osbuild: convert to jsoncomm

Convert the hard-coded DGRAM communication to util.jsoncomm. This
avoids hard-coding any IPC-details and simplifies the callers quite a
bit.

runners/org.osbuild.linux

@@ -1,34 +1,21 @@
 #!/usr/bin/python3
 
-import array
-import json
 import os
-import socket
 import subprocess
 import sys
+from osbuild.util import jsoncomm
 
 
-def load_fds(sock, msglen):
-    fds = array.array("i")   # Array of ints
-    msg, ancdata, _, addr = sock.recvmsg(msglen, socket.CMSG_LEN(253 * fds.itemsize))
-    for cmsg_level, cmsg_type, cmsg_data in ancdata:
-        if (cmsg_level == socket.SOL_SOCKET and cmsg_type == socket.SCM_RIGHTS):
-            # Append data, ignoring any truncated integers at the end.
-            fds.frombytes(cmsg_data[:len(cmsg_data) - (len(cmsg_data) % fds.itemsize)])
-    return json.loads(msg), list(fds), addr
-
 def setup_stdio():
-    with socket.socket(socket.AF_UNIX, socket.SOCK_DGRAM) as sock:
-        sock.setsockopt(socket.SOL_SOCKET, socket.SO_PASSCRED, 1)
-        sock.connect("/run/osbuild/api/osbuild")
+    with jsoncomm.Socket.new_client("/run/osbuild/api/osbuild") as client:
         req = {'method': 'setup-stdio'}
-        sock.send(json.dumps(req).encode('utf-8'))
-        msg, fds, _ = load_fds(sock, 1024)
+        client.send(req)
+        msg, fds, _ = client.recv()
         for io in ['stdin', 'stdout', 'stderr']:
             target = getattr(sys, io)
             source = fds[msg[io]]
             os.dup2(source, target.fileno())
-            os.close(source)
+        fds.close()
 
 
 if __name__ == "__main__":