Add Version()

memcache/memcache.go

@@ -419,9 +419,10 @@ func (c *Client) flushAllFromAddr(addr net.Addr) error {
 	})
 }
 
-// ping sends the version command to the given addr
-func (c *Client) ping(addr net.Addr) error {
-	return c.withAddrRw(addr, func(conn *conn) error {
+// version sends the version command to the given addr. returns the version string
+func (c *Client) version(addr net.Addr) (string, error) {
+	var version string
+	err := c.withAddrRw(addr, func(conn *conn) error {
 		rw := conn.rw
 		if _, err := fmt.Fprintf(rw, "version\r\n"); err != nil {
 			return err
@@ -433,15 +434,20 @@ func (c *Client) ping(addr net.Addr) error {
 		if err != nil {
 			return err
 		}
-
-		switch {
-		case bytes.HasPrefix(line, versionPrefix):
-			break
-		default:
-			return fmt.Errorf("memcache: unexpected response line from ping: %q", string(line))
+		if !bytes.HasPrefix(line, versionPrefix) {
+			return fmt.Errorf("memcache: unexpected response line from version: %q", string(line))
 		}
+		// Then we expect a space and the version string
+		version = string(bytes.TrimSpace(line[len(versionPrefix):]))
 		return nil
 	})
+	return version, err
+}
+
+// ping sends the version command to the given addr
+func (c *Client) ping(addr net.Addr) error {
+	_, err := c.version(addr)
+	return err
 }
 
 func (c *Client) touchFromAddr(addr net.Addr, keys []string, expiration int32) error {
@@ -784,6 +790,35 @@ func (c *Client) Ping() error {
 	return c.selector.Each(c.ping)
 }
 
+// VersionAll returns map of the version strings of all instances, keyed by
+// their address string. If any instance is down, its version string is
+// returned as an empty string.
+func (c *Client) VersionAll() (map[string]string, error) {
+	versionMap := make(map[string]string)
+	err := c.selector.Each(func(addr net.Addr) error {
+		version, err := c.version(addr)
+		if err != nil {
+			version = ""
+		}
+		versionMap[addr.String()] = version
+		return nil
+	})
+	return versionMap, err
+}
+
+// Version returns the version string of the instance at the given key.
+func (c *Client) Version(key string) (string, error) {
+	addr, err := c.selector.PickServer(key)
+	if err != nil {
+		return "", err
+	}
+	version, err := c.version(addr)
+	if err != nil {
+		return "", err
+	}
+	return version, nil
+}
+
 // Increment atomically increments key by delta. The return value is
 // the new value after being incremented or an error. If the value
 // didn't exist in memcached the error is ErrCacheMiss. The value in

memcache/memcache_test.go

@@ -343,6 +343,33 @@ func testWithClient(t *testing.T, c *Client) {
 		t.Errorf("post-DeleteAll want ErrCacheMiss, got %v", err)
 	}
 
+	// Test Version
+	versions, err := c.VersionAll()
+	if err != nil {
+		t.Fatalf("VersionAll: %v", err)
+	}
+	if len(versions) != 1 {
+		t.Fatalf("VersionAll returned %d addresses, expected 1", len(versions))
+	}
+
+	expected_key := c.selector.(*ServerList).addrs[0].String()
+	_, ok := versions[expected_key]
+	if !ok {
+		var found_key string = ""
+		for k := range versions {
+			found_key = k
+		}
+		t.Fatalf("VersionAll key %q not found in %v. Found %q instead", expected_key, versions, found_key)
+	}
+
+	version, err := c.Version(expected_key)
+	if err != nil {
+		t.Fatalf("Version: %v", err)
+	}
+	if version != versions[expected_key] {
+		t.Fatalf("Version: expected %q, got %q", versions[expected_key], version)
+	}
+
 	// Test Ping
 	err = c.Ping()
 	checkErr(err, "error ping: %s", err)

memcache/selector.go

@@ -90,6 +90,8 @@ func (ss *ServerList) SetServers(servers ...string) error {
 }
 
 // Each iterates over each server calling the given function
+// with the server address. If the function returns an error,
+// the iteration stops immediately and the error is returned.
 func (ss *ServerList) Each(f func(net.Addr) error) error {
 	ss.mu.RLock()
 	defer ss.mu.RUnlock()
@@ -127,3 +129,8 @@ func (ss *ServerList) PickServer(key string) (net.Addr, error) {
 
 	return ss.addrs[cs%uint32(len(ss.addrs))], nil
 }
+
+var (
+	_ ServerSelector = (*ServerList)(nil)
+	_ net.Addr       = (*staticAddr)(nil)
+)