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# Connection lifecycle ## Current implementation `HTTPConnection` should be instantiated with `host` and `port` of the first origin being connected to to reach the target origin. This either means the target origin itself or the proxy origin if one is desired. ```python import urllib3.connection # Initialize the HTTPSConnection ('https://...') conn = urllib3.connection.HTTPSConnection( host="example.com", # Here you can configure other options like # 'ssl_minimum_version', 'ca_certs', etc. ) # Set the connect timeout either in the # constructor above or via the property. conn.timeout = 3.0 # (connect timeout) ``` If using CONNECT tunneling with the proxy, call `HTTPConnection.set_tunnel()` with the tunneled host, port, and headers. This should be called before calling `HTTPConnection.connect()` or sending a request. ```python conn = urllib3.connection.HTTPConnection( # Remember that the first origin we want to connect to should # be configured as 'host' and 'port', not the target origin. host="myproxy.net", port=8080, proxy="http://myproxy.net:8080" ) conn.set_tunnel("example.com", scheme="http", headers={"Proxy-Header": "value"}) ``` Connect to the first origin by calling the `HTTPConnection.connect()` method. If an error occurs here you can check whether the error occurred during the connection to the proxy if `HTTPConnection.has_connected_to_proxy` is false. If the value is true then the error didn't occur while connecting to a proxy. ```python # Explicitly connect to the origin. This isn't # required as sending the first request will # automatically connect if not done explicitly. conn.connect() ``` After connecting to the origin, the connection can be checked to see if `is_verified` is set to true. If not the `HTTPConnectionPool` would emit a warning. The warning only matters for when verification is disabled, because otherwise an error is raised on unverified TLS handshake. ```python if not conn.is_verified: # There isn't a verified TLS connection to target origin. if not conn.proxy_is_verified: # There isn't a verified TLS connection to proxy origin. ``` If the read timeout is different from the connect timeout then the `HTTPConnection.timeout` property can be changed at this point. ```python conn.timeout = 5.0 # (read timeout) ``` Then the HTTP request can be sent with `HTTPConnection.request()`. If a `BrokenPipeError` is raised while sending the request body it can be swallowed as a response can still be received from the origin even when the request isn't completely sent. ```python try: conn.request("GET", "/") except BrokenPipeError: # We can still try to get a response! resp = conn.getresponse() ``` Then response headers (and other info) are read from the connection via `HTTPConnection.getresponse()` and returned as a `urllib3.HTTPResponse`. The `HTTPResponse` instance carries a reference to the `HTTPConnection` instance so the connection can be closed if the connection gets into an undefined protocol state. ```python assert resp.connection is conn ``` If pooling is in use the `HTTPConnectionPool` will set `_pool` on the `HTTPResponse` instance. This will return the connection to the pool once the response is exhausted. If retries are in use set `retries` on the `HTTPResponse` instance. ```python # Set by the HTTPConnectionPool before returning to the caller. resp = conn.getresponse() resp._pool = pool # This will call resp._pool._put_conn(resp.connection) # Connection can get auto-released by exhausting. resp.release_conn() ``` If any error is received from connecting to the origin, sending the request, or receiving the response, the caller will call `HTTPConnection.close()` and discard the connection. Connections can be re-used after being closed, a new TCP connection to proxies and origins will be established. If instead of a tunneling proxy we were using a forwarding proxy then we configure the `HTTPConnection` similarly, except instead of `set_tunnel()` we send absolute URLs to `HTTPConnection.request()`: ```python import urllib3.connection # Initialize the HTTPConnection. conn = urllib3.connection.HTTPConnection( host="myproxy.net", port=8080, proxy="http://myproxy.net:8080" ) # You can request HTTP or HTTPS resources over the proxy # using the absolute URL. conn.request("GET", "http://example.com") resp = conn.getresponse() conn.request("GET", "https://example.com") resp = conn.getresponse() ``` ### HTTP/HTTPS/proxies This is how `HTTPConnection` instances will be configured and used when a `PoolManager` or `ProxyManager` receives a given config: - No proxy, HTTP origin -> `HTTPConnection` - No proxy, HTTPS origin -> `HTTPSConnection` - HTTP proxy, HTTP origin -> `HTTPConnection` in forwarding mode - HTTP proxy, HTTPS origin -> `HTTPSConnection` in tunnel mode - HTTPS proxy, HTTP origin -> `HTTPSConnection` in forwarding mode - HTTPS proxy, HTTPS origin -> `HTTPSConnection` in tunnel mode - HTTPS proxy, HTTPS origin, `ProxyConfig.use_forwarding_for_https=True` -> `HTTPSConnection` in forwarding mode

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