sigoden/aichat · error

Unrecognized message, message_type

Error message

Unrecognized message, message_type: {message_type}, smithy_type: {smithy_type}

What it means

The Bedrock EventStream decoder received a message whose (message_type, smithy_type) pair matches none of the known branches (event/exception variants). The library bails with 'Unrecognized message' echoing both identifiers. This guards against new or unknown smithy event shapes being silently dropped.

Solutions

1. Log the message_type and smithy_type values reported and compare against Bedrock's EventStream API docs
2. Update the library (and aws-smithy event-stream handling) to a version that knows the new event type
3. File/track an issue upstream to add a handler for the reported smithy_type
4. Bypass intermediaries/proxies that might rewrite the event stream
5. Pin to a Bedrock API version/model whose stream events are supported

Example fix

// before
rig = "0.x"  # old client without new event handler
// after
rig = "latest"  # or patch the match in src/client/bedrock.rs to handle the new smithy_type

match client.chat_completions_streaming(req).await {
    Err(e) if e.to_string().starts_with("Unrecognized message") => {
        log::warn!("unknown bedrock event: {e}; falling back to non-streaming");
        client.chat_completions(req).await
    }
    r => r,
}

When it happens

Trigger: chat_completions_streaming decodes an event-stream message whose message_type/smithy_type combination falls into the catch-all '_' arm of the match in the streaming loop.

Common situations: AWS introduced a new event type not yet handled by this library version, a protocol/SDK version mismatch between reqwest eventsource handling and Bedrock's stream, or corrupted/unexpected framing from a proxy.

Understand the failure class

Background: "invalid response format", "malformed payload", "missing data field": when an API returns 200 but the response shape is wrong — this error's family across 23 libraries.

Related errors

• Invalid response data
• Invalid response data
• The model does not support network images
• {err}
• Failed to read json stream

AI-assisted analysis of sigoden/aichat@82976d349a (2026-09-09). Data as JSON: /api/errors/9f338676466ba0b9. Report an issue: GitHub.

Appendix: source

Thrown at src/client/bedrock.rs:294

                                })?;
                                handler.tool_call(ToolCall::new(
                                    function_name.clone(),
                                    arguments,
                                    Some(function_id.clone()),
                                ))?;
                            }
                        }
                        _ => {}
                    }
                }
                ("exception", _) => {
                    let payload = base64_decode(message.payload())?;
                    let data = String::from_utf8_lossy(&payload);

                    bail!("Invalid response data: {data} (smithy_type: {smithy_type})")
                }
                _ => {
                    bail!("Unrecognized message, message_type: {message_type}, smithy_type: {smithy_type}",);
                }
            }
        }
    }
    Ok(())
}

async fn embeddings(builder: RequestBuilder) -> Result<EmbeddingsOutput> {
    let res = builder.send().await?;
    let status = res.status();
    let data: Value = res.json().await?;

    if !status.is_success() {
        catch_error(&data, status.as_u16())?;
    }

    let res_body: EmbeddingsResBody =
        serde_json::from_value(data).context("Invalid embeddings data")?;

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