Just An Application

June 14, 2013

Programming With Rust — Part Eight: Invoking The Listen Function

After all that we should now be in a position to write some code to invoke the listen function.

1.0 The Arguments

So let’s see. As arguments to the listen function we need

1.1 host_ip

We can get an IpAddress by parsing a string representing the IPv4 loopback address using the function std::net::ip::v4::parse_addr.

The parse_address function takes a borrowed pointer to a string, so for now we can hardwire the loopback address as a string literal.

1.2 port

The port number is easy. Just pick a number greater than 1024 and less than 65536 that nobody else is using.

1.3 backlog

The canonical value for the backlog argument to any listen function in any programming language is 5.[1]

1.4 iotask

IoTasks seem to be in fairly short supply.

The only way to obtain one seems to be to call the function std::uv_iotask::spawn_iotask.

Not sure what the implications of doing this are. The documentation for that particular function is less than forthcoming.

We will just have to do it and see what happens.

1.5 on_establish_cb And new_connect_cb

We can supply lambda expressions for the two callbacks. This will automatically result in the creation of the necessary owned closures.

2.0 The Return Type

The return type of the listen function is defined to be

    result::Result<(), TcpListenErrData>

The Result type is defined in the module result like this,

    pub enum Result<T, U> {
        /// Contains the successful result value
        /// Contains the error value

so it is a generic enum type.

The value returned from a call to the listen function is going to be either

  • an instance of the Ok variant with an associated value of the unit type, that is, nothing, or

  • an instance of the Err variant with an associated value of type TcpListenErrData

3.0 The Code

What all that looks like in practice is this


            io::println(fmt!("on_establish_callback(%?)", chan));
        |newConn, chan|
            io::println(fmt!("new_connection_callback(%?, %?)", newConn, chan));
            fail!(~"Now what ?");


The function io:println takes a borrowed pointer to a string and prints the string to stdout followed by a newline.

fmt! is like sprintf and fail! stops the Task.

For the moment we are going to ignore the return value.


  1. Its a tradition, or an old charter, or something.

Update: 27.07.2014

The socket functions as described above no longer exist in Rust.

See here for some discussion of the equivalent functionality in the current version of Rust

Copyright (c) 2013 By Simon Lewis. All Rights Reserved.

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1 Comment »

  1. […] as we have already seen is a parameterized enum […]

    Pingback by Programming With Rust — Part Ten: More Fun With Sockets | Just An Application — June 17, 2013 @ 7:16 am

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