netReceivePosix

fn netReceivePosix(
    socket_handle: net.Socket.Handle,
    message: *net.IncomingMessage,
    data_buffer: []u8,
    flags: net.ReceiveFlags,
    nonblocking: bool,
) (net.Socket.ReceiveError || error{WouldBlock})!void {
    // recvmmsg is useless, here's why:
    // * [timeout bug](https://bugzilla.kernel.org/show_bug.cgi?id=75371)
    // * it wants iovecs for each message but we have a better API: one data
    //   buffer to handle all the messages. The better API cannot be lowered to
    //   the split vectors though because reducing the buffer size might make
    //   some messages unreceivable.
    const posix_flags: u32 =
        @as(u32, if (flags.oob) posix.MSG.OOB else 0) |
        @as(u32, if (flags.peek) posix.MSG.PEEK else 0) |
        @as(u32, if (flags.trunc) posix.MSG.TRUNC else 0) |
        posix.MSG.NOSIGNAL |
        @as(u32, if (nonblocking) posix.MSG.DONTWAIT else 0);

    var storage: PosixAddress = undefined;
    var iov: posix.iovec = .{ .base = data_buffer.ptr, .len = data_buffer.len };
    var msg: posix.msghdr = .{
        .name = &storage.any,
        .namelen = @sizeOf(PosixAddress),
        .iov = (&iov)[0..1],
        .iovlen = 1,
        .control = message.control.ptr,
        .controllen = @intCast(message.control.len),
        .flags = undefined,
    };

    const syscall = try Syscall.start();
    while (true) {
        const rc = posix.system.recvmsg(socket_handle, &msg, posix_flags);
        switch (posix.errno(rc)) {
            .SUCCESS => {
                syscall.finish();
                const data = data_buffer[0..@intCast(rc)];
                message.* = .{
                    .from = addressFromPosix(&storage),
                    .data = data,
                    .control = if (msg.control) |ptr| @as([*]u8, @ptrCast(ptr))[0..msg.controllen] else message.control,
                    .flags = .{
                        .eor = (msg.flags & posix.MSG.EOR) != 0,
                        .trunc = (msg.flags & posix.MSG.TRUNC) != 0,
                        .ctrunc = (msg.flags & posix.MSG.CTRUNC) != 0,
                        .oob = (msg.flags & posix.MSG.OOB) != 0,
                        .errqueue = if (@hasDecl(posix.MSG, "ERRQUEUE")) (msg.flags & posix.MSG.ERRQUEUE) != 0 else false,
                    },
                };
                return;
            },
            .INTR => {
                try syscall.checkCancel();
                continue;
            },
            .NFILE => return syscall.fail(error.SystemFdQuotaExceeded),
            .MFILE => return syscall.fail(error.ProcessFdQuotaExceeded),
            .NOBUFS => return syscall.fail(error.SystemResources),
            .NOMEM => return syscall.fail(error.SystemResources),
            .NOTCONN => return syscall.fail(error.SocketUnconnected),
            .MSGSIZE => return syscall.fail(error.MessageOversize),
            .PIPE => return syscall.fail(error.SocketUnconnected),
            .CONNRESET => return syscall.fail(error.ConnectionResetByPeer),
            .TIMEDOUT => return syscall.fail(error.ConnectionTimedOut),
            .NETDOWN => return syscall.fail(error.NetworkDown),
            .AGAIN => return syscall.fail(error.WouldBlock),
            .BADF => |err| return syscall.errnoBug(err),
            .FAULT => |err| return syscall.errnoBug(err),
            .INVAL => |err| return syscall.errnoBug(err),
            .NOTSOCK => |err| return syscall.errnoBug(err),
            .OPNOTSUPP => |err| return syscall.errnoBug(err),
            else => |err| return syscall.unexpectedErrno(err),
        }
    }
}