bootctl: refactor get_file_version() to use proper PE parsing

This irked me for a while. Let's not scan for strings stupidly, but
properly parse PE files to find the magic marker.

It's easy with our own PE APIs, hence we should do it.

This moves logging to the callers (previously, this was all mixed up).

test/units/TEST-87-AUX-UTILS-VM.bootctl.sh

@@ -113,6 +113,48 @@ testcase_bootctl_basic() {
     basic_tests
 }
 
+cleanup_file_version() {
+    if [[ -n "${FILE_VERSION_GARBAGE:-}" ]]; then
+        rm -f "$FILE_VERSION_GARBAGE"
+        unset FILE_VERSION_GARBAGE
+    fi
+    restore_esp
+}
+
+testcase_bootctl_file_version() {
+    # Exercise get_file_version() (src/bootctl/bootctl-util.c), which reads the
+    # version marker that systemd-boot/-stub store in their ".sdmagic" PE
+    # section, e.g. "#### LoaderInfo: systemd-boot 257 ####". 'bootctl status'
+    # surfaces the inner part next to each .efi file it finds in the ESP, e.g.
+    # ".../systemd-bootx64.efi (systemd-boot 257)".
+
+    backup_esp
+    trap cleanup_file_version RETURN ERR
+
+    bootctl install
+
+    local ESP
+    ESP="$(bootctl --print-esp-path)"
+
+    # The freshly installed systemd-boot binary must be listed with the version
+    # extracted from its ".sdmagic" section.
+    bootctl status | grep -E "systemd-boot[a-z0-9]*\.efi \(systemd-boot [^)]+\)" >/dev/null
+
+    # A non-PE/non-systemd file must be handled gracefully (get_file_version()
+    # returns -ESRCH): it is still listed, but without a version annotation, and
+    # 'bootctl status' must not fail.
+    FILE_VERSION_GARBAGE="$ESP/EFI/systemd/not-a-loader.efi"
+    echo "this is not a PE binary" >"$FILE_VERSION_GARBAGE"
+
+    local status
+    status="$(bootctl status)"
+    grep -F "not-a-loader.efi" <<<"$status" >/dev/null
+    (! grep -E "not-a-loader\.efi .*\(" <<<"$status" >/dev/null)
+
+    rm -f "$FILE_VERSION_GARBAGE"
+    unset FILE_VERSION_GARBAGE
+}
+
 cleanup_image() (
     set +e