fish: In edit command, upload to a new file.

If the upload fails, this means we don't leave a partially
written file.

Also add a test for the edit command.

fish/Makefile.am

@@ -247,6 +247,7 @@ TESTS = \
 if ENABLE_APPLIANCE
 TESTS += \
 	test-copy.sh \
+	test-edit.sh \
 	test-find0.sh \
 	test-read_file.sh \
 	test-remote.sh \

fish/edit.c

@@ -26,9 +26,12 @@
 #include <inttypes.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <assert.h>
 
 #include "fish.h"
 
+static char *generate_random_name (const char *filename);
+
 /* guestfish edit command, suggested by Ján Ondrej, implemented by RWMJ */
 
 int
@@ -37,7 +40,7 @@ run_edit (const char *cmd, size_t argc, char *argv[])
   TMP_TEMPLATE_ON_STACK (filename);
   char buf[256];
   const char *editor;
-  char *remotefilename;
+  char *remotefilename, *newname;
   struct stat oldstat, newstat;
   int r, fd;
 
@@ -111,14 +114,29 @@ run_edit (const char *cmd, size_t argc, char *argv[])
     return 0;
   }
 
-  /* Write new content. */
-  if (guestfs_upload (g, filename, remotefilename) == -1)
+  /* Upload to a new file in the same directory, so if it fails we
+   * don't end up with a partially written file.  Give the new file
+   * a completely random name so we have only a tiny chance of
+   * overwriting some existing file.
+   */
+  newname = generate_random_name (remotefilename);
+  if (!newname)
     goto error2;
 
+  /* Write new content. */
+  if (guestfs_upload (g, filename, newname) == -1)
+    goto error3;
+
+  if (guestfs_mv (g, newname, remotefilename) == -1)
+    goto error3;
+
+  free (newname);
   unlink (filename);
   free (remotefilename);
   return 0;
 
+ error3:
+  free (newname);
  error2:
   unlink (filename);
  error1:
@@ -126,3 +144,37 @@ run_edit (const char *cmd, size_t argc, char *argv[])
  error0:
   return -1;
 }
+
+static char
+random_char (void)
+{
+  char c[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
+  return c[random () % (sizeof c - 1)];
+}
+
+static char *
+generate_random_name (const char *filename)
+{
+  char *ret, *p;
+  size_t i;
+
+  ret = malloc (strlen (filename) + 16);
+  if (!ret) {
+    perror ("malloc");
+    return NULL;
+  }
+  strcpy (ret, filename);
+
+  p = strrchr (ret, '/');
+  assert (p);
+  p++;
+
+  /* Because of "+ 16" above, there should be enough space in the
+   * output buffer to write 8 random characters here.
+   */
+  for (i = 0; i < 8; ++i)
+    *p++ = random_char ();
+  *p++ = '\0';
+
+  return ret; /* caller will free */
+}

fish/fish.c

@@ -163,6 +163,9 @@ main (int argc, char *argv[])
   bindtextdomain (PACKAGE, LOCALEBASEDIR);
   textdomain (PACKAGE);
 
+  /* We use random(3) in edit.c. */
+  srandom (time (NULL));
+
   parse_config ();
 
   enum { HELP_OPTION = CHAR_MAX + 1 };

fish/test-edit.sh

@@ -0,0 +1,51 @@
+#!/bin/bash -
+# libguestfs
+# Copyright (C) 2012 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+# Test guestfish edit command.
+
+# This test fails on some versions of mock which lack /dev/fd
+# directory.  Skip this test in that case.
+
+test -d /dev/fd || {
+    echo "$0: Skipping this test because /dev/fd is missing."
+    exit 0
+}
+
+set -e
+
+rm -f test1.img
+
+# The command will be 'echo ... >>/tmp/tmpfile'
+export EDITOR="echo second line of text >>"
+
+output=$(
+../fish/guestfish -N fs -m /dev/sda1 <<EOF
+write /file.txt "this is a test\n"
+edit /file.txt
+cat /file.txt
+EOF
+)
+
+if [ "$output" != "this is a test
+second line of text" ]; then
+    echo "$0: error: output of guestfish after edit command did not match expected output"
+    echo "$output"
+    exit 1
+fi
+
+rm -f test1.img