compression only when Connect-Accept-Encoding present
• First-match-wins negotiation (no q-value weighting)
• Respects q=0 as "not acceptable"