109 lines
3.3 KiB
Markdown
109 lines
3.3 KiB
Markdown
# Magic bytes
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[](https://github.com/LarsKoelpin/magic-bytes/actions/workflows/build-and-test.yml)
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Magic Bytes is a javascript library analyzing the first bytes of a file to tell you its type.
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Use it inside your browser or serversided using nodejs.
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The procedure is based on https://en.wikipedia.org/wiki/List_of_file_signatures.
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> [!NOTE]
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> A small note on versioning.
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> Strictly speaking, each new filetype which is supported by this library can break someones' API.
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> Please note that this library adds new filetypes with minor release.
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> This means files, which validate to "null" in some versions, may find a result in a new version.
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>
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> Or in some cases the library will find more results, than before. So don't depend on the found-array size in
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> any shape or form.
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> Filetypes will not be remoevd tho
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# Installation
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Run `npm install magic-bytes.js`
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# Interactive example
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There is an interactive example present at https://larskoelpin.github.io/magic-bytes/.
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# Usage
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The following functions are available:
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* `filetypeinfo(bytes: number[])` Contains typeinformation like name, extension and mime type: `[{typename: "zip"}, {typename: "jar"}]`
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* `filetypename(bytes: number[])` : Contains type names only: `["zip", "jar"]`
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* `filetypemime(bytes: number[])` : Contains type mime types only: `["application/zip", "application/jar"]`
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* `filetypeextension(bytes: number[])` : Contains type extensions only: `["zip", "jar"]`
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Both function return an empty array `[]` otherwise, which means it could not detect the file signature. Keep in mind that
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txt files for example fall in this category.
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You don't have to load the whole file in memory. For validating a file uploaded to S3 using Lambda for example, it may be
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enough to load the files first 100 bytes and validate against them. This is especially useful for big files.
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see examples for practical usage.
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On server:
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```javascript
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import filetype from 'magic-bytes.js'
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filetype(fs.readFileSync("myimage.png")) // ["png"]
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```
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To run an HTML-Example checkout the project and run
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```
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npm install; npm run example
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```
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This opens an HTML example using magic bytes as a window variable. It kinda looks like that.
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```html
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<input type="file" id="file" />
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<script src="node_modules/magic-bytes.js/dist/browser.js" type="application/javascript"></script>
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<script>
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document.getElementById("file").addEventListener('change', (event, x) => {
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const fileReader = new FileReader();
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fileReader.onloadend = (f) => {
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const bytes = new Uint8Array(f.target.result);
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console.log("Possible filetypes: " + filetypeinfo(bytes))
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}
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fileReader.readAsArrayBuffer(event.target.files[0])
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})
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</script>
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```
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# Tests
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Run `npm test`
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# Example
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See examples/
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# How does it work
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The `create-snapshot.js` creates a new tree. The tree has a similar shape to the following
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```json
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{
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"0x47": {
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"0x49": {
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"0x46": {
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"0x38": {
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"0x37": {
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"0x61": {
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"matches": [
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{
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"typename": "gif",
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"mime": "image/gif",
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"extension": "gif"
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}
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]
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}
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},
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}
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}
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}
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}
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}
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```
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It acts as a giant lookup map for the given byte signatures.
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