guestfs_cat: Reimplement to avoid protocol limits.

6 files changed, 123 insertions, 88 deletions

diff --git a/TODO b/TODO
index 3832371c..452b9f7d 100644
--- a/TODO
+++ b/TODO
@@ -565,7 +565,6 @@ with the non-daemon versions implemented using guestfs_upload and
 guestfs_download (and others).  This change should be transparent from
 the p.o.v of the API and ABI.
 
- - guestfs_cat
  - guestfs_find
  - guestfs_lstatlist
  - guestfs_lxattrlist
diff --git a/daemon/file.c b/daemon/file.c
index cdf6b1bc..2ea8b738 100644
--- a/daemon/file.c
+++ b/daemon/file.c
@@ -85,75 +85,6 @@ do_touch (const char *path)
   return 0;
 }
 
-char *
-do_cat (const char *path)
-{
-  int fd;
-  size_t alloc, size, max;
-  ssize_t r;
-  char *buf, *buf2;
-
-  CHROOT_IN;
-  fd = open (path, O_RDONLY|O_CLOEXEC);
-  CHROOT_OUT;
-
-  if (fd == -1) {
-    reply_with_perror ("open: %s", path);
-    return NULL;
-  }
-
-  /* Read up to GUESTFS_MESSAGE_MAX - <overhead> bytes.  If it's
-   * larger than that, we need to return an error instead (for
-   * correctness).
-   */
-  max = GUESTFS_MESSAGE_MAX - 1000;
-  buf = NULL;
-  size = alloc = 0;
-
-  for (;;) {
-    if (size >= alloc) {
-      alloc += 8192;
-      if (alloc > max) {
-        reply_with_error ("%s: file is too large for message buffer",
-                          path);
-        free (buf);
-        close (fd);
-        return NULL;
-      }
-      buf2 = realloc (buf, alloc);
-      if (buf2 == NULL) {
-        reply_with_perror ("realloc");
-        free (buf);
-        close (fd);
-        return NULL;
-      }
-      buf = buf2;
-    }
-
-    r = read (fd, buf + size, alloc - size);
-    if (r == -1) {
-      reply_with_perror ("read: %s", path);
-      free (buf);
-      close (fd);
-      return NULL;
-    }
-    if (r == 0) {
-      buf[size] = '\0';
-      break;
-    }
-    if (r > 0)
-      size += r;
-  }
-
-  if (close (fd) == -1) {
-    reply_with_perror ("close: %s", path);
-    free (buf);
-    return NULL;
-  }
-
-  return buf;			/* caller will free */
-}
-
 char **
 do_read_lines (const char *path)
 {
diff --git a/generator/generator_actions.ml b/generator/generator_actions.ml
index f370b795..2d9dbc9d 100644
--- a/generator/generator_actions.ml
+++ b/generator/generator_actions.ml
@@ -1970,6 +1970,30 @@ need to call C<guestfs_close> afterwards.
 C<guestfs_close> will call this if you don't do it explicitly,
 but note that any errors are ignored in that case." };
 
+  { defaults with
+    name = "cat";
+    style = RString "content", [Pathname "path"], [];
+    tests = [
+      InitISOFS, Always, TestOutput (
+        [["cat"; "/known-2"]], "abcdef\n")
+    ];
+    shortdesc = "list the contents of a file";
+    longdesc = "\
+Return the contents of the file named C<path>.
+
+Because, in C, this function returns a C<char *>, there is no
+way to differentiate between a C<\\0> character in a file and
+end of string.  To handle binary files, use the C<guestfs_read_file>
+or C<guestfs_download> functions.
+
+In libguestfs E<lt> 1.19.32, this API was also subject to
+a limit in the protocol which limited the effective size of
+a file that it could read.  In later versions of libguestfs,
+this limit has been lifted and the call can download and
+return arbitrary sized files (limited by the amount of
+memory available).  In either case you should check the size
+of the file before downloading it or consider alternate APIs." };
+
 ]
 
 (* daemon_functions are any functions which cause some action
@@ -2046,24 +2070,6 @@ This command only works on regular files, and will fail on other
 file types such as directories, symbolic links, block special etc." };
 
   { defaults with
-    name = "cat";
-    style = RString "content", [Pathname "path"], [];
-    proc_nr = Some 4;
-    protocol_limit_warning = true;
-    tests = [
-      InitISOFS, Always, TestOutput (
-        [["cat"; "/known-2"]], "abcdef\n")
-    ];
-    shortdesc = "list the contents of a file";
-    longdesc = "\
-Return the contents of the file named C<path>.
-
-Note that this function cannot correctly handle binary files
-(specifically, files containing C<\\0> character which is treated
-as end of string).  For those you need to use the C<guestfs_read_file>
-or C<guestfs_download> functions which have a more complex interface." };
-
-  { defaults with
     name = "ll";
     style = RString "listing", [Pathname "directory"], [];
     proc_nr = Some 5;
diff --git a/po/POTFILES b/po/POTFILES
index 08d2ab86..60887dc2 100644
--- a/po/POTFILES
+++ b/po/POTFILES
@@ -209,6 +209,7 @@ src/dbdump.c
 src/errnostring-gperf.c
 src/errnostring.c
 src/events.c
+src/file.c
 src/filearch.c
 src/fuse.c
 src/guestfs.c
diff --git a/src/Makefile.am b/src/Makefile.am
index 750c07be..ff6149c7 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -127,6 +127,7 @@ libguestfs_la_SOURCES = \
 	bindtests.c \
 	dbdump.c \
 	events.c \
+	file.c \
 	filearch.c \
 	fuse.c \
 	inspect.c \
diff --git a/src/file.c b/src/file.c
new file mode 100644
index 00000000..b76900d2
--- /dev/null
+++ b/src/file.c
@@ -0,0 +1,97 @@
+/* libguestfs
+ * Copyright (C) 2012 Red Hat Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <config.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <inttypes.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#include "full-read.h"
+
+#include "guestfs.h"
+#include "guestfs-internal.h"
+#include "guestfs-internal-actions.h"
+#include "guestfs_protocol.h"
+
+char *
+guestfs__cat (guestfs_h *g, const char *path)
+{
+  int fd = -1;
+  size_t size;
+  char *tmpfile = NULL, *ret = NULL;
+  struct stat statbuf;
+
+  tmpfile = safe_asprintf (g, "%s/cat%d", g->tmpdir, ++g->unique);
+
+  if (guestfs_download (g, path, tmpfile) == -1)
+    goto err;
+
+  fd = open (tmpfile, O_RDONLY|O_CLOEXEC);
+  if (fd == -1) {
+    perrorf (g, "open: %s", tmpfile);
+    goto err;
+  }
+
+  unlink (tmpfile);
+  free (tmpfile);
+  tmpfile = NULL;
+
+  /* Read the whole file into memory. */
+  if (fstat (fd, &statbuf) == -1) {
+    perrorf (g, "stat: %s", tmpfile);
+    goto err;
+  }
+
+  /* Don't use safe_malloc, because we want to return an errno to the caller. */
+  size = statbuf.st_size;
+  ret = malloc (size + 1);
+  if (!ret) {
+    perrorf (g, "malloc: %zu bytes", size + 1);
+    goto err;
+  }
+
+  if (full_read (fd, ret, size) != size) {
+    perrorf (g, "full-read: %s: %zu bytes", tmpfile, size + 1);
+    goto err;
+  }
+
+  ret[size] = '\0';
+
+  if (close (fd) == -1) {
+    perrorf (g, "close: %s", tmpfile);
+    goto err;
+  }
+
+  return ret;
+
+ err:
+  free (ret);
+  if (fd >= 0)
+    close (fd);
+  if (tmpfile) {
+    unlink (tmpfile);
+    free (tmpfile);
+  }
+  return NULL;
+}