Just An Application

June 20, 2013

Programming With Rust — Part Thirteen: Reading An HTTP Request

Now we have a connection we can read the incoming HTTP request.

1.0 An HTTP Request

An HTTP request arrives over a connection as

  • a request line

followed by

  • zero or more header lines

followed by

  • an empty line

followed by

  • a message body

which is optional.

A line is terminated by a carriage-return (CR == ASCII 13) immediately followed by a line-feed (LF == ASCII 10).

Ideally we would like to read the entire request from the connection “in one go” but that is not possible because there is no way of knowing how big a given HTTP request is before we read it.

To abstract out the unfortunately indeterminate nature of an incoming HTTP request, we will start by defining a RequestBuffer type which will deal with the vagaries of reading the necessary bytes from the connection and converting them into lines.

2.0 RequestBuffer: Take One

The original idea was that RequestBuffer would look something like this

    struct RequestBuffer
    {
        priv socketBuf:     TcpSocketBuf,
        priv bytes:         ~[u8],
        priv size:          uint,
        priv available:     uint,
        priv position:      uint,
        priv lastLineEnd:   uint
    }

and there would be a readLine method which would look something like this

    impl RequestBuffer
    {
        ...
        
        fn readLine(&mut self) -> ~str
        {
            let mut state = 0;
		
            loop
            {
                if (self.position == self.available)
                {
                    // read all the bytes currently available from the connection
            
                    ...
                }
            
                let b = self.bytes[self.position];
			
                self.position += 1;
            
                match state
                {
                    0 => 
                    {
                        if (b == 13) // CR
                        {
                            state = 1;
                        }
                    },
						
                    1 => 
                    {
                        if (b == 10) // LF
                        {
                            // make string representing line from buffered bytes
                    
                            let line = ...
                        
                            self.lastLineEnd = self.position;
                            return line;
                        }
                        else
                        {
                            state = 0;
                        }
                    },
						
                    _ => 
                    {
                        fail!(fmt!("state == %u !", state));
                    }
                }
            }
        }
        
        ...
        
    }

but at the moment there does not seem to be any way of simply reading all the bytes currently available on the connection in one go that actually works.

2.1 RequestBuffer: Take Two

This is a version that works but there really isn’t a whole lot of buffering going on.

2.1.1 RequestBuffer

    struct RequestBuffer
    {
        priv socketBuf: TcpSocketBuf,
        priv bytes:     ~[u8],
    }

2.1.2 The readLine Method

    ...

    static CR: u8 = 13;

    static LF: u8 = 10;

    ...

    impl RequestBuffer
    {
    
        ...
        
        fn readLine(&mut self) -> ~str
        {
            self.bytes.clear();
        
            let mut state = 0;
		
            loop
            {
                let i = self.socketBuf.read_byte();
			
                if (i < 0)
                {
                    fail!(~"EOF");
                }
            
                let b = i as u8;
            
                match state
                {
                    0 => 
                    {
                        if (b == CR)
                        {
                            state = 1;
                        }
                    },
						
                    1 => 
                    {
                        if (b == LF)
                        {
                            return str::from_bytes(vec::const_slice(self.bytes, 0, self.bytes.len() - 1));
                        }
                        else
                        {
                            state = 0;
                        }
                    },
						
                    _ => 
                    {
                        fail!(fmt!("state == %u !", state));
                    }
                }
                self.bytes.push(b);
            }
        }

        ...
        
    }

2.1.3 The new Method

The new method is a static method which can be used to create a RequestBuffer.

    fn new(socketBuf: TcpSocketBuf) -> RequestBuffer
    {
        RequestBuffer { socketBuf: socketBuf, bytes: ~[0u8, ..SIZE] }
    }

3.0 The handleConnection Function

If the accept function is successful we now call the handleConnection function which is defined like this

    fn handleConnection(socket: TcpSocket)
    {	
        let mut buffer      = RequestBuffer::new(socket_buf(socket));
        let     requestLine = buffer.readLine();
	
        io::println(requestLine);
        loop
        {
            let line = buffer.readLine();
		
            io::println(line);
            if (str::len(line) == 0)
            {
                break;
            }
        }
        io::stdout().flush();
        fail!(~"Now what ?");
    }

4.0 Running The Code

Running the code and pointing a web browser at 127.0.0.1:3534 produces this

 
    ./httpd
    on_establish_callback({x: {data: (0x1007094f0 as *())}})
    new_connection_callback(NewTcpConn((0x10200b000 as *())), {x: {data: (0x1007094f0 as *())}})
    accept succeeded
    GET / HTTP/1.1
    Host: 127.0.0.1:3534
    User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:21.0) Gecko/20100101 Firefox/21.0
    Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
    Accept-Language: en-US,en;q=0.5
    Accept-Encoding: gzip, deflate
    DNT: 1
    Connection: keep-alive

    rust: task failed at 'Now what ?', httpd.rc:172
    rust: domain main @0x10201ee10 root task failed
    rust: task failed at 'killed', /Users/simon/Src/lang/rust-0.6/src/libcore/pipes.rs:314

5.0 The Source Code For httpd v0.3


// httpd.rc

// v0.3

extern mod std;

use core::comm::SharedChan;

use core::option::Option;


use core::task;

use std::net::ip;
use std::net::tcp;
use std::net::tcp::TcpErrData;
use std::net::tcp::TcpNewConnection;
use std::net::tcp::TcpSocket;
use std::net::tcp::TcpSocketBuf;

use std::net::tcp::socket_buf;

use std::sync::Mutex;

use std::uv_iotask;

// RequestBuffer

struct RequestBuffer
{
    priv socketBuf: TcpSocketBuf,
    priv bytes:     ~[u8],
}

//

static SIZE: uint = 4096;

// 

static CR: u8 = 13;

static LF: u8 = 10;

impl RequestBuffer
{    
    fn new(socketBuf: TcpSocketBuf) -> RequestBuffer
    {
        RequestBuffer { socketBuf: socketBuf, bytes: ~[0u8, ..SIZE] }
    }

    fn readLine(&mut self) -> ~str
    {
        self.bytes.clear();
        
        let mut state = 0;
		
        loop
        {
            let i = self.socketBuf.read_byte();
			
            if (i < 0)
            {
                fail!(~"EOF");
            }
            
            let b = i as u8;
            
            match state
            {
                0 => 
                {
                    if (b == CR)
                    {
                        state = 1;
                    }
                },
						
                1 => 
                {
                    if (b == LF)
                    {
                        return str::from_bytes(vec::const_slice(self.bytes, 0, self.bytes.len() - 1));
                    }
                    else
                    {
                        state = 0;
                    }
                },
						
                _ => 
                {
                    fail!(fmt!("state == %u !", state));
                }
            }
            self.bytes.push(b);
        }
    }
}


static BACKLOG: uint = 5;
static PORT:    uint = 3534;

static IPV4_LOOPBACK: &'static str = "127.0.0.1";


fn on_establish_callback(chan: SharedChan<Option<TcpErrData>>)
{
    io::println(fmt!("on_establish_callback(%?)", chan));
}

fn new_connection_callback(newConn :TcpNewConnection, chan: SharedChan<Option<TcpErrData>>)
{
    io::println(fmt!("new_connection_callback(%?, %?)", newConn, chan));
	
    let mx = Mutex();
	
    do mx.lock_cond
        |cv|
        {
            let mxc = ~mx.clone();

            do task::spawn 
            {
                match tcp::accept(newConn)
                {
                    Ok(socket) => 
                    {
                        io::println("accept succeeded");
                        do mxc.lock_cond
                            |cv|
                            {
                                cv.signal();
                            }
                        handleConnection(socket);
				                
                    },
                    Err(error) => 
                    {
                        io::println(fmt!("accept failed: %?", error));
                        do mxc.lock_cond
                            |cv|
                            {
                                cv.signal();
                            }
                    }
                }
            }
            cv.wait();
        }
}

fn handleConnection(socket: TcpSocket)
{	
    let mut buffer      = RequestBuffer::new(socket_buf(socket));
    let     requestLine = buffer.readLine();
	
    io::println(requestLine);
    loop
    {
        let line = buffer.readLine();
		
        io::println(line);
        if (str::len(line) == 0)
        {
            break;
        }
    }
    io::stdout().flush();
    fail!(~"Now what ?");
}

fn main()
{	
    tcp::listen(
        ip::v4::parse_addr(IPV4_LOOPBACK),
        PORT,
        BACKLOG,
        &uv_iotask::spawn_iotask(task::task()),
        on_establish_callback,
        new_connection_callback);
}


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

Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and owner Simon Lewis is strictly prohibited.

Excerpts and links may be used, provided that full and clear credit is given to Simon Lewis and justanapplication.wordpress.com with appropriate and specific direction to the original content.

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