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fix(mcp-agent): stream native mcp-server stderr to logs

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The previous implementation buffered stderr from the native mcp-server process and only logged the full buffer content when the process exited. This prevented real-time viewing of logs from the server.

This change modifies the native process startup logic (`startProcess_locked`) to use `cmd.StderrPipe()` instead of assigning `cmd.Stderr` to a buffer. A separate goroutine is now launched within the process monitoring goroutine. This new goroutine uses a `bufio.Scanner` to continuously read lines from the stderr pipe and logs them using the Navidrome logger (`log.Info`) with an `[MCP-SERVER]` prefix.

This ensures logs from the native mcp-server appear in Navidrome's logs immediately as they are written.

(Note: Also includes update to McpServerPath constant to point to the native binary.)

Signed-off-by: Deluan <deluan@navidrome.org>
This commit is contained in:
Deluan 2025-04-19 19:42:22 -04:00
parent bcc3643c81
commit c7d7ec306e
2 changed files with 25 additions and 5 deletions
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1
core/agents/mcp/mcp_agent.go
View File

@ -24,6 +24,7 @@ const (
McpAgentName = "mcp"
initializationTimeout = 5 * time.Second
// McpServerPath defines the location of the MCP server executable or WASM module.
// McpServerPath = "./core/agents/mcp/mcp-server/mcp-server"
McpServerPath = "./core/agents/mcp/mcp-server/mcp-server.wasm"
McpToolNameGetBio = "get_artist_biography"
McpToolNameGetURL = "get_artist_url"

29
core/agents/mcp/mcp_process_native.go
View File

@ -1,6 +1,7 @@
package mcp
import (
"bufio"
"context"
"errors"
"fmt"
@ -197,12 +198,18 @@ func (n *MCPNative) startProcess_locked(ctx context.Context) (stdin io.WriteClos
return nil, nil, nil, fmt.Errorf("native stdout pipe: %w", err)
}
var stderrBuf strings.Builder
cmd.Stderr = &stderrBuf
// Get stderr pipe to stream logs
stderrPipe, err := cmd.StderrPipe()
if err != nil {
_ = stdinPipe.Close()
_ = stdoutPipe.Close()
return nil, nil, nil, fmt.Errorf("native stderr pipe: %w", err)
}
if err = cmd.Start(); err != nil {
_ = stdinPipe.Close()
_ = stdoutPipe.Close()
// stderrPipe gets closed implicitly if cmd.Start() fails
return nil, nil, nil, fmt.Errorf("native start: %w", err)
}
@ -210,12 +217,24 @@ func (n *MCPNative) startProcess_locked(ctx context.Context) (stdin io.WriteClos
currentCmd := cmd // Capture the current cmd pointer for the goroutine
log.Info(ctx, "Native MCP server process started", "pid", currentPid)
// Start monitoring goroutine
// Start monitoring goroutine for process exit
go func() {
// Start separate goroutine to stream stderr
go func() {
scanner := bufio.NewScanner(stderrPipe)
for scanner.Scan() {
log.Info("[MCP-SERVER] " + scanner.Text())
}
if err := scanner.Err(); err != nil {
log.Error("Error reading MCP server stderr", "pid", currentPid, "error", err)
}
log.Debug("MCP server stderr pipe closed", "pid", currentPid)
}()
waitErr := currentCmd.Wait() // Wait for the specific process this goroutine monitors
n.mu.Lock()
stderrStr := stderrBuf.String()
log.Warn("Native MCP server process exited", "pid", currentPid, "error", waitErr, "stderr", stderrStr)
// Stderr is now streamed, so we don't capture it here anymore.
log.Warn("Native MCP server process exited", "pid", currentPid, "error", waitErr)
// Critical: Check if the agent's current command is STILL the one we were monitoring.
// If it's different, it means cleanup/restart already happened, so we shouldn't cleanup again.