Isolated content of pkg/loader

pkg/loader/loader.go

@@ -0,0 +1,101 @@
+/*
+Copyright 2018 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package loader
+
+import "fmt"
+
+// Loader interface exposes methods to read bytes in a scheme-agnostic manner.
+// The Loader encapsulating a root location to calculate where to read from.
+type Loader interface {
+	// Root returns the scheme-specific string representing the root location for this Loader.
+	Root() string
+	// New returns Loader located at newRoot.
+	New(newRoot string) (Loader, error)
+	// Load returns the bytes read from the location or an error.
+	Load(location string) ([]byte, error)
+}
+
+// Private implmentation of Loader interface.
+type loaderImpl struct {
+	root    string
+	schemes []SchemeLoader
+}
+
+// Interface for different types of loaders (e.g. fileLoader, httpLoader, etc.)
+type SchemeLoader interface {
+	// Does this location correspond to this scheme.
+	IsScheme(root string, location string) bool
+	// Combines the root and path into a full location string.
+	FullLocation(root string, path string) (string, error)
+	// Load bytes at scheme-specific location or an error.
+	Load(location string) ([]byte, error)
+}
+
+const emptyRoot = ""
+
+// Init initializes the first loader with the supported schemes.
+// Example schemes: fileLoader, httpLoader, gitLoader.
+func Init(schemes []SchemeLoader) Loader {
+	return &loaderImpl{root: emptyRoot, schemes: schemes}
+}
+
+// Root returns the scheme-specific root location for this Loader.
+func (l *loaderImpl) Root() string {
+	return l.root
+}
+
+// Returns a new Loader rooted at newRoot. "newRoot" MUST be
+// a directory (not a file). The directory can have a trailing
+// slash or not.
+// Example: "/home/seans/project" or "/home/seans/project/"
+// NOT "/home/seans/project/file.yaml".
+func (l *loaderImpl) New(newRoot string) (Loader, error) {
+	scheme, err := l.getSchemeLoader(newRoot)
+	if err != nil {
+		return nil, err
+	}
+	root, err := scheme.FullLocation(l.root, newRoot)
+	if err != nil {
+		return nil, err
+	}
+	return &loaderImpl{root: root, schemes: l.schemes}, nil
+}
+
+// Load returns all the bytes read from scheme-specific location or an error.
+// "location" can be an absolute path, or if relative, full location is
+// calculated from the Root().
+func (l *loaderImpl) Load(location string) ([]byte, error) {
+	scheme, err := l.getSchemeLoader(location)
+	if err != nil {
+		return nil, err
+	}
+	fullLocation, err := scheme.FullLocation(l.root, location)
+	if err != nil {
+		return nil, err
+	}
+	return scheme.Load(fullLocation)
+}
+
+// Helper function to parse scheme from location parameter.
+func (l *loaderImpl) getSchemeLoader(location string) (SchemeLoader, error) {
+	for _, scheme := range l.schemes {
+		if scheme.IsScheme(l.root, location) {
+			return scheme, nil
+		}
+	}
+	return nil, fmt.Errorf("Unknown Scheme: %s, %s\n", l.root, location)
+}