fix location parser for archives with @ char, add test, fixes #1930

we must exclude colon and slash chars from the username, otherwise the term for the user part
will match everything up to a @ char in the archive name.

a slash can't be in a username as the home directory would contain a illegal slash (slash is path sep),

a colon likely also should not be in a username because chown user:group ... syntax.

borg/helpers.py

@@ -791,7 +791,7 @@ class Location:
     # regexes for misc. kinds of supported location specifiers:
     ssh_re = re.compile(r"""
         (?P<proto>ssh)://                                   # ssh://
-        (?:(?P<user>[^@]+)@)?                               # user@  (optional)
+        (?:(?P<user>[^@:/]+)@)?                             # user@  (optional) - username must not contain : or /
         (?P<host>[^:/]+)(?::(?P<port>\d+))?                 # host or host:port
         """ + path_re + optional_archive_re, re.VERBOSE)    # path or path::archive
 
@@ -802,7 +802,7 @@ class Location:
     # note: scp_re is also use for local pathes
     scp_re = re.compile(r"""
         (
-            (?:(?P<user>[^@]+)@)?                           # user@  (optional)
+            (?:(?P<user>[^@:/]+)@)?                         # user@  (optional) - username must not contain : or /
             (?P<host>[^:/]+):                               # host: (don't match / in host to disambiguate from file:)
         )?                                                  # user@host: part is optional
         """ + path_re + optional_archive_re, re.VERBOSE)    # path with optional archive

borg/testsuite/helpers.py

@@ -94,6 +94,13 @@ class TestLocationWithoutEnv:
         assert repr(Location('/abs/path:with:colons')) == \
             "Location(proto='file', user=None, host=None, port=None, path='/abs/path:with:colons', archive=None)"
 
+    def test_user_parsing(self):
+        # see issue #1930
+        assert repr(Location('host:path::2016-12-31@23:59:59')) == \
+            "Location(proto='ssh', user=None, host='host', port=None, path='path', archive='2016-12-31@23:59:59')"
+        assert repr(Location('ssh://host/path::2016-12-31@23:59:59')) == \
+            "Location(proto='ssh', user=None, host='host', port=None, path='/path', archive='2016-12-31@23:59:59')"
+
     def test_underspecified(self, monkeypatch):
         monkeypatch.delenv('BORG_REPO', raising=False)
         with pytest.raises(ValueError):