Bug#642159: Do we need a separate mirror/apt/proxy option?

[Javier Lopez <chilicuil@ubuntu.com>]

I've dug a little bit in the code and agree with Matt that probably we require
and extra option (or even more if we want to control when to leave the mirror in
/etc/apt/apt.conf), it seems for me that http_proxy (mirror/http/proxy) is being
abused. It's set|retrieve several times during installation, and used for
several purposes.

/usr/lib/fetch-url/http (debian-installer-utils)
  23    # use the proxy for wgets (should speed things up)
  24    if db_get mirror/$proto/proxy; then
  25            export ${proto}_proxy="$RET"
  26    fi

/bin/choose-mirror (choose-mirror.c, choose-mirror)
  656 static int set_proxy(void) {   
  657   char *px = add_protocol("proxy");
  658   char *proxy_var;       
  659 
  660   proxy_var = xasprintf("%s_proxy", protocol);
  661 
  662   debconf_get(debconf, px);
  663   if (debconf->value != NULL && strlen(debconf->value)) {
  664           if (strstr(debconf->value, "://")) {
  665                   setenv(proxy_var, debconf->value, 1);

/usr/lib/apt-setup/generators/50mirror (apt-setup)
  225  if [ "$protocol" = http ]; then
  226     db_get mirror/$protocol/proxy
  227     proxy="$RET"
  228     if [ -n "$proxy" ]; then
  229         if ! grep -iq "Acquire::$protocol::Proxy" $ROOT/etc/apt/apt.conf.new; then
  230            echo "Acquire::$protocol::Proxy \"$proxy\";" >> $ROOT/etc/apt/apt.conf.new

This make the installer to fail on several situations, let's suppose
mirror/http/proxy is set on a PXE APPEND environment this way:

APPEND DEBCONF_DEBUG=5 priority=critical locale=en_US interface=auto mirror/http/proxy=http://10.99.88.1:3142 url=http://domain.com/file.preseed initrd=initrd.gz

The installer will fail while fetching http://domain.com/file.preseed. This is
because /usr/lib/fetch-url/http set 'export http_proxy=http://10.99.88.1:3142
before retrieving the preseed file.

Now, if export ${proto}_proxy="$RET" is commented on /usr/lib/fetch-url/http,
the installer will go one step further, it'll retrieve the preseed file, but
still will fail when downloading other files on preseed/run, preseed/include and
preseed/late_command. This is due to /bin/choose-mirror setting again http_proxy
on setenv(proxy_var, debconf->value, 1);

Finally, if that line is commented as well, the installer will finish
successfully while still using the mirror because apt-setup use the variable to
configure apt-get before base-installer get into the action. The proxy will also
be available on next boot after installation.

I think this can be fixed, if we add a mirror/apt/proxy debconf variable and use
it on /usr/lib/apt-setup/generators/50mirror while leaving choose-mirror and
/usr/lib/fetch-url/http untouched. Then people could use mirror/http/proxy to
control connections for general applications and mirror/apt/proxy for
controlling debian repositories.