Fix is_docker_running function when dockerd is not running

Ignore PS command error when looking for docker URLs

When docker daemon is not found running but default URL is
readable then check it is valid before raising an error.

Change-Id: I9bc39930bf4ce1960d327a21c3d9b9d7abc854f3

tobiko/docker/_shell.py

@@ -33,45 +33,74 @@ def discover_docker_urls(
         ssh_client: ssh.SSHClientType = None,
         default_url='unix:/var/run/docker.sock',
         check_urls=True,
-        sudo=False):
+        sudo=False) \
+        -> typing.List[str]:
+    last_error: typing.Optional[Exception] = None
     urls = []
-    processes = sh.list_processes(command='^dockerd',
-                                  ssh_client=ssh_client,
-                                  sudo=sudo)
+    try:
+        urls += list_docker_urls(ssh_client=ssh_client,
+                                 sudo=sudo)
+    except _exception.DockerUrlNotFoundError as ex:
+        last_error = ex
+    if default_url not in urls:
+        urls.append(default_url)
+    if check_urls:
+        urls = select_valid_urls(ssh_client=ssh_client,
+                                 urls=urls,
+                                 sudo=sudo,
+                                 last_error=last_error)
+    return urls
+
+
+def list_docker_urls(
+        ssh_client: ssh.SSHClientType,
+        sudo=False) \
+        -> typing.List[str]:
+    urls = []
+    try:
+        processes = sh.list_processes(command='^dockerd',
+                                      ssh_client=ssh_client,
+                                      sudo=sudo)
+    except sh.PsError as ex:
+        raise _exception.DockerUrlNotFoundError(
+            "Docker demon is not running") from ex
 
     for process in processes:
         if process.command_line:
             urls += urls_from_command_line(process.command_line)
-
-    urls.append(default_url)
     urls = list(collections.OrderedDict.fromkeys(urls))
-
-    error: typing.Optional[Exception] = None
-    if check_urls:
-        valid_urls = []
-        for url in urls:
-            parsed_url = parse.urlparse(url)
-            if (parsed_url.scheme == 'unix' and
-                    parsed_url.path.startswith('/')):
-                try:
-                    sh.execute(f"test -r '{parsed_url.path}'",
-                               ssh_client=ssh_client,
-                               sudo=sudo)
-                except sh.ShellCommandFailed as ex:
-                    LOG.exception(
-                        f"Can't read from socket: {parsed_url.path}")
-                    ex.__cause__ = error
-                    error = ex
-                else:
-                    valid_urls.append(url)
-
-        if not valid_urls:
-            raise _exception.DockerUrlNotFoundError(
-                "Docker is not running") from error
-        urls = valid_urls
     return urls
 
 
+def select_valid_urls(
+        ssh_client: ssh.SSHClientType,
+        urls: typing.List[str],
+        sudo=False,
+        last_error: Exception = None) \
+        -> typing.List[str]:
+    valid_urls = []
+    for url in urls:
+        parsed_url = parse.urlparse(url)
+        if (parsed_url.scheme == 'unix' and
+                parsed_url.path.startswith('/')):
+            try:
+                sh.execute(f"test -r '{parsed_url.path}'",
+                           ssh_client=ssh_client,
+                           sudo=sudo)
+            except sh.ShellCommandFailed as ex:
+                LOG.exception(
+                    f"Can't read from socket: {parsed_url.path}")
+                ex.__cause__ = last_error
+                last_error = ex
+            else:
+                valid_urls.append(url)
+
+    if not valid_urls:
+        raise _exception.DockerUrlNotFoundError(
+            "Docker is not running") from last_error
+    return valid_urls
+
+
 def urls_from_command_line(command_line: sh.ShellCommand,
                            default_url='unix:/var/run/docker.sock') \
         -> typing.List[str]: