Move 'search' to the registry subsystem

This continues the effort to separate all registry logic from the
deprecated `Server` object.

* 'search' is exposed by `github.com/dotcloud/docker/registry/Service`
* Added proper documentation of Search while I was at it

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)

docs/service.go

@@ -9,7 +9,7 @@ import (
 // following calls:
 //
 //  'auth': Authenticate against the public registry
-//  'search': Search for images on the public registry (TODO)
+//  'search': Search for images on the public registry
 //  'pull': Download images from any registry (TODO)
 //  'push': Upload images to any registry (TODO)
 type Service struct {
@@ -24,6 +24,7 @@ func NewService() *Service {
 // Install installs registry capabilities to eng.
 func (s *Service) Install(eng *engine.Engine) error {
 	eng.Register("auth", s.Auth)
+	eng.Register("search", s.Search)
 	return nil
 }
 
@@ -52,3 +53,52 @@ func (s *Service) Auth(job *engine.Job) engine.Status {
 	job.Printf("%s\n", status)
 	return engine.StatusOK
 }
+
+// Search queries the public registry for images matching the specified
+// search terms, and returns the results.
+//
+// Argument syntax: search TERM
+//
+// Option environment:
+//	'authConfig': json-encoded credentials to authenticate against the registry.
+//		The search extends to images only accessible via the credentials.
+//
+//	'metaHeaders': extra HTTP headers to include in the request to the registry.
+//		The headers should be passed as a json-encoded dictionary.
+//
+// Output:
+//	Results are sent as a collection of structured messages (using engine.Table).
+//	Each result is sent as a separate message.
+//	Results are ordered by number of stars on the public registry.
+func (s *Service) Search(job *engine.Job) engine.Status {
+	if n := len(job.Args); n != 1 {
+		return job.Errorf("Usage: %s TERM", job.Name)
+	}
+	var (
+		term        = job.Args[0]
+		metaHeaders = map[string][]string{}
+		authConfig  = &AuthConfig{}
+	)
+	job.GetenvJson("authConfig", authConfig)
+	job.GetenvJson("metaHeaders", metaHeaders)
+
+	r, err := NewRegistry(authConfig, HTTPRequestFactory(metaHeaders), IndexServerAddress())
+	if err != nil {
+		return job.Error(err)
+	}
+	results, err := r.SearchRepositories(term)
+	if err != nil {
+		return job.Error(err)
+	}
+	outs := engine.NewTable("star_count", 0)
+	for _, result := range results.Results {
+		out := &engine.Env{}
+		out.Import(result)
+		outs.Add(out)
+	}
+	outs.ReverseSort()
+	if _, err := outs.WriteListTo(job.Stdout); err != nil {
+		return job.Error(err)
+	}
+	return engine.StatusOK
+}