71 lines
2.5 KiB
Markdown
71 lines
2.5 KiB
Markdown
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[](https://github.com/dart-lang/tools/actions/workflows/mime.yml)
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[](https://pub.dev/packages/mime)
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[](https://pub.dev/packages/mime/publisher)
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Package for working with MIME type definitions and for processing
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streams of MIME multipart media types.
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## Determining the MIME type for a file
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The `MimeTypeResolver` class can be used to determine the MIME type of
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a file. It supports both using the extension of the file name and
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looking at magic bytes from the beginning of the file.
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There is a builtin instance of `MimeTypeResolver` accessible through
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the top level function `lookupMimeType`. This builtin instance has
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the most common file name extensions and magic bytes registered.
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```dart
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import 'package:mime/mime.dart';
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void main() {
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print(lookupMimeType('test.html'));
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// text/html
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print(lookupMimeType('test', headerBytes: [0xFF, 0xD8]));
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// image/jpeg
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print(lookupMimeType('test.html', headerBytes: [0xFF, 0xD8]));
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// image/jpeg
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}
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```
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You can build you own resolver by creating an instance of
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`MimeTypeResolver` and adding file name extensions and magic bytes
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using `addExtension` and `addMagicNumber`.
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## Processing MIME multipart media types
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The class `MimeMultipartTransformer` is used to process a `Stream` of
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bytes encoded using a MIME multipart media types encoding. The
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transformer provides a new `Stream` of `MimeMultipart` objects each of
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which have the headers and the content of each part. The content of a
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part is provided as a stream of bytes.
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Below is an example showing how to process an HTTP request and print
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the length of the content of each part.
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```dart
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// HTTP request with content type multipart/form-data.
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HttpRequest request = ...;
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// Determine the boundary form the content type header
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String boundary = request.headers.contentType.parameters['boundary'];
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// Process the body just calculating the length of each part.
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request
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.transform(new MimeMultipartTransformer(boundary))
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.map((part) => part.fold(0, (p, d) => p + d))
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.listen((length) => print('Part with length $length'));
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```
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## Determining file extension by MIME type
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The top level function `extensionFromMime` can be used to determine the
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file extension of a given MIME type.
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```dart
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print(extensionFromMime('text/html')); // Prints "html".
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print(extensionFromMime('image/jpeg')); // Prints "jpg".
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print(extensionFromMime('application/pdf')); // Prints "pdf".
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```
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