feat: add Docker support and logging enhancements

- Introduced Dockerfile and .dockerignore for containerization of the backend service.
- Added logging configuration with support for daily rolling logs and customizable log levels.
- Enhanced the server to utilize structured logging with zap, including detailed request and error logging.
- Updated configuration to include logging parameters and proxy settings.
- Implemented tests for logging configuration and proxy settings.

backend/internal/api/handler.go

@@ -4,9 +4,11 @@ import (
 	"context"
 	"errors"
 	"net/http"
+	"strings"
 	"time"
 
 	"github.com/gin-gonic/gin"
+	"go.uber.org/zap"
 
 	"monica-go-completion-backend/internal/completion"
 )
@@ -67,6 +69,13 @@ func RegisterRoutes(router *gin.Engine, service CompletionService, options ...Ro
 		c.Request.Body = http.MaxBytesReader(c.Writer, c.Request.Body, opts.MaxBodyBytes)
 		var req completion.Request
 		if err := c.ShouldBindJSON(&req); err != nil {
+			zap.L().Warn(
+				"invalid completion json payload",
+				zap.String("traceId", traceIDFromGin(c)),
+				zap.String("routeLanguage", c.Param("language")),
+				zap.String("clientIP", c.ClientIP()),
+				zap.Error(err),
+			)
 			c.JSON(http.StatusBadRequest, gin.H{"error": "invalid JSON payload"})
 			return
 		}
@@ -84,19 +93,51 @@ func RegisterRoutes(router *gin.Engine, service CompletionService, options ...Ro
 		resp, err := service.Complete(ctx, req)
 		if err != nil {
 			if errors.Is(err, completion.ErrInvalidRequest) {
+				zap.L().Warn(
+					"completion request invalid",
+					zap.String("traceId", traceIDFromGin(c)),
+					zap.String("clientIP", c.ClientIP()),
+					zap.String("language", req.Language),
+					zap.String("uri", req.URI),
+					zap.Error(err),
+				)
 				c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
 				return
 			}
 			if errors.Is(err, completion.ErrUnsupportedLanguage) {
+				zap.L().Warn(
+					"completion language not supported",
+					zap.String("traceId", traceIDFromGin(c)),
+					zap.String("clientIP", c.ClientIP()),
+					zap.String("language", req.Language),
+					zap.Error(err),
+				)
 				c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
 				return
 			}
 			if errors.Is(err, completion.ErrTooManySessions) {
+				zap.L().Warn(
+					"completion rejected due to session limit",
+					zap.String("traceId", traceIDFromGin(c)),
+					zap.String("clientIP", c.ClientIP()),
+					zap.String("language", req.Language),
+					zap.String("sessionId", req.SessionID),
+					zap.Error(err),
+				)
 				c.JSON(http.StatusTooManyRequests, gin.H{"error": err.Error()})
 				return
 			}
 			var ownedErr *completion.ErrSessionOwnedByOtherInstance
 			if errors.As(err, &ownedErr) {
+				zap.L().Info(
+					"completion routed to session owner",
+					zap.String("traceId", traceIDFromGin(c)),
+					zap.String("clientIP", c.ClientIP()),
+					zap.String("language", req.Language),
+					zap.String("sessionId", req.SessionID),
+					zap.String("ownerId", ownedErr.OwnerID),
+					zap.String("routeTo", ownedErr.OwnerEndpoint),
+				)
 				if ownedErr.OwnerEndpoint != "" {
 					c.Header("X-LSP-Route-To", ownedErr.OwnerEndpoint)
 				}
@@ -107,9 +148,28 @@ func RegisterRoutes(router *gin.Engine, service CompletionService, options ...Ro
 				})
 				return
 			}
+			zap.L().Error(
+				"completion failed",
+				zap.String("traceId", traceIDFromGin(c)),
+				zap.String("clientIP", c.ClientIP()),
+				zap.String("language", req.Language),
+				zap.String("sessionId", req.SessionID),
+				zap.String("uri", req.URI),
+				zap.Error(err),
+			)
 			c.JSON(http.StatusInternalServerError, gin.H{"error": "completion failed"})
 			return
 		}
+		zap.L().Info(
+			"completion success",
+			zap.String("traceId", traceIDFromGin(c)),
+			zap.String("clientIP", c.ClientIP()),
+			zap.String("language", req.Language),
+			zap.String("sessionId", req.SessionID),
+			zap.String("uri", req.URI),
+			zap.Int("items", len(resp.Items)),
+			zap.Bool("isIncomplete", resp.IsIncomplete),
+		)
 
 		c.JSON(http.StatusOK, resp)
 	}
@@ -118,3 +178,14 @@ func RegisterRoutes(router *gin.Engine, service CompletionService, options ...Ro
 		handleCompletion(c)
 	})
 }
+
+func traceIDFromGin(c *gin.Context) string {
+	if c == nil {
+		return ""
+	}
+	traceID := strings.TrimSpace(c.GetString("traceId"))
+	if traceID != "" {
+		return traceID
+	}
+	return strings.TrimSpace(c.GetString("requestId"))
+}