objAPI: Implement CopyObject API. (#3487)

This is written so that to simplify our handler code
and provide a way to only update metadata instead of
the data when source and destination in CopyObject
request are same.

Fixes #3316

cmd/handler-utils.go

@@ -65,6 +65,45 @@ var supportedHeaders = []string{
 	// Add more supported headers here.
 }
 
+// isMetadataDirectiveValid - check if metadata-directive is valid.
+func isMetadataDirectiveValid(h http.Header) bool {
+	_, ok := h[http.CanonicalHeaderKey("X-Amz-Metadata-Directive")]
+	if ok {
+		// Check atleast set metadata-directive is valid.
+		return (isMetadataCopy(h) || isMetadataReplace(h))
+	}
+	// By default if x-amz-metadata-directive is not we
+	// treat it as 'COPY' this function returns true.
+	return true
+}
+
+// Check if the metadata COPY is requested.
+func isMetadataCopy(h http.Header) bool {
+	return h.Get("X-Amz-Metadata-Directive") == "COPY"
+}
+
+// Check if the metadata REPLACE is requested.
+func isMetadataReplace(h http.Header) bool {
+	return h.Get("X-Amz-Metadata-Directive") == "REPLACE"
+}
+
+// Splits an incoming path into bucket and object components.
+func path2BucketAndObject(path string) (bucket, object string) {
+	// Skip the first element if it is '/', split the rest.
+	path = strings.TrimPrefix(path, "/")
+	pathComponents := strings.SplitN(path, "/", 2)
+
+	// Save the bucket and object extracted from path.
+	switch len(pathComponents) {
+	case 1:
+		bucket = pathComponents[0]
+	case 2:
+		bucket = pathComponents[0]
+		object = pathComponents[1]
+	}
+	return bucket, object
+}
+
 // extractMetadataFromHeader extracts metadata from HTTP header.
 func extractMetadataFromHeader(header http.Header) map[string]string {
 	metadata := make(map[string]string)