Prevent HostsFileProvider from barfing on non-UTF8 characters

This should fix #153.

vpn_slice/posix.py

@@ -99,14 +99,13 @@ def __init__(self, path):
 
     def write_hosts(self, host_map, name):
         tag = f'vpn-slice-{name} AUTOCREATED'
-        with open(self.path, 'r+') as hostf:
+        with open(self.path, 'r+b') as hostf:
             fcntl.flock(hostf, fcntl.LOCK_EX)  # POSIX only, obviously
             lines = hostf.readlines()
-            keeplines = [l for l in lines if not l.endswith(f'# {tag}\n')]
+            keeplines = [l for l in lines if not l.endswith(f'# {tag}\n'.encode())]
             hostf.seek(0, 0)
             hostf.writelines(keeplines)
-            for ip, names in host_map:
-                print(f"{ip} {' '.join(names)}\t\t# {tag}", file=hostf)
+            hostf.writelines(f"{ip} {' '.join(names)}\t\t# {tag}\n".encode() for ip, name in host_map)
             hostf.truncate()
         return len(host_map) or len(lines) - len(keeplines)
 

vpn_slice/provider.py

@@ -128,14 +128,15 @@ def lookup_srv(self, query):
 
 class HostsProvider(metaclass=ABCMeta):
     @abstractmethod
-    def write_hosts(self, host_map, name):
-        """Write information to the hosts file.
+    def write_hosts(self, host_map: "Dict[Union[ip_address, str], List[str]]", name):
+        """Update local overrides for hostname-to-IP address mapping.
 
-        Lines include a tag so we can identify which lines to remove.
-        The tag is derived from the name.
-
-        host_map maps IP addresses to host names, like the hosts file expects.
+        Each local override added by this instance of vpn-slice should include a tag
+        a tag derived from the 'name' parameter, so that we can later identify those
+        owned by this instance in order to remove/replace them, while leaving others
+        untouched.
 
+        'host_map' should map from IP addresses to lists of hostnames.
         """
 
 class TunnelPrepProvider: