Added a simple implementation of urlencode.

include/libp2p/utils/urlencode.h

@@ -0,0 +1,4 @@
+#pragma once
+
+char *libp2p_utils_url_encode(char *src);
+char *libp2p_utils_url_decode(char *src);

utils/urlencode.c

@@ -0,0 +1,51 @@
+#include <stdlib.h>
+#include <string.h>
+#include <ctype.h>
+
+char *libp2p_utils_url_encode(char *src)
+{
+	const char *hex = "0123456789abcdef";
+	char *p, *dst = malloc (strlen(src) * 3);
+
+	if (!dst) return NULL;
+
+	for(p = dst ; *src ; src++ ) {
+		if( isalnum(*src)){
+			*p++ = *src;
+		} else {
+			*p++ = '%';
+			*p++ = hex[*src >> 4];
+			*p++ = hex[*src & 15];
+		}
+	}
+        *p++ = '\0';
+	return realloc(dst, (size_t) (p - dst));
+}
+
+int h2b(int c)
+{
+	if (c >= '0' && c <= '9') {
+		return c - '0';
+	} else if (c >= 'a' && c <= 'f') {
+		return c - 'a' + 10;
+	} else if (c >= 'A' && c <= 'F') {
+		return c - 'A' + 10;
+	}
+ 	return 0; // ?
+}
+
+char *libp2p_utils_url_decode(char *src)
+{
+	char *p, *dst = malloc (strlen(src));
+
+	for(p = dst ; *src ; src++ ) {
+		if(*src != '%'){
+			*p++ = *src;
+		} else {
+			*p    = h2b(*(++src)) << 4;
+			*p++ |= h2b(*(++src)) & 15;
+		}
+	}
+        *p++ = '\0';
+	return realloc(dst, (size_t) (p - dst));
+}