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Merged
lpcox merged 4 commits into from
Jan 16, 2026
Merged

Propagate HTTP backend errors to clients with full context #286

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d3c0f12
Initial plan
Copilot Jan 16, 2026
9cf9f99
Fix HTTP backend error propagation to clients
Copilot Jan 16, 2026
9dc1bc8
Add comprehensive unit and integration tests for HTTP error propagation
Copilot Jan 16, 2026
cfb4d23
Fix formatting issues in test files
Copilot Jan 16, 2026
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46 changes: 41 additions & 5 deletions internal/mcp/connection.go
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Original file line number Diff line number Diff line change
Expand Up @@ -636,11 +636,6 @@ func (c *Connection) sendHTTPRequest(ctx context.Context, method string, params

logConn.Printf("Received HTTP response: status=%d, body_len=%d", httpResp.StatusCode, len(responseBody))

// Check for HTTP errors
if httpResp.StatusCode != http.StatusOK {
return nil, fmt.Errorf("HTTP error: status=%d, body=%s", httpResp.StatusCode, string(responseBody))
}

// Parse JSON-RPC response
// The response might be in SSE format (event: message\ndata: {...})
// Try to parse as JSON first, if that fails, try SSE format
Expand All @@ -651,6 +646,19 @@ func (c *Connection) sendHTTPRequest(ctx context.Context, method string, params
logConn.Printf("Initial JSON parse failed, attempting SSE format parsing")
sseData, sseErr := parseSSEResponse(responseBody)
if sseErr != nil {
// If we have a non-OK HTTP status and can't parse the response,
// construct a JSON-RPC error response with HTTP error details
if httpResp.StatusCode != http.StatusOK {
logConn.Printf("HTTP error status=%d, body cannot be parsed as JSON-RPC", httpResp.StatusCode)
return &Response{
JSONRPC: "2.0",
Error: &ResponseError{
Code: -32603, // Internal error
Message: fmt.Sprintf("HTTP %d: %s", httpResp.StatusCode, http.StatusText(httpResp.StatusCode)),
Data: json.RawMessage(responseBody),
},
}, nil
}
// Include the response body to help debug what the server actually returned
bodyPreview := string(responseBody)
if len(bodyPreview) > 500 {
Expand All @@ -661,11 +669,39 @@ func (c *Connection) sendHTTPRequest(ctx context.Context, method string, params

// Successfully extracted JSON from SSE, now parse it
if err := json.Unmarshal(sseData, &rpcResponse); err != nil {
// If we have a non-OK HTTP status and can't parse the SSE data,
// construct a JSON-RPC error response with HTTP error details
if httpResp.StatusCode != http.StatusOK {
logConn.Printf("HTTP error status=%d, SSE data cannot be parsed as JSON-RPC", httpResp.StatusCode)
return &Response{
JSONRPC: "2.0",
Error: &ResponseError{
Code: -32603, // Internal error
Message: fmt.Sprintf("HTTP %d: %s", httpResp.StatusCode, http.StatusText(httpResp.StatusCode)),
Data: json.RawMessage(responseBody),
},
}, nil
}
return nil, fmt.Errorf("failed to parse JSON data extracted from SSE response: %w\nJSON data: %s", err, string(sseData))
}
logConn.Printf("Successfully parsed SSE-formatted response")
}

// Check for HTTP errors after parsing
// If we have a non-OK status but successfully parsed a JSON-RPC response,
// pass it through (it may already contain an error field)
if httpResp.StatusCode != http.StatusOK {
logConn.Printf("HTTP error status=%d with valid JSON-RPC response, passing through", httpResp.StatusCode)
// If the response doesn't already have an error, construct one
if rpcResponse.Error == nil {
rpcResponse.Error = &ResponseError{
Code: -32603, // Internal error
Message: fmt.Sprintf("HTTP %d: %s", httpResp.StatusCode, http.StatusText(httpResp.StatusCode)),
Data: responseBody,
}
}
}

return &rpcResponse, nil
}

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