snapshot of https://github.com/zulip/zulip.git @ 48c69911c7dd4e03b20552eb3bd77ad8151c1357 (2026-09-15)

zerver/lib/string_validation.py

@@ -0,0 +1,65 @@
+import unicodedata
+
+from django.utils.translation import gettext as _
+
+from zerver.lib.exceptions import JsonableError
+from zerver.models import Stream
+
+# There are 66 Unicode non-characters; see
+# https://www.unicode.org/faq/private_use.html#nonchar4
+unicode_non_chars = {
+    chr(x)
+    for r in [
+        range(0xFDD0, 0xFDF0),  # FDD0 through FDEF, inclusive
+        range(0xFFFE, 0x110000, 0x10000),  # 0xFFFE, 0x1FFFE, ... 0x10FFFE inclusive
+        range(0xFFFF, 0x110000, 0x10000),  # 0xFFFF, 0x1FFFF, ... 0x10FFFF inclusive
+    ]
+    for x in r
+}
+
+
+def is_character_printable(char: str) -> bool:
+    unicode_category = unicodedata.category(char)
+    if (unicode_category in ["Cc", "Cs"]) or char in unicode_non_chars:
+        return False
+
+    return True
+
+
+def check_string_is_printable(var: str) -> int | None:
+    # Return position (1-indexed!) of the character which is not
+    # printable, None if no such character is present.
+    for i, char in enumerate(var):
+        if not is_character_printable(char):
+            return i + 1
+    return None
+
+
+def check_stream_name(stream_name: str) -> None:
+    if stream_name.strip() == "":
+        raise JsonableError(_("Channel name can't be empty."))
+
+    if len(stream_name) > Stream.MAX_NAME_LENGTH:
+        raise JsonableError(
+            _("Channel name too long (limit: {max_length} characters).").format(
+                max_length=Stream.MAX_NAME_LENGTH
+            )
+        )
+
+    invalid_character_pos = check_string_is_printable(stream_name)
+    if invalid_character_pos is not None:
+        raise JsonableError(
+            _("Invalid character in channel name, at position {position}.").format(
+                position=invalid_character_pos
+            )
+        )
+
+
+def check_stream_topic(topic_name: str) -> None:
+    invalid_character_pos = check_string_is_printable(topic_name)
+    if invalid_character_pos is not None:
+        raise JsonableError(
+            _("Invalid character in topic, at position {position}!").format(
+                position=invalid_character_pos
+            )
+        )