Add structured logging and better error handling

internal/server/respond.go

@@ -3,6 +3,7 @@ package server
 import (
 	"encoding/json"
 	"errors"
+	"log/slog"
 	"net/http"
 
 	"ddc/internal/diskspace"
@@ -11,24 +12,55 @@ import (
 	"ddc/internal/preferences"
 )
 
+type errorResponse struct {
+	Error     string `json:"error"`
+	RequestID string `json:"requestId,omitempty"`
+}
+
 func writeJSON(writer http.ResponseWriter, status int, payload any) {
 	writer.Header().Set("Content-Type", "application/json; charset=utf-8")
 	writer.WriteHeader(status)
-	json.NewEncoder(writer).Encode(payload)
+	if err := json.NewEncoder(writer).Encode(payload); err != nil {
+		slog.Debug("could not write response", "error", err)
+	}
 }
 
 func writeError(writer http.ResponseWriter, status int, message string) {
-	writeJSON(writer, status, map[string]string{"error": message})
+	writeJSON(writer, status, errorResponse{Error: message, RequestID: writer.Header().Get("X-Request-ID")})
 }
 
-func writeFailure(writer http.ResponseWriter, err error) {
-	writeError(writer, statusFor(err), err.Error())
+func writeFailure(writer http.ResponseWriter, request *http.Request, err error) {
+	status := statusFor(err)
+	if status != http.StatusInternalServerError {
+		writeError(writer, status, err.Error())
+		return
+	}
+
+	requestID := requestIDFrom(request)
+	slog.Error("request failed",
+		"request_id", requestID,
+		"method", request.Method,
+		"path", request.URL.Path,
+		"error", err,
+	)
+	writeError(writer, status, internalErrorMessage(requestID))
 }
 
-func decodeJSON(request *http.Request, target any) error {
+func decodeBody(writer http.ResponseWriter, request *http.Request, target any) bool {
 	decoder := json.NewDecoder(request.Body)
 	decoder.DisallowUnknownFields()
-	return decoder.Decode(target)
+	err := decoder.Decode(target)
+	if err == nil {
+		return true
+	}
+
+	var tooLarge *http.MaxBytesError
+	if errors.As(err, &tooLarge) {
+		writeError(writer, http.StatusRequestEntityTooLarge, "request body is too large")
+		return false
+	}
+	writeError(writer, http.StatusBadRequest, "invalid request body: "+err.Error())
+	return false
 }
 
 func statusFor(err error) int {