Guestfish feature: remote control of guestfish over a pipe.

The use case is to have a long-running guestfish process in
a shell script, and thus to avoid the overhead of starting
guestfish each time.  Do:

 eval `guestfish --listen`

 guestfish --remote somecmd
 guestfish --remote someothercmd
 guestfish --remote exit

This patch also supports having multiple guestfish processes
at the same time.

The protocol is simple XDR messages over a Unix domain socket.

1 files changed, 272 insertions, 0 deletions

diff --git a/fish/rc.c b/fish/rc.c
new file mode 100644
index 00000000..0d67a62b
--- /dev/null
+++ b/fish/rc.c
@@ -0,0 +1,272 @@
+/* guestfish - the filesystem interactive shell
+ * Copyright (C) 2009 Red Hat Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <config.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/un.h>
+#include <signal.h>
+
+#include <rpc/types.h>
+#include <rpc/xdr.h>
+
+#include "fish.h"
+#include "rc_protocol.h"
+
+#define UNIX_PATH_MAX 108
+
+static void
+create_sockpath (pid_t pid, char *sockpath, int len, struct sockaddr_un *addr)
+{
+  char dir[128];
+  uid_t euid = geteuid ();
+
+  snprintf (dir, sizeof dir, "/tmp/.guestfish-%d", euid);
+  mkdir (dir, 0700);
+
+  snprintf (sockpath, len, "/tmp/.guestfish-%d/socket-%d", euid, pid);
+
+  addr->sun_family = AF_UNIX;
+  strcpy (addr->sun_path, sockpath);
+}
+
+/* Remote control server. */
+void
+rc_listen (void)
+{
+  char sockpath[128];
+  pid_t pid;
+  struct sockaddr_un addr;
+  int sock, s, i, fd;
+  FILE *fp;
+  XDR xdr, xdr2;
+  guestfish_hello hello;
+  guestfish_call call;
+  guestfish_reply reply;
+  char **argv;
+  int argc;
+
+  memset (&hello, 0, sizeof hello);
+  memset (&call, 0, sizeof call);
+
+  pid = fork ();
+  if (pid == -1) {
+    perror ("fork");
+    exit (1);
+  }
+
+  if (pid > 0) {
+    /* Parent process. */
+    printf ("export GUESTFISH_PID=%d\n", pid);
+    fflush (stdout);
+    _exit (0);
+  }
+
+  /* Child process.
+   *
+   * Create the listening socket for accepting commands.
+   *
+   * Unfortunately there is a small but unavoidable race here.  We
+   * don't know the PID until after we've forked, so we cannot be
+   * sure the socket is created from the point of view of the parent
+   * (if the child is very slow).
+   */
+  pid = getpid ();
+  create_sockpath (pid, sockpath, sizeof sockpath, &addr);
+
+  sock = socket (AF_UNIX, SOCK_STREAM, 0);
+  if (sock == -1) {
+    perror ("socket");
+    exit (1);
+  }
+  unlink (sockpath);
+  if (bind (sock, (struct sockaddr *) &addr, sizeof addr) == -1) {
+    perror (sockpath);
+    exit (1);
+  }
+  if (listen (sock, 4) == -1) {
+    perror ("listen");
+    exit (1);
+  }
+
+  /* Now close stdout and substitute /dev/null.  This is necessary
+   * so that eval `guestfish --listen` doesn't block forever.
+   */
+  fd = open ("/dev/null", O_WRONLY);
+  if (fd == -1)
+    perror ("/dev/null");
+  else {
+    dup2 (fd, 1);
+    close (fd);
+  }
+
+  /* Read commands and execute them. */
+  while (!quit) {
+    s = accept (sock, NULL, NULL);
+    if (s == -1)
+      perror ("accept");
+    else {
+      fp = fdopen (s, "r+");
+      xdrstdio_create (&xdr, fp, XDR_DECODE);
+
+      if (!xdr_guestfish_hello (&xdr, &hello)) {
+	fprintf (stderr, _("guestfish: protocol error: could not read 'hello' message\n"));
+	goto error;
+      }
+
+      if (strcmp (hello.vers, PACKAGE_VERSION) != 0) {
+	fprintf (stderr, _("guestfish: protocol error: version mismatch, server version '%s' does not match client version '%s'.  The two versions must match exactly.\n"),
+		 PACKAGE_VERSION,
+		 hello.vers);
+	xdr_free ((xdrproc_t) xdr_guestfish_hello, (char *) &hello);
+	goto error;
+      }
+      xdr_free ((xdrproc_t) xdr_guestfish_hello, (char *) &hello);
+
+      while (xdr_guestfish_call (&xdr, &call)) {
+	/* We have to extend and NULL-terminate the argv array. */
+	argc = call.args.args_len;
+	argv = realloc (call.args.args_val, (argc+1) * sizeof (char *));
+	if (argv == NULL) {
+	  perror ("realloc");
+	  exit (1);
+	}
+	call.args.args_val = argv;
+	argv[argc] = NULL;
+
+	if (verbose) {
+	  fprintf (stderr, "guestfish(%d): %s", pid, call.cmd);
+	  for (i = 0; i < argc; ++i)
+	    fprintf (stderr, " %s", argv[i]);
+	  fprintf (stderr, "\n");
+	}
+
+	/* Run the command. */
+	reply.r = issue_command (call.cmd, argv, NULL);
+
+	xdr_free ((xdrproc_t) xdr_guestfish_call, (char *) &call);
+
+	/* Send the reply. */
+	xdrstdio_create (&xdr2, fp, XDR_ENCODE);
+	(void) xdr_guestfish_reply (&xdr2, &reply);
+	xdr_destroy (&xdr2);
+
+	/* Exit on error? */
+	if (call.exit_on_error && reply.r == -1) {
+	  unlink (sockpath);
+	  exit (1);
+	}
+      }
+
+    error:
+      xdr_destroy (&xdr);	/* NB. This doesn't close 'fp'. */
+      fclose (fp);		/* Closes the underlying socket 's'. */
+    }
+  }
+
+  unlink (sockpath);
+  exit (0);
+}
+
+/* Remote control client. */
+int
+rc_remote (int pid, const char *cmd, int argc, char *argv[],
+	   int exit_on_error)
+{
+  guestfish_hello hello;
+  guestfish_call call;
+  guestfish_reply reply;
+  char sockpath[128];
+  struct sockaddr_un addr;
+  int sock;
+  FILE *fp;
+  XDR xdr;
+
+  memset (&reply, 0, sizeof reply);
+
+  /* This is fine as long as we never try to xdr_free this struct. */
+  hello.vers = (char *) PACKAGE_VERSION;
+
+  /* Check the other end is still running. */
+  if (kill (pid, 0) == -1) {
+    fprintf (stderr, _("guestfish: remote: looks like the server is not running\n"));
+    return -1;
+  }
+
+  create_sockpath (pid, sockpath, sizeof sockpath, &addr);
+
+  sock = socket (AF_UNIX, SOCK_STREAM, 0);
+  if (sock == -1) {
+    perror ("socket");
+    return -1;
+  }
+
+  if (connect (sock, (struct sockaddr *) &addr, sizeof addr) == -1) {
+    perror (sockpath);
+    fprintf (stderr, _("guestfish: remote: looks like the server is not running\n"));
+    close (sock);
+    return -1;
+  }
+
+  /* Send the greeting. */
+  fp = fdopen (sock, "r+");
+  xdrstdio_create (&xdr, fp, XDR_ENCODE);
+
+  if (!xdr_guestfish_hello (&xdr, &hello)) {
+    fprintf (stderr, _("guestfish: protocol error: could not send initial greeting to server\n"));
+    fclose (fp);
+    xdr_destroy (&xdr);
+    return -1;
+  }
+
+  /* Send the command.  The server supports reading multiple commands
+   * per connection, but this code only ever sends one command.
+   */
+  call.cmd = (char *) cmd;
+  call.args.args_len = argc;
+  call.args.args_val = argv;
+  call.exit_on_error = exit_on_error;
+  if (!xdr_guestfish_call (&xdr, &call)) {
+    fprintf (stderr, _("guestfish: protocol error: could not send initial greeting to server\n"));
+    fclose (fp);
+    xdr_destroy (&xdr);
+    return -1;
+  }
+  xdr_destroy (&xdr);
+
+  /* Wait for the reply. */
+  xdrstdio_create (&xdr, fp, XDR_DECODE);
+
+  if (!xdr_guestfish_reply (&xdr, &reply)) {
+    fprintf (stderr, _("guestfish: protocol error: could not decode reply from server\n"));
+    fclose (fp);
+    xdr_destroy (&xdr);
+    return -1;
+  }
+
+  fclose (fp);
+  xdr_destroy (&xdr);
+
+  return reply.r;
+}