API: add writePartTooSmallErrorResponse to extend standard error responses. (#2005)

This function is added to extend the standard error responses.
Which is needed in some cases for example CompleteMultipartUpload
should respond with ErrPartTooSmall error when parts uploaded are
lesser than 5MB (i.e minimum allowed size per part).

Fixes #1536

server_xl_test.go

@@ -2002,6 +2002,114 @@ func (s *MyAPIXLSuite) TestObjectMultipartListError(c *C) {
 	verifyError(c, response4, "InvalidArgument", "Argument maxParts must be an integer between 1 and 10000.", http.StatusBadRequest)
 }
 
+// TestMultipartErrorEntityTooSmall - initiates a new multipart upload,
+// uploads 2 parts of size less than 5MB, upon complete multipart upload
+// validates EntityTooSmall error returned by the operation.
+func (s *MyAPIXLSuite) TestMultipartErrorEntityTooSmall(c *C) {
+	// generate a random bucket name.
+	bucketName := getRandomBucketName()
+	// HTTP request to create the bucket.
+	request, err := newTestRequest("PUT", getMakeBucketURL(s.endPoint, bucketName),
+		0, nil, s.accessKey, s.secretKey)
+	c.Assert(err, IsNil)
+
+	client := http.Client{}
+	// execute the HTTP request to create bucket.
+	response, err := client.Do(request)
+	c.Assert(err, IsNil)
+	c.Assert(response.StatusCode, Equals, 200)
+
+	objectName := "test-multipart-object"
+	// construct HTTP request to initiate a NewMultipart upload.
+	request, err = newTestRequest("POST", getNewMultipartURL(s.endPoint, bucketName, objectName),
+		0, nil, s.accessKey, s.secretKey)
+	c.Assert(err, IsNil)
+
+	client = http.Client{}
+	// execute the HTTP request initiating the new multipart upload.
+	response, err = client.Do(request)
+	c.Assert(err, IsNil)
+	// expecting the response status code to be http.StatusOK(200 OK).
+	c.Assert(response.StatusCode, Equals, http.StatusOK)
+	// parse the response body and obtain the new upload ID.
+	decoder := xml.NewDecoder(response.Body)
+	newResponse := &InitiateMultipartUploadResponse{}
+
+	err = decoder.Decode(newResponse)
+	c.Assert(err, IsNil)
+	c.Assert(len(newResponse.UploadID) > 0, Equals, true)
+	// uploadID to be used for rest of the multipart operations on the object.
+	uploadID := newResponse.UploadID
+
+	// content for the part to be uploaded.
+	// Create a byte array of 4MB.
+	data := bytes.Repeat([]byte("0123456789abcdef"), 4*1024*1024/16)
+	// calculate md5Sum of the data.
+	hasher := md5.New()
+	hasher.Write(data)
+	md5Sum := hasher.Sum(nil)
+
+	buffer1 := bytes.NewReader(data)
+	// HTTP request for the part to be uploaded.
+	request, err = newTestRequest("PUT", getPartUploadURL(s.endPoint, bucketName, objectName, uploadID, "1"),
+		int64(buffer1.Len()), buffer1, s.accessKey, s.secretKey)
+	// set the Content-Md5 header to the base64 encoding the md5Sum of the content.
+	request.Header.Set("Content-Md5", base64.StdEncoding.EncodeToString(md5Sum))
+	c.Assert(err, IsNil)
+
+	client = http.Client{}
+	// execute the HTTP request to upload the first part.
+	response1, err := client.Do(request)
+	c.Assert(err, IsNil)
+	c.Assert(response1.StatusCode, Equals, http.StatusOK)
+
+	// content for the second part to be uploaded will be same as first part.
+	hasher = md5.New()
+	hasher.Write(data)
+	// calculate md5Sum of the data.
+	md5Sum = hasher.Sum(nil)
+
+	buffer2 := bytes.NewReader(data)
+	// HTTP request for the second part to be uploaded.
+	request, err = newTestRequest("PUT", getPartUploadURL(s.endPoint, bucketName, objectName, uploadID, "2"),
+		int64(buffer2.Len()), buffer2, s.accessKey, s.secretKey)
+	// set the Content-Md5 header to the base64 encoding the md5Sum of the content.
+	request.Header.Set("Content-Md5", base64.StdEncoding.EncodeToString(md5Sum))
+	c.Assert(err, IsNil)
+
+	client = http.Client{}
+	// execute the HTTP request to upload the second part.
+	response2, err := client.Do(request)
+	c.Assert(err, IsNil)
+	c.Assert(response2.StatusCode, Equals, http.StatusOK)
+
+	// Complete multipart upload
+	completeUploads := &completeMultipartUpload{
+		Parts: []completePart{
+			{
+				PartNumber: 1,
+				ETag:       response1.Header.Get("ETag"),
+			},
+			{
+				PartNumber: 2,
+				ETag:       response2.Header.Get("ETag"),
+			},
+		},
+	}
+
+	completeBytes, err := xml.Marshal(completeUploads)
+	c.Assert(err, IsNil)
+	// Indicating that all parts are uploaded and initiating completeMultipartUpload.
+	request, err = newTestRequest("POST", getCompleteMultipartUploadURL(s.endPoint, bucketName, objectName, uploadID), int64(len(completeBytes)), bytes.NewReader(completeBytes), s.accessKey, s.secretKey)
+	c.Assert(err, IsNil)
+
+	// Execute the complete multipart request.
+	response, err = client.Do(request)
+	c.Assert(err, IsNil)
+	// verify whether complete multipart was successfull.
+	verifyError(c, response, "EntityTooSmall", "Your proposed upload is smaller than the minimum allowed object size.", http.StatusOK)
+}
+
 // TestObjectMultipart - Initiates a NewMultipart upload, uploads 2 parts,
 // completes the multipart upload and validates the status of the operation.
 func (s *MyAPIXLSuite) TestObjectMultipart(c *C) {