cpp-httplib/docs-src/pages/en/cookbook/c10-stream-response.md

title, order, status

title	order	status
C10. Receive a Response as a Stream	10	draft

To receive a response body chunk by chunk, use a ContentReceiver. It's the obvious choice for large files, but it's equally handy for NDJSON (newline-delimited JSON) or log streams where you want to start processing data as it arrives.

Process each chunk

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

auto res = cli.Get("/logs/stream",
  [](const char *data, size_t len) {
    std::cout.write(data, len);
    std::cout.flush();
    return true; // return false to stop receiving
  });

Data arrives in the lambda in the order it's received from the server. Return false from the callback to stop the download partway through.

Parse NDJSON line by line

Here's a buffered approach for processing newline-delimited JSON one line at a time.

std::string buffer;

auto res = cli.Get("/events",
  [&](const char *data, size_t len) {
    buffer.append(data, len);
    size_t pos;
    while ((pos = buffer.find('\n')) != std::string::npos) {
      auto line = buffer.substr(0, pos);
      buffer.erase(0, pos + 1);
      if (!line.empty()) {
        auto j = nlohmann::json::parse(line);
        handle_event(j);
      }
    }
    return true;
  });

Accumulate into a buffer, then pull out and parse one line each time you see a newline. This is the standard pattern for consuming a streaming API in real time.

Warning: When you pass a ContentReceiver, res->body stays empty. Store or process the body inside the callback yourself.

To track download progress, combine this with C11. Use the Progress Callback. For Server-Sent Events (SSE), see E04. Receive SSE on the Client.