[PATCH] util/hex-escape.[ch]: encoding/decoding strings into restricted character set

[David Bremner]

From: David Bremner <bremner at debian.org>

The character set is chosen to be suitable for pathnames, and the same
as that used by contrib/nmbug. The new encoded/decoded strings are
allocated using talloc.
---
This isn't urgent, but it is useful for a couple projects I have
brewing (nmbug compatible dump/restore and tag logging), so I thought
I would get some feedback on it.


 util/Makefile.local |    4 +-
 util/hex-escape.c   |  110 +++++++++++++++++++++++++++++++++++++++++++++++++++
 util/hex-escape.h   |   10 +++++
 3 files changed, 122 insertions(+), 2 deletions(-)
 create mode 100644 util/hex-escape.c
 create mode 100644 util/hex-escape.h

diff --git a/util/Makefile.local b/util/Makefile.local
index 0340899..2e63932 100644
--- a/util/Makefile.local
+++ b/util/Makefile.local
@@ -3,11 +3,11 @@
 dir := util
 extra_cflags += -I$(srcdir)/$(dir)
 
-libutil_c_srcs := $(dir)/xutil.c $(dir)/error_util.c
+libutil_c_srcs := $(dir)/xutil.c $(dir)/error_util.c $(dir)/hex-escape.c
 
 libutil_modules := $(libutil_c_srcs:.c=.o)
 
 $(dir)/libutil.a: $(libutil_modules)
 	$(call quiet,AR) rcs $@ $^
 
-CLEAN := $(CLEAN) $(dir)/xutil.o $(dir)/error_util.o $(dir)/libutil.a
+CLEAN := $(CLEAN) $(libutil_modules) $(dir)/libutil.a
diff --git a/util/hex-escape.c b/util/hex-escape.c
new file mode 100644
index 0000000..c294bb5
--- /dev/null
+++ b/util/hex-escape.c
@@ -0,0 +1,110 @@
+/* hex-escape.c -  Manage encoding and decoding of byte strings into
+ *		   a restricted character set.
+ *
+ * Copyright (c) 2011 David Bremner
+ *
+ * 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 3 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, see http://www.gnu.org/licenses/ .
+ *
+ * Author: David Bremner <david at tethera.net>
+ */
+
+#include <string.h>
+#include <talloc.h>
+#include "error_util.h"
+#include "hex-escape.h"
+
+static int
+escapes_needed (const char *str){
+    int escapes = 0;
+
+    while (*str) {
+	if (index (HEX_NO_ESCAPE, *str) == NULL)
+	    escapes++;
+	str++;
+    }
+
+   return escapes;
+}
+
+char *
+hex_encode (void *ctx, const char *str) {
+    char *newstr = talloc_size (ctx, strlen (str)+3*escapes_needed (str)+1);
+
+    char *out = newstr;
+
+    while (*str) {
+	if (index (HEX_NO_ESCAPE, *str)) {
+	    *out++ = *str++;
+	} else {
+	    sprintf (out, "%%%02x", *str);
+	    str++;
+	    out += 3;
+	}
+    }
+    *out = 0;
+    return newstr;
+}
+
+inline static int
+_digit (char c) {
+    if ('0' <= c && c <= '9')
+	return c - '0';
+
+    if ('A' <= c && c <= 'F')
+	return c - 'A';
+
+    if ('a' <= c && c <= 'f')
+	return c - 'a';
+
+    INTERNAL_ERROR ("Illegal hex digit %c", c);
+    /*NOTREACHED*/
+    return 0;
+}
+
+char *hex_decode (void *ctx, const char *str) {
+
+    int len = strlen(str);
+
+    const char *p;
+    char *q;
+    char *newstr;
+    int escapes = 0;
+
+    for (p = str; *p; p++)
+	escapes += (*p == HEX_ESCAPE_CHAR);
+
+    newstr = talloc_size (ctx, len - escapes*2 + 1);
+
+    p = str;
+    q = newstr;
+
+    while (*p) {
+
+	if (*p == HEX_ESCAPE_CHAR) {
+
+	    if (len < 3) INTERNAL_ERROR ("Syntax error decoding %s", str);
+
+	    *q = _digit(p[1]) * 16;
+	    *q += _digit(p[2]);
+
+	    len -= 3;
+	    p += 3;
+	    q++;
+	} else {
+	    *q++ = *p++;
+	}
+    }
+
+    return newstr;
+}
diff --git a/util/hex-escape.h b/util/hex-escape.h
new file mode 100644
index 0000000..7caff15
--- /dev/null
+++ b/util/hex-escape.h
@@ -0,0 +1,10 @@
+#ifndef _HEX_ESCAPE_H
+#define _HEX_ESCAPE_H
+
+#define HEX_ESCAPE_CHAR '%'
+#define HEX_NO_ESCAPE 	"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz" \
+			"0123456789+-_@=.:,"
+
+char *hex_encode (void *talloc_ctx, const char *string);
+char *hex_decode (void *talloc_ctx, const char *hex);
+#endif
-- 
1.7.7.3