pipeline: deliver stage arguments via a file

Instead of using the jsoncomm API to transmit stagge arguments,
write them out to a file that is then mapped into the container.
The `api.arguments` function is re-written just read that file
from within the container.

osbuild/api.py

@@ -207,32 +207,11 @@ def exception_handler(path="/run/osbuild/api/osbuild"):
         exception(e, path)
 
 
-def arguments(path="/run/osbuild/api/osbuild"):
+def arguments(path="/run/osbuild/api/arguments"):
     """Retrieve the input arguments that were supplied to API"""
-    with jsoncomm.Socket.new_client(path) as client:
-        req = {"method": "get-arguments"}
-        client.send(req)
-        msg, fds, _ = client.recv()
-        assert msg["type"] == "fd"
-        fd = msg["fd"]
-        with os.fdopen(fds.steal(fd), encoding="utf-8") as f:
-            data = json.load(f)
-
-        # Root relative paths: since paths are different on the
-        # host and in the container they are transmitted not as
-        # absolute but relative paths. For all items that have
-        # registered roots, re-root their path entries here
-        for name, root in data.get("paths", {}).items():
-            group = data.get(name)
-            if not group or not isinstance(group, dict):
-                continue
-            for item in group.values():
-                path = item.get("path")
-                if not path:
-                    continue
-                item["path"] = os.path.join(root, path)
-
-        return data
+    with open(path, "r", encoding="utf-8") as fp:
+        data = json.load(fp)
+    return data
 
 
 def metadata(data: Dict, path="/run/osbuild/api/osbuild"):

osbuild/pipeline.py

@@ -79,6 +79,29 @@ class Stage:
         self.mounts[name] = mount
         return mount
 
+    def prepare_arguments(self, args, location):
+        args["options"] = self.options
+        args["meta"] = {
+            "id": self.id
+        }
+
+        # Root relative paths: since paths are different on the
+        # host and in the container they need to be mapped to
+        # their path within the container. For all items that
+        # have registered roots, re-root their path entries here
+        for name, root in args.get("paths", {}).items():
+            group = args.get(name)
+            if not group or not isinstance(group, dict):
+                continue
+            for item in group.values():
+                path = item.get("path")
+                if not path:
+                    continue
+                item["path"] = os.path.join(root, path)
+
+        with open(location, "w", encoding="utf-8") as fp:
+            json.dump(args, fp)
+
     def run(self, tree, runner, build_tree, store, monitor, libdir):
         with contextlib.ExitStack() as cm:
 
@@ -101,9 +124,11 @@ class Stage:
             mounts_mapped = "/run/osbuild/mounts"
             mounts = {}
 
+            os.makedirs(os.path.join(tmpdir, "api"))
+            args_path = os.path.join(tmpdir, "api", "arguments")
+
             args = {
                 "tree": "/run/osbuild/tree",
-                "options": self.options,
                 "paths": {
                     "devices": devices_mapped,
                     "inputs": inputs_mapped,
@@ -112,14 +137,12 @@ class Stage:
                 "devices": devices,
                 "inputs": inputs,
                 "mounts": mounts,
-                "meta": {
-                    "id": self.id
-                }
             }
 
             ro_binds = [
                 f"{self.info.path}:/run/osbuild/bin/{self.name}",
-                f"{inputs_tmpdir}:{inputs_mapped}"
+                f"{inputs_tmpdir}:{inputs_mapped}",
+                f"{args_path}:/run/osbuild/api/arguments"
             ]
 
             binds = [
@@ -147,6 +170,8 @@ class Stage:
                 data = mount.mount(mgr, abspath, mounts_tmpdir)
                 mounts[key] = data
 
+            self.prepare_arguments(args, args_path)
+
             api = API(args)
             build_root.register_api(api)