Readonly support on the client side

For now, the client can "tmate show-messages" to get it

cmd-attach-session.c

@@ -21,6 +21,7 @@
 #include <stdlib.h>
 
 #include "tmux.h"
+#include "tmate.h"
 
 /*
  * Attach existing session to the current terminal.

cmd-switch-client.c

@@ -60,6 +60,10 @@ cmd_switch_client_key_binding(struct cmd *self, int key)
 enum cmd_retval
 cmd_switch_client_exec(struct cmd *self, struct cmd_q *cmdq)
 {
+#ifdef TMATE_SLAVE
+	cmdq_error(cmdq, "client switch is not supported");
+	return (CMD_RETURN_ERROR);
+#else
 	struct args	*args = self->args;
 	struct client	*c;
 	struct session	*s;
@@ -111,4 +115,5 @@ cmd_switch_client_exec(struct cmd *self, struct cmd_q *cmdq)
 	s->curw->flags &= ~WINLINK_ALERTFLAGS;
 
 	return (CMD_RETURN_NORMAL);
+#endif
 }

resize.c

@@ -61,6 +61,10 @@ recalculate_sizes(void)
 			c = ARRAY_ITEM(&clients, j);
 			if (c == NULL || c->flags & CLIENT_SUSPENDED)
 				continue;
+#ifdef TMATE_SLAVE
+			if (c->flags & CLIENT_READONLY)
+				continue;
+#endif
 			if (c->session == s) {
 				if (c->tty.sx < ssx)
 					ssx = c->tty.sx;

tmate-decoder.c

@@ -109,6 +109,9 @@ static void tmate_header(struct tmate_unpacker *uk)
 	if (gethostname(hostname, sizeof(hostname)) < 0)
 		tmate_fatal("cannot get hostname");
 
+	tmate_notify("Remote session read only: ssh ro-%s@%s.%s (clear your screen if you share this)",
+		     tmate_session_token_ro, hostname, TMATE_DOMAIN);
+
 	tmate_notify("Remote session: ssh %s@%s.%s",
 		     tmate_session_token, hostname, TMATE_DOMAIN);
 }

tmate-slave.c

@@ -20,6 +20,7 @@
 struct tmate_encoder *tmate_encoder;
 int tmux_socket_fd;
 const char *tmate_session_token = "main";
+const char *tmate_session_token_ro = "ro-main";
 
 static char *log_path; /* NULL means stderr */
 static char *cmdline;
@@ -97,19 +98,6 @@ int main(int argc, char **argv, char **envp)
 	tmate_ssh_server_main(keys_dir, port);
 	return 0;
 }
-static void set_session_token(struct tmate_ssh_client *client,
-			      const char *token)
-{
-	tmate_session_token = xstrdup(token);
-	strcpy(socket_path, TMATE_WORKDIR "/sessions/");
-	strcat(socket_path, token);
-
-	memset(cmdline, 0, cmdline_end - cmdline);
-	sprintf(cmdline, "tmate-slave [%s] %s %s",
-		tmate_session_token,
-		client->role == TMATE_ROLE_SERVER ? "(server)" : "(client)",
-		client->ip_address);
-}
 
 static char tmate_token_digits[] = "abcdefghijklmnopqrstuvwxyz"
 				   "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
@@ -126,11 +114,37 @@ static char *get_random_token(void)
 		token[i] = tmate_token_digits[token[i] % NUM_DIGITS];
 	token[i] = 0;
 
+	return token;
+}
+
+static void set_session_token(struct tmate_ssh_client *client,
+			      const char *token)
+{
+	tmate_session_token = xstrdup(token);
+	strcpy(socket_path, TMATE_WORKDIR "/sessions/");
+	strcat(socket_path, token);
+
+	memset(cmdline, 0, cmdline_end - cmdline);
+	sprintf(cmdline, "tmate-slave [%s] %s %s",
+		tmate_session_token,
+		client->role == TMATE_ROLE_SERVER ? "(server)" : "(client)",
+		client->ip_address);
+}
+static void create_session_ro_symlink(void)
+{
+	char session_ro_path[MAXPATHLEN];
+
+	tmate_session_token_ro = get_random_token();
 #ifdef DEVENV
-	strcpy(token, "SUPERSECURETOKENFORDEVENV");
+	strcpy((char *)tmate_session_token_ro, "READONLYTOKENFORDEVENV000");
 #endif
 
-	return token;
+	strcpy(session_ro_path, TMATE_WORKDIR "/sessions/");
+	strcat(session_ro_path, tmate_session_token_ro);
+
+	unlink(session_ro_path);
+	if (symlink(tmate_session_token, session_ro_path) < 0)
+		tmate_fatal("Cannot create read-only symlink");
 }
 
 static int validate_token(const char *token)
@@ -254,6 +268,10 @@ static void tmate_spawn_slave_server(struct tmate_ssh_client *client)
 	struct tmate_decoder decoder;
 
 	token = get_random_token();
+#ifdef DEVENV
+	strcpy(token, "SUPERSECURETOKENFORDEVENV");
+#endif
+
 	set_session_token(client, token);
 	free(token);
 
@@ -263,6 +281,8 @@ static void tmate_spawn_slave_server(struct tmate_ssh_client *client)
 	if (tmux_socket_fd < 0)
 		tmate_fatal("Cannot create to the tmux socket");
 
+	create_session_ro_symlink();
+
 	/*
 	 * Needed to initialize the database used in tty-term.c.
 	 * We won't have access to it once in the jail.
@@ -286,11 +306,19 @@ static void tmate_spawn_slave_server(struct tmate_ssh_client *client)
 
 static void tmate_spawn_slave_client(struct tmate_ssh_client *client)
 {
-	char *argv[] = {(char *)"attach", NULL};
+	char *argv_rw[] = {(char *)"attach", NULL};
+	char *argv_ro[] = {(char *)"attach", (char *)"-r", NULL};
+	char **argv = argv_rw;
+	int argc = 1;
 	char *token = client->username;
+	struct stat fstat;
 	int slave_pty;
 	int ret;
 
+	/* the "ro-" part is just sugar, we don't care about it */
+	if (!memcmp("ro-", token, 3))
+		token += 3;
+
 	if (validate_token(token) < 0) {
 		ssh_echo(client, BAD_TOKEN_ERROR_STR);
 		tmate_fatal("Bad token");
@@ -307,6 +335,22 @@ static void tmate_spawn_slave_client(struct tmate_ssh_client *client)
 		tmate_fatal("Expired token");
 	}
 
+	/*
+	 * If we are connecting through a symlink, it means that we are a
+	 * readonly client.
+	 * 1) We mark the client as CLIENT_READONLY on the server
+	 * 2) We prevent any input (aside from the window size) to go through
+	 *    to the server.
+	 */
+	client->readonly = 0;
+	if (lstat(socket_path, &fstat) < 0)
+		tmate_fatal("Cannot fstat()");
+	if (S_ISLNK(fstat.st_mode)) {
+		client->readonly = 1;
+		argv = argv_ro;
+		argc = 2;
+	}
+
 	if (openpty(&client->pty, &slave_pty, NULL, NULL, NULL) < 0)
 		tmate_fatal("Cannot allocate pty");
 
@@ -324,7 +368,7 @@ static void tmate_spawn_slave_client(struct tmate_ssh_client *client)
 
 	tmate_ssh_client_pty_init(client);
 
-	ret = client_main(1, argv, IDENTIFY_UTF8 | IDENTIFY_256COLOURS);
+	ret = client_main(argc, argv, IDENTIFY_UTF8 | IDENTIFY_256COLOURS);
 	tmate_flush_pty(client);
 	exit(ret);
 }

tmate-ssh-client-pty.c

@@ -26,6 +26,9 @@ static void consume_channel(struct tmate_ssh_client *client)
 		if (len == 0)
 			return;
 
+		if (client->readonly)
+			continue;
+
 		ptr = buf;
 		setblocking(client->pty, 1);
 		while (len > 0) {

tmate.h

@@ -102,6 +102,7 @@ struct tmate_ssh_client {
 	/* only for client-pty */
 	int pty;
 	struct event ev_pty;
+	int readonly;
 };
 extern void tmate_ssh_client_init(struct tmate_ssh_client *client,
 				  struct tmate_encoder *encoder,
@@ -136,6 +137,7 @@ extern void tmate_ssh_server_main(const char *keys_dir, int port);
 extern struct tmate_encoder *tmate_encoder;
 extern int tmux_socket_fd;
 extern const char *tmate_session_token;
+extern const char *tmate_session_token_ro;
 
 extern void tmate_get_random_bytes(void *buffer, ssize_t len);
 extern long tmate_get_random_long(void);