Merge branch 'wip/p3732/truncate-middle' into 'main'

gutf8: Add a g_utf8_truncate_middle() function

See merge request GNOME/glib!3440

docs/reference/glib/glib-sections.txt.in

@@ -3131,6 +3131,7 @@ g_utf8_strchr
 g_utf8_strrchr
 g_utf8_strreverse
 g_utf8_substring
+g_utf8_truncate_middle
 g_utf8_validate
 g_utf8_validate_len
 g_utf8_make_valid

glib/gunicode.h

@@ -833,6 +833,10 @@ gchar   *g_utf8_strncpy           (gchar       *dest,
                                    const gchar *src,
                                    gsize        n);
 
+GLIB_AVAILABLE_IN_2_78
+gchar   *g_utf8_truncate_middle   (const gchar *string,
+                                   gsize        truncate_length);
+
 /* Find the UTF-8 character corresponding to ch, in string p. These
    functions are equivalants to strchr and strrchr */
 GLIB_AVAILABLE_IN_ALL

glib/gutf8.c

@@ -460,6 +460,72 @@ g_utf8_strncpy (gchar       *dest,
   return dest;
 }
 
+/**
+ * g_utf8_truncate_middle:
+ * @string: (transfer none): a nul-terminated UTF-8 encoded string
+ * @truncate_length: the new size of @string, in characters, including the ellipsis character
+ *
+ * Cuts off the middle of the string, preserving half of @truncate_length
+ * characters at the beginning and half at the end.
+ * 
+ * If @string is already short enough, this returns a copy of @string.
+ * If @truncate_length is `0`, an empty string is returned.
+ *
+ * Returns: (transfer full): a newly-allocated copy of @string ellipsized in the middle
+ *
+ * Since: 2.78
+ */
+gchar *
+g_utf8_truncate_middle (const gchar *string,
+                        gsize        truncate_length)
+{
+  const gchar *ellipsis = "…";
+  const gsize ellipsis_bytes = strlen (ellipsis);
+
+  gsize length;
+  gsize left_substring_length;
+  gchar *left_substring_end;
+  gchar *right_substring_begin;
+  gchar *right_substring_end;
+  gsize left_bytes;
+  gsize right_bytes;
+  gchar *result;
+
+  g_return_val_if_fail (string != NULL, NULL);
+
+  length = g_utf8_strlen (string, -1);
+  /* Current string already smaller than requested length */
+  if (length <= truncate_length)
+    return g_strdup (string);
+  if (truncate_length == 0)
+    return g_strdup ("");
+
+  /* Find substrings to keep, ignore ellipsis character for that */
+  truncate_length -= 1;
+
+  left_substring_length = truncate_length / 2;
+
+  left_substring_end = g_utf8_offset_to_pointer (string, left_substring_length);
+  right_substring_begin = g_utf8_offset_to_pointer (left_substring_end,
+                                                    length - truncate_length);
+  right_substring_end = g_utf8_offset_to_pointer (right_substring_begin,
+                                                  truncate_length - left_substring_length);
+
+  g_assert (*right_substring_end == '\0');
+
+  left_bytes = left_substring_end - string;
+  right_bytes = right_substring_end - right_substring_begin;
+
+  result = g_malloc (left_bytes + ellipsis_bytes + right_bytes + 1);
+
+  strncpy (result, string, left_bytes);
+  memcpy (result + left_bytes, ellipsis, ellipsis_bytes);
+  strncpy (result + left_bytes + ellipsis_bytes, right_substring_begin, right_bytes);
+  result[left_bytes + ellipsis_bytes + right_bytes] = '\0';
+
+  return result;
+}
+
 /* unicode_strchr */
 
 /**

glib/tests/utf8-misc.c

@@ -162,6 +162,58 @@ test_utf8_make_valid (void)
   g_free (r);
 }
 
+static void
+truncate_middle_helper (const char *in_str,
+                        gsize       truncate_len,
+                        const char *out_str)
+{
+  gchar *string = g_utf8_truncate_middle (in_str, truncate_len);
+  g_assert_cmpstr (string, ==, out_str);
+  g_free (string);
+}
+
+static void
+test_utf8_truncate_middle (void)
+{
+  truncate_middle_helper ("foo", 0, "");
+  truncate_middle_helper ("foo", 1, "…");
+  truncate_middle_helper ("foo", 2, "…o");
+  truncate_middle_helper ("foo", 3, "foo");
+  truncate_middle_helper ("foo", 4, "foo");
+  truncate_middle_helper ("foo", 5, "foo");
+  truncate_middle_helper ("foo", 6, "foo");
+  truncate_middle_helper ("foo", 7, "foo");
+
+  truncate_middle_helper ("a_much_longer_foo", 0, "");
+  truncate_middle_helper ("a_much_longer_foo", 1, "…");
+  truncate_middle_helper ("a_much_longer_foo", 2, "…o");
+  truncate_middle_helper ("a_much_longer_foo", 3, "a…o");
+  truncate_middle_helper ("a_much_longer_foo", 4, "a…oo");
+  truncate_middle_helper ("a_much_longer_foo", 5, "a_…oo");
+  truncate_middle_helper ("a_much_longer_foo", 6, "a_…foo");
+  truncate_middle_helper ("a_much_longer_foo", 7, "a_m…foo");
+  truncate_middle_helper ("a_much_longer_foo", 8, "a_m…_foo");
+  truncate_middle_helper ("a_much_longer_foo", 9, "a_mu…_foo");
+
+  truncate_middle_helper ("something_even", 8, "som…even");
+  truncate_middle_helper ("something_odd", 8, "som…_odd");
+  truncate_middle_helper ("something_even", 9, "some…even");
+  truncate_middle_helper ("something_odd", 9, "some…_odd");
+  truncate_middle_helper ("something_even", 10, "some…_even");
+  truncate_middle_helper ("something_odd", 10, "some…g_odd");
+  truncate_middle_helper ("something_even", 11, "somet…_even");
+  truncate_middle_helper ("something_odd", 11, "somet…g_odd");
+  truncate_middle_helper ("something_even", 12, "somet…g_even");
+  truncate_middle_helper ("something_odd", 12, "somet…ng_odd");
+  truncate_middle_helper ("something_even", 13, "someth…g_even");
+  truncate_middle_helper ("something_odd", 13, "something_odd");
+  truncate_middle_helper ("something_even", 14, "something_even");
+  truncate_middle_helper ("something_odd", 13, "something_odd");
+
+  truncate_middle_helper ("ääääääääää", 5, "ää…ää");
+  truncate_middle_helper ("あぃいぅうぇえぉ", 7, "あぃい…ぇえぉ");
+}
+
 int
 main (int   argc,
       char *argv[])
@@ -174,6 +226,7 @@ main (int   argc,
   g_test_add_func ("/utf8/reverse", test_utf8_reverse);
   g_test_add_func ("/utf8/substring", test_utf8_substring);
   g_test_add_func ("/utf8/make-valid", test_utf8_make_valid);
+  g_test_add_func ("/utf8/truncate-middle", test_utf8_truncate_middle);
 
   return g_test_run();
 }