/
binaryToBase64.js
81 lines (63 loc) · 2.33 KB
/
binaryToBase64.js
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onmessage = function(ev) {
var id = ev.data.id;
var url = ev.data.url;
var baseUrl = ev.data.baseUrl;
baseUrl = unescape(baseUrl);
if (!/\/\//.test(url)) {
url = url.replace(/^\/?/, baseUrl);
}
var xhr = new XMLHttpRequest();
xhr.responseType = 'arraybuffer';
xhr.open('GET', url);
xhr.onreadystatechange = onChange;
xhr.send();
function onChange() {
if (xhr.readyState === 4 && xhr.status === 200) {
var result = base64ArrayBuffer(xhr.response);
postMessage({
response: result,
id: id
});
}
};
}
// Thanks, jonleighton.
// https://gist.github.com/jonleighton/958841
function base64ArrayBuffer(arrayBuffer) {
var base64 = '';
var encodings = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
var bytes = new Uint8Array(arrayBuffer);
var byteLength = bytes.byteLength;
var byteRemainder = byteLength % 3;
var mainLength = byteLength - byteRemainder;
var a, b, c, d;
var chunk;
// Main loop deals with bytes in chunks of 3
for (var i = 0; i < mainLength; i = i + 3) {
// Combine the three bytes into a single integer
chunk = (bytes[i] << 16) | (bytes[i + 1] << 8) | bytes[i + 2];
// Use bitmasks to extract 6-bit segments from the triplet
a = (chunk & 16515072) >> 18; // 16515072 = (2^6 - 1) << 18
b = (chunk & 258048) >> 12; // 258048 = (2^6 - 1) << 12
c = (chunk & 4032) >> 6; // 4032 = (2^6 - 1) << 6
d = chunk & 63; // 63 = 2^6 - 1
// Convert the raw binary segments to the appropriate ASCII encoding
base64 += encodings[a] + encodings[b] + encodings[c] + encodings[d];
}
// Deal with the remaining bytes and padding
if (byteRemainder == 1) {
chunk = bytes[mainLength];
a = (chunk & 252) >> 2; // 252 = (2^6 - 1) << 2
// Set the 4 least significant bits to zero
b = (chunk & 3) << 4; // 3 = 2^2 - 1
base64 += encodings[a] + encodings[b] + '==';
} else if (byteRemainder == 2) {
chunk = (bytes[mainLength] << 8) | bytes[mainLength + 1];
a = (chunk & 64512) >> 10; // 64512 = (2^6 - 1) << 10
b = (chunk & 1008) >> 4; // 1008 = (2^6 - 1) << 4
// Set the 2 least significant bits to zero
c = (chunk & 15) << 2; // 15 = 2^4 - 1
base64 += encodings[a] + encodings[b] + encodings[c] + '=';
}
return base64;
}