Environment Variables
=====================

The HTTPX library can be configured via environment variables.
Here is a list of environment variables that HTTPX recognizes
and what function they serve:

`HTTPX_DEBUG`
-----------

Valid values: `1`, `true`

If this environment variable is set to a valid value then low-level
details about the execution of HTTP requests will be logged to `stderr`.

This can help you debug issues and see what's exactly being sent
over the wire and to which location.

Example:

```python
# test_script.py

import httpx
client = httpx.Client()
client.get("https://google.com")
```

```console
user@host:~$ HTTPX_DEBUG=1 python test_script.py
20:54:17.585 - httpx.dispatch.connection_pool - acquire_connection origin=Origin(scheme='https' host='www.google.com' port=443)
20:54:17.585 - httpx.dispatch.connection_pool - new_connection connection=HTTPConnection(origin=Origin(scheme='https' host='www.google.com' port=443))
20:54:17.590 - httpx.dispatch.connection - start_connect host='www.google.com' port=443 timeout=TimeoutConfig(timeout=5.0)
20:54:17.651 - httpx.dispatch.connection - connected http_version='HTTP/2'
20:54:17.651 - httpx.dispatch.http2 - send_headers stream_id=1 headers=[(b':method', b'GET'), (b':authority', b'www.google.com'), ...]
20:54:17.652 - httpx.dispatch.http2 - end_stream stream_id=1
20:54:17.681 - httpx.dispatch.http2 - receive_event stream_id=0 event=<RemoteSettingsChanged changed_settings:{...}>
20:54:17.681 - httpx.dispatch.http2 - receive_event stream_id=0 event=<WindowUpdated stream_id:0, delta:983041>
20:54:17.682 - httpx.dispatch.http2 - receive_event stream_id=0 event=<SettingsAcknowledged changed_settings:{}>
20:54:17.739 - httpx.dispatch.http2 - receive_event stream_id=1 event=<ResponseReceived stream_id:1, headers:[(b':status', b'200'), ...]>
20:54:17.741 - httpx.dispatch.http2 - receive_event stream_id=1 event=<DataReceived stream_id:1, flow_controlled_length:5224 data:>
20:54:17.742 - httpx.dispatch.http2 - receive_event stream_id=1 event=<DataReceived stream_id:1, flow_controlled_length:59, data:>
20:54:17.742 - httpx.dispatch.http2 - receive_event stream_id=1 event=<StreamEnded stream_id:1>
20:54:17.742 - httpx.dispatch.http2 - receive_event stream_id=0 event=<PingReceived ping_data:0000000000000000>
20:54:17.743 - httpx.dispatch.connection_pool - release_connection connection=HTTPConnection(origin=Origin(scheme='https' host='www.google.com' port=443))
```

`SSLKEYLOGFILE`
-----------

Valid values: a filename

If this environment variable is set, TLS keys will be appended to the specified file, creating it if it doesn't exist, whenever key material is generated or received. The keylog file is designed for debugging purposes only.

Support for `SSLKEYLOGFILE` requires Python 3.8 and OpenSSL 1.1.1 or newer.

Example:

```python
# test_script.py

import httpx
client = httpx.Client()
client.get("https://google.com")
```

```console
SSLKEYLOGFILE=test.log python test_script.py
cat test.log
# TLS secrets log file, generated by OpenSSL / Python
SERVER_HANDSHAKE_TRAFFIC_SECRET XXXX
EXPORTER_SECRET XXXX
SERVER_TRAFFIC_SECRET_0 XXXX
CLIENT_HANDSHAKE_TRAFFIC_SECRET XXXX
CLIENT_TRAFFIC_SECRET_0 XXXX
SERVER_HANDSHAKE_TRAFFIC_SECRET XXXX
EXPORTER_SECRET XXXX
SERVER_TRAFFIC_SECRET_0 XXXX
CLIENT_HANDSHAKE_TRAFFIC_SECRET XXXX
CLIENT_TRAFFIC_SECRET_0 XXXX
```