registry: getting Endpoint ironned out

Signed-off-by: Vincent Batts <vbatts@redhat.com>

docs/endpoint.go

@@ -0,0 +1,129 @@
+package registry
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"net/url"
+	"strings"
+
+	"github.com/docker/docker/pkg/log"
+)
+
+// scans string for api version in the URL path. returns the trimmed hostname, if version found, string and API version.
+func scanForApiVersion(hostname string) (string, APIVersion) {
+	var (
+		chunks        []string
+		apiVersionStr string
+	)
+	if strings.HasSuffix(hostname, "/") {
+		chunks = strings.Split(hostname[:len(hostname)-1], "/")
+		apiVersionStr = chunks[len(chunks)-1]
+	} else {
+		chunks = strings.Split(hostname, "/")
+		apiVersionStr = chunks[len(chunks)-1]
+	}
+	for k, v := range apiVersions {
+		if apiVersionStr == v {
+			hostname = strings.Join(chunks[:len(chunks)-1], "/")
+			return hostname, k
+		}
+	}
+	return hostname, DefaultAPIVersion
+}
+
+func NewEndpoint(hostname string) (*Endpoint, error) {
+	var (
+		endpoint        Endpoint
+		trimmedHostname string
+		err             error
+	)
+	if !strings.HasPrefix(hostname, "http") {
+		hostname = "https://" + hostname
+	}
+	trimmedHostname, endpoint.Version = scanForApiVersion(hostname)
+	endpoint.URL, err = url.Parse(trimmedHostname)
+	if err != nil {
+		return nil, err
+	}
+
+	endpoint.URL.Scheme = "https"
+	if _, err := endpoint.Ping(); err != nil {
+		log.Debugf("Registry %s does not work (%s), falling back to http", endpoint, err)
+		// TODO: Check if http fallback is enabled
+		endpoint.URL.Scheme = "http"
+		if _, err = endpoint.Ping(); err != nil {
+			return nil, errors.New("Invalid Registry endpoint: " + err.Error())
+		}
+	}
+
+	return &endpoint, nil
+}
+
+type Endpoint struct {
+	URL     *url.URL
+	Version APIVersion
+}
+
+// Get the formated URL for the root of this registry Endpoint
+func (e Endpoint) String() string {
+	return fmt.Sprintf("%s/v%d/", e.URL.String(), e.Version)
+}
+
+func (e Endpoint) VersionString(version APIVersion) string {
+	return fmt.Sprintf("%s/v%d/", e.URL.String(), version)
+}
+
+func (e Endpoint) Ping() (RegistryInfo, error) {
+	if e.String() == IndexServerAddress() {
+		// Skip the check, we now this one is valid
+		// (and we never want to fallback to http in case of error)
+		return RegistryInfo{Standalone: false}, nil
+	}
+
+	req, err := http.NewRequest("GET", e.String()+"_ping", nil)
+	if err != nil {
+		return RegistryInfo{Standalone: false}, err
+	}
+
+	resp, _, err := doRequest(req, nil, ConnectTimeout)
+	if err != nil {
+		return RegistryInfo{Standalone: false}, err
+	}
+
+	defer resp.Body.Close()
+
+	jsonString, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return RegistryInfo{Standalone: false}, fmt.Errorf("Error while reading the http response: %s", err)
+	}
+
+	// If the header is absent, we assume true for compatibility with earlier
+	// versions of the registry. default to true
+	info := RegistryInfo{
+		Standalone: true,
+	}
+	if err := json.Unmarshal(jsonString, &info); err != nil {
+		log.Debugf("Error unmarshalling the _ping RegistryInfo: %s", err)
+		// don't stop here. Just assume sane defaults
+	}
+	if hdr := resp.Header.Get("X-Docker-Registry-Version"); hdr != "" {
+		log.Debugf("Registry version header: '%s'", hdr)
+		info.Version = hdr
+	}
+	log.Debugf("RegistryInfo.Version: %q", info.Version)
+
+	standalone := resp.Header.Get("X-Docker-Registry-Standalone")
+	log.Debugf("Registry standalone header: '%s'", standalone)
+	// Accepted values are "true" (case-insensitive) and "1".
+	if strings.EqualFold(standalone, "true") || standalone == "1" {
+		info.Standalone = true
+	} else if len(standalone) > 0 {
+		// there is a header set, and it is not "true" or "1", so assume fails
+		info.Standalone = false
+	}
+	log.Debugf("RegistryInfo.Standalone: %q", info.Standalone)
+	return info, nil
+}