tor: add GETINFO method to check liveness of onion service

tor/cmd_info.go

@@ -0,0 +1,72 @@
+package tor
+
+import (
+	"errors"
+	"fmt"
+)
+
+var (
+	// ErrServiceNotCreated is used when we want to query info on an onion
+	// service while it's not been created yet.
+	ErrServiceNotCreated = errors.New("onion service hasn't been created")
+
+	// ErrServiceIDUnmatch is used when the serviceID the controller has
+	// doesn't match the serviceID the Tor daemon has.
+	ErrServiceIDUnmatch = errors.New("onion serviceIDs not match")
+
+	// ErrNoServiceFound is used when the Tor daemon replies no active
+	// onion services found for the current control connection while we
+	// expect one.
+	ErrNoServiceFound = errors.New("no active service found")
+)
+
+// CheckOnionService checks that the onion service created by the controller
+// is active. It queries the Tor daemon using the endpoint "onions/current" to
+// get the current onion service and checks that service ID matches the
+// activeServiceID.
+func (c *Controller) CheckOnionService() error {
+	// Check that we have a hidden service created.
+	if c.activeServiceID == "" {
+		return ErrServiceNotCreated
+	}
+
+	// Fetch the onion services that live in current control connection.
+	cmd := "GETINFO onions/current"
+	code, reply, err := c.sendCommand(cmd)
+
+	// Exit early if we got an error or Tor daemon didn't respond success.
+	// TODO(yy): unify the usage of err and code so we could rely on a
+	// single source to change our state.
+	if err != nil || code != success {
+		log.Debugf("query service:%v got err:%v, reply:%v",
+			c.activeServiceID, err, reply)
+
+		return fmt.Errorf("%w: %v", err, reply)
+	}
+
+	// Parse the reply, which should have the following format,
+	//      onions/current=serviceID
+	// After parsing, we get a map as,
+	// 	[onion/current: serviceID]
+	//
+	// NOTE: our current tor controller does NOT support multiple onion
+	// services to be created at the same time, thus we expect the reply to
+	// only contain one serviceID. If multiple serviceIDs are returned, we
+	// would expected the reply to have the following format,
+	//      onions/current=serviceID1, serviceID2, serviceID3,...
+	// Thus a new parser is need to parse that reply.
+	resp := parseTorReply(reply)
+	serviceID, ok := resp["onions/current"]
+	if !ok {
+		return ErrNoServiceFound
+	}
+
+	// Check that our active service is indeed the service acknowledged by
+	// Tor daemon.
+	if c.activeServiceID != serviceID {
+		return fmt.Errorf("%w: controller has: %v, Tor daemon has: %v",
+			ErrServiceIDUnmatch, c.activeServiceID, serviceID)
+	}
+
+	return nil
+}