C01. Get the Response Body / Save to a File

Get it as a string

httplib::Client cli("http://localhost:8080");
auto res = cli.Get("/hello");
if (res && res->status == 200) {
  std::cout << res->body << std::endl;
}

httplib::Client cli("http://localhost:8080");
auto res = cli.Get("/hello");
if (res && res->status == 200) {
  std::cout << res->body << std::endl;
}

res->body is a std::string, ready to use as-is. The entire response is loaded into memory.

Warning: If you fetch a large file with res->body, it all goes into memory. For large downloads, use a ContentReceiver as shown below.

Save to a file

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

std::ofstream ofs("output.bin", std::ios::binary);
if (!ofs) {
  std::cerr << "Failed to open file" << std::endl;
  return 1;
}

auto res = cli.Get("/large-file",
  [&](const char *data, size_t len) {
    ofs.write(data, len);
    return static_cast<bool>(ofs);
  });

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

std::ofstream ofs("output.bin", std::ios::binary);
if (!ofs) {
  std::cerr << "Failed to open file" << std::endl;
  return 1;
}

auto res = cli.Get("/large-file",
  [&](const char *data, size_t len) {
    ofs.write(data, len);
    return static_cast<bool>(ofs);
  });

With a ContentReceiver, data arrives in chunks. You can write each chunk straight to disk without buffering the whole body in memory — perfect for large file downloads.

Return false from the callback to abort the download. In the example above, if writing to ofs fails, the download stops automatically.

Detail: Want to check response headers like Content-Length before downloading? Combine a ResponseHandler with a ContentReceiver.

auto res = cli.Get("/large-file",
  [](const httplib::Response &res) {
    auto len = res.get_header_value("Content-Length");
    std::cout << "Size: " << len << std::endl;
    return true; // return false to skip the download
  },
  [&](const char *data, size_t len) {
    ofs.write(data, len);
    return static_cast<bool>(ofs);
  });

auto res = cli.Get("/large-file",
  [](const httplib::Response &res) {
    auto len = res.get_header_value("Content-Length");
    std::cout << "Size: " << len << std::endl;
    return true; // return false to skip the download
  },
  [&](const char *data, size_t len) {
    ofs.write(data, len);
    return static_cast<bool>(ofs);
  });

The ResponseHandler is called after headers arrive but before the body. Return false to skip the download entirely.

To show download progress, see C11. Use the progress callback.