hare

commit 86425c7d0d5337c4187b2e7e5de8c813a9e31cbd
parent 2ab02483e5356939d332ee44933787f6bc3e7cc2
Author: Drew DeVault <sir@cmpwn.com>
Date:   Wed, 24 Mar 2021 11:33:39 -0400

encoding::hex: add decode

Diffstat:
M
encoding/hex/hex.ha
 | 
31
+++++++++++++++++++++++++++++++

1 file changed, 31 insertions(+), 0 deletions(-)
diff --git a/encoding/hex/hex.ha b/encoding/hex/hex.ha
@@ -1,8 +1,12 @@
+use bytes;
 use io;
 use strconv;
 use strings;
 use strio;
 
+// Error returned when attempting to decode an invalid hex string.
+export type invalid = void!;
+
 // Encodes a byte slice to hex and writes it to a string. The caller must free
 // this string.
 export fn encode(b: []u8) str = {
@@ -23,3 +27,30 @@ export fn encode(b: []u8) str = {
 	defer free(s);
 	assert(s == "cafebabedeadf00d");
 };
+
+// Decodes a string of hexadecimal bytes into a byte slice. The caller must free
+// the return value.
+export fn decode(s: str) ([]u8 | invalid) = {
+	if (len(s) % 2 != 0) {
+		return invalid;
+	};
+	let buf: []u8 = alloc([], len(s) / 2);
+	let s = strings::to_utf8(s);
+	for (let i = 0z; i < len(s) / 2; i += 1) {
+		let oct = strings::from_utf8_unsafe(s[i * 2..i * 2 + 2]);
+		let u = match (strconv::stou8b(oct, 16)) {
+			(strconv::invalid | strconv::overflow) => return invalid,
+			u: u8 => u,
+		};
+		append(buf, u);
+	};
+	return buf;
+};
+
+@test fn decode() void = {
+	let s = decode("cafebabedeadf00d") as []u8;
+	defer free(s);
+	assert(bytes::equal(s, [0xCA, 0xFE, 0xBA, 0xBE, 0xDE, 0xAD, 0xF0, 0x0D]));
+
+	decode("this is not hex") as invalid;
+};