pub const hex = structpub fn encode(encoded: []u8, bin: []const u8, comptime case: std.fmt.Case) errorEncodes a binary buffer into a hexadecimal string. The output buffer must be twice the size of the input buffer.
pub fn decode(bin: []u8, encoded: []const u8) errorDecodes a hexadecimal string into a binary buffer. The output buffer must be half the size of the input buffer.
pub fn decoderWithIgnore(ignore_chars: []const u8) errorCreates a new decoder that ignores certain characters. The decoder will skip any characters that are in the ignore list. The ignore list must not contain any valid hexadecimal characters.
fn decodeAny(bin: []u8, encoded: []const u8, ignored_chars: ?StaticBitSet(256)) error20
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144pub const hex = struct {
/// Encodes a binary buffer into a hexadecimal string.
/// The output buffer must be twice the size of the input buffer.
pub fn encode(encoded: []u8, bin: []const u8, comptime case: std.fmt.Case) error{SizeMismatch}!void {
if (encoded.len / 2 != bin.len) {
return error.SizeMismatch;
}
for (bin, 0..) |v, i| {
const b: u16 = v >> 4;
const c: u16 = v & 0xf;
const off = if (case == .upper) 32 else 0;
const x =
((87 - off + c + (((c -% 10) >> 8) & ~@as(u16, 38 - off))) & 0xff) << 8 |
((87 - off + b + (((b -% 10) >> 8) & ~@as(u16, 38 - off))) & 0xff);
encoded[i * 2] = @truncate(x);
encoded[i * 2 + 1] = @truncate(x >> 8);
}
}
/// Decodes a hexadecimal string into a binary buffer.
/// The output buffer must be half the size of the input buffer.
pub fn decode(bin: []u8, encoded: []const u8) error{ SizeMismatch, InvalidCharacter, InvalidPadding }!void {
if (encoded.len % 2 != 0) {
return error.InvalidPadding;
}
if (bin.len < encoded.len / 2) {
return error.SizeMismatch;
}
_ = decodeAny(bin, encoded, null) catch |err| {
switch (err) {
error.InvalidCharacter, error.InvalidPadding => |e| return e,
else => unreachable,
}
};
}
/// A decoder that ignores certain characters.
/// The decoder will skip any characters that are in the ignore list.
pub const DecoderWithIgnore = struct {
/// The characters to ignore.
ignored_chars: StaticBitSet(256) = undefined,
/// Decodes a hexadecimal string into a binary buffer.
/// The output buffer must be half the size of the input buffer.
pub fn decode(
self: DecoderWithIgnore,
bin: []u8,
encoded: []const u8,
) error{ NoSpaceLeft, InvalidCharacter, InvalidPadding }![]const u8 {
return decodeAny(bin, encoded, self.ignored_chars);
}
/// Returns the decoded length of a hexadecimal string, ignoring any characters in the ignore list.
/// This operation does not run in constant time, but it aims to avoid leaking information about the underlying hexadecimal string.
pub fn decodedLenForSlice(decoder: DecoderWithIgnore, encoded: []const u8) !usize {
var hex_len = encoded.len;
for (encoded) |c| {
if (decoder.ignored_chars.isSet(c)) hex_len -= 1;
}
if (hex_len % 2 != 0) {
return error.InvalidPadding;
}
return hex_len / 2;
}
/// Returns the maximum possible decoded size for a given input length after skipping ignored characters.
pub fn decodedLenUpperBound(hex_len: usize) usize {
return hex_len / 2;
}
};
/// Creates a new decoder that ignores certain characters.
/// The decoder will skip any characters that are in the ignore list.
/// The ignore list must not contain any valid hexadecimal characters.
pub fn decoderWithIgnore(ignore_chars: []const u8) error{InvalidCharacter}!DecoderWithIgnore {
var ignored_chars = StaticBitSet(256).empty;
for (ignore_chars) |c| {
switch (c) {
'0'...'9', 'a'...'f', 'A'...'F' => return error.InvalidCharacter,
else => if (ignored_chars.isSet(c)) return error.InvalidCharacter,
}
ignored_chars.set(c);
}
return DecoderWithIgnore{ .ignored_chars = ignored_chars };
}
fn decodeAny(
bin: []u8,
encoded: []const u8,
ignored_chars: ?StaticBitSet(256),
) error{ NoSpaceLeft, InvalidCharacter, InvalidPadding }![]const u8 {
var bin_pos: usize = 0;
var state: bool = false;
var c_acc: u8 = 0;
for (encoded) |c| {
const c_num = c ^ 48;
const c_num0: u8 = @truncate((@as(u16, c_num) -% 10) >> 8);
const c_alpha: u8 = (c & ~@as(u8, 32)) -% 55;
const c_alpha0: u8 = @truncate(((@as(u16, c_alpha) -% 10) ^ (@as(u16, c_alpha) -% 16)) >> 8);
if ((c_num0 | c_alpha0) == 0) {
if (ignored_chars) |set| {
if (set.isSet(c)) {
continue;
}
}
return error.InvalidCharacter;
}
const c_val = (c_num0 & c_num) | (c_alpha0 & c_alpha);
if (bin_pos >= bin.len) {
return error.NoSpaceLeft;
}
if (!state) {
c_acc = c_val << 4;
} else {
bin[bin_pos] = c_acc | c_val;
bin_pos += 1;
}
state = !state;
}
if (state) {
return error.InvalidPadding;
}
return bin[0..bin_pos];
}
}
(best-effort) constant time hexadecimal encoding and decoding.