sgl-project/sglang · error · ValueError

Missing closing bracket in IPv6 address: {addr!r}

Error message

Missing closing bracket in IPv6 address: {addr!r}

What it means

In NetworkAddress.parse, a leading '[' enters the bracketed-IPv6 branch; if no matching ']' is found the string is malformed (e.g., '[::1' or '[::1]8080' missing the port separator handled later) and ValueError is raised naming the address.

Source

Thrown at python/sglang/srt/utils/network.py:532

            [::1]:8000          → NetworkAddress("::1", 8000)
            127.0.0.1:8000      → NetworkAddress("127.0.0.1", 8000)
            my-hostname:8000    → NetworkAddress("my-hostname", 8000)

        IPv6 addresses **must** be bracketed.  Bare ``::1:8000`` is
        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):

View on GitHub (pinned to 0132848349)

Solutions

1. Use the canonical form [ipv6]:port, e.g. "[::1]:8000".
2. Quote the address in shell/YAML to prevent bracket stripping.
3. Construct via NetworkAddress(host, port) directly when building programmatically.

Example fix

# before
NetworkAddress.parse("fe80::1:8000")   # ambiguous / unbracketed

# after
NetworkAddress.parse("[fe80::1]:8000")

def valid_endpoint(s: str) -> bool:
    return s.count("[") == s.count("]") and (not s.startswith("[") or s.find("]") != -1)

When it happens

Trigger: parse("[fe80::1") — an IPv6 endpoint where the closing bracket was lost in quoting/shell interpolation.

Common situations: Shell commands dropping brackets, YAML configs mangling [..] syntax, or hand-built address strings concatenating host and port without the ']:' separator.

Related errors

• invalid IPv6 address format: missing ']'
• invalid IPv6 address: {host}
• received IPv6 address format: expected ':' after ']'
• a port must be specified in IPv6 address (format: [ipv6]:por
• Invalid port number: {s!r}

AI-assisted analysis of sgl-project/sglang@0132848349 (2026-08-28). Data as JSON: /api/errors/4ca36d7e9d8ff535. Report an issue: GitHub.