api: Set appropriate content-type for success/error responses. (#3537)

Golang HTTP client automatically detects content-type but
for S3 clients this content-type might be incorrect or
might misbehave.

For example:

```
Content-Type: text/xml; charset=utf-8
```

Should be
```
Content-Type: application/xml
```

Allow this to be set properly.

cmd/bucket-handlers.go

@@ -80,18 +80,18 @@ func (api objectAPIHandlers) GetBucketLocationHandler(w http.ResponseWriter, r *
 
 	objectAPI := api.ObjectAPI()
 	if objectAPI == nil {
-		writeErrorResponse(w, r, ErrServerNotInitialized, r.URL.Path)
+		writeErrorResponse(w, ErrServerNotInitialized, r.URL)
 		return
 	}
 
 	if s3Error := checkRequestAuthType(r, bucket, "s3:GetBucketLocation", "us-east-1"); s3Error != ErrNone {
-		writeErrorResponse(w, r, s3Error, r.URL.Path)
+		writeErrorResponse(w, s3Error, r.URL)
 		return
 	}
 
 	if _, err := objectAPI.GetBucketInfo(bucket); err != nil {
 		errorIf(err, "Unable to fetch bucket info.")
-		writeErrorResponse(w, r, toAPIErrorCode(err), r.URL.Path)
+		writeErrorResponse(w, toAPIErrorCode(err), r.URL)
 		return
 	}
 
@@ -104,8 +104,9 @@ func (api objectAPIHandlers) GetBucketLocationHandler(w http.ResponseWriter, r *
 			Location: region,
 		})
 	}
-	setCommonHeaders(w) // Write headers.
-	writeSuccessResponse(w, encodedSuccessResponse)
+
+	// Write success response.
+	writeSuccessResponseXML(w, encodedSuccessResponse)
 }
 
 // ListMultipartUploadsHandler - GET Bucket (List Multipart uploads)
@@ -122,24 +123,24 @@ func (api objectAPIHandlers) ListMultipartUploadsHandler(w http.ResponseWriter,
 
 	objectAPI := api.ObjectAPI()
 	if objectAPI == nil {
-		writeErrorResponse(w, r, ErrServerNotInitialized, r.URL.Path)
+		writeErrorResponse(w, ErrServerNotInitialized, r.URL)
 		return
 	}
 
 	if s3Error := checkRequestAuthType(r, bucket, "s3:ListBucketMultipartUploads", serverConfig.GetRegion()); s3Error != ErrNone {
-		writeErrorResponse(w, r, s3Error, r.URL.Path)
+		writeErrorResponse(w, s3Error, r.URL)
 		return
 	}
 
 	prefix, keyMarker, uploadIDMarker, delimiter, maxUploads, _ := getBucketMultipartResources(r.URL.Query())
 	if maxUploads < 0 {
-		writeErrorResponse(w, r, ErrInvalidMaxUploads, r.URL.Path)
+		writeErrorResponse(w, ErrInvalidMaxUploads, r.URL)
 		return
 	}
 	if keyMarker != "" {
 		// Marker not common with prefix is not implemented.
 		if !strings.HasPrefix(keyMarker, prefix) {
-			writeErrorResponse(w, r, ErrNotImplemented, r.URL.Path)
+			writeErrorResponse(w, ErrNotImplemented, r.URL)
 			return
 		}
 	}
@@ -147,16 +148,15 @@ func (api objectAPIHandlers) ListMultipartUploadsHandler(w http.ResponseWriter,
 	listMultipartsInfo, err := objectAPI.ListMultipartUploads(bucket, prefix, keyMarker, uploadIDMarker, delimiter, maxUploads)
 	if err != nil {
 		errorIf(err, "Unable to list multipart uploads.")
-		writeErrorResponse(w, r, toAPIErrorCode(err), r.URL.Path)
+		writeErrorResponse(w, toAPIErrorCode(err), r.URL)
 		return
 	}
 	// generate response
 	response := generateListMultipartUploadsResponse(bucket, listMultipartsInfo)
 	encodedSuccessResponse := encodeResponse(response)
-	// write headers.
-	setCommonHeaders(w)
+
 	// write success response.
-	writeSuccessResponse(w, encodedSuccessResponse)
+	writeSuccessResponseXML(w, encodedSuccessResponse)
 }
 
 // ListBucketsHandler - GET Service.
@@ -166,7 +166,7 @@ func (api objectAPIHandlers) ListMultipartUploadsHandler(w http.ResponseWriter,
 func (api objectAPIHandlers) ListBucketsHandler(w http.ResponseWriter, r *http.Request) {
 	objectAPI := api.ObjectAPI()
 	if objectAPI == nil {
-		writeErrorResponse(w, r, ErrServerNotInitialized, r.URL.Path)
+		writeErrorResponse(w, ErrServerNotInitialized, r.URL)
 		return
 	}
 
@@ -177,24 +177,23 @@ func (api objectAPIHandlers) ListBucketsHandler(w http.ResponseWriter, r *http.R
 		s3Error = checkRequestAuthType(r, "", "", serverConfig.GetRegion())
 	}
 	if s3Error != ErrNone {
-		writeErrorResponse(w, r, s3Error, r.URL.Path)
+		writeErrorResponse(w, s3Error, r.URL)
 		return
 	}
 	// Invoke the list buckets.
 	bucketsInfo, err := objectAPI.ListBuckets()
 	if err != nil {
 		errorIf(err, "Unable to list buckets.")
-		writeErrorResponse(w, r, toAPIErrorCode(err), r.URL.Path)
+		writeErrorResponse(w, toAPIErrorCode(err), r.URL)
 		return
 	}
 
 	// Generate response.
 	response := generateListBucketsResponse(bucketsInfo)
 	encodedSuccessResponse := encodeResponse(response)
-	// Write headers.
-	setCommonHeaders(w)
+
 	// Write response.
-	writeSuccessResponse(w, encodedSuccessResponse)
+	writeSuccessResponseXML(w, encodedSuccessResponse)
 }
 
 // DeleteMultipleObjectsHandler - deletes multiple objects.
@@ -204,26 +203,26 @@ func (api objectAPIHandlers) DeleteMultipleObjectsHandler(w http.ResponseWriter,
 
 	objectAPI := api.ObjectAPI()
 	if objectAPI == nil {
-		writeErrorResponse(w, r, ErrServerNotInitialized, r.URL.Path)
+		writeErrorResponse(w, ErrServerNotInitialized, r.URL)
 		return
 	}
 
 	if s3Error := checkRequestAuthType(r, bucket, "s3:DeleteObject", serverConfig.GetRegion()); s3Error != ErrNone {
-		writeErrorResponse(w, r, s3Error, r.URL.Path)
+		writeErrorResponse(w, s3Error, r.URL)
 		return
 	}
 
 	// Content-Length is required and should be non-zero
 	// http://docs.aws.amazon.com/AmazonS3/latest/API/multiobjectdeleteapi.html
 	if r.ContentLength <= 0 {
-		writeErrorResponse(w, r, ErrMissingContentLength, r.URL.Path)
+		writeErrorResponse(w, ErrMissingContentLength, r.URL)
 		return
 	}
 
 	// Content-Md5 is requied should be set
 	// http://docs.aws.amazon.com/AmazonS3/latest/API/multiobjectdeleteapi.html
 	if _, ok := r.Header["Content-Md5"]; !ok {
-		writeErrorResponse(w, r, ErrMissingContentMD5, r.URL.Path)
+		writeErrorResponse(w, ErrMissingContentMD5, r.URL)
 		return
 	}
 
@@ -233,7 +232,7 @@ func (api objectAPIHandlers) DeleteMultipleObjectsHandler(w http.ResponseWriter,
 	// Read incoming body XML bytes.
 	if _, err := io.ReadFull(r.Body, deleteXMLBytes); err != nil {
 		errorIf(err, "Unable to read HTTP body.")
-		writeErrorResponse(w, r, ErrInternalError, r.URL.Path)
+		writeErrorResponse(w, ErrInternalError, r.URL)
 		return
 	}
 
@@ -241,7 +240,7 @@ func (api objectAPIHandlers) DeleteMultipleObjectsHandler(w http.ResponseWriter,
 	deleteObjects := &DeleteObjectsRequest{}
 	if err := xml.Unmarshal(deleteXMLBytes, deleteObjects); err != nil {
 		errorIf(err, "Unable to unmarshal delete objects request XML.")
-		writeErrorResponse(w, r, ErrMalformedXML, r.URL.Path)
+		writeErrorResponse(w, ErrMalformedXML, r.URL)
 		return
 	}
 
@@ -289,10 +288,9 @@ func (api objectAPIHandlers) DeleteMultipleObjectsHandler(w http.ResponseWriter,
 	// Generate response
 	response := generateMultiDeleteResponse(deleteObjects.Quiet, deletedObjects, deleteErrors)
 	encodedSuccessResponse := encodeResponse(response)
-	// Write headers
-	setCommonHeaders(w)
+
 	// Write success response.
-	writeSuccessResponse(w, encodedSuccessResponse)
+	writeSuccessResponseXML(w, encodedSuccessResponse)
 
 	// Notify deleted event for objects.
 	for _, dobj := range deletedObjects {
@@ -315,13 +313,13 @@ func (api objectAPIHandlers) DeleteMultipleObjectsHandler(w http.ResponseWriter,
 func (api objectAPIHandlers) PutBucketHandler(w http.ResponseWriter, r *http.Request) {
 	objectAPI := api.ObjectAPI()
 	if objectAPI == nil {
-		writeErrorResponse(w, r, ErrServerNotInitialized, r.URL.Path)
+		writeErrorResponse(w, ErrServerNotInitialized, r.URL)
 		return
 	}
 
 	// PutBucket does not have any bucket action.
 	if s3Error := checkRequestAuthType(r, "", "", "us-east-1"); s3Error != ErrNone {
-		writeErrorResponse(w, r, s3Error, r.URL.Path)
+		writeErrorResponse(w, s3Error, r.URL)
 		return
 	}
 
@@ -331,7 +329,7 @@ func (api objectAPIHandlers) PutBucketHandler(w http.ResponseWriter, r *http.Req
 	// Validate if incoming location constraint is valid, reject
 	// requests which do not follow valid region requirements.
 	if s3Error := isValidLocationConstraint(r); s3Error != ErrNone {
-		writeErrorResponse(w, r, s3Error, r.URL.Path)
+		writeErrorResponse(w, s3Error, r.URL)
 		return
 	}
 
@@ -343,12 +341,14 @@ func (api objectAPIHandlers) PutBucketHandler(w http.ResponseWriter, r *http.Req
 	err := objectAPI.MakeBucket(bucket)
 	if err != nil {
 		errorIf(err, "Unable to create a bucket.")
-		writeErrorResponse(w, r, toAPIErrorCode(err), r.URL.Path)
+		writeErrorResponse(w, toAPIErrorCode(err), r.URL)
 		return
 	}
+
 	// Make sure to add Location information here only for bucket
 	w.Header().Set("Location", getLocation(r))
-	writeSuccessResponse(w, nil)
+
+	writeSuccessResponseHeadersOnly(w)
 }
 
 // PostPolicyBucketHandler - POST policy
@@ -358,7 +358,7 @@ func (api objectAPIHandlers) PutBucketHandler(w http.ResponseWriter, r *http.Req
 func (api objectAPIHandlers) PostPolicyBucketHandler(w http.ResponseWriter, r *http.Request) {
 	objectAPI := api.ObjectAPI()
 	if objectAPI == nil {
-		writeErrorResponse(w, r, ErrServerNotInitialized, r.URL.Path)
+		writeErrorResponse(w, ErrServerNotInitialized, r.URL)
 		return
 	}
 
@@ -367,14 +367,14 @@ func (api objectAPIHandlers) PostPolicyBucketHandler(w http.ResponseWriter, r *h
 	reader, err := r.MultipartReader()
 	if err != nil {
 		errorIf(err, "Unable to initialize multipart reader.")
-		writeErrorResponse(w, r, ErrMalformedPOSTRequest, r.URL.Path)
+		writeErrorResponse(w, ErrMalformedPOSTRequest, r.URL)
 		return
 	}
 
 	fileBody, fileName, formValues, err := extractPostPolicyFormValues(reader)
 	if err != nil {
 		errorIf(err, "Unable to parse form values.")
-		writeErrorResponse(w, r, ErrMalformedPOSTRequest, r.URL.Path)
+		writeErrorResponse(w, ErrMalformedPOSTRequest, r.URL)
 		return
 	}
 	bucket := mux.Vars(r)["bucket"]
@@ -390,25 +390,25 @@ func (api objectAPIHandlers) PostPolicyBucketHandler(w http.ResponseWriter, r *h
 	// Verify policy signature.
 	apiErr := doesPolicySignatureMatch(formValues)
 	if apiErr != ErrNone {
-		writeErrorResponse(w, r, apiErr, r.URL.Path)
+		writeErrorResponse(w, apiErr, r.URL)
 		return
 	}
 
 	policyBytes, err := base64.StdEncoding.DecodeString(formValues["Policy"])
 	if err != nil {
-		writeErrorResponse(w, r, ErrMalformedPOSTRequest, r.URL.Path)
+		writeErrorResponse(w, ErrMalformedPOSTRequest, r.URL)
 		return
 	}
 
 	postPolicyForm, err := parsePostPolicyForm(string(policyBytes))
 	if err != nil {
-		writeErrorResponse(w, r, ErrMalformedPOSTRequest, r.URL.Path)
+		writeErrorResponse(w, ErrMalformedPOSTRequest, r.URL)
 		return
 	}
 
 	// Make sure formValues adhere to policy restrictions.
 	if apiErr = checkPostPolicy(formValues, postPolicyForm); apiErr != ErrNone {
-		writeErrorResponse(w, r, apiErr, r.URL.Path)
+		writeErrorResponse(w, apiErr, r.URL)
 		return
 	}
 
@@ -442,7 +442,7 @@ func (api objectAPIHandlers) PostPolicyBucketHandler(w http.ResponseWriter, r *h
 	objInfo, err := objectAPI.PutObject(bucket, object, -1, fileBody, metadata, sha256sum)
 	if err != nil {
 		errorIf(err, "Unable to create object.")
-		writeErrorResponse(w, r, toAPIErrorCode(err), r.URL.Path)
+		writeErrorResponse(w, toAPIErrorCode(err), r.URL)
 		return
 	}
 	w.Header().Set("ETag", "\""+objInfo.MD5Sum+"\"")
@@ -471,10 +471,9 @@ func (api objectAPIHandlers) PostPolicyBucketHandler(w http.ResponseWriter, r *h
 					ETag:     "\"" + objInfo.MD5Sum + "\"",
 					Location: getObjectLocation(bucket, object),
 				})
-				writeResponse(w, http.StatusCreated, resp)
-
+				writeResponse(w, http.StatusCreated, resp, "application/xml")
 			case "200":
-				writeSuccessResponse(w, nil)
+				writeSuccessResponseHeadersOnly(w)
 			default:
 				writeSuccessNoContent(w)
 			}
@@ -504,12 +503,12 @@ func (api objectAPIHandlers) HeadBucketHandler(w http.ResponseWriter, r *http.Re
 
 	objectAPI := api.ObjectAPI()
 	if objectAPI == nil {
-		writeErrorResponse(w, r, ErrServerNotInitialized, r.URL.Path)
+		writeErrorResponseHeadersOnly(w, ErrServerNotInitialized)
 		return
 	}
 
 	if s3Error := checkRequestAuthType(r, bucket, "s3:ListBucket", serverConfig.GetRegion()); s3Error != ErrNone {
-		writeErrorResponse(w, r, s3Error, r.URL.Path)
+		writeErrorResponseHeadersOnly(w, s3Error)
 		return
 	}
 
@@ -519,23 +518,24 @@ func (api objectAPIHandlers) HeadBucketHandler(w http.ResponseWriter, r *http.Re
 
 	if _, err := objectAPI.GetBucketInfo(bucket); err != nil {
 		errorIf(err, "Unable to fetch bucket info.")
-		writeErrorResponse(w, r, toAPIErrorCode(err), r.URL.Path)
+		writeErrorResponseHeadersOnly(w, toAPIErrorCode(err))
 		return
 	}
-	writeSuccessResponse(w, nil)
+
+	writeSuccessResponseHeadersOnly(w)
 }
 
 // DeleteBucketHandler - Delete bucket
 func (api objectAPIHandlers) DeleteBucketHandler(w http.ResponseWriter, r *http.Request) {
 	objectAPI := api.ObjectAPI()
 	if objectAPI == nil {
-		writeErrorResponse(w, r, ErrServerNotInitialized, r.URL.Path)
+		writeErrorResponse(w, ErrServerNotInitialized, r.URL)
 		return
 	}
 
 	// DeleteBucket does not have any bucket action.
 	if s3Error := checkRequestAuthType(r, "", "", serverConfig.GetRegion()); s3Error != ErrNone {
-		writeErrorResponse(w, r, s3Error, r.URL.Path)
+		writeErrorResponse(w, s3Error, r.URL)
 		return
 	}
 
@@ -549,7 +549,7 @@ func (api objectAPIHandlers) DeleteBucketHandler(w http.ResponseWriter, r *http.
 	// Attempt to delete bucket.
 	if err := objectAPI.DeleteBucket(bucket); err != nil {
 		errorIf(err, "Unable to delete a bucket.")
-		writeErrorResponse(w, r, toAPIErrorCode(err), r.URL.Path)
+		writeErrorResponse(w, toAPIErrorCode(err), r.URL)
 		return
 	}