cpp-httplib/docs-src/pages/en/cookbook/c09-chunked-upload.md

title, order, status

title	order	status
C09. Send the Body with Chunked Transfer	9	draft

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.

Basic usage

httplib::Client cli("http://localhost:8080");

auto res = cli.Post("/stream",
  [&](size_t offset, httplib::DataSink &sink) {
    std::string chunk = produce_next_chunk();
    if (chunk.empty()) {
      sink.done(); // done sending
      return true;
    }
    return sink.write(chunk.data(), chunk.size());
  },
  "application/octet-stream");

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.

When the size is known

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.

size_t total_size = get_total_size();

auto res = cli.Post("/upload", total_size,
  [&](size_t offset, size_t length, httplib::DataSink &sink) {
    auto data = read_range(offset, length);
    return sink.write(data.data(), data.size());
  },
  "application/octet-stream");

With a known size, the request carries a Content-Length header — so the server can show progress. Prefer this form when you can.

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.

If you're just sending a file, make_file_body() is easier. See C08. POST a File as Raw Binary.