Message Limits

Configure size limits for incoming requests and outgoing responses to protect against memory exhaustion and oversized payloads.

Configuration

use connectrpc_axum::{MakeServiceBuilder, MessageLimits};

// Default: no limits
let limits = MessageLimits::new();

// Set receive limit only
let limits = MessageLimits::new()
    .receive_max_bytes(16 * 1024 * 1024);  // 16MB

// Set both receive and send limits
let limits = MessageLimits::new()
    .receive_max_bytes(16 * 1024 * 1024)  // 16MB for requests
    .send_max_bytes(8 * 1024 * 1024);     // 8MB for responses

MakeServiceBuilder::new()
    .add_router(router)
    .message_limits(limits)
    .build()

Receive Limit

receive_max_bytes limits the size of incoming request messages. This protects the server from clients sending oversized requests that could exhaust memory.

Setting	Default	Error
receive_max_bytes	No limit	ResourceExhausted

When exceeded, the server returns a ResourceExhausted error before processing the request.

Axum Router Behavior

When you add plain HTTP routes via add_axum_router(), the receive limit is applied using Tower's RequestBodyLimitLayer. This provides consistent size limiting across your entire service.

Route Type	Error Response
Connect routes	ResourceExhausted (JSON error)
Axum routes	413 Payload Too Large (HTTP status)

TIP

Both route types respect the same receive_max_bytes configuration, but return errors appropriate to their protocol.

Send Limit

send_max_bytes limits the size of outgoing response messages. This prevents the server from accidentally sending oversized responses that could overwhelm clients.

Setting	Default	Error
send_max_bytes	No limit	ResourceExhausted

// Convenience method for setting send limit only
MakeServiceBuilder::new()
    .add_router(router)
    .send_max_bytes(8 * 1024 * 1024)  // 8MB
    .build()

Compression Interaction

Following connect-go's behavior, the send size is checked after encoding and compression. This means:

• If compression reduces the message below the limit, it succeeds
• If compression is not applied (message too small or disabled), the uncompressed size is checked
• Error messages indicate whether the checked size was compressed or not

Streaming

For streaming responses, each message is checked individually. If a message exceeds the limit:

1. All previous messages are delivered successfully
2. The oversized message triggers a ResourceExhausted error
3. The stream terminates with the error

WARNING

By default, no limits are applied. For production environments, consider setting appropriate limits to protect against memory exhaustion attacks.