Allow handling proxy headers from AF_UNIX sockets #2760
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added 8 commits
November 12, 2025 15:51
When uvicorn is listening on an AF_UNIX socket (--uds), the "server" scope parameter should be (socket_path, None). This allows the application/middleware to detect that a Unix socket is in use. The test_get_local_addr test case needs to be updated accordingly; previously it was assumed that get_local_addr would return None for a Unix socket. The test_get_local_addr_with_socket test case was nonsensical: if the 'family' is AF_UNIX then the 'sockname' must be a string. Fix this test case to check that get_local_addr works in both cases.
On Linux, if an AF_UNIX socket is bound to an abstract address (starting with a NUL byte), then Python's socket API reports the address as a 'bytes' object rather than a 'str'. Check that this is handled correctly by get_local_addr. The server address reported to the ASGI application should always be a Unicode string.
The test_get_remote_addr_with_socket test case was nonsensical. If the socket family is AF_UNIX then the peer address must be a string (usually an empty string.) Change this test case to realistically reflect what happens when an AF_UNIX client is connected.
When uvicorn is behind a reverse proxy, we want a way to report the real client IP address and protocol based on the X-Forwarded-For and X-Forwarded-Proto headers. If we don't want people to be able to impersonate arbitrary addresses, we need to identify which proxies are trusted. In order to allow AF_UNIX proxies to be trusted, use the string "unix:" as a placeholder address. Thus, "--forwarded-allow-ips=unix:" means to trust AF_UNIX proxies but not IPv4 or IPv6 proxies. (This syntax is borrowed from nginx: if an nginx proxy server is itself listening on an AF_UNIX socket, "unix:" is what it will display in X-Forwarded-For. Thus, "--forwarded-allow-ips=unix:" allows us to trust a chain of multiple AF_UNIX proxies.)
When the client connects via an AF_UNIX socket (scope["client"] is None; scope["server"] is (socket_path, None)), ProxyHeadersMiddleware should trust the proxy headers if either "unix:" or "*" is listed as a trusted host. When the client connects via an unknown socket type (scope["client"] and scope["server"] are both None), ProxyHeadersMiddleware should only trust the proxy headers if "*" is listed as a trusted host.
In ASGI, the "server" scope field is an optional field containing the
listening socket address and port number.
In ASGI spec_version 2.1, this field was defined as:
server (Iterable[Unicode string, int]) - A two-item iterable of
[host, port], where host is the listening address for this server,
and port is the integer listening port. Optional; if missing
defaults to None.
In ASGI spec_version 2.2, this was revised to:
server (Iterable[Unicode string, Optional[int]]) - Either a
two-item iterable of [host, port], where host is the listening
address for this server, and port is the integer listening port,
or [path, None] where path is that of the unix socket. Optional;
if missing defaults to None.
Author
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Added a couple of fixes for type-checking. The thoroughness of the CI in this project is impressive; kudos. |
Author
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Note that the first patch here is equivalent in essence to #2561 . I didn't see that pull request and would be happy to rebase on top of that if you prefer. |
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Summary
The
--forwarded-allow-ipsoption allows uvicorn to identify "trusted" proxies by their IP address. However, if a proxy is connecting to uvicorn via an AF_UNIX socket (usinguvicorn --uds), then it has no IP address. We still need a way to identify that the proxy is trusted in this case.To allow middleware and applications to reliably tell that they are talking to an AF_UNIX peer, the ASGI spec says that
scope["server"]should be set to[path, None]. (This was added by ASGI spec_version 2.2; earlier versions didn't mention Unix sockets. uvicorn claims to support spec_version 2.3.)Then, in uvicorn's built-in middleware, treat an AF_UNIX peer as trusted if
--forwarded-allow-ipsincludes the literal stringunix:.Discussion thread: #2743
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