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Add option to start decoding after start index #25

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Add option to start decoding after start index #25

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2 changes: 1 addition & 1 deletion index.d.ts
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
declare module 'base64-arraybuffer' {
export function encode(buffer: ArrayBuffer): string;
export function decode(str: string): ArrayBuffer;
export function decode(str: string, start?: number): ArrayBuffer;
}
12 changes: 8 additions & 4 deletions lib/base64-arraybuffer.js
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Original file line number Diff line number Diff line change
Expand Up @@ -36,9 +36,13 @@
return base64;
};

exports.decode = function(base64) {
var bufferLength = base64.length * 0.75,
len = base64.length, i, p = 0,
exports.decode = function(base64, start) {
var len = base64.length
var i = 0;
if(start < len && start > 0) i = start;
else if(start > len) i = len;

var bufferLength = (len - i) * 0.75, p = 0,
encoded1, encoded2, encoded3, encoded4;

if (base64[base64.length - 1] === "=") {
Expand All @@ -51,7 +55,7 @@
var arraybuffer = new ArrayBuffer(bufferLength),
bytes = new Uint8Array(arraybuffer);

for (i = 0; i < len; i+=4) {
for (i; i < len; i+=4) {
encoded1 = lookup[base64.charCodeAt(i)];
encoded2 = lookup[base64.charCodeAt(i+1)];
encoded3 = lookup[base64.charCodeAt(i+2)];
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2 changes: 2 additions & 0 deletions test/base64-arraybuffer_test.js
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Expand Up @@ -52,5 +52,7 @@ describe('decode', () => {
it('decode "Man"', () => ok(testArrayBuffers(decode("TWFu"), stringArrayBuffer("Man"))));
it('decode "Hello world"', () => ok(testArrayBuffers(decode("SGVsbG8gd29ybGQ="), stringArrayBuffer("Hello world"))));
it('decode "Hello worlds!"', () => ok(testArrayBuffers(decode("SGVsbG8gd29ybGRzIQ=="), stringArrayBuffer("Hello worlds!"))));
it('decode "Hello world" - discard start < 0', () => ok(testArrayBuffers(decode("SGVsbG8gd29ybGQ=", -1), stringArrayBuffer("Hello world"))));
it('decode "Hello world" after header when start < length', () => ok(testArrayBuffers(decode("data:image/bmp;base64,SGVsbG8gd29ybGQ=", 22), stringArrayBuffer("Hello world"))));
it('decode all binary characters', () => ok(testArrayBuffers(decode("AAECAwQFBgcICQoLDA0ODxAREhMUFRYXGBkaGxwdHh8gISIjJCUmJygpKissLS4vMDEyMzQ1Njc4OTo7PD0+P0BBQkNERUZHSElKS0xNTk9QUVJTVFVWV1hZWltcXV5fYGFiY2RlZmdoaWprbG1ub3BxcnN0dXZ3eHl6e3x9fn+AgYKDhIWGh4iJiouMjY6PkJGSk5SVlpeYmZqbnJ2en6ChoqOkpaanqKmqq6ytrq+wsbKztLW2t7i5uru8vb6/wMHCw8TFxsfIycrLzM3Oz9DR0tPU1dbX2Nna29zd3t/g4eLj5OXm5+jp6uvs7e7v8PHy8/T19vf4+fr7/P3+/w=="), rangeArrayBuffer())));
});