Add fake "podman network exists" command

Motivation:

podman-compose uses the "podman network exists" command to avoid
creating the same network twice.  This command was added with podman
v3.1.0.

Debian stable has an older version of podman (v3.0.1) that doesn't
support the "podman network exists" command.

A symptom of this problem is podman-compose failing with lines like:

    subprocess.CalledProcessError: Command '['podman', 'network', 'exists', 'scicatlive_default']' returned non-zero exit status 125.

    During handling of the above exception, another exception occurred:

    [...]
    subprocess.CalledProcessError: Command '['podman', 'network', 'create', '--labelect=scicatlive', 'scicatlive_default']' returned non-zero exit status 125.

Modification:

Abstract the two places where podman-compose checks if a network already
exists.  This is now handled by a specific method.

Check the podman version.  If the podman version is earlier than v3.1.0
then simulate the "podman network exists" command by parsing the output
from "podman network ls", otherwise simply call the "podman network
exists" command directly.

Result:

podman-compose is now able to create a network with versions of podman
before v3.1.0.

Signed-off-by: Paul Millar <paul.millar@desy.de>

Author: paulmillar

podman_compose.py

@@ -26,6 +26,7 @@
 from threading import Thread
 
 import shlex
+import semantic_version as sv
 
 try:
     from shlex import quote as cmd_quote
@@ -669,6 +670,22 @@ def norm_ports(ports_in):
         ports_out.append(port)
     return ports_out
 
+def assert_network_exists(compose, net_name):
+    podman_version = sv.Version(compose.podman_version)
+    if sv.SimpleSpec('<3.1.0').match(podman_version):
+          output = compose.podman.output([], "network", ["ls"])
+          offset = None
+          for raw_line in output.splitlines():
+              line = raw_line.decode("utf-8")
+              if not offset:
+                  offset = line.find("VERSION")
+              else:
+                  this_net_name = line[:offset].rstrip()
+                  if (this_net_name == net_name):
+                      return ''
+          raise subprocess.CalledProcessError(1, "docker network exists " +  net_name)
+    else:
+          return compose.podman.output([], "network", ["exists", net_name])
 
 def assert_cnt_nets(compose, cnt):
     """
@@ -693,7 +710,7 @@ def assert_cnt_nets(compose, cnt):
             ext_desc.get("name", None) or net_desc.get("name", None) or default_net_name
         )
         try:
-            compose.podman.output([], "network", ["exists", net_name])
+            assert_network_exists(compose, net_name)
         except subprocess.CalledProcessError as e:
             if is_ext:
                 raise RuntimeError(
@@ -735,7 +752,7 @@ def assert_cnt_nets(compose, cnt):
                     args.extend(("--gateway", gateway))
             args.append(net_name)
             compose.podman.output([], "network", args)
-            compose.podman.output([], "network", ["exists", net_name])
+            assert_network_exists(compose, net_name)
 
 
 def get_net_args(compose, cnt):

requirements.txt

@@ -4,4 +4,5 @@
 
 pyyaml
 python-dotenv
+semantic-version
 

setup.py

@@ -34,6 +34,7 @@
     install_requires=[
         "pyyaml",
         "python-dotenv",
+        "semantic-version",
     ],
     # test_suite='tests',
     # tests_require=[