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8. Streaming

Streaming Download

awaitDownload(sink) delivers the response body to the sink chunk by chunk, without buffering it. The returned response holds the status and headers, with an empty body. Chunks are delivered as received, and content-encoding decoding is not applied (regardless of the compression option).

Files.newOutputStream(Path.of("report.bin")).use { file ->
    val response = client.get("/reports/large").awaitDownload { chunk -> file.write(chunk) }
}
  • The sink has type (ByteArray) -> Unit and is called on the transport thread reading the body.
  • The accumulated size is limited by maxResponseBodySize.

Streaming Upload

bodyStream(provider, contentType) sends the request body chunk by chunk with chunked transfer-encoding. The body ends when the provider returns null.

client.post("/upload-stream")
    .bodyStream({ nextChunk() }, "application/octet-stream")
    .awaitRaw()

A streaming upload's provider can't be rewound, so it's excluded from automatic retry (Chapter 10).

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