LogDog: Add Butler stream server package.

client/logdog/butlerlib/streamclient/registry.go

Index: client/logdog/butlerlib/streamclient/registry.go
diff --git a/client/logdog/butlerlib/streamclient/registry.go b/client/logdog/butlerlib/streamclient/registry.go
new file mode 100644
index 0000000000000000000000000000000000000000..270c841604850bd8c768ba8deb4bb30f610cc180
--- /dev/null
+++ b/client/logdog/butlerlib/streamclient/registry.go
@@ -0,0 +1,66 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package streamclient
+
+import (
+	"fmt"
+	"strings"
+	"sync"
+)
+
+var (
+	// defaultRegistry is the default protocol registry.
+	defaultRegistry = &protocolRegistry{}
+)
+
+// protocolRegistry maps protocol prefix strings to their Client generator
+// functions.
+//
+// This allows multiple Butler stream protocols (e.g., "unix:", "net.pipe:",
+// etc.) to be parsed from string.
+type protocolRegistry struct {
+	sync.Mutex
+
+	// protocols is the set of registered protocols. Each client should register
+	// via registerProtocol in its init() method.
+	protocols map[string]clientFactory
+}
+
+func (r *protocolRegistry) register(name string, f clientFactory) {
+	r.Lock()
+	defer r.Unlock()
+
+	if _, ok := r.protocols[name]; ok {
+		panic(fmt.Errorf("streamclient: protocol already registered for [%s]", name))
+	}
+	if r.protocols == nil {
+		r.protocols = make(map[string]clientFactory)
+	}
+	r.protocols[name] = f
+}
+
+// newClient invokes the protocol clientFactory generator for the
+// supplied protocol/address string, returning the generated Client.
+func (r *protocolRegistry) newClient(path string) (Client, error) {
+	parts := strings.SplitN(path, ":", 2)
+	params := ""
+	if len(parts) == 2 {
+		params = parts[1]
+	}
+
+	r.Lock()
+	defer r.Unlock()
+
+	if f, ok := r.protocols[parts[0]]; ok {
+		return f(params)
+	}
+	return nil, fmt.Errorf("streamclient: no protocol registered for [%s]", parts[0])
+}
+
+// registerProtocol registers a protocol with the default (global) protocol
+// registry.
+func registerProtocol(name string, f clientFactory) {
+	defaultRegistry.register(name, f)
+}