Presigend Post: Error out when File is not found (#3723)

Follow S3 behavior when no File is sent in the presigned
post request form.

cmd/api-errors.go

@@ -83,6 +83,7 @@ const (
 	ErrInvalidPartOrder
 	ErrAuthorizationHeaderMalformed
 	ErrMalformedPOSTRequest
+	ErrPOSTFileRequired
 	ErrSignatureVersionNotSupported
 	ErrBucketNotEmpty
 	ErrAllAccessDisabled
@@ -333,6 +334,11 @@ var errorCodeResponse = map[APIErrorCode]APIError{
 		Description:    "The body of your POST request is not well-formed multipart/form-data.",
 		HTTPStatusCode: http.StatusBadRequest,
 	},
+	ErrPOSTFileRequired: {
+		Code:           "InvalidArgument",
+		Description:    "POST requires exactly one file upload per request.",
+		HTTPStatusCode: http.StatusBadRequest,
+	},
 	ErrSignatureVersionNotSupported: {
 		Code:           "InvalidRequest",
 		Description:    "The authorization mechanism you have provided is not supported. Please use AWS4-HMAC-SHA256.",

cmd/bucket-handlers.go

@@ -428,6 +428,12 @@ func (api objectAPIHandlers) PostPolicyBucketHandler(w http.ResponseWriter, r *h
 		return
 	}
 
+	// Check if file is provided, error out otherwise.
+	if fileBody == nil {
+		writeErrorResponse(w, ErrPOSTFileRequired, r.URL)
+		return
+	}
+
 	// Close multipart file
 	defer fileBody.Close()
 

cmd/handler-utils.go

@@ -167,7 +167,7 @@ func extractPostPolicyFormValues(form *multipart.Form) (filePart io.ReadCloser,
 		canonicalFormName := http.CanonicalHeaderKey(k)
 		// Check if value's field exceeds S3 limit
 		if int64(len(v[0])) > maxFormFieldSize {
-			return nil, "", 0, nil, errSizeUnexpected
+			return nil, "", 0, nil, traceError(errSizeUnexpected)
 		}
 		// Set the form value
 		formValues[canonicalFormName] = v[0]
@@ -178,7 +178,7 @@ func extractPostPolicyFormValues(form *multipart.Form) (filePart io.ReadCloser,
 		canonicalFormName := http.CanonicalHeaderKey(k)
 		if canonicalFormName == "File" {
 			if len(v) == 0 {
-				return nil, "", 0, nil, errInvalidArgument
+				return nil, "", 0, nil, traceError(errInvalidArgument)
 			}
 			// Fetch fileHeader which has the uploaded file information
 			fileHeader := v[0]
@@ -186,15 +186,18 @@ func extractPostPolicyFormValues(form *multipart.Form) (filePart io.ReadCloser,
 			fileName = fileHeader.Filename
 			// Open the uploaded part
 			filePart, err = fileHeader.Open()
+			if err != nil {
+				return nil, "", 0, nil, traceError(err)
+			}
 			// Compute file size
 			fileSize, err = filePart.(io.Seeker).Seek(0, 2)
 			if err != nil {
-				return nil, "", 0, nil, err
+				return nil, "", 0, nil, traceError(err)
 			}
 			// Reset Seek to the beginning
 			_, err = filePart.(io.Seeker).Seek(0, 0)
 			if err != nil {
-				return nil, "", 0, nil, err
+				return nil, "", 0, nil, traceError(err)
 			}
 			// File found and ready for reading
 			break