service: add user run

This enables to run commands as other users, like sudo.

This is useful for eg fixing a user networks on their behalf.

service.go

@@ -128,7 +128,10 @@ func handleServicePRIVMSG(ctx *serviceContext, text string) {
 		ctx.print(fmt.Sprintf(`error: failed to parse command: %v`, err))
 		return
 	}
+	handleServiceCommand(ctx, words)
+}
 
+func handleServiceCommand(ctx *serviceContext, words []string) {
 	cmd, params, err := serviceCommands.Get(words)
 	if err != nil {
 		ctx.print(fmt.Sprintf(`error: %v (type "help" for a list of commands)`, err))
@@ -285,6 +288,12 @@ func init() {
 					desc:   "delete a user",
 					handle: handleUserDelete,
 				},
+				"run": {
+					usage:  "<username> <command>",
+					desc:   "run a command as another user",
+					handle: handleUserRun,
+					admin:  true,
+				},
 			},
 		},
 		"channel": {
@@ -1047,6 +1056,57 @@ func handleUserDelete(ctx *serviceContext, params []string) error {
 	return nil
 }
 
+func handleUserRun(ctx *serviceContext, params []string) error {
+	if !ctx.user.Admin {
+		return fmt.Errorf("only admins may run command as other users")
+	}
+	if len(params) < 2 {
+		return fmt.Errorf("expected at least two arguments")
+	}
+
+	username := params[0]
+	params = params[1:]
+	if username == ctx.user.Username {
+		handleServiceCommand(ctx, params)
+		return nil
+	}
+
+	u := ctx.user.srv.getUser(username)
+	if u == nil {
+		return fmt.Errorf("unknown username %q", username)
+	}
+
+	printCh := make(chan string, 1)
+	ev := eventUserRun{
+		params: params,
+		print:  printCh,
+	}
+	select {
+	case <-ctx.Done():
+		return ctx.Err()
+	case u.events <- ev:
+	}
+	for {
+		select {
+		case <-ctx.Done():
+			// This handles a possible race condition:
+			// - we send ev to u.events
+			// - the user goroutine for u stops (because of a crash or user deletion)
+			// - we would block on printCh
+			// Quitting on ctx.Done() prevents us from blocking indefinitely
+			// in case the event is never processed.
+			// TODO: Properly fix this condition by flushing the u.events queue
+			//       and running close(ev.print) in a defer
+			return nil
+		case text, ok := <-printCh:
+			if !ok {
+				return nil
+			}
+			ctx.print(text)
+		}
+	}
+}
+
 func handleServiceChannelStatus(ctx *serviceContext, params []string) error {
 	var defaultNetworkName string
 	if ctx.network != nil {

user.go

@@ -82,6 +82,11 @@ type eventTryRegainNick struct {
 	nick string
 }
 
+type eventUserRun struct {
+	params []string
+	print  chan string
+}
+
 type deliveredClientMap map[string]string // client name -> msg ID
 
 type deliveredStore struct {
@@ -769,6 +774,22 @@ func (u *user) run() {
 			}
 		case eventTryRegainNick:
 			e.uc.tryRegainNick(e.nick)
+		case eventUserRun:
+			ctx := context.TODO()
+			handleServiceCommand(&serviceContext{
+				Context: ctx,
+				user:    u,
+				print: func(text string) {
+					// Avoid blocking on e.print in case our context is canceled.
+					// This is a no-op right now because we use context.TODO(),
+					// but might be useful later when we add timeouts.
+					select {
+					case <-ctx.Done():
+					case e.print <- text:
+					}
+				},
+			}, e.params)
+			close(e.print)
 		case eventStop:
 			for _, dc := range u.downstreamConns {
 				dc.Close()