Serve only listed mirrors and report a failed default-branch lookupops/git-mirrors

- git-http-backend no longer exports every directory under the mirror
  root: GIT_HTTP_EXPORT_ALL is gone, git-mirror marks each listed mirror
  with git-daemon-export-ok, and a mirror taken off the list loses the
  mark and is deleted on the next run. Tried live: an unlisted bare
  repository answered 404 and was removed by the next run.
- git-mirror checks git ls-remote before it reads the default branch
  and fails the run when the lookup fails.
- The README explains the /usr/bin spelling of the fcgiwrap label (an
  equivalence of /usr/sbin), the stock label of /srv/*/www, and where
  the DNS record is kept.

1 files changed, 23 insertions, 3 deletions

diff --git a/ops/git/git-mirror.sh b/ops/git/git-mirror.sh
index 25bed02..a36f978 100644
--- a/ops/git/git-mirror.sh
+++ b/ops/git/git-mirror.sh
@@ -40,9 +40,16 @@ for name in $names; do
       git -C "$repository" repack -a -d -b -q
       touch "$repository/info/web/repacked"
     fi
-    # HEAD follows the default branch of GitHub.
-    head=$(git -C "$repository" ls-remote --symref origin HEAD | sed -n 's|^ref: refs/heads/\([^[:space:]]*\)[[:space:]]*HEAD$|\1|p')
-    [ -n "$head" ] && git -C "$repository" symbolic-ref HEAD "refs/heads/$head"
+    # HEAD follows the default branch of GitHub; a failed lookup fails the run.
+    if advertised=$(git -C "$repository" ls-remote --symref origin HEAD); then
+      head=$(printf '%s\n' "$advertised" | sed -n 's|^ref: refs/heads/\([^[:space:]]*\)[[:space:]]*HEAD$|\1|p')
+      [ -n "$head" ] && git -C "$repository" symbolic-ref HEAD "refs/heads/$head"
+    else
+      echo "git-mirror: the default branch of $name could not be read" >&2
+      status=1
+    fi
+    # git-http-backend serves only repositories with this file.
+    touch "$repository/git-daemon-export-ok"
     # cgit shows the age of the last change of a repository from this file.
     git -C "$repository" for-each-ref --sort=-committerdate --count=1 \
       --format='%(committerdate:iso8601)' refs/heads > "$repository/info/web/last-modified"
@@ -51,4 +58,17 @@ for name in $names; do
     status=1
   fi
 done
+# A repository no longer listed stops being served at once and is removed.
+for repository in "$root"/*.git; do
+  [ -d "$repository" ] || continue
+  name=$(basename "$repository" .git)
+  case " $(printf '%s ' $names)" in
+    *" $name "*) ;;
+    *)
+      rm -f "$repository/git-daemon-export-ok"
+      rm -rf -- "$repository"
+      echo "git-mirror: removed $name, which is no longer listed" >&2
+      ;;
+  esac
+done
 exit "$status"