Map errors to HTTP statuses (#666)

The initial motivation is to map ENAMETOOLONG from 500 Internal Error
to 400 Bad Request.  This prevents clients like gcsfuse from
unnecessarily retrying requests.  This commit also remove some panic
call paths.

fakestorage/json_response.go

@@ -2,7 +2,10 @@ package fakestorage
 
 import (
 	"encoding/json"
+	"errors"
 	"net/http"
+	"os"
+	"syscall"
 )
 
 type jsonResponse struct {
@@ -53,3 +56,12 @@ func (r *jsonResponse) getErrorMessage(status int) string {
 	}
 	return http.StatusText(status)
 }
+
+func errToJsonResponse(err error) jsonResponse {
+	status := 0
+	var pathError *os.PathError
+	if errors.As(err, &pathError) && pathError.Err == syscall.ENAMETOOLONG {
+		status = http.StatusBadRequest
+	}
+	return jsonResponse{errorMessage: err.Error(), status: status}
+}

fakestorage/object.go

@@ -556,7 +556,10 @@ func (s *Server) setObjectACL(r *http.Request) jsonResponse {
 		Role:   role,
 	}}
 
-	s.CreateObject(obj)
+	_, err = s.createObject(obj)
+	if err != nil {
+		return errToJsonResponse(err)
+	}
 
 	return jsonResponse{data: newACLListResponse(obj.ObjectAttrs)}
 }
@@ -607,7 +610,11 @@ func (s *Server) rewriteObject(r *http.Request) jsonResponse {
 		Content: append([]byte(nil), obj.Content...),
 	}
 
-	s.CreateObject(newObject)
+	_, err = s.createObject(newObject)
+	if err != nil {
+		return errToJsonResponse(err)
+	}
+
 	return jsonResponse{data: newObjectRewriteResponse(newObject.ObjectAttrs)}
 }
 

fakestorage/upload.go

@@ -196,7 +196,7 @@ func (s *Server) simpleUpload(bucketName string, r *http.Request) jsonResponse {
 	}
 	obj, err = s.createObject(obj)
 	if err != nil {
-		return jsonResponse{errorMessage: err.Error()}
+		return errToJsonResponse(err)
 	}
 	return jsonResponse{data: obj}
 }
@@ -239,7 +239,7 @@ func (s *Server) signedUpload(bucketName string, r *http.Request) jsonResponse {
 	}
 	obj, err = s.createObject(obj)
 	if err != nil {
-		return jsonResponse{errorMessage: err.Error()}
+		return errToJsonResponse(err)
 	}
 	return jsonResponse{data: obj}
 }
@@ -319,7 +319,7 @@ func (s *Server) multipartUpload(bucketName string, r *http.Request) jsonRespons
 	}
 	obj, err = s.createObject(obj)
 	if err != nil {
-		return jsonResponse{errorMessage: err.Error()}
+		return errToJsonResponse(err)
 	}
 	return jsonResponse{data: obj}
 }
@@ -433,7 +433,7 @@ func (s *Server) uploadFileContent(r *http.Request) jsonResponse {
 		s.uploads.Delete(uploadID)
 		obj, err = s.createObject(obj)
 		if err != nil {
-			return jsonResponse{errorMessage: err.Error()}
+			return errToJsonResponse(err)
 		}
 	} else {
 		if _, no308 := r.Header["X-Guploader-No-308"]; no308 {