fix mmdebstrap hanging if apt in download step failed (closes: #1017795)

coverage.txt

@@ -323,3 +323,5 @@ Modes: root unshare
 Needs-QEMU: true
 
 Test: error-if-stdout-is-tty
+
+Test: variant-custom-timeout

mmdebstrap

@@ -979,19 +979,24 @@ sub run_apt_download_progress {
     my $flags = fcntl($wfh, F_GETFD, 0)        or error "fcntl F_GETFD: $!";
     fcntl($wfh, F_SETFD, $flags & ~FD_CLOEXEC) or error "fcntl F_SETFD: $!";
     my $fd = fileno $wfh;
+    # run_apt_progress() can raise an exception which would leave this function
+    # without cleaning up the other thread we started, making mmdebstrap hang
+    # in case run_apt_progress() fails -- so wrap this in eval() instead
+    eval {
         # 2022-05-02, #debian-apt on OFTC, times in UTC+2
-    # 16:57 < josch> DonKult: how is -oDebug::pkgDpkgPm=1 -oDir::Log=/dev/null
+        # 16:57 < josch> DonKult: how is -oDebug::pkgDpkgPm=1
-    #                a "fancy no-op"?
+        #                -oDir::Log=/dev/null a "fancy no-op"?
-    # 11:52 < DonKult> josch: "fancy no-op" in sofar as it does nothing to the
+        # 11:52 < DonKult> josch: "fancy no-op" in sofar as it does nothing to
-    #                  system even through its not in a special mode ala
+        #                  the system even through its not in a special mode
-    #                  simulation or download-only. It does all the things it
+        #                  ala simulation or download-only. It does all the
-    #                  normally does, except that it just prints the dpkg calls
+        #                  things it normally does, except that it just prints
-    #                  instead of execv() them which in practice amounts means
+        #                  the dpkg calls instead of execv() them which in
-    #                  it does nothing (the Dir::Log just prevents libapt from
+        #                  practice amounts means it does nothing (the Dir::Log
-    #                  creating the /var/log/apt directories. As the code
+        #                  just prevents libapt from creating the /var/log/apt
-    #                  creates them even if no logs will be placed there…). As
+        #                  directories. As the code creates them even if no
-    #                  said, midterm an apt --print-install-packages or
+        #                  logs will be placed there…). As said, midterm an apt
-    #                  something would be nice to avoid running everything.
+        #                  --print-install-packages or something would be nice
+        #                  to avoid running everything.
         run_apt_progress({
                 ARGV => [
                     'apt-get',
@@ -1012,13 +1017,21 @@ sub run_apt_download_progress {
                     @{ $options->{APT_ARGV} },
                 ],
             });
+    };
+    my $err = '';
+    if ($@) {
+        $err = "apt download failed: $@";
+    }
     # signal the child process that we are done
     close $wfh;
     # and then read from it what it got
     my @listofdebs = <$fh>;
     close $fh;
     if ($? != 0) {
-        error "status child failed";
+        $err = "status child failed";
+    }
+    if ($err) {
+        error $err;
     }
     # remove trailing newlines
     chomp @listofdebs;

tests/variant-custom-timeout

@@ -0,0 +1,11 @@
+#!/bin/sh
+set -eu
+export LC_ALL=C.UTF-8
+
+# mmdebstrap used to hang forever if apt in custom mode failed to resolve
+# dependencies because a process died without cleaning up its children.
+# https://bugs.debian.org/1017795
+ret=0
+{{ CMD }} --mode={{ MODE }} --variant=custom \
+	--include=this-package-does-not-exist {{ DIST }} /dev/null {{ MIRROR }} || ret=1
+[ $ret -eq 1 ]