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Add starter file sniffer for detecting file types

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codedread 2020-03-16 21:17:58 -07:00
parent c85f5ae2cb
commit 59d677c6bb
2 changed files with 90 additions and 0 deletions
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63
file/sniffer.js Normal file
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/**
* File Sniffer.
*
* Licensed under the MIT License
*
* Copyright(c) 2020 Google Inc.
*/
const fileSignatures = {
'image/png': [0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A],
};
// TODO: Build a tree of signature bytes that end in a MIME type.
class Node {
/**
* @param {number} value
*/
constructor(value) {
this.value = value;
this.children = {};
this.mimeType = undefined;
}
}
// Top-level node in the tree.
const root = new Node();
let maxDepth = 0;
// Construct the tree.
(function() {
for (const mimeType in fileSignatures) {
let curNode = root;
let depth = 0;
for (const byte of fileSignatures[mimeType]) {
if (curNode.children[byte] === undefined) {
curNode.children[byte] = new Node(byte);
}
depth++;
curNode = curNode.children[byte];
}
if (maxDepth < depth) {
maxDepth = depth;
}
curNode.mimeType = mimeType;
}
})();
/**
* @param {ArrayBuffer} ab
* @return {string} The MIME type of the buffer, or undefined.
*/
export function findMimeType(ab) {
const depth = ab.byteLength < maxDepth ? ab.byteLength : maxDepth;
const arr = new Uint8Array(ab).subarray(0, depth);
let curNode = root;
for (const byte of arr) {
if (curNode.children[byte] === undefined) return undefined;
curNode = curNode.children[byte];
if (curNode.mimeType) return curNode.mimeType;
}
}
debugger;

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tests/file-sniffer-test.html Normal file
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<!DOCTYPE html>
<html>
<head>
<title>Unit tests for bitjs.io.ByteStreamBitStream</title>
<script src="muther.js"></script>
</head>
<body>
<script type="module">
debugger;
import {findMimeType} from '../file/sniffer.js';
const assert = muther.assert;
const assertEquals = muther.assertEquals;
const assertThrows = muther.assertThrows;
let array;
muther.go({
setUp: function() {
array = new Uint8Array(16);
},
tests: {
testPNG() {
array.set([0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A, 0xFF]);
assertEquals('image/png', findMimeType(array.buffer));
},
},
});
</script>