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denoland-deno/std/encoding/hex.ts
2020-01-02 15:13:47 -05:00

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TypeScript

// Ported from Go
// https://github.com/golang/go/blob/go1.12.5/src/encoding/hex/hex.go
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
const hextable = new TextEncoder().encode("0123456789abcdef");
export function errInvalidByte(byte: number): Error {
return new Error(
"encoding/hex: invalid byte: " +
new TextDecoder().decode(new Uint8Array([byte]))
);
}
export function errLength(): Error {
return new Error("encoding/hex: odd length hex string");
}
// fromHexChar converts a hex character into its value and a success flag.
function fromHexChar(byte: number): [number, boolean] {
switch (true) {
case 48 <= byte && byte <= 57: // '0' <= byte && byte <= '9'
return [byte - 48, true];
case 97 <= byte && byte <= 102: // 'a' <= byte && byte <= 'f'
return [byte - 97 + 10, true];
case 65 <= byte && byte <= 70: // 'A' <= byte && byte <= 'F'
return [byte - 65 + 10, true];
}
return [0, false];
}
/**
* EncodedLen returns the length of an encoding of n source bytes. Specifically,
* it returns n * 2.
* @param n
*/
export function encodedLen(n: number): number {
return n * 2;
}
/**
* Encode encodes `src` into `encodedLen(src.length)` bytes of `dst`.
* As a convenience, it returns the number of bytes written to `dst`
* but this value is always `encodedLen(src.length)`.
* Encode implements hexadecimal encoding.
* @param dst
* @param src
*/
export function encode(dst: Uint8Array, src: Uint8Array): number {
const srcLength = encodedLen(src.length);
if (dst.length !== srcLength) {
throw new Error("Out of index.");
}
for (let i = 0; i < src.length; i++) {
const v = src[i];
dst[i * 2] = hextable[v >> 4];
dst[i * 2 + 1] = hextable[v & 0x0f];
}
return srcLength;
}
/**
* EncodeToString returns the hexadecimal encoding of `src`.
* @param src
*/
export function encodeToString(src: Uint8Array): string {
const dest = new Uint8Array(encodedLen(src.length));
encode(dest, src);
return new TextDecoder().decode(dest);
}
/**
* Decode decodes `src` into `decodedLen(src.length)` bytes
* returning the actual number of bytes written to `dst`.
* Decode expects that `src` contains only hexadecimal characters and that `src`
* has even length.
* If the input is malformed, Decode returns the number of bytes decoded before
* the error.
* @param dst
* @param src
*/
export function decode(
dst: Uint8Array,
src: Uint8Array
): [number, Error | void] {
let i = 0;
for (; i < Math.floor(src.length / 2); i++) {
const [a, aOK] = fromHexChar(src[i * 2]);
if (!aOK) {
return [i, errInvalidByte(src[i * 2])];
}
const [b, bOK] = fromHexChar(src[i * 2 + 1]);
if (!bOK) {
return [i, errInvalidByte(src[i * 2 + 1])];
}
dst[i] = (a << 4) | b;
}
if (src.length % 2 == 1) {
// Check for invalid char before reporting bad length,
// since the invalid char (if present) is an earlier problem.
const [, ok] = fromHexChar(src[i * 2]);
if (!ok) {
return [i, errInvalidByte(src[i * 2])];
}
return [i, errLength()];
}
return [i, undefined];
}
/**
* DecodedLen returns the length of a decoding of `x` source bytes.
* Specifically, it returns `x / 2`.
* @param x
*/
export function decodedLen(x: number): number {
return Math.floor(x / 2);
}
/**
* DecodeString returns the bytes represented by the hexadecimal string `s`.
* DecodeString expects that src contains only hexadecimal characters and that
* src has even length.
* If the input is malformed, DecodeString will throws an error.
* @param s the `string` need to decode to `Uint8Array`
*/
export function decodeString(s: string): Uint8Array {
const src = new TextEncoder().encode(s);
// We can use the source slice itself as the destination
// because the decode loop increments by one and then the 'seen' byte is not
// used anymore.
const [n, err] = decode(src, src);
if (err) {
throw err;
}
return src.slice(0, n);
}