Add /logs endpoint to monitor upstream processes

- outputs last 10KB of logs from upstream processes
- supports streaming

README.md

@@ -59,6 +59,26 @@ models:
     * _Note: Windows currently untested._
 1. Run the binary with `llama-swap --config path/to/config.yaml`
 
+## Monitoring Logs
+
+The `/logs` endpoint is available to monitor what llama-swap is doing. It will send the last 10KB of logs. Useful for monitoring the output of llama-server. It also supports streaming of logs.
+
+Usage:
+
+```
+# basic, sends up to the last 10KB of logs
+curl http://host/logs'
+
+# add `stream` to stream new logs as they come in
+curl -Ns 'http://host/logs?stream'
+
+# add `skip` to skip history (only useful if used with stream)
+curl -Ns 'http://host/logs?stream&skip'
+
+# will output nothing :)
+curl -Ns 'http://host/logs?skip'
+```
+
 ## Systemd Unit Files
 
 Use this unit file to start llama-swap on boot. This is only tested on Ubuntu.

proxy/logMonitor.go

@@ -0,0 +1,83 @@
+package proxy
+
+import (
+	"container/ring"
+	"os"
+	"sync"
+)
+
+type LogMonitor struct {
+	clients  map[chan string]bool
+	mu       sync.RWMutex
+	buffer   *ring.Ring
+	bufferMu sync.RWMutex
+}
+
+func NewLogMonitor() *LogMonitor {
+	return &LogMonitor{
+		clients: make(map[chan string]bool),
+		buffer:  ring.New(10 * 1024), // keep 10KB of buffered logs
+	}
+}
+
+func (w *LogMonitor) Write(p []byte) (n int, err error) {
+	n, err = os.Stdout.Write(p)
+	if err != nil {
+		return n, err
+	}
+
+	content := string(p)
+
+	w.bufferMu.Lock()
+	w.buffer.Value = content
+	w.buffer = w.buffer.Next()
+	w.bufferMu.Unlock()
+
+	w.Broadcast(content)
+	return n, nil
+}
+
+func (w *LogMonitor) getHistory() string {
+	w.bufferMu.RLock()
+	defer w.bufferMu.RUnlock()
+
+	var history string
+	w.buffer.Do(func(p interface{}) {
+		if p != nil {
+			if content, ok := p.(string); ok {
+				history += content
+			}
+		}
+	})
+	return history
+}
+
+func (w *LogMonitor) Subscribe() chan string {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+
+	ch := make(chan string, 100)
+	w.clients[ch] = true
+	return ch
+}
+
+func (w *LogMonitor) Unsubscribe(ch chan string) {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+
+	delete(w.clients, ch)
+	close(ch)
+}
+
+func (w *LogMonitor) Broadcast(msg string) {
+	w.mu.RLock()
+	defer w.mu.RUnlock()
+
+	for client := range w.clients {
+		select {
+		case client <- msg:
+		default:
+			// If client buffer is full, skip
+		}
+	}
+}

proxy/manager.go

@@ -8,7 +8,6 @@ import (
 	"io"
 	"net/http"
 	"net/url"
-	"os"
 	"os/exec"
 	"strings"
 	"sync"
@@ -22,10 +21,11 @@ type ProxyManager struct {
 	config        *Config
 	currentCmd    *exec.Cmd
 	currentConfig ModelConfig
+	logMonitor    *LogMonitor
 }
 
 func New(config *Config) *ProxyManager {
-	return &ProxyManager{config: config}
+	return &ProxyManager{config: config, logMonitor: NewLogMonitor()}
 }
 
 func (pm *ProxyManager) HandleFunc(w http.ResponseWriter, r *http.Request) {
@@ -36,12 +36,55 @@ func (pm *ProxyManager) HandleFunc(w http.ResponseWriter, r *http.Request) {
 		pm.proxyChatRequest(w, r)
 	} else if r.URL.Path == "/v1/models" {
 		pm.listModels(w, r)
+	} else if r.URL.Path == "/logs" {
+		pm.streamLogs(w, r)
 	} else {
 		pm.proxyRequest(w, r)
 	}
 }
 
-func (pm *ProxyManager) listModels(w http.ResponseWriter, r *http.Request) {
+func (pm *ProxyManager) streamLogs(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "text/plain")
+	w.Header().Set("Transfer-Encoding", "chunked")
+	w.Header().Set("X-Content-Type-Options", "nosniff")
+
+	ch := pm.logMonitor.Subscribe()
+	defer pm.logMonitor.Unsubscribe(ch)
+
+	notify := r.Context().Done()
+	flusher, ok := w.(http.Flusher)
+	if !ok {
+		http.Error(w, "Streaming unsupported", http.StatusInternalServerError)
+		return
+	}
+
+	skipHistory := r.URL.Query().Has("skip")
+	if !skipHistory {
+		// Send history first
+		history := pm.logMonitor.getHistory()
+		if history != "" {
+			fmt.Fprint(w, history)
+			flusher.Flush()
+		}
+	}
+
+	if !r.URL.Query().Has("stream") {
+		return
+	}
+
+	// Stream new logs
+	for {
+		select {
+		case msg := <-ch:
+			fmt.Fprint(w, msg)
+			flusher.Flush()
+		case <-notify:
+			return
+		}
+	}
+}
+
+func (pm *ProxyManager) listModels(w http.ResponseWriter, _ *http.Request) {
 	data := []interface{}{}
 	for id := range pm.config.Models {
 		data = append(data, map[string]interface{}{
@@ -92,8 +135,12 @@ func (pm *ProxyManager) swapModel(requestedModel string) error {
 		return fmt.Errorf("unable to get sanitized command: %v", err)
 	}
 	cmd := exec.Command(args[0], args[1:]...)
-	cmd.Stdout = os.Stdout
+
-	cmd.Stderr = os.Stderr
+	// logMonitor only writes to stdout
+	// so the upstream's stderr will go to os.Stdout
+	cmd.Stdout = pm.logMonitor
+	cmd.Stderr = pm.logMonitor
+
 	cmd.Env = modelConfig.Env
 
 	err = cmd.Start()