bug#61916: 30.0.50; url.el; Can not change User-Agent temporarily when url-retrieve

[xhcoding]

The following code cannot be used to temporarily change User-Agent

(require 'url)
(setq url-debug t)
(let ((url-user-agent "Mozilla/5.0 (Windows NT 10.0; Win64; x64) 
AppleWebKit/537.36 (KHTML, like Gecko) Chrome/110.0.0.0 Safari/537.36 
Edg/110.0.1587.57"))
  (url-retrieve "https://httpbin.org/get?a=b"; (lambda (_))))


Because the url-retrieve is asynchronous, when the url-user-agent is actually 
used (eg. url-http-create-request be called),
it may be out of the let scope.



In GNU Emacs 30.0.50 (build 5, x86_64-w64-mingw32)
Repository revision: 07a76a06f9a438e2a1bf1e565e3e78f7927c37f2
Repository branch: master
Windowing system distributor 'Microsoft Corp.', version 10.0.22621
System Description: Microsoft Windows 10 Home China (v10.0.2009.22621.1105)

Configured using:
 'configure --prefix=/d/emacs-build/pkg/master-x86_64 'CFLAGS=-Ofast 
-fno-finite-math-only -fomit-frame-pointer'
 --with-zlib --with-xpm --with-xml2 --with-tree-sitter --without-tiff 
--with-rsvg --with-png --with-lcms2 --with-json
 --with-jpeg --with-harfbuzz --with-gnutls --with-gif --without-cairo 
--disable-build-details --without-dbus
 --with-compress-install --with-small-ja-dic'

Configured features:
ACL GIF GMP GNUTLS HARFBUZZ JPEG JSON LCMS2 LIBXML2 MODULES NOTIFY W32NOTIFY 
PDUMPER PNG RSVG SOUND SQLITE3 THREADS
TOOLKIT_SCROLL_BARS TREE_SITTER WEBP XPM ZLIB

Important settings:
  value of $LANG: CHS
  locale-coding-system: cp936

Major mode: ELisp/d