Add inplace file editing extension.

1 files changed, 241 insertions, 0 deletions

diff --git a/extension/inplace.c b/extension/inplace.c
new file mode 100644
index 00000000..69b188b8
--- /dev/null
+++ b/extension/inplace.c
@@ -0,0 +1,241 @@
+/*
+ * inplace.c - Provide support for in-place editing.
+ */
+
+/*
+ * Copyright (C) 2013 the Free Software Foundation, Inc.
+ * 
+ * This file is part of GAWK, the GNU implementation of the
+ * AWK Programming Language.
+ * 
+ * GAWK 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 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * GAWK 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
+ */
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <stdio.h>
+#include <assert.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#include "gawkapi.h"
+
+#include "gettext.h"
+#define _(msgid)  gettext(msgid)
+#define N_(msgid) msgid
+
+static const gawk_api_t *api;	/* for convenience macros to work */
+static awk_ext_id_t *ext_id;
+static const char *ext_version = "inplace extension: version 1.0";
+
+int plugin_is_GPL_compatible;
+
+static struct {
+	char *tname;
+	int default_stdout;
+	int posrc;	/* return code from fgetpos */
+	fpos_t pos;
+} state = { NULL, -1 };
+
+/*
+ * XXX Known problems:
+ * 1. Should copy ACL.
+ * 2. Not reentrant, so will not work if multiple files are open at
+ *    the same time.  I'm not sure this is a meaningful problem in practice.
+ */
+
+static void
+at_exit(void *data, int exit_status)
+{
+	if (state.tname) {
+		unlink(state.tname);
+		free(state.tname);
+		state.tname = NULL;
+	}
+}
+
+/*
+ * N.B. Almost everything is a fatal error because this feature is typically
+ * used for one-liners where the user is not going to be worrying about
+ * checking errors.  If anything unexpected occurs, we want to abort
+ * immediately!
+ */
+
+static int
+invalid_filename(const awk_string_t *filename)
+{
+	return filename->len == 0 ||
+		(filename->len == 1 && *filename->str == '-');
+}
+
+/* do_inplace_begin --- start in-place editing */
+
+static awk_value_t *
+do_inplace_begin(int nargs, awk_value_t *result)
+{
+	awk_value_t filename, suffix;
+	struct stat sbuf;
+	char *p;
+	int fd;
+
+	assert(result != NULL);
+
+	if (state.tname)
+		fatal(ext_id, _("inplace_begin: in-place editing already active"));
+
+	if (nargs != 2)
+		fatal(ext_id, _("inplace_begin: expects 2 arguments but called with %d"), nargs);
+		
+	if (! get_argument(0, AWK_STRING, &filename))
+		fatal(ext_id, _("inplace_begin: cannot retrieve 1st argument as a string filename"));
+
+	if (! get_argument(1, AWK_STRING, &suffix))
+		suffix.str_value.str = NULL;
+
+	if (invalid_filename(&filename.str_value)) {
+		warning(ext_id, _("inplace_begin: disabling in-place editing for invalid FILENAME `%s'"),
+			filename.str_value.str);
+		unset_ERRNO();
+		return make_number(-1, result);
+	}
+
+	if (stat(filename.str_value.str, & sbuf) < 0) {
+		warning(ext_id, _("inplace_begin: Cannot stat `%s' (%s)"),
+			filename.str_value.str, strerror(errno));
+		update_ERRNO_int(errno);
+		return make_number(-1, result);
+	}
+
+	if (! S_ISREG(sbuf.st_mode)) {
+		warning(ext_id, _("inplace_begin: `%s' is not a regular file"),
+			filename.str_value.str);
+		unset_ERRNO();
+		return make_number(-1, result);
+	}
+
+	/* create a temporary file to which to redirect stdout */
+	emalloc(state.tname, char *, filename.str_value.len+14, "do_inplace_begin");
+	sprintf(state.tname, "%s.gawk.XXXXXX", filename.str_value.str);
+
+	if ((fd = mkstemp(state.tname)) < 0)
+		fatal(ext_id, _("inplace_begin: mkstemp(`%s') failed (%s)"),
+			state.tname, strerror(errno));
+
+	/* N.B. chown/chmod should be more portable than fchown/fchmod */
+	if (chown(state.tname, sbuf.st_uid, sbuf.st_gid) < 0)
+	   chown(state.tname, -1, sbuf.st_gid);
+	if (chmod(state.tname, sbuf.st_mode) < 0)
+		fatal(ext_id, _("inplace_begin: chmod failed (%s)"),
+			strerror(errno));
+
+	fflush(stdout);
+	/* N.B. fgetpos fails when stdout is a tty */
+	state.posrc = fgetpos(stdout, &state.pos);
+	if ((state.default_stdout = dup(STDOUT_FILENO)) < 0)
+		fatal(ext_id, _("inplace_begin: dup(stdout) failed (%s)"),
+			strerror(errno));
+	if (dup2(fd, STDOUT_FILENO) < 0)
+		fatal(ext_id, _("inplace_begin: dup2(%d, stdout) failed (%s)"),
+			fd, strerror(errno));
+	if (close(fd) < 0)
+		fatal(ext_id, _("inplace_begin: close(%d) failed (%s)"),
+			fd, strerror(errno));
+	rewind(stdout);
+	return make_number(0, result);
+}
+
+/* do_inplace_end --- finish in-place editing */
+
+static awk_value_t *
+do_inplace_end(int nargs, awk_value_t *result)
+{
+	awk_value_t filename, suffix;
+
+	assert(result != NULL);
+
+	if (nargs != 2)
+		fatal(ext_id, _("inplace_begin: expects 2 arguments but called with %d"), nargs);
+
+	if (! get_argument(0, AWK_STRING, &filename))
+		fatal(ext_id, _("inplace_end: cannot retrieve 1st argument as a string filename"));
+
+	if (! get_argument(1, AWK_STRING, &suffix))
+		suffix.str_value.str = NULL;
+
+	if (! state.tname) {
+		if (! invalid_filename(&filename.str_value))
+			warning(ext_id, _("inplace_end: in-place editing not active"));
+		return make_number(0, result);
+	}
+
+	fflush(stdout);
+	if (dup2(state.default_stdout, STDOUT_FILENO) < 0)
+		fatal(ext_id, _("inplace_end: dup2(%d, stdout) failed (%s)"),
+			state.default_stdout, strerror(errno));
+	if (close(state.default_stdout) < 0)
+		fatal(ext_id, _("inplace_end: close(%d) failed (%s)"),
+			state.default_stdout, strerror(errno));
+	state.default_stdout = -1;
+	if (state.posrc == 0 && fsetpos(stdout, &state.pos) < 0)
+		fatal(ext_id, _("inplace_end: fsetpos(stdout) failed (%s)"),
+			strerror(errno));
+
+	if (suffix.str_value.str && suffix.str_value.str[0]) {
+		/* backup requested */
+		char *bakname;
+
+		emalloc(bakname, char *, filename.str_value.len+suffix.str_value.len+1,
+			"do_inplace_end");
+		sprintf(bakname, "%s%s",
+			filename.str_value.str, suffix.str_value.str);
+		unlink(bakname); /* if backup file exists already, remove it */
+		if (link(filename.str_value.str, bakname) < 0)
+			fatal(ext_id, _("inplace_end: link(`%s', `%s') failed (%s)"),
+				filename.str_value.str, bakname, strerror(errno));
+		free(bakname);
+	}
+
+	if (rename(state.tname, filename.str_value.str) < 0)
+		fatal(ext_id, _("inplace_end: rename(`%s', `%s') failed (%s)"),
+			state.tname, filename.str_value.str, strerror(errno));
+	free(state.tname);
+	state.tname = NULL;
+	return make_number(0, result);
+}
+
+static awk_ext_func_t func_table[] = {
+	{ "inplace_begin", do_inplace_begin, 2 },
+	{ "inplace_end", do_inplace_end, 2 },
+};
+
+static awk_bool_t init_inplace(void)
+{
+	awk_atexit(at_exit, NULL);
+	return awk_true;
+}
+
+static awk_bool_t (*init_func)(void) = init_inplace;
+
+/* define the dl_load function using the boilerplate macro */
+
+dl_load_func(func_table, inplace, "")