🧹 fix: harden request-body size handling and error unwrapping

Tighten oversized request handling across relay paths and make error matching reliable.

- Align `MAX_REQUEST_BODY_MB` fallback to `32` in request body reader and decompression middleware
- Stop ignoring `GetRequestBody` errors in relay retry paths; return consistent **413** on oversized bodies (400 for other read errors)
- Add `Unwrap()` to `types.NewAPIError` so `errors.Is/As` can match wrapped underlying errors
- `go test ./...` passes

common/gin.go

@@ -40,7 +40,7 @@ func GetRequestBody(c *gin.Context) ([]byte, error) {
 	}
 	maxMB := constant.MaxRequestBodyMB
 	if maxMB <= 0 {
-		maxMB = 64
+		maxMB = 32
 	}
 	maxBytes := int64(maxMB) << 20
 

controller/relay.go

@@ -179,15 +179,24 @@ func Relay(c *gin.Context, relayFormat types.RelayFormat) {
 	}
 
 	for ; retryParam.GetRetry() <= common.RetryTimes; retryParam.IncreaseRetry() {
-		channel, err := getChannel(c, relayInfo, retryParam)
+		channel, channelErr := getChannel(c, relayInfo, retryParam)
-		if err != nil {
+		if channelErr != nil {
-			logger.LogError(c, err.Error())
+			logger.LogError(c, channelErr.Error())
-			newAPIError = err
+			newAPIError = channelErr
 			break
 		}
 
 		addUsedChannel(c, channel.Id)
-		requestBody, _ := common.GetRequestBody(c)
+		requestBody, bodyErr := common.GetRequestBody(c)
+		if bodyErr != nil {
+			// Ensure consistent 413 for oversized bodies even when error occurs later (e.g., retry path)
+			if common.IsRequestBodyTooLargeError(bodyErr) || errors.Is(bodyErr, common.ErrRequestBodyTooLarge) {
+				newAPIError = types.NewErrorWithStatusCode(bodyErr, types.ErrorCodeReadRequestBodyFailed, http.StatusRequestEntityTooLarge, types.ErrOptionWithSkipRetry())
+			} else {
+				newAPIError = types.NewErrorWithStatusCode(bodyErr, types.ErrorCodeReadRequestBodyFailed, http.StatusBadRequest, types.ErrOptionWithSkipRetry())
+			}
+			break
+		}
 		c.Request.Body = io.NopCloser(bytes.NewBuffer(requestBody))
 
 		switch relayFormat {
@@ -473,7 +482,15 @@ func RelayTask(c *gin.Context) {
 		logger.LogInfo(c, fmt.Sprintf("using channel #%d to retry (remain times %d)", channel.Id, retryParam.GetRetry()))
 		//middleware.SetupContextForSelectedChannel(c, channel, originalModel)
 
-		requestBody, _ := common.GetRequestBody(c)
+		requestBody, err := common.GetRequestBody(c)
+		if err != nil {
+			if common.IsRequestBodyTooLargeError(err) || errors.Is(err, common.ErrRequestBodyTooLarge) {
+				taskErr = service.TaskErrorWrapperLocal(err, "read_request_body_failed", http.StatusRequestEntityTooLarge)
+			} else {
+				taskErr = service.TaskErrorWrapperLocal(err, "read_request_body_failed", http.StatusBadRequest)
+			}
+			break
+		}
 		c.Request.Body = io.NopCloser(bytes.NewBuffer(requestBody))
 		taskErr = taskRelayHandler(c, relayInfo)
 	}

middleware/gzip.go

@@ -30,7 +30,7 @@ func DecompressRequestMiddleware() gin.HandlerFunc {
 		}
 		maxMB := constant.MaxRequestBodyMB
 		if maxMB <= 0 {
-			maxMB = 64
+			maxMB = 32
 		}
 		maxBytes := int64(maxMB) << 20
 

types/error.go

@@ -94,6 +94,14 @@ type NewAPIError struct {
 	StatusCode     int
 }
 
+// Unwrap enables errors.Is / errors.As to work with NewAPIError by exposing the underlying error.
+func (e *NewAPIError) Unwrap() error {
+	if e == nil {
+		return nil
+	}
+	return e.Err
+}
+
 func (e *NewAPIError) GetErrorCode() ErrorCode {
 	if e == nil {
 		return ""