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48 lines
1.7 KiB
Markdown
48 lines
1.7 KiB
Markdown
---
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title: "C09. Send the Body with Chunked Transfer"
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order: 9
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status: "draft"
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---
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When you don't know the body size up front — for data generated on the fly or piped from another stream — use `ContentProviderWithoutLength`. The client sends the body with HTTP chunked transfer encoding.
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## Basic usage
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```cpp
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httplib::Client cli("http://localhost:8080");
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auto res = cli.Post("/stream",
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[&](size_t offset, httplib::DataSink &sink) {
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std::string chunk = produce_next_chunk();
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if (chunk.empty()) {
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sink.done(); // done sending
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return true;
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}
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return sink.write(chunk.data(), chunk.size());
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},
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"application/octet-stream");
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```
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The lambda's job is just: produce the next chunk and send it with `sink.write()`. When there's no more data, call `sink.done()` and you're finished.
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## When the size is known
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If you **do** know the total size ahead of time, use the `ContentProvider` overload (taking `size_t offset, size_t length, DataSink &sink`) and pass the total size as well.
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```cpp
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size_t total_size = get_total_size();
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auto res = cli.Post("/upload", total_size,
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[&](size_t offset, size_t length, httplib::DataSink &sink) {
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auto data = read_range(offset, length);
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return sink.write(data.data(), data.size());
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},
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"application/octet-stream");
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```
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With a known size, the request carries a Content-Length header — so the server can show progress. Prefer this form when you can.
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> **Detail:** `sink.write()` returns a `bool` indicating whether the write succeeded. If it returns `false`, the connection is gone — return `false` from the lambda to stop.
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> If you're just sending a file, `make_file_body()` is easier. See [C08. POST a file as raw binary](../c08-post-file-body).
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