stages: add org.osbuild.resolv-conf

Add new stage that can be used to configure the resolver(3) via
the /etc/resolv.conf(5) configuration file.

stages/org.osbuild.resolv-conf

@@ -0,0 +1,68 @@
+#!/usr/bin/python3
+"""
+Configure the resolver
+
+This stage configures the resolver(3) via the resolv.conf(5)
+configure file. See the man page for more details. Currently
+only a subset of options are supported. If no options are
+specified but the stage is included it will create an empty
+`/etc/resolv.conf` file.
+"""
+
+
+import contextlib
+import os
+import sys
+
+import osbuild.api
+
+
+SCHEMA = """
+"additionalProperties": false,
+"properties": {
+  "nameserver": {
+    "description": "Array of IP addresses the resolver should query",
+    "type": "array",
+    "items": { "type": "string" }
+  },
+  "search": {
+    "description": "Array of ",
+    "type": "array",
+    "items": { "type": "string" }
+  }
+}
+"""
+
+
+def main(tree, options):
+    nameserver = options.get("nameserver", [])
+    search = options.get("search", [])
+
+    filepath = "etc/resolv.conf"
+    fullpath = os.path.join(tree, filepath)
+
+    with contextlib.suppress(FileNotFoundError):
+        os.remove(fullpath)
+        print(f"Replacing existing file: /{filepath}")
+
+    data = ["# This file was created by osbuild"]
+
+    if search:
+        data += [
+            "search " + " ".join(search)
+        ]
+
+    for ns in nameserver:
+        data += ["nameserver " + str(ns)]
+
+    os.makedirs(os.path.join(tree, "etc"), exist_ok=True)
+    with open(fullpath, "w") as f:
+        f.write("\n".join(data) + "\n")
+
+    return 0
+
+
+if __name__ == '__main__':
+    args = osbuild.api.arguments()
+    r = main(args["tree"], args["options"])
+    sys.exit(r)