sgl-project/sglang · error · ValueError

Expected ':port' after closing bracket, got: {rest!r}

Error message

Expected ':port' after closing bracket, got: {rest!r}

What it means

NetworkAddress.parse found a closing ']' in the address but the remainder after it is not a ':port' suffix (either it does not start with ':' or is just ':' with no digits). Bracketed IPv6 addresses must be followed immediately by a colon and a port number.

Source

Thrown at python/sglang/srt/utils/network.py:538

        ambiguous and will raise ``ValueError``.

        Raises:
            ValueError: If the string cannot be unambiguously parsed.
        """
        if not addr:
            raise ValueError("Empty address string")

        # --- Bracketed IPv6: [addr]:port ---
        if addr.startswith("["):
            close = addr.find("]")
            if close == -1:
                raise ValueError(f"Missing closing bracket in IPv6 address: {addr!r}")
            host = addr[1:close]
            if not _is_ipv6(host):
                raise ValueError(f"Invalid IPv6 address inside brackets: {host!r}")
            rest = addr[close + 1 :]
            if not rest.startswith(":") or len(rest) < 2:
                raise ValueError(
                    f"Expected ':port' after closing bracket, got: {rest!r}"
                )
            return NetworkAddress(host, _parse_port(rest[1:]))

        # --- Plain host:port (IPv4 / hostname) ---
        if ":" not in addr:
            raise ValueError(f"Missing port in address (expected host:port): {addr!r}")
        host, port_str = addr.rsplit(":", 1)
        if not host:
            raise ValueError(f"Empty host in address: {addr!r}")
        # Guard against bare IPv6 slipping through
        if ":" in host and _is_ipv6(host):
            raise ValueError(
                f"Bare IPv6 address without brackets is ambiguous: {addr!r}. "
                f"Use [{host}]:{port_str} instead."
            )
        return NetworkAddress(host, _parse_port(port_str))

View on GitHub (pinned to 0132848349)

Solutions

  1. Append ':<port>' directly after the bracket: '[::1]:8080'
  2. Check for stray characters or whitespace between ']' and ':'
  3. Validate address strings with a regex like ^\[[0-9a-fA-F:]+\]:\d+$ before passing them in

Example fix

# before
addr = NetworkAddress.parse('[::1]')
# after
addr = NetworkAddress.parse('[::1]:8080')
Defensive patterns

Strategy: validation

Validate before calling

import re
def has_ipv6_port(addr: str) -> bool:
    m = re.match(r'^\[[^\]]+\](:.+)?$', addr or '')
    return m is not None and bool(m.group(1)) and len(m.group(1)) > 1

Type guard

null

Try / catch

try:
    NetworkAddress.parse(addr)
except ValueError as e:
    if 'after closing bracket' in str(e):
        addr = addr + ':8080'  # apply default port and retry

Prevention

When it happens

Trigger: NetworkAddress.parse('[::1]'), '[::1]:', '[::1]8080', or '[::1]/24:8080'.

Common situations: Copy-pasting bare IPv6 literals without appending a port, or config values where the port was stripped or separated by whitespace.

Related errors

AI-assisted analysis of sgl-project/sglang@0132848349 (2026-08-28). Data as JSON: /api/errors/9b9f0f61911e537a. Report an issue: GitHub.