feat(http/mw): structured request logger middleware

internal/transport/http/middleware/logger.go

@@ -0,0 +1,51 @@
+package middleware
+
+import (
+	"log/slog"
+	"net/http"
+	"time"
+)
+
+// statusRecorder wraps http.ResponseWriter to capture the response status
+// code so the Logger middleware can include it in the structured log line.
+//
+// The default status is initialised to http.StatusOK because net/http
+// implicitly emits a 200 when a handler writes a body without calling
+// WriteHeader explicitly; mirroring that behaviour keeps logs accurate.
+type statusRecorder struct {
+	http.ResponseWriter
+	status int
+}
+
+// WriteHeader records the status code before delegating to the wrapped
+// ResponseWriter so the original response semantics are preserved.
+func (s *statusRecorder) WriteHeader(code int) {
+	s.status = code
+	s.ResponseWriter.WriteHeader(code)
+}
+
+// Logger returns HTTP middleware that emits a single structured log line
+// per request once the downstream handler has finished. The line includes
+// method, path, response status, elapsed duration in milliseconds, and the
+// request ID (if RequestID middleware is mounted upstream).
+//
+// The middleware is intentionally placed *inside* RequestID so the
+// generated identifier is available via context; placing it outside would
+// log an empty request_id.
+func Logger(log *slog.Logger) func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			start := time.Now()
+			rec := &statusRecorder{ResponseWriter: w, status: http.StatusOK}
+			next.ServeHTTP(rec, r)
+			ctx := r.Context()
+			log.LogAttrs(ctx, slog.LevelInfo, "http",
+				slog.String("method", r.Method),
+				slog.String("path", r.URL.Path),
+				slog.Int("status", rec.status),
+				slog.Int64("duration_ms", time.Since(start).Milliseconds()),
+				slog.String("request_id", RequestIDFromContext(ctx)),
+			)
+		})
+	}
+}