Issue #4473: Add a POP3.capa() method to query the capabilities advertised by the POP3 server.

Patch by Lorenzo Catucci.

Lib/test/test_poplib.py

@@ -33,6 +33,8 @@ line3\r\n\
 
 class DummyPOP3Handler(asynchat.async_chat):
 
+    CAPAS = {'UIDL': [], 'IMPLEMENTATION': ['python-testlib-pop-server']}
+
     def __init__(self, conn):
         asynchat.async_chat.__init__(self, conn)
         self.set_terminator(b"\r\n")
@@ -112,6 +114,16 @@ class DummyPOP3Handler(asynchat.async_chat):
         self.push('+OK closing.')
         self.close_when_done()
 
+    def cmd_capa(self, arg):
+        self.push('+OK Capability list follows')
+        if self.CAPAS:
+            for cap, params in self.CAPAS.items():
+                _ln = [cap]
+                if params:
+                    _ln.extend(params)
+                self.push(' '.join(_ln))
+        self.push('.')
+
 
 class DummyPOP3Server(asyncore.dispatcher, threading.Thread):
 
@@ -232,6 +244,10 @@ class TestPOP3Class(TestCase):
         self.client.uidl()
         self.client.uidl('foo')
 
+    def test_capa(self):
+        capa = self.client.capa()
+        self.assertTrue('IMPLEMENTATION' in capa.keys())
+
     def test_quit(self):
         resp = self.client.quit()
         self.assertTrue(resp)