fix(hoster.py): Refactor event handling and hosts file update

Refactored the Docker event handling to use json parsing for more robust event processing. Updated the hosts file update logic to correctly handle existing sections and ensure atomic writes. Improved container info extraction and error handling.

hoster.py

@@ -1,25 +1,27 @@
-#!/usr/bin/python3
 import docker
 import argparse
 import shutil
 import signal
-import time
 import sys
-import os
+import json
 
 label_name = "hoster.domains"
-enclosing_pattern = "#-----------Docker-Hoster-Domains----------\n"
+start_pattern = "#-----------Docker-Hoster-Domains----------\n"
+end_pattern = "#-----Do-not-add-hosts-after-this-line-----\n"
 hosts_path = "/tmp/hosts"
 hosts = {}
 
-def signal_handler(signal, frame):
+dockerClient = docker.DockerClient(base_url="unix:///var/run/docker.sock")
+
+
+def signal_handler(sig, frame):
     global hosts
     hosts = {}
     update_hosts_file()
     sys.exit(0)
 
+
 def main():
-    # register the exit signals
     signal.signal(signal.SIGINT, signal_handler)
     signal.signal(signal.SIGTERM, signal_handler)
 
@@ -27,112 +29,156 @@ def main():
     global hosts_path
     hosts_path = args.file
 
-    dockerClient = docker.APIClient(base_url='unix://%s' % args.socket)
+    global dockerClient
-    events = dockerClient.events(decode=True)
+    dockerClient = docker.DockerClient(base_url=f"unix://{args.socket}")
-    #get running containers
+
-    for c in dockerClient.containers(quiet=True, all=False):
+    # load running containers
-        container_id = c["Id"]
+    for c in dockerClient.containers.list():
-        container = get_container_data(dockerClient, container_id)
+        hosts[c.id] = extract_container_info(c)
-        hosts[container_id] = container
 
     update_hosts_file()
 
-    #listen for events to keep the hosts file updated
+    print("Listening for Docker events...")
-    for e in events:
+
-        if e["Type"]!="container": 
+    # listen for container events
+    for raw in dockerClient.events(decode=False):
+        try:
+            event = json.loads(raw.decode("utf-8"))
+        except (json.JSONDecodeError, UnicodeDecodeError):
             continue
 
-        status = e["status"]
+        if event.get("Type") != "container":
-        if status =="start":
+            continue
-            container_id = e["id"]
+
-            container = get_container_data(dockerClient, container_id)
+        action = event.get("Action")
-            hosts[container_id] = container
+        container_id = event.get("id")
+
+        if action == "start":
+            c = get_container(container_id)
+            if c:
+                hosts[container_id] = extract_container_info(c)
                 update_hosts_file()
 
-        if status=="stop" or status=="die" or status=="destroy":
+        elif action in ("stop", "die", "destroy"):
-            container_id = e["id"]
             if container_id in hosts:
                 hosts.pop(container_id)
                 update_hosts_file()
 
-        if status=="rename":
+        elif action == "rename":
-            container_id = e["id"]
+            c = get_container(container_id)
-            if container_id in hosts:
+            if c:
-                container = get_container_data(dockerClient, container_id)
+                hosts[container_id] = extract_container_info(c)
-                hosts[container_id] = container
                 update_hosts_file()
 
 
-def get_container_data(dockerClient, container_id):
+def get_container(container_id):
-    #extract all the info with the docker api
+    try:
-    info = dockerClient.inspect_container(container_id)
+        return dockerClient.containers.get(container_id)
-    container_hostname = info["Config"]["Hostname"]
+    except docker.errors.NotFound:
-    container_name = info["Name"].strip("/")
+        return None
-    container_ip = info["NetworkSettings"]["IPAddress"]
+
-    if info["Config"]["Domainname"]:
+
-        container_hostname = container_hostname + "." + info["Config"]["Domainname"]
+def extract_container_info(container):
+    info = container.attrs
+
+    name = info["Name"].strip("/")
+    hostname = info["Config"]["Hostname"]
+    domain = info["Config"]["Domainname"]
+
+    if domain:
+        hostname = f"{hostname}.{domain}"
 
     result = []
 
-    for values in info["NetworkSettings"]["Networks"].values():
+    networks = info["NetworkSettings"]["Networks"]
-        
+    for net_name, net in networks.items():
-        if not values["Aliases"]: 
+        ip = net.get("IPAddress")
+        if not ip:
             continue
 
+        aliases = net.get("Aliases") or []
+        domains = set(aliases + [name, hostname])
+
         result.append({
-                "ip": values["IPAddress"] , 
+            "ip": ip,
-                "name": container_name,
+            "name": name,
-                "domains": set(values["Aliases"] + [container_name, container_hostname])
+            "domains": domains
         })
 
-    if container_ip:
+    # fallback IP
-        result.append({"ip": container_ip, "name": container_name, "domains": [container_name, container_hostname ]})
+    default_ip = info["NetworkSettings"].get("IPAddress")
+    if default_ip:
+        result.append({
+            "ip": default_ip,
+            "name": name,
+            "domains": set([name, hostname])
+        })
+
+    # add extra domains from label if present
+    labels = info["Config"]["Labels"]
+    extra_domains = []
+    if label_name in labels:
+        extra = labels[label_name]
+        extra_domains = [d.strip() for d in extra.split(",") if d.strip()]
+
+    for res in result:
+        res["domains"].update(extra_domains)
 
     return result
 
 
 def update_hosts_file():
-    if len(hosts)==0:
+    if len(hosts) == 0:
-        print("Removing all hosts before exit...")
+        print("Clearing hosts file...")
     else:
         print("Updating hosts file with:")
 
-    for id,addresses in hosts.items():
-        for addr in addresses:
-            print("ip: %s domains: %s" % (addr["ip"], addr["domains"]))
-
-    #read all the lines of thge original file
-    lines = []
-    with open(hosts_path,"r+") as hosts_file:
-        lines = hosts_file.readlines()
-
-    #remove all the lines after the known pattern
-    for i,line in enumerate(lines):
-        if line==enclosing_pattern:
-            lines = lines[:i]
-            break;
-
-    #remove all the trailing newlines on the line list
-    if lines:
-        while lines[-1].strip()=="": lines.pop()
-
-    #append all the domain lines
-    if len(hosts)>0:
-        lines.append("\n\n"+enclosing_pattern)
-        
     for id, addresses in hosts.items():
         for addr in addresses:
-                lines.append("%s    %s\n"%(addr["ip"],"   ".join(addr["domains"])))
+            print(f"ip: {addr['ip']} domains: {addr['domains']}")
 
-        lines.append("#-----Do-not-add-hosts-after-this-line-----\n\n")
+    # read existing hosts
+    try:
+        with open(hosts_path, "r") as f:
+            lines = f.readlines()
+    except FileNotFoundError:
+        lines = []
 
-    #write it on the auxiliar file
+    # remove existing section(s) properly
-    aux_file_path = hosts_path+".aux"
+    clean_lines = []
-    with open(aux_file_path,"w") as aux_hosts:
+    i = 0
-        aux_hosts.writelines(lines)
+    while i < len(lines):
+        if lines[i] == start_pattern:
+            # skip until after end_pattern
+            while i < len(lines) and lines[i] != end_pattern:
+                i += 1
+            if i < len(lines) and lines[i] == end_pattern:
+                i += 1  # skip the end_pattern
+        else:
+            clean_lines.append(lines[i])
+            i += 1
 
-    #replace etc/hosts with aux file, making it atomic
+    lines = clean_lines
-    shutil.move(aux_file_path, hosts_path)
+
+    # trim trailing empty lines
+    while lines and not lines[-1].strip():
+        lines.pop()
+
+    # add new entries
+    if hosts:
+        lines.append("\n")  # single empty line before section
+        lines.append(start_pattern)
+        for id, addrs in hosts.items():
+            for addr in addrs:
+                domains_str = " ".join(sorted(addr["domains"]))
+                lines.append(f"{addr['ip']}\t{domains_str}\n")
+        lines.append(end_pattern)
+
+    aux = hosts_path + ".aux"
+    with open(aux, "w") as f:
+        f.writelines(lines)
+
+    shutil.move(aux, hosts_path)
 
 
 def parse_args():
@@ -141,6 +187,6 @@ def parse_args():
     parser.add_argument('file', type=str, nargs="?", default="/tmp/hosts", help='The /etc/hosts file to sync the containers with.')
     return parser.parse_args()
 
-if __name__ == '__main__':
-    main()
 
+if __name__ == "__main__":
+    main()