core/manager: move environment serialization out to basic/env-util.c

This protocol is generally useful, we might just as well reuse it for the
env. generators.

The implementation is changed a bit: instead of making a new strv and freeing
the old one, just mutate the original. This is much faster with larger arrays,
while in fact atomicity is preserved, since we only either insert the new
entry or not, without being in inconsistent state.

v2:
- fix confusion with return value

src/basic/env-util.c

@@ -26,6 +26,7 @@
 
 #include "alloc-util.h"
 #include "env-util.h"
+#include "escape.h"
 #include "extract-word.h"
 #include "macro.h"
 #include "parse-util.h"
@@ -644,3 +645,36 @@ int getenv_bool(const char *p) {
 
         return parse_boolean(e);
 }
+
+int serialize_environment(FILE *f, char **environment) {
+        char **e;
+
+        STRV_FOREACH(e, environment) {
+                _cleanup_free_ char *ce;
+
+                ce = cescape(*e);
+                if (!ce)
+                        return -ENOMEM;
+
+                fprintf(f, "env=%s\n", *e);
+        }
+
+        /* caller should call ferror() */
+
+        return 0;
+}
+
+int deserialize_environment(char ***environment, const char *line) {
+        char *uce = NULL;
+        int r;
+
+        assert(line);
+        assert(environment);
+
+        assert(startswith(line, "env="));
+        r = cunescape(line + 4, UNESCAPE_RELAX, &uce);
+        if (r < 0)
+                return r;
+
+        return strv_env_replace(environment, uce);
+}