Add URL/percent decoding tool

urldecode.c is entirely written by OrIdow6 except for one bug fix (char → uint8_t in the mallocs) and whitespace changes. The test suite is by JAA.

Co-authored-by: OrIdow6 <68304414+OrIdow6@users.noreply.github.com>

.urldecode-test

@@ -0,0 +1,42 @@
+#!/usr/bin/python3
+import io
+import itertools
+import subprocess
+
+
+def test(input, output):
+	p = subprocess.Popen(['./.make-and-exec-binaries/urldecode'], text = False, stdin = subprocess.PIPE, stdout = subprocess.PIPE)
+	stdout, stderr = p.communicate(input)
+	assert not stderr
+	if stdout != output:
+		for i in range(0, len(stdout), 3):
+			print(repr(stdout[i : i+3]))
+		for i in range(0, len(output), 3):
+			print(repr(output[i : i+3]))
+	assert stdout == output
+
+
+BUFFER_SIZE = 1024 * 300
+
+
+test(b'', b'')
+test(b'a', b'a')
+test(b'%', b'%')
+test(b'%2', b'%2')
+test(b'%20', b' ')
+test(b'%gg', b'%gg')
+#test(b'%\xc3\xa4', b'%\xc3\xa4')
+for i in range(256):
+	test(f'%{i:02X}'.encode('ascii'), bytes.fromhex(f'{i:02x}'))
+	test(f'%{i:02x}'.encode('ascii'), bytes.fromhex(f'{i:02x}'))
+hexbytes = tuple(f'{i:02x}' for i in range(256)) # ('00', '01', .., 'ff')
+data = bytes.fromhex(''.join(map(''.join, filter(lambda x: any(c < '30' or '39' < c < '41' or '46' < c < '61' or '66' < c for c in x[1:]), itertools.product(('25',), hexbytes, hexbytes)))))
+test(data, data)
+for offset in range(-3, 1):
+	test(b'a' * (BUFFER_SIZE + offset) + b'%25', b'a' * (BUFFER_SIZE + offset) + b'%')
+	test(b'a' * (BUFFER_SIZE + offset) + b'%gg', b'a' * (BUFFER_SIZE + offset) + b'%gg')
+	test(b'a' * (BUFFER_SIZE + offset) + b'%', b'a' * (BUFFER_SIZE + offset) + b'%')
+	test(b'a' * (BUFFER_SIZE + offset) + b'%2', b'a' * (BUFFER_SIZE + offset) + b'%2')
+	test(b'a' * (BUFFER_SIZE + offset) + b'%g', b'a' * (BUFFER_SIZE + offset) + b'%g')
+for i in range(10):
+	test(b'%' * i + b'%20', b'%' * i + b' ')

urldecode

@@ -0,0 +1 @@
+.make-and-exec

urldecode.c

@@ -0,0 +1,114 @@
+/*
+    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 <https://www.gnu.org/licenses/>.
+*/
+
+// OrIdow6, late November 2021
+
+
+// stdin - a urlencoded string
+// stdout - the decoded string
+
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+
+#define BUFFER_SIZE 1024 * 300
+
+
+int main(int argc, char** argv) {
+	uint8_t* inbuf = malloc(sizeof(uint8_t) * BUFFER_SIZE);
+	uint8_t* outbuf = malloc(sizeof(uint8_t) * BUFFER_SIZE + 2);
+	size_t outp = 0;
+	int state = -1;
+	int8_t digita = 0x0;
+	int8_t digitb = 0x0;
+	uint8_t digita_real;
+	uint8_t digitb_real;
+
+	// https://stackoverflow.com/questions/10324/convert-a-hexadecimal-string-to-an-integer-efficiently-in-c
+	// Because I can't be bothered to generate this manually
+	// Could be faster if you had a table for 16-bit integers, depending on caching
+	static const int8_t hextable[] = {
+		-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
+		-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
+		-1,-1, 0,1,2,3,4,5,6,7,8,9,-1,-1,-1,-1,-1,-1,-1,10,11,12,13,14,15,-1,
+		-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
+		-1,-1,10,11,12,13,14,15,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
+		-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
+		-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
+		-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
+		-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
+		-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
+		-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1
+	};
+
+	while (1) {
+		size_t readS = fread(inbuf, sizeof(char), BUFFER_SIZE, stdin);
+		if (readS == 0) {
+			break;
+		}
+		for (size_t p = 0; p < readS; p++) {
+			if (state == -1) {
+				if (inbuf[p] != '%') {
+					outbuf[outp++] = inbuf[p];
+				} else {
+					state = 0;
+				}
+			} else if (state == 0) {
+				digita = hextable[inbuf[p]];
+				if (digita == (int8_t)-1 ) {
+					outbuf[outp++] = '%';
+					if (inbuf[p] != '%') {
+						outbuf[outp++] = inbuf[p];
+						state = -1;
+					} // else state remains 0
+					continue;
+				}
+				digita_real = inbuf[p];
+				state = 1;
+			} else {
+				digitb = hextable[inbuf[p]];
+				if (digitb == (int8_t)-1 ) {
+					digitb_real = inbuf[p];
+					outbuf[outp++] = '%';
+					outbuf[outp++] = digita_real;
+					if (inbuf[p] != '%') {
+						outbuf[outp++] = digitb_real;
+						state = -1;
+					} else {
+						state = 0;
+					}
+					continue;
+				}
+				outbuf[outp++] = digita << 4 | digitb;
+				state = -1;
+			}
+		}
+
+		fwrite(outbuf, outp, 1, stdout);
+		outp = 0;
+
+		if (readS < BUFFER_SIZE) {
+			break;
+		}
+	}
+
+	if (state == 0 || state == 1) {
+		fwrite("%", 1, 1, stdout);
+	}
+	if (state == 1) {
+		fwrite(&digita_real, 1, 1, stdout);
+	}
+}