1 files changed, 337 insertions, 0 deletions
diff --git a/extension/revtwoway.c b/extension/revtwoway.c
new file mode 100644
index 00000000..13f0e778
--- /dev/null
+++ b/extension/revtwoway.c
@@ -0,0 +1,337 @@
+/*
+ * revtwoway.c --- Provide a two-way processor that reverses lines.
+ *
+ * Arnold Robbins
+ * arnold@skeeve.com
+ * Written 8/2012
+ */
+
+/*
+ * Copyright (C) 2012 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 <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 = "revtwoway extension: version 1.0";
+
+static awk_bool_t init_revtwoway(void);
+static awk_bool_t (*init_func)(void) = init_revtwoway;
+
+int plugin_is_GPL_compatible;
+
+/*
+ * Use this variable to provide a value != INVALID_HANDLE in the awk_input_buf_t
+ * and != NULL in the awk_output_buf_t.  The idea is to have a value that
+ * is greater than the largest allowable file descriptor.
+ */
+static size_t max_fds;
+
+#ifndef HAVE_GETDTABLESIZE
+/* getdtablesize --- replacement version that should be good enough */
+
+static inline int
+getdtablesize()
+{
+	/*
+	 * Algorithm for the GNULIB folks:
+	 *
+	 * Set up a bitmap of 2048 elements.
+	 * Initialize it to zero.
+	 * In a loop, do
+	 * 	fd = open("/dev/null", O_RDONLY)
+	 * 	set the bit corresponding to fd in the bit map
+	 * until it fails.
+	 * Get the highest value that succeeded and increment it by one
+	 * --> that is how many descriptors we have.
+	 * Loop over the bitmap to close all the file descriptors we opened.
+	 *
+	 * Do all this upon the first call and return static values upon
+	 * subsequent calls.
+	 */
+
+	/* In the meantime, this is good enough for us: */
+	return 1024;
+}
+#endif
+
+/*
+ * IMPORTANT NOTE: This is a NOT a true general purpose
+ * extension.  It is intended to demonstrate how to set up
+ * all the "plumbing" and to work one record at a time, ONLY.
+ *
+ * While it would be possible to set up buffering and manage it,
+ * that would duplicate a large chunk of the code in gawk's
+ * get_a_record() function, and there's no real point in doing that.
+ */
+
+/* the data in the opaque pointer */
+typedef struct two_way_proc_data {
+	size_t size;	/* size of allocated buffer */
+	size_t len;	/* how much is actually in use */
+	char *data;
+	size_t in_use;	/* use count, must hit zero to be freed */
+} two_way_proc_data_t;
+
+/* close_two_proc_data --- release the data */
+
+static void
+close_two_proc_data(two_way_proc_data_t *proc_data)
+{
+	if (proc_data->in_use > 1) {
+		proc_data->in_use--;
+		return;
+	}
+
+	free(proc_data->data);
+	free(proc_data);
+}
+
+/*
+ * Input side of the two-way processor (input TO gawk)
+ */
+
+/* rev2way_get_record --- get one record at a time out of a directory */
+
+static int
+rev2way_get_record(char **out, awk_input_buf_t *iobuf, int *errcode,
+		char **rt_start, size_t *rt_len)
+{
+	int len = 0;	/* for now */
+	two_way_proc_data_t *proc_data;
+
+	/*
+	 * The caller sets *errcode to 0, so we should set it only if an
+	 * error occurs.
+	 */
+
+	if (out == NULL || iobuf == NULL || iobuf->opaque == NULL)
+		return EOF;
+
+	proc_data = (two_way_proc_data_t *) iobuf->opaque;
+	if (proc_data->len == 0)
+		return 0;
+
+	*out = proc_data->data;
+
+	len = proc_data->len;
+	proc_data->len = 0;
+
+	*rt_len = 0;	/* default: set RT to "" */
+	if (proc_data->data[len-1] == '\n') {
+		while (proc_data->data[len-1] == '\n') {
+			len--;
+			(*rt_len)++;
+		}
+		*rt_start = proc_data->data + len;
+	}
+
+	return len;
+}
+
+/* rev2way_close --- close up input side when done */
+
+static void
+rev2way_close(awk_input_buf_t *iobuf)
+{
+	two_way_proc_data_t *proc_data;
+
+	if (iobuf == NULL || iobuf->opaque == NULL)
+		return;
+
+	proc_data = (two_way_proc_data_t *) iobuf->opaque;
+	close_two_proc_data(proc_data);
+
+	iobuf->fd = INVALID_HANDLE;
+}
+
+
+/*
+ * Output side of the two-way processor (output FROM gawk)
+ */
+
+/* rev2way_fwrite --- write out characters in reverse order */
+
+static size_t
+rev2way_fwrite(const void *buf, size_t size, size_t count, FILE *fp, void *opaque)
+{
+	two_way_proc_data_t *proc_data;
+	size_t amount, char_count;
+	char *src, *dest;
+
+	if (opaque == NULL)
+		return 0;	/* error */
+
+	proc_data = (two_way_proc_data_t *) opaque;
+	amount = size * count;
+
+	/* do the dance */
+	if (amount > proc_data->size || proc_data->len > 0) {
+		if (proc_data->data == NULL)
+			emalloc(proc_data->data, char *,  amount, "rev2way_fwrite");
+		else
+			erealloc(proc_data->data, char *, proc_data->size + amount, "rev2way_fwrite");
+		proc_data->size += amount;
+	}
+
+	src = (char *) buf + amount -1;
+	dest = proc_data->data + proc_data->len;
+	for (char_count = amount; char_count > 0; char_count--) {
+		/* copy in backwards */
+		*dest++ = *src--;
+	}
+	proc_data->len += amount;
+
+	return amount;
+}
+
+/* rev2way_fflush --- do nothing hook for fflush */
+
+static int
+rev2way_fflush(FILE *fp, void *opaque)
+{
+	(void) fp;
+	(void) opaque;
+
+	return 0;
+}
+
+/* rev2way_ferror --- do nothing hook for ferror */
+
+static int
+rev2way_ferror(FILE *fp, void *opaque)
+{
+	(void) fp;
+	(void) opaque;
+
+	return 0;
+}
+
+/* rev2way_fclose --- close output side of two-way processor */
+
+static int
+rev2way_fclose(FILE *fp, void *opaque)
+{
+	two_way_proc_data_t *proc_data;
+
+	if (opaque == NULL)
+		return EOF;	/* error */
+
+	(void) fp;
+
+	proc_data = (two_way_proc_data_t *) opaque;
+	close_two_proc_data(proc_data);
+
+	return 0;
+}
+
+
+/* revtwoway_can_two_way --- return true if we want the file */
+
+static awk_bool_t
+revtwoway_can_take_two_way(const char *name)
+{
+	return (name != NULL && strcmp(name, "/magic/mirror") == 0);
+}
+
+/*
+ * revtwoway_take_control_of --- set up two way processor
+ * We can assume that revtwoway_can_take_two_way just returned true,
+ * and no state has changed since then.
+ */
+
+static awk_bool_t
+revtwoway_take_control_of(const char *name, awk_input_buf_t *inbuf, awk_output_buf_t *outbuf)
+{
+	two_way_proc_data_t *proc_data;
+
+	if (inbuf == NULL || outbuf == NULL)
+		return awk_false;
+
+	emalloc(proc_data, two_way_proc_data_t *, sizeof(two_way_proc_data_t), "revtwoway_take_control_of");
+	proc_data->in_use = 2;
+	proc_data->size = 0;
+	proc_data->len = 0;
+	proc_data->data = NULL;
+
+	if (max_fds + 1 == 0)	/* wrapped. ha! */
+		max_fds = getdtablesize();
+
+	/* input side: */
+	inbuf->get_record = rev2way_get_record;
+	inbuf->close_func = rev2way_close;
+	inbuf->fd = max_fds;
+	inbuf->opaque = proc_data;
+
+	/* output side: */
+	outbuf->fp = (FILE *) max_fds++;
+	outbuf->opaque = proc_data;
+	outbuf->gawk_fwrite = rev2way_fwrite;
+	outbuf->gawk_fflush = rev2way_fflush;
+	outbuf->gawk_ferror = rev2way_ferror;
+	outbuf->gawk_fclose = rev2way_fclose;
+	outbuf->redirected = awk_true;
+
+	return awk_true;
+}
+
+static awk_two_way_processor_t two_way_processor = {
+	"revtwoway",
+	revtwoway_can_take_two_way,
+	revtwoway_take_control_of,
+	NULL
+};
+
+/* init_revtwoway --- set things ups */
+
+static awk_bool_t
+init_revtwoway()
+{
+	register_two_way_processor(& two_way_processor);
+
+	max_fds = getdtablesize();
+
+	return awk_true;
+}
+
+static awk_ext_func_t func_table[] = {
+	{ NULL, NULL, 0 }
+};
+
+/* define the dl_load function using the boilerplate macro */
+
+dl_load_func(func_table, revtwoway, "")