Dump request headers

[adaamz]

Hi,
is it possible to gather request headers somehow?
There are headers as an option, but the library itself also modifies the headers by other configuration options for eg authorization, maybe certificates, content type, content length etc.
Thanks

[Lion504]

yes—use a request event hook to inspect the headers after HTTPX prepares the request and applies authentication, just before passing it to the transport:

import httpx

def dump_headers(request: httpx.Request) -> None:
    hidden = {"authorization", "proxy-authorization", "cookie"}
    for name, value in request.headers.multi_items():
        print(name, "<redacted>" if name.lower() in hidden else value)

with httpx.Client(event_hooks={"request": [dump_headers]}) as client:
    response = client.post(
        "https://your-api.example/items",  # replace with your endpoint
        json={"name": "example"},
    )

The hook sees generated headers such as Host, Content-Type, and Content-Length, as well as client-level auth headers. The example masks credential values in the output. multi_items() preserves repeated headers instead of collapsing them into a dictionary.

For inspection after the call, use response.request.headers. If redirects were followed, that is the final request; earlier requests are available through each response in response.history. The request hook runs for each request in that redirect flow.

client.build_request(...) is useful for inspecting preparation without sending, but it is too early to see everything: client-level authentication is applied during send(). For AsyncClient, make the hook an async def function.

Client certificates are part of TLS, not HTTP headers. Also, this exposes HTTPX's request headers, not a byte-for-byte capture of the transport's HTTP/2 encoding or proxy exchanges.

Verified with HTTPX 0.28.1 against a local HTTP server: JSON plus Basic auth, a followed redirect, multipart content headers, and an async hook. Testing and drafting were AI-assisted.

HTTPX event-hook documentation.