guestfs_read_file: Reimplement to avoid protocol limits.

TODO

@@ -567,7 +567,6 @@ the p.o.v of the API and ABI.
 
  - guestfs_lstatlist
  - guestfs_lxattrlist
- - guestfs_read_file
  - guestfs_read_lines
  - guestfs_readlinklist
  - guestfs_write

daemon/file.c

@@ -314,65 +314,6 @@ do_write_append (const char *path, const char *content, size_t size)
   return 0;
 }
 
-char *
-do_read_file (const char *path, size_t *size_r)
-{
-  int fd;
-  struct stat statbuf;
-  char *r;
-
-  CHROOT_IN;
-  fd = open (path, O_RDONLY|O_CLOEXEC);
-  CHROOT_OUT;
-
-  if (fd == -1) {
-    reply_with_perror ("open: %s", path);
-    return NULL;
-  }
-
-  if (fstat (fd, &statbuf) == -1) {
-    reply_with_perror ("fstat: %s", path);
-    close (fd);
-    return NULL;
-  }
-
-  /* The actual limit on messages is smaller than this.  This
-   * check just limits the amount of memory we'll try and allocate
-   * here.  If the message is larger than the real limit, that will
-   * be caught later when we try to serialize the message.
-   */
-  if (statbuf.st_size >= GUESTFS_MESSAGE_MAX) {
-    reply_with_error ("%s: file is too large for the protocol, use guestfs_download instead", path);
-    close (fd);
-    return NULL;
-  }
-  r = malloc (statbuf.st_size);
-  if (r == NULL) {
-    reply_with_perror ("malloc");
-    close (fd);
-    return NULL;
-  }
-
-  if (xread (fd, r, statbuf.st_size) == -1) {
-    reply_with_perror ("read: %s", path);
-    close (fd);
-    free (r);
-    return NULL;
-  }
-
-  if (close (fd) == -1) {
-    reply_with_perror ("close: %s", path);
-    free (r);
-    return NULL;
-  }
-
-  /* Mustn't touch *size_r until we are sure that we won't return any
-   * error (RHBZ#589039).
-   */
-  *size_r = statbuf.st_size;
-  return r;
-}
-
 static char *
 pread_fd (int fd, int count, int64_t offset, size_t *size_r,
           const char *display_path)

generator/generator_actions.ml

@@ -2044,6 +2044,21 @@ this limit has been lifted and the call can download and
 return an arbitrary list of files (limited by the amount of
 memory available)." };
 
+  { defaults with
+    name = "read_file";
+    style = RBufferOut "content", [Pathname "path"], [];
+    tests = [
+      InitISOFS, Always, TestOutputBuffer (
+        [["read_file"; "/known-4"]], "abc\ndef\nghi")
+    ];
+    shortdesc = "read a file";
+    longdesc = "\
+This calls returns the contents of the file C<path> as a
+buffer.
+
+Unlike C<guestfs_cat>, this function can correctly
+handle files that contain embedded ASCII NUL characters." };
+
 ]
 
 (* daemon_functions are any functions which cause some action
@@ -5168,38 +5183,6 @@ This calls removes a mountpoint that was previously created
 with C<guestfs_mkmountpoint>.  See C<guestfs_mkmountpoint>
 for full details." };
 
-  { defaults with
-    name = "read_file";
-    style = RBufferOut "content", [Pathname "path"], [];
-    proc_nr = Some 150;
-    protocol_limit_warning = true;
-    tests = [
-      InitISOFS, Always, TestOutputBuffer (
-        [["read_file"; "/known-4"]], "abc\ndef\nghi");
-      (* Test various near large, large and too large files (RHBZ#589039). *)
-      InitScratchFS, Always, TestLastFail (
-        [["touch"; "/read_file"];
-         ["truncate_size"; "/read_file"; "4194303"]; (* GUESTFS_MESSAGE_MAX - 1 *)
-         ["read_file"; "/read_file"]]);
-      InitScratchFS, Always, TestLastFail (
-        [["touch"; "/read_file2"];
-         ["truncate_size"; "/read_file2"; "4194304"]; (* GUESTFS_MESSAGE_MAX *)
-         ["read_file"; "/read_file2"]]);
-      InitScratchFS, Always, TestLastFail (
-        [["touch"; "/read_file3"];
-         ["truncate_size"; "/read_file3"; "41943040"]; (* GUESTFS_MESSAGE_MAX * 10 *)
-         ["read_file"; "/read_file3"]])
-    ];
-    shortdesc = "read a file";
-    longdesc = "\
-This calls returns the contents of the file C<path> as a
-buffer.
-
-Unlike C<guestfs_cat>, this function can correctly
-handle files that contain embedded ASCII NUL characters.
-However unlike C<guestfs_download>, this function is limited
-in the total size of file that can be handled." };
-
   { defaults with
     name = "grep";
     style = RStringList "lines", [String "regex"; Pathname "path"], [OBool "extended"; OBool "fixed"; OBool "insensitive"; OBool "compressed"];

src/file.c

@@ -50,6 +50,14 @@ sort_strings (char **argv, size_t len)
 
 char *
 guestfs__cat (guestfs_h *g, const char *path)
+{
+  size_t size;
+
+  return guestfs_read_file (g, path, &size);
+}
+
+char *
+guestfs__read_file (guestfs_h *g, const char *path, size_t *size_r)
 {
   int fd = -1;
   size_t size;
@@ -97,6 +105,10 @@ guestfs__cat (guestfs_h *g, const char *path)
     goto err;
   }
 
+  /* Mustn't touch *size_r until we are sure that we won't return any
+   * error (RHBZ#589039).
+   */
+  *size_r = size;
   return ret;
 
  err: