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  5. TransformStream

TransformStream

​​ Background

A transform stream consists of a pair of streams: a writable stream, known as its writable side, and a readable stream, known as its readable side. Writes to the writable side result in new data being made available for reading from the readable side.

Workers currently only implements an identity transform stream, a type of transform stream which forwards all chunks written to its writable side to its readable side, without any changes.

​​ Constructor 


let { readable, writable } = new TransformStream();

  • TransformStream() TransformStream

    • Returns a new identity transform stream.

​​ Properties

​​ IdentityTransformStream

The current implementation of TransformStream in the Workers platform is not current compliant with the Streams Standard and we will soon be making changes to the implementation to make it conform with the specification. In preparation for doing so, we have introduced the IdentityTransformStream class that implements behavior identical to the current TransformStream class. This type of stream forwards all chunks of byte data (in the form of TypedArrays) written to its writable side to its readable side, without any changes.

The IdentityTransformStream readable side supports bring your own buffer (BYOB) reads.

​​ Constructor 


let { readable, writable } = new IdentityTransformStream();

  • IdentityTransformStream() IdentityTransformStream

    • Returns a new identity transform stream.

​​ Properties

​​ FixedLengthStream

The FixedLengthStream is a specialization of IdentityTransformStream that limits the total number of bytes that the stream will passthrough. It is useful primarily because, when using FixedLengthStream to produce either a Response or Request, the fixed length of the stream will be used as the Content-Length header value as opposed to use chunked encoding when using any other type of stream. An error will occur if too many, or too few bytes are written through the stream.

​​ Constructor 


let { readable, writable } = new FixedLengthStream(1000);

  • FixedLengthStream(length) FixedLengthStream

    • Returns a new identity transform stream.
    • length maybe a number or bigint with a maximum value of 2^53 - 1.

​​ Properties