add swidth call to determine string width on terminal

on posix platforms, this is a small wrapper around wcswidth(3).

borg/platform.py

@@ -1,10 +1,10 @@
 import sys
 
-from .platform_base import acl_get, acl_set, SyncFile, sync_dir, set_flags, get_flags, API_VERSION
+from .platform_base import acl_get, acl_set, SyncFile, sync_dir, set_flags, get_flags, swidth, API_VERSION
 
 if sys.platform.startswith('linux'):  # pragma: linux only
-    from .platform_linux import acl_get, acl_set, SyncFile, set_flags, get_flags, API_VERSION
+    from .platform_linux import acl_get, acl_set, SyncFile, set_flags, get_flags, swidth, API_VERSION
 elif sys.platform.startswith('freebsd'):  # pragma: freebsd only
-    from .platform_freebsd import acl_get, acl_set, API_VERSION
+    from .platform_freebsd import acl_get, acl_set, swidth, API_VERSION
 elif sys.platform == 'darwin':  # pragma: darwin only
-    from .platform_darwin import acl_get, acl_set, API_VERSION
+    from .platform_darwin import acl_get, acl_set, swidth, API_VERSION

borg/platform_base.py

@@ -90,3 +90,11 @@ class SyncFile:
         self.sync()
         self.fd.close()
         sync_dir(os.path.dirname(self.fd.name))
+
+
+def swidth(s):
+    """terminal output width of string <s>
+
+    For western scripts, this is just len(s), but for cjk glyphs, 2 cells are used.
+    """
+    return len(s)

borg/platform_darwin.pyx

@@ -3,6 +3,12 @@ from .helpers import user2uid, group2gid, safe_decode, safe_encode
 
 API_VERSION = 3
 
+cdef extern from "wchar.h":
+    cdef int wcswidth(const Py_UNICODE *str, size_t n)
+
+def swidth(s):
+    return wcswidth(s, len(s))
+
 cdef extern from "sys/acl.h":
     ctypedef struct _acl_t:
         pass

borg/platform_freebsd.pyx

@@ -7,6 +7,12 @@ cdef extern from "errno.h":
     int errno
     int EINVAL
 
+cdef extern from "wchar.h":
+    cdef int wcswidth(const Py_UNICODE *str, size_t n)
+
+def swidth(s):
+    return wcswidth(s, len(s))
+
 cdef extern from "sys/types.h":
     int ACL_TYPE_ACCESS
     int ACL_TYPE_DEFAULT

borg/platform_linux.pyx

@@ -9,6 +9,12 @@ from libc cimport errno
 
 API_VERSION = 3
 
+cdef extern from "wchar.h":
+    cdef int wcswidth(const Py_UNICODE *str, size_t n)
+
+def swidth(s):
+    return wcswidth(s, len(s))
+
 cdef extern from "sys/types.h":
     int ACL_TYPE_ACCESS
     int ACL_TYPE_DEFAULT

borg/testsuite/platform.py

@@ -4,7 +4,7 @@ import sys
 import tempfile
 import unittest
 
-from ..platform import acl_get, acl_set
+from ..platform import acl_get, acl_set, swidth
 from . import BaseTestCase
 
 
@@ -138,3 +138,16 @@ class PlatformDarwinTestCase(BaseTestCase):
         self.set_acl(file2.name, b'!#acl 1\ngroup:ABCDEFAB-CDEF-ABCD-EFAB-CDEF00000000:staff:0:allow:read\nuser:FFFFEEEE-DDDD-CCCC-BBBB-AAAA00000000:root:0:allow:read\n', numeric_owner=True)
         self.assert_in(b'group:ABCDEFAB-CDEF-ABCD-EFAB-CDEF00000000:wheel:0:allow:read', self.get_acl(file2.name)[b'acl_extended'])
         self.assert_in(b'group:ABCDEFAB-CDEF-ABCD-EFAB-CDEF00000000::0:allow:read', self.get_acl(file2.name, numeric_owner=True)[b'acl_extended'])
+
+
+@unittest.skipUnless(sys.platform.startswith(('linux', 'freebsd', 'darwin')), 'POSIX only tests')
+class PlatformPosixTestCase(BaseTestCase):
+
+    def test_swidth_ascii(self):
+        self.assert_equal(swidth("borg"), 4)
+
+    def test_swidth_cjk(self):
+        self.assert_equal(swidth("バックアップ"), 6 * 2)
+
+    def test_swidth_mixed(self):
+        self.assert_equal(swidth("borgバックアップ"), 4 + 6 * 2)