Add compose short names

This allows compose service names to be used without the project name.

README.md

@@ -75,7 +75,12 @@ an exact match is required. If a generated domain address doesn't match the list
    ```
 
    When the project's name is in the list of _allowed domains_ (`ALLOWED_DOMAINS=.docker,.someproject`), then the
-   `default_domain` will not be appended:
+   `default_domain` will not be appended.
+
+   If a `<service>` name is unique, then it is available also as `<service>.<default_domain>`.
+   ```
+   host   webserver.docker                                    #   webserver.docker has address 172.16.238.3
+   ```
 
 If configured correctly then `resolvectl status` should show the configured link-specific DNS server:
 

src/systemd_resolved_docker/dockerwatcher.py

@@ -42,6 +42,9 @@ class DockerWatcher(Thread):
     def collect_from_containers(self):
         domain_records = {}
 
+        non_unique_hostnames = set()
+        duplicate_hostnames = set()
+
         for c in self.cli.containers.list():
             common_hostnames = []
 
@@ -64,14 +67,20 @@ class DockerWatcher(Thread):
             # for docker-compose services service.project (.docker) names are created
             if c.attrs['Config'].get('Labels') and c.attrs['Config']['Labels'].get('com.docker.compose.service') and \
                     c.attrs['Config']['Labels'].get('com.docker.compose.project'):
-                common_hostnames.append("%s.%s" % (c.attrs['Config']['Labels'].get('com.docker.compose.service'),
-                                                   c.attrs['Config']['Labels'].get('com.docker.compose.project')))
+                compose_service = c.attrs['Config']['Labels'].get('com.docker.compose.service')
+                compose_project = c.attrs['Config']['Labels'].get('com.docker.compose.project')
+
+                common_hostnames.append(compose_service)
+                common_hostnames.append("%s.%s" % (compose_service, compose_project))
 
-                if c.attrs['Config']['Labels'].get('com.docker.compose.container-number'):
-                    common_hostnames.append("%s.%s.%s" % (c.attrs['Config']['Labels'].get('com.docker.compose.container-number'),
-                                                          c.attrs['Config']['Labels'].get('com.docker.compose.service'),
-                                                          c.attrs['Config']['Labels'].get(
-                                                              'com.docker.compose.project')))
+                if compose_service in non_unique_hostnames:
+                    duplicate_hostnames.add(compose_service)
+                else:
+                    non_unique_hostnames.add(compose_service)
+
+                compose_container_number = c.attrs['Config']['Labels'].get('com.docker.compose.container-number')
+                if compose_container_number:
+                    common_hostnames.append("%s.%s.%s" % (compose_container_number, compose_service, compose_project))
 
             name = c.attrs['Name'][1:]
             settings = c.attrs['NetworkSettings']
@@ -93,6 +102,9 @@ class DockerWatcher(Thread):
 
                 domain_records[ip] = record
 
+        for ip, hosts in domain_records.items():
+            domain_records[ip] = list(filter(lambda h: h not in duplicate_hostnames, hosts))
+
         hostnames = [DockerHost(hosts, ip) for ip, hosts in domain_records.items()]
 
         self.handler.handle_hosts(hostnames)

test/integration/test_compose.sh

@@ -26,9 +26,26 @@ networks:
      - $TEST_LABEL
     ipam:
       driver: default
-      config:
-        - subnet: 172.16.238.0/24
-          gateway: 172.16.238.1
+EOF
+
+exec 20<<EOF
+version: "2.1"
+services:
+  broker:
+    image: redis
+    labels:
+     - $TEST_LABEL
+    networks:
+      - network
+
+networks:
+  network:
+    driver: bridge
+    enable_ipv6: false
+    labels:
+     - $TEST_LABEL
+    ipam:
+      driver: default
 EOF
 
 ALLOWED_DOMAINS=.docker,.$TEST_PREFIX start_systemd_resolved_docker
@@ -46,3 +63,8 @@ query_ok     webserver.$TEST_PREFIX $webserver1_ip
 query_ok     webserver.$TEST_PREFIX $webserver2_ip
 query_ok   1.webserver.$TEST_PREFIX $webserver1_ip
 query_ok   2.webserver.$TEST_PREFIX $webserver2_ip
+
+query_ok     broker.docker $broker1_ip
+
+docker-compose --file /dev/fd/20 --project-name ${TEST_PREFIX}_2 up --detach
+query_fail   broker.docker