net/http/httputil: always deep copy the Request.Header map in ReverseProxy

We used to do it sometimes as an optimization, but the optimization is
flawed: in all non-contrived cases we need to deep clone the map
anyway. So do it always, which both simplifies the code but also fixes
the X-Forward-For value leaking to the caller's Request, as well as
modifications from the optional Director func.

Fixes #18327

Change-Id: I0c86d10c557254bf99fdd988227dcb15f968770b
Reviewed-by: Ian Lance Taylor <>
2 files changed
tree: 65397b43e439c2b5f0f78d7ca2a49bef0608d7f2
  1. .github/
  2. api/
  3. doc/
  4. lib/
  5. misc/
  6. src/
  7. test/
  8. .gitattributes
  9. .gitignore
  13. favicon.ico
  17. robots.txt

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