* reverseproxy: Keep own headers after 1xx responses
Since #6656 the 1xx handler clears the whole header map after writing the
informational response, which also drops headers set before proxying (for
example by the header handler). Restore those after clearing, as #5091 did.
* reverseproxy: Use maps.Copy to restore own headers
* reverseproxy: Check the 103 reaches the client in the 1xx headers test
When a request arrives via a Unix domain socket (RemoteAddr == "@"),
net.SplitHostPort fails, causing addForwardedHeaders to strip all
X-Forwarded-* headers even when the connection is trusted via
trusted_proxies_unix.
Handle Unix socket connections before parsing RemoteAddr: if untrusted,
strip headers for security; if trusted, let clientIP remain empty (no
peer IP for a Unix socket hop) and fall through to the shared header
logic, preserving the existing XFF chain without appending a spurious
entry.
Amp-Thread-ID: https://ampcode.com/threads/T-019c4225-a0ad-7283-ac56-e2c01eae1103
Co-authored-by: Amp <amp@ampcode.com>
Jay Hemnani