cpp-httplib v0.46.0
DRAFT

C16. Send Requests Through a Proxy

To route traffic through a corporate network or a specific path, send requests via an HTTP proxy. Just pass the proxy host and port to set_proxy().

Basic usage

httplib::Client cli("https://api.example.com");
cli.set_proxy("proxy.internal", 8080);

auto res = cli.Get("/users");

httplib::Client cli("https://api.example.com");
cli.set_proxy("proxy.internal", 8080);

auto res = cli.Get("/users");

The request goes through the proxy. For HTTPS, the client uses the CONNECT method to tunnel through — no extra setup required.

Proxy authentication

If the proxy itself requires authentication, use set_proxy_basic_auth() or set_proxy_bearer_token_auth().

cli.set_proxy("proxy.internal", 8080);
cli.set_proxy_basic_auth("user", "password");

cli.set_proxy("proxy.internal", 8080);
cli.set_proxy_basic_auth("user", "password");

cli.set_proxy_bearer_token_auth("token");

cli.set_proxy_bearer_token_auth("token");

If cpp-httplib is built with OpenSSL (or another TLS backend), you can also use Digest authentication for the proxy.

cli.set_proxy_digest_auth("user", "password");

cli.set_proxy_digest_auth("user", "password");

Combine with end-server authentication

Proxy authentication is separate from authenticating to the end server (C05. Use Basic authentication, C06. Call an API with a Bearer token). When both are needed, set both.

cli.set_proxy("proxy.internal", 8080);
cli.set_proxy_basic_auth("proxy-user", "proxy-pass");

cli.set_bearer_token_auth("api-token"); // for the end server

cli.set_proxy("proxy.internal", 8080);
cli.set_proxy_basic_auth("proxy-user", "proxy-pass");

cli.set_bearer_token_auth("api-token"); // for the end server

Proxy-Authorization is sent to the proxy, Authorization to the end server.

Bypass the proxy for specific hosts

You often want internal endpoints to skip the proxy. Configure a bypass list with set_no_proxy().

cli.set_proxy("proxy.internal", 8080);
cli.set_no_proxy({"internal.corp", "10.0.0.0/8", "*.dev.local"});

cli.set_proxy("proxy.internal", 8080);
cli.set_no_proxy({"internal.corp", "10.0.0.0/8", "*.dev.local"});

Each entry is one of:

  • * — bypass the proxy for all hosts
  • a hostname suffix (e.g. example.com) — matches example.com itself and any subdomain (foo.example.com). A leading dot is permitted but informational; both forms are equivalent.
  • a single IP literal (e.g. 192.168.1.1, ::1)
  • a CIDR block (e.g. 10.0.0.0/8, fe80::/10)

Hostname matching is case-insensitive and uses a dot-boundary rule, so an entry of example.com does not match evilexample.com. IP comparisons are normalized through inet_pton, so 127.0.0.1 cannot be bypassed via alternate string forms (e.g. 127.000.000.001). When an entry matches, the Proxy-Authorization header is suppressed as well.

Malformed entries are silently dropped. Port-specific entries such as example.com:8080 are not supported (cpp-httplib's other host-keyed APIs are also keyed on hostname only).

Read proxy settings from the environment

cpp-httplib doesn't touch HTTP_PROXY / HTTPS_PROXY / NO_PROXY on its own — the config API is always explicit, the same way set_ca_cert_path() is. If you'd like that behavior, read the variables in your application and feed them to set_proxy() and set_no_proxy().

if (const char *v = std::getenv("no_proxy")) {
  std::vector<std::string> patterns;
  std::stringstream ss(v);
  for (std::string item; std::getline(ss, item, ',');) {
    if (!item.empty()) { patterns.push_back(item); }
  }
  cli.set_no_proxy(patterns);
}

if (const char *v = std::getenv("no_proxy")) {
  std::vector<std::string> patterns;
  std::stringstream ss(v);
  for (std::string item; std::getline(ss, item, ',');) {
    if (!item.empty()) { patterns.push_back(item); }
  }
  cli.set_no_proxy(patterns);
}

If you also read HTTP_PROXY yourself, honor the lowercase http_proxy only. The uppercase form is poisoned in CGI/FastCGI environments by the Proxy: request header (CVE-2016-5385 / "httpoxy"). HTTPS_PROXY and NO_PROXY are safe in either case because their names don't begin with HTTP_.

ESC