Implement "head", "head-n", "tail", "tail-n" commands.

These commands let you view parts of a large file without
passing the whole file over the network connection.

4 files changed, 166 insertions, 1 deletions

diff --git a/TODO b/TODO
index 20f5ca0a..7696daa2 100644
--- a/TODO
+++ b/TODO
@@ -117,7 +117,6 @@ Supermin appliance should be moved into febootstrap.
 Extra commands / functionality:
 
   General glibc / core programs:
-    head, tail
     chgrp
     grep (do it locally using pipe?)
     dd (?)
diff --git a/daemon/Makefile.am b/daemon/Makefile.am
index b58ec3d7..4228ad06 100644
--- a/daemon/Makefile.am
+++ b/daemon/Makefile.am
@@ -39,6 +39,7 @@ guestfsd_SOURCES = \
 	glob.c \
 	grub.c \
 	guestfsd.c \
+	headtail.c \
 	hexdump.c \
 	ls.c \
 	lvm.c \
diff --git a/daemon/headtail.c b/daemon/headtail.c
new file mode 100644
index 00000000..b522c55f
--- /dev/null
+++ b/daemon/headtail.c
@@ -0,0 +1,107 @@
+/* libguestfs - the guestfsd daemon
+ * 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 "../src/guestfs_protocol.h"
+#include "daemon.h"
+#include "actions.h"
+
+static char **
+headtail (const char *prog, const char *flag, const char *n, char *path)
+{
+  char *buf;
+  char *out, *err;
+  int r, len;
+  char **lines;
+
+  NEED_ROOT (NULL);
+  ABS_PATH (path, NULL);
+
+  /* Make the path relative to /sysroot. */
+  len = strlen (path) + 9;
+  buf = malloc (len);
+  if (!buf) {
+    reply_with_perror ("malloc");
+    return NULL;
+  }
+  snprintf (buf, len, "/sysroot%s", path);
+
+  r = command (&out, &err, prog, flag, n, buf, NULL);
+  free (buf);
+  if (r == -1) {
+    reply_with_error ("%s %s %s: %s", prog, flag, n, err);
+    free (out);
+    free (err);
+    return NULL;
+  }
+
+  free (err);
+
+#if 0
+  /* Split it at the first whitespace. */
+  len = strcspn (out, " \t\n");
+  out[len] = '\0';
+#endif
+
+  lines = split_lines (out);
+  free (out);
+  if (lines == NULL) return NULL;
+
+  return lines;
+}
+
+char **
+do_head (char *path)
+{
+  return headtail ("head", "-n", "10", path);
+}
+
+char **
+do_tail (char *path)
+{
+  return headtail ("tail", "-n", "10", path);
+}
+
+char **
+do_head_n (int n, char *path)
+{
+  char nbuf[16];
+
+  snprintf (nbuf, sizeof nbuf, "%d", n);
+
+  return headtail ("head", "-n", nbuf, path);
+}
+
+char **
+do_tail_n (int n, char *path)
+{
+  char nbuf[16];
+
+  if (n >= 0)
+    snprintf (nbuf, sizeof nbuf, "%d", n);
+  else
+    snprintf (nbuf, sizeof nbuf, "+%d", -n);
+
+  return headtail ("tail", "-n", nbuf, path);
+}
diff --git a/src/generator.ml b/src/generator.ml
index aecb152b..abc73da0 100755
--- a/src/generator.ml
+++ b/src/generator.ml
@@ -2500,6 +2500,64 @@ C<wc -w> external command.");
 This command counts the characters in a file, using the
 C<wc -c> external command.");
 
+  ("head", (RStringList "lines", [String "path"]), 121, [ProtocolLimitWarning],
+   [InitBasicFS, Always, TestOutputList (
+      [["mount_vfs"; "ro"; "squashfs"; "/dev/sdd"; "/"];
+       ["head"; "/10klines"]], ["0abcdefghijklmnopqrstuvwxyz";"1abcdefghijklmnopqrstuvwxyz";"2abcdefghijklmnopqrstuvwxyz";"3abcdefghijklmnopqrstuvwxyz";"4abcdefghijklmnopqrstuvwxyz";"5abcdefghijklmnopqrstuvwxyz";"6abcdefghijklmnopqrstuvwxyz";"7abcdefghijklmnopqrstuvwxyz";"8abcdefghijklmnopqrstuvwxyz";"9abcdefghijklmnopqrstuvwxyz"])],
+   "return first 10 lines of a file",
+   "\
+This command returns up to the first 10 lines of a file as
+a list of strings.");
+
+  ("head_n", (RStringList "lines", [Int "nrlines"; String "path"]), 122, [ProtocolLimitWarning],
+   [InitBasicFS, Always, TestOutputList (
+      [["mount_vfs"; "ro"; "squashfs"; "/dev/sdd"; "/"];
+       ["head_n"; "3"; "/10klines"]], ["0abcdefghijklmnopqrstuvwxyz";"1abcdefghijklmnopqrstuvwxyz";"2abcdefghijklmnopqrstuvwxyz"]);
+    InitBasicFS, Always, TestOutputList (
+      [["mount_vfs"; "ro"; "squashfs"; "/dev/sdd"; "/"];
+       ["head_n"; "-9997"; "/10klines"]], ["0abcdefghijklmnopqrstuvwxyz";"1abcdefghijklmnopqrstuvwxyz";"2abcdefghijklmnopqrstuvwxyz"]);
+    InitBasicFS, Always, TestOutputList (
+      [["mount_vfs"; "ro"; "squashfs"; "/dev/sdd"; "/"];
+       ["head_n"; "0"; "/10klines"]], [])],
+   "return first N lines of a file",
+   "\
+If the parameter C<nrlines> is a positive number, this returns the first
+C<nrlines> lines of the file C<path>.
+
+If the parameter C<nrlines> is a negative number, this returns lines
+from the file C<path>, excluding the last C<nrlines> lines.
+
+If the parameter C<nrlines> is zero, this returns an empty list.");
+
+  ("tail", (RStringList "lines", [String "path"]), 123, [ProtocolLimitWarning],
+   [InitBasicFS, Always, TestOutputList (
+      [["mount_vfs"; "ro"; "squashfs"; "/dev/sdd"; "/"];
+       ["tail"; "/10klines"]], ["9990abcdefghijklmnopqrstuvwxyz";"9991abcdefghijklmnopqrstuvwxyz";"9992abcdefghijklmnopqrstuvwxyz";"9993abcdefghijklmnopqrstuvwxyz";"9994abcdefghijklmnopqrstuvwxyz";"9995abcdefghijklmnopqrstuvwxyz";"9996abcdefghijklmnopqrstuvwxyz";"9997abcdefghijklmnopqrstuvwxyz";"9998abcdefghijklmnopqrstuvwxyz";"9999abcdefghijklmnopqrstuvwxyz"])],
+   "return last 10 lines of a file",
+   "\
+This command returns up to the last 10 lines of a file as
+a list of strings.");
+
+  ("tail_n", (RStringList "lines", [Int "nrlines"; String "path"]), 124, [ProtocolLimitWarning],
+   [InitBasicFS, Always, TestOutputList (
+      [["mount_vfs"; "ro"; "squashfs"; "/dev/sdd"; "/"];
+       ["tail_n"; "3"; "/10klines"]], ["9997abcdefghijklmnopqrstuvwxyz";"9998abcdefghijklmnopqrstuvwxyz";"9999abcdefghijklmnopqrstuvwxyz"]);
+    InitBasicFS, Always, TestOutputList (
+      [["mount_vfs"; "ro"; "squashfs"; "/dev/sdd"; "/"];
+       ["tail_n"; "-9998"; "/10klines"]], ["9997abcdefghijklmnopqrstuvwxyz";"9998abcdefghijklmnopqrstuvwxyz";"9999abcdefghijklmnopqrstuvwxyz"]);
+    InitBasicFS, Always, TestOutputList (
+      [["mount_vfs"; "ro"; "squashfs"; "/dev/sdd"; "/"];
+       ["tail_n"; "0"; "/10klines"]], [])],
+   "return last N lines of a file",
+   "\
+If the parameter C<nrlines> is a positive number, this returns the last
+C<nrlines> lines of the file C<path>.
+
+If the parameter C<nrlines> is a negative number, this returns lines
+from the file C<path>, starting with the C<-nrlines>th line.
+
+If the parameter C<nrlines> is zero, this returns an empty list.");
+
 ]
 
 let all_functions = non_daemon_functions @ daemon_functions