Net errors¶

NetError: the error vocabulary every net module answers.

Import¶

use <net/error>

Overview¶

NetError is a predefined enum -- the compiler synthesizes it, and no unit declares it -- and this module is its HOME. The import is what brings the bare name into a unit, exactly as <io/fs> brings FileMode and <collections/hashmap> brings HashMap; use <net/error> as ne puts it behind the dot instead (ne.NetError.TimedOut). Every net module re-exports this one (docs/design/unit-namespaces.md, section 8.1), so a unit that matches on a net module's error needs no second import: use <net/tcp> alone brings NetError.

public enum NetError:
    ConnectionRefused    ConnectionReset      TimedOut
    Closed               AddressInUse         AddressNotAvailable
    NetworkUnreachable   HostUnreachable      ResolveFailed
    PermissionDenied     TooManyOpen          InvalidAddress
    Interrupted          MessageTooLarge      Other

The variant ORDER is the ABI: the index is the tag the socket layer stores into a Result payload, so a variant is only ever appended. The mapping from errno is on the socket primitives page.

Functions¶

`to_io() -> IoError`¶

extend NetError to_io() IoError

Turns a socket error into the one channel the io contracts answer. Every NetError variant with no twin in IoError belongs to a connect, a bind or a resolve, so nothing a contract method can answer is lost; the rest map to IoError.Other. The conversion runs INSIDE the stdlib -- TcpStream.read is sock_recv with its error passed through to_io() -- and a program never needs to call it.

Example¶

use <net/tcp>

fn main() i32:
    match connect("localhost", 1):
        Result.Ok(_) -> println("connected")
        Result.Err(NetError.ConnectionRefused) -> println("nothing listens there")
        Result.Err(_) -> println("failed")
    return Result.Ok(0)