Improve LogMonitor to handle empty writes and ensure buffer immutability

- Add a check to return immediately if the write buffer is empty
- Create a copy of new history data to ensure it is immutable
- Update the `GetHistory` method to use the `any` type for the buffer interface
- Add a test case to verify that the buffer remains unchanged
  even if the original message is modified after writing

Makefile

@@ -9,6 +9,9 @@ all: mac linux simple-responder
 clean:
 	rm -rf $(BUILD_DIR)
 
+test:
+	go test -v ./proxy
+
 # Build OSX binary
 mac:
 	@echo "Building Mac binary..."

README.md

@@ -1,12 +1,14 @@
 # llama-swap
 
-[llama.cpp's server](https://github.com/ggerganov/llama.cpp/tree/master/examples/server) can't swap models, so let's swap llama-server instead!
+![llama-swap header image](header.jpeg)
+
+[llama.cpp's server](https://github.com/ggerganov/llama.cpp/tree/master/examples/server) can't swap models on demand. So let's swap the server on demand instead!
 
 llama-swap is a proxy server that sits in front of llama-server. When a request for `/v1/chat/completions` comes in it will extract the `model` requested and change the underlying llama-server automatically.
 
 - ✅ easy to deploy: single binary with no dependencies
 - ✅ full control over llama-server's startup settings
-- ✅ ❤️ for nvidia P40 users who are rely on llama.cpp for inference
+- ✅ ❤️ for users who are rely on llama.cpp for LLM inference
 
 ## config.yaml
 
@@ -20,10 +22,10 @@ healthCheckTimeout: 60
 # define valid model values and the upstream server start
 models:
   "llama":
-    cmd: "llama-server --port 8999 -m Llama-3.2-1B-Instruct-Q4_K_M.gguf"
+    cmd: llama-server --port 8999 -m Llama-3.2-1B-Instruct-Q4_K_M.gguf
 
-    # Where to proxy to, important it matches this format
-    proxy: "http://127.0.0.1:8999"
+    # where to reach the server started by cmd
+    proxy: http://127.0.0.1:8999
 
     # aliases model names to use this configuration for
     aliases:
@@ -35,14 +37,19 @@ models:
     #
     # use "none" to skip endpoint checking. This may cause requests to fail
     # until the server is ready
-    checkEndpoint: "/custom-endpoint"
+    checkEndpoint: /custom-endpoint
 
   "qwen":
     # environment variables to pass to the command
     env:
       - "CUDA_VISIBLE_DEVICES=0"
-    cmd: "llama-server --port 8999 -m path/to/Qwen2.5-1.5B-Instruct-Q4_K_M.gguf"
-    proxy: "http://127.0.0.1:8999"
+
+    # multiline for readability
+    cmd: >
+      llama-server --port 8999
+      --model path/to/Qwen2.5-1.5B-Instruct-Q4_K_M.gguf
+
+    proxy: http://127.0.0.1:8999
 ```
 
 ## Installation
@@ -52,6 +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.

config.example.yaml

@@ -1,6 +1,6 @@
 # Seconds to wait for llama.cpp to be available to serve requests
 # Default (and minimum): 15 seconds
-healthCheckTimeout: 60
+healthCheckTimeout: 15
 
 models:
   "llama":
@@ -35,7 +35,10 @@ models:
     # until the upstream server is ready for traffic
     checkEndpoint: none
 
-  # don't use this, just for testing if things are broken
+  # don't use these, just for testing if things are broken
   "broken":
     cmd: models/llama-server-osx --port 8999 -m models/doesnotexist.gguf
-    proxy: http://127.0.0.1:8999
+    proxy: http://127.0.0.1:8999
+  "broken_timeout":
+    cmd: models/llama-server-osx --port 8999 -m models/Qwen2.5-1.5B-Instruct-Q4_K_M.gguf
+    proxy: http://127.0.0.1:9000

proxy/logMonitor.go

@@ -0,0 +1,96 @@
+package proxy
+
+import (
+	"container/ring"
+	"io"
+	"os"
+	"sync"
+)
+
+type LogMonitor struct {
+	clients  map[chan []byte]bool
+	mu       sync.RWMutex
+	buffer   *ring.Ring
+	bufferMu sync.RWMutex
+
+	// typically this can be os.Stdout
+	stdout io.Writer
+}
+
+func NewLogMonitor() *LogMonitor {
+	return NewLogMonitorWriter(os.Stdout)
+}
+
+func NewLogMonitorWriter(stdout io.Writer) *LogMonitor {
+	return &LogMonitor{
+		clients: make(map[chan []byte]bool),
+		buffer:  ring.New(10 * 1024), // keep 10KB of buffered logs
+		stdout:  stdout,
+	}
+}
+
+func (w *LogMonitor) Write(p []byte) (n int, err error) {
+	if len(p) == 0 {
+		return 0, nil
+	}
+
+	n, err = w.stdout.Write(p)
+	if err != nil {
+		return n, err
+	}
+
+	w.bufferMu.Lock()
+	bufferCopy := make([]byte, len(p))
+	copy(bufferCopy, p)
+	w.buffer.Value = bufferCopy
+	w.buffer = w.buffer.Next()
+	w.bufferMu.Unlock()
+
+	w.broadcast(p)
+	return n, nil
+}
+
+func (w *LogMonitor) GetHistory() []byte {
+	w.bufferMu.RLock()
+	defer w.bufferMu.RUnlock()
+
+	var history []byte
+	w.buffer.Do(func(p any) {
+		if p != nil {
+			if content, ok := p.([]byte); ok {
+				history = append(history, content...)
+			}
+		}
+	})
+	return history
+}
+
+func (w *LogMonitor) Subscribe() chan []byte {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+
+	ch := make(chan []byte, 100)
+	w.clients[ch] = true
+	return ch
+}
+
+func (w *LogMonitor) Unsubscribe(ch chan []byte) {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+
+	delete(w.clients, ch)
+	close(ch)
+}
+
+func (w *LogMonitor) broadcast(msg []byte) {
+	w.mu.RLock()
+	defer w.mu.RUnlock()
+
+	for client := range w.clients {
+		select {
+		case client <- msg:
+		default:
+			// If client buffer is full, skip
+		}
+	}
+}

proxy/logMonitor_test.go

@@ -0,0 +1,95 @@
+package proxy
+
+import (
+	"bytes"
+	"io"
+	"sync"
+	"testing"
+)
+
+func TestLogMonitor(t *testing.T) {
+	logMonitor := NewLogMonitorWriter(io.Discard)
+
+	// Test subscription
+	client1 := logMonitor.Subscribe()
+	client2 := logMonitor.Subscribe()
+
+	defer logMonitor.Unsubscribe(client1)
+	defer logMonitor.Unsubscribe(client2)
+
+	client1Messages := make([]byte, 0)
+	client2Messages := make([]byte, 0)
+
+	var wg sync.WaitGroup
+	wg.Add(1)
+
+	go func() {
+		defer wg.Done()
+		for {
+			select {
+			case data := <-client1:
+				client1Messages = append(client1Messages, data...)
+			case data := <-client2:
+				client2Messages = append(client2Messages, data...)
+			default:
+				return
+			}
+		}
+	}()
+
+	logMonitor.Write([]byte("1"))
+	logMonitor.Write([]byte("2"))
+	logMonitor.Write([]byte("3"))
+
+	// Wait for the goroutine to finish
+	wg.Wait()
+
+	// Check the buffer
+	expectedHistory := "123"
+	history := string(logMonitor.GetHistory())
+
+	if history != expectedHistory {
+		t.Errorf("Expected history: %s, got: %s", expectedHistory, history)
+	}
+
+	c1Data := string(client1Messages)
+	if c1Data != expectedHistory {
+		t.Errorf("Client1 expected %s, got: %s", expectedHistory, c1Data)
+	}
+
+	c2Data := string(client2Messages)
+	if c2Data != expectedHistory {
+		t.Errorf("Client2 expected %s, got: %s", expectedHistory, c2Data)
+	}
+}
+
+func TestWrite_ImmutableBuffer(t *testing.T) {
+	// Create a new LogMonitor instance
+	lm := NewLogMonitorWriter(io.Discard)
+
+	// Prepare a message to write
+	msg := []byte("Hello, World!")
+	lenmsg := len(msg)
+
+	// Write the message to the LogMonitor
+	n, err := lm.Write(msg)
+	if err != nil {
+		t.Fatalf("Write failed: %v", err)
+	}
+
+	if n != lenmsg {
+		t.Errorf("Expected %d bytes written but got %d", lenmsg, n)
+	}
+
+	// Change the original message
+	msg[0] = 'B' // This should not affect the buffer
+
+	// Get the history from the LogMonitor
+	history := lm.GetHistory()
+
+	// Check that the history contains the original message, not the modified one
+	expected := []byte("Hello, World!")
+	if !bytes.Equal(history, expected) {
+		t.Errorf("Expected history to be %q, got %q", expected, history)
+	}
+}

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 len(history) != 0 {
+			w.Write(history)
+			flusher.Flush()
+		}
+	}
+
+	if !r.URL.Query().Has("stream") {
+		return
+	}
+
+	// Stream new logs
+	for {
+		select {
+		case msg := <-ch:
+			w.Write(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()
@@ -102,14 +149,28 @@ func (pm *ProxyManager) swapModel(requestedModel string) error {
 	}
 	pm.currentCmd = cmd
 
-	if err := pm.checkHealthEndpoint(); err != nil {
+	// watch for the command to exist
+	cmdCtx, cancel := context.WithCancelCause(context.Background())
+
+	// monitor the command's exist status
+	go func() {
+		err := cmd.Wait()
+		if err != nil {
+			cancel(fmt.Errorf("command [%s] %s", strings.Join(cmd.Args, " "), err.Error()))
+		} else {
+			cancel(nil)
+		}
+	}()
+
+	// wait for checkHealthEndpoint
+	if err := pm.checkHealthEndpoint(cmdCtx); err != nil {
 		return err
 	}
 
 	return nil
 }
 
-func (pm *ProxyManager) checkHealthEndpoint() error {
+func (pm *ProxyManager) checkHealthEndpoint(cmdCtx context.Context) error {
 
 	if pm.currentConfig.Proxy == "" {
 		return fmt.Errorf("no upstream available to check /health")
@@ -132,6 +193,7 @@ func (pm *ProxyManager) checkHealthEndpoint() error {
 	if err != nil {
 		return fmt.Errorf("failed to create health url with with %s and path %s", proxyTo, checkEndpoint)
 	}
+
 	client := &http.Client{}
 	startTime := time.Now()
 
@@ -140,33 +202,47 @@ func (pm *ProxyManager) checkHealthEndpoint() error {
 		if err != nil {
 			return err
 		}
-		ctx, cancel := context.WithTimeout(req.Context(), 250*time.Millisecond)
+
+		ctx, cancel := context.WithTimeout(cmdCtx, 250*time.Millisecond)
 		defer cancel()
 		req = req.WithContext(ctx)
 		resp, err := client.Do(req)
-		if err != nil {
-			if strings.Contains(err.Error(), "connection refused") {
 
-				// if TCP dial can't connect any HTTP response after 5 seconds
-				// exit quickly.
-				if time.Since(startTime) > 5*time.Second {
-					return fmt.Errorf("health check endpoint took more than 5 seconds to respond")
-				}
+		ttl := (maxDuration - time.Since(startTime)).Seconds()
+
+		if err != nil {
+			// check if the context was cancelled
+			select {
+			case <-ctx.Done():
+				return context.Cause(ctx)
+			default:
 			}
 
-			if time.Since(startTime) >= maxDuration {
+			// wait a bit longer for TCP connection issues
+			if strings.Contains(err.Error(), "connection refused") {
+				fmt.Fprintf(pm.logMonitor, "Connection refused on %s, ttl %.0fs\n", healthURL, ttl)
+
+				time.Sleep(5 * time.Second)
+			} else {
+				time.Sleep(time.Second)
+			}
+
+			if ttl < 0 {
 				return fmt.Errorf("failed to check health from: %s", healthURL)
 			}
-			time.Sleep(time.Second)
+
 			continue
 		}
+
 		defer resp.Body.Close()
 		if resp.StatusCode == http.StatusOK {
 			return nil
 		}
-		if time.Since(startTime) >= maxDuration {
+
+		if ttl < 0 {
 			return fmt.Errorf("failed to check health from: %s", healthURL)
 		}
+
 		time.Sleep(time.Second)
 	}
 }
@@ -189,7 +265,7 @@ func (pm *ProxyManager) proxyChatRequest(w http.ResponseWriter, r *http.Request)
 	}
 
 	if err := pm.swapModel(model); err != nil {
-		http.Error(w, fmt.Sprintf("unable to swap to model: %s", err.Error()), http.StatusNotFound)
+		http.Error(w, fmt.Sprintf("unable to swap to model, %s", err.Error()), http.StatusNotFound)
 		return
 	}