Add logging service

New Go program (logger/) that:
- Accepts POSTed JSON log messages via POST /log
- Stores last N messages in a ring buffer (default 1M)
- Retrieves logs via GET /logs with limit/before/after filters
- Shows status via GET /status

Also updates express/logging.ts to POST messages to the logger service.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

express/logging.ts

@@ -32,15 +32,39 @@ type FilterArgument = {
     match?: (string | RegExp)[];
 };
 
-const log = (_message: Message) => {
+const loggerUrl = `http://${cli.logAddress.host}:${cli.logAddress.port}`;
-    // WRITEME
+
-    console.log(
+const log = (message: Message) => {
-        `will POST a message to ${cli.logAddress.host}:${cli.logAddress.port}`,
+    const payload = {
-    );
+        timestamp: message.timestamp ?? Date.now(),
+        source: message.source,
+        text: message.text,
+    };
+
+    fetch(`${loggerUrl}/log`, {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify(payload),
+    }).catch((err) => {
+        console.error("[logging] Failed to send log:", err.message);
+    });
 };
 
-const getLogs = (filter: FilterArgument) => {
+const getLogs = async (filter: FilterArgument): Promise<Message[]> => {
-    // WRITEME
+    const params = new URLSearchParams();
+    if (filter.limit) {
+        params.set("limit", String(filter.limit));
+    }
+    if (filter.before) {
+-        params.set("before", String(filter.before));
+    }
+    if (filter.after) {
+        params.set("after", String(filter.after));
+    }
+
+    const url = `${loggerUrl}/logs?${params.toString()}`;
+    const response = await fetch(url);
+    return response.json();
 };
 
 // FIXME: there's scope for more specialized functions although they

logger/.gitignore

@@ -0,0 +1 @@
+logger-bin

logger/go.mod

@@ -0,0 +1,3 @@
+module philologue.net/diachron/logger-bin
+
+go 1.23.3

logger/main.go

@@ -0,0 +1,70 @@
+package main
+
+import (
+	"encoding/json"
+	"flag"
+	"fmt"
+	"log"
+	"net/http"
+	"strconv"
+)
+
+func main() {
+	port := flag.Int("port", 8085, "port to listen on")
+	capacity := flag.Int("capacity", 1000000, "max messages to store")
+
+	flag.Parse()
+
+	store := NewLogStore(*capacity)
+
+	http.HandleFunc("POST /log", func(w http.ResponseWriter, r *http.Request) {
+		var msg Message
+		if err := json.NewDecoder(r.Body).Decode(&msg); err != nil {
+			http.Error(w, "invalid JSON", http.StatusBadRequest)
+			return
+		}
+
+		store.Add(msg)
+		w.WriteHeader(http.StatusCreated)
+	})
+
+	http.HandleFunc("GET /logs", func(w http.ResponseWriter, r *http.Request) {
+		params := FilterParams{}
+
+		if limit := r.URL.Query().Get("limit"); limit != "" {
+			if n, err := strconv.Atoi(limit); err == nil {
+				params.Limit = n
+			}
+		}
+		if before := r.URL.Query().Get("before"); before != "" {
+			if ts, err := strconv.ParseInt(before, 10, 64); err == nil {
+				params.Before = ts
+			}
+		}
+		if after := r.URL.Query().Get("after"); after != "" {
+			if ts, err := strconv.ParseInt(after, 10, 64); err == nil {
+				params.After = ts
+			}
+		}
+
+		messages := store.GetFiltered(params)
+
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(messages)
+	})
+
+	http.HandleFunc("GET /status", func(w http.ResponseWriter, r *http.Request) {
+		status := map[string]any{
+			"count":    store.Count(),
+			"capacity": *capacity,
+		}
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(status)
+	})
+
+	listenAddr := fmt.Sprintf(":%d", *port)
+	log.Printf("[logger] Listening on %s (capacity: %d)", listenAddr, *capacity)
+	if err := http.ListenAndServe(listenAddr, nil); err != nil {
+		log.Fatalf("[logger] Failed to start: %v", err)
+	}
+}

logger/store.go

@@ -0,0 +1,126 @@
+package main
+
+import (
+	"sync"
+)
+
+// Message represents a log entry from the express backend
+type Message struct {
+	Timestamp int64    `json:"timestamp"`
+	Source    string   `json:"source"` // "logging" | "diagnostic" | "user"
+	Text      []string `json:"text"`
+}
+
+// LogStore is a thread-safe ring buffer for log messages
+type LogStore struct {
+	mu       sync.RWMutex
+	messages []Message
+	head     int  // next write position
+	full     bool // whether buffer has wrapped
+	capacity int
+}
+
+// NewLogStore creates a new log store with the given capacity
+func NewLogStore(capacity int) *LogStore {
+	return &LogStore{
+		messages: make([]Message, capacity),
+		capacity: capacity,
+	}
+}
+
+// Add inserts a new message into the store
+func (s *LogStore) Add(msg Message) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	s.messages[s.head] = msg
+	s.head++
+	if s.head >= s.capacity {
+		s.head = 0
+		s.full = true
+	}
+}
+
+// Count returns the number of messages in the store
+func (s *LogStore) Count() int {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
+	if s.full {
+		return s.capacity
+	}
+	return s.head
+}
+
+// GetRecent returns the most recent n messages, newest first
+func (s *LogStore) GetRecent(n int) []Message {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
+	count := s.Count()
+	if n > count {
+		n = count
+	}
+	if n == 0 {
+		return nil
+	}
+
+	result := make([]Message, n)
+	pos := s.head - 1
+	for i := 0; i < n; i++ {
+		if pos < 0 {
+			pos = s.capacity - 1
+		}
+		result[i] = s.messages[pos]
+		pos--
+	}
+	return result
+}
+
+// Filter parameters for retrieving logs
+type FilterParams struct {
+	Limit  int   // max messages to return (0 = default 100)
+	Before int64 // only messages before this timestamp
+	After  int64 // only messages after this timestamp
+}
+
+// GetFiltered returns messages matching the filter criteria
+func (s *LogStore) GetFiltered(params FilterParams) []Message {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
+	limit := params.Limit
+	if limit <= 0 {
+		limit = 100
+	}
+
+	count := s.Count()
+	if count == 0 {
+		return nil
+	}
+
+	result := make([]Message, 0, limit)
+	pos := s.head - 1
+
+	for i := 0; i < count && len(result) < limit; i++ {
+		if pos < 0 {
+			pos = s.capacity - 1
+		}
+		msg := s.messages[pos]
+
+		// Apply filters
+		if params.Before > 0 && msg.Timestamp >= params.Before {
+			pos--
+			continue
+		}
+		if params.After > 0 && msg.Timestamp <= params.After {
+			pos--
+			continue
+		}
+
+		result = append(result, msg)
+		pos--
+	}
+
+	return result
+}