gen_tcp:listen(Port, Options)，Options 为一个参数列表

之前介绍过 {active, Boolean} 这个 opt，现在介绍一下 {packet, PacketType}

引用

    {packet, PacketType} (TCP/IP sockets)
    Defines the type of packets to use for a socket. The following values are valid:
    raw | 0
    No packaging is done.
    1 | 2 | 4
    Packets consist of a header specifying the number of bytes in the packet, followed by that number of bytes. The length of header can be one, two, or four bytes; the order of the bytes is big-endian. Each send operation will generate the header, and the header will be stripped off on each receive operation.
    asn1 | cdr | sunrm | fcgi | tpkt | line
    These packet types only have effect on receiving. When sending a packet, it is the responsibility of the application to supply a correct header. On receiving, however, there will be one message sent to the controlling process for each complete packet received, and, similarly, each call to gen_tcp:recv/2,3 returns one complete packet. The header is not stripped off.
    The meanings of the packet types are as follows:
    asn1 - ASN.1 BER,
    sunrm - Sun’s RPC encoding,
    cdr - CORBA (GIOP 1.1),
    fcgi - Fast CGI,
    tpkt - TPKT format [RFC1006],
    line - Line mode, a packet is a line terminated with newline, lines longer than the receive buffer are truncated.

之前介绍过一个愚蠢的方案，用于演示Binary的匹配。现在完全可以这样做：

gen_tcp:listen(Port, [binary, {active, true}, {packet, 2}])
…
receive
{tcp, Socket, Binary} ->
…

这样主动发送过来的Binary，就是一个完整的Body，不包含头部的Size信息，也无需自行处理tcp packet的完整性问题。

此外它还支持 asn1 | cdr | sunrm | fcgi | tpkt | line 这些协议，大大方便开发。

转贴注：

    Erlang的 tcp_gen:listen 参数中有一个 backlog 据说是 undocument 的参数（参考这篇 a fast web server demostrating some undocument erlang feature），看来 ericsson 也会在 opensource 的 erlang 中留一手啊。呵呵。