Fsockopen Power Plays

PHP's function fsockopen lets you open an Internet or Unix domain socket connection for connecting to a resource, and is one of the most powerful functions. fsockopen could be described as creating a direct link to the wire connected to a resource, which means you can send any information (EBCDIC, ASCII, Hex, C arrays, Raw) directly to the target server.

A Socket is like /dev/null

In unix you can send anything to the /dev/null device, for Windows think Recycle Bin, and likewise you can send anything to a socket created with fsockopen. I've seen fsockopen code that sends custom exploits to cisco routers, including being used by the metasploit framework. I've seen fsockopen telnet emulation, smtp/pop3 login, and a lot of other advanced raw networking that is exciting for me see.

Some Definitions for Fsockopen

client

A program that establishes connections for the purpose of sending requests.

server

An application program that accepts connections in order to service requests by sending back responses.

Simple Socket Explantion

A web server host listens on TCP port 80. When a client host wishes to view a resource on the web server, it establishes a TCP connection with the server host by opening a socket to send the request for the resource. When the connection is established, the client and server exchange requests and responses (respectively) until the connection is closed or aborted.

HTTP and fsockopen

The Snoopy class is bundled with WordPress distributions and uses fsockopen to achieve most of its cool features. WordPress core, plugins, and other included files and classes also use the fsockopen function to communicate via HTTP.

Fsockopen Examples

Note the warning sign, fsockopen is dangerous in the sense that you can crash your server, perform a DOS against your own server or other site, use up all your servers available sockets and fd descriptors, use up your bandwidth, etc.. Shouldn't be a problem unless you are being malicious or careless.

Here are some BOSS fsockopen functions I hacked together yesterday for use in my AskApache Crazy Cache WordPress Plugin. I've used code and ideas from 100's of authors, projects, and docs to try to make this the very best I can.

Intro

This is a working example employing as many of the best-practices, tips, and tricks for using fsockopen on remote streams that I could find.

<?php
// max time for script execution
if(!@defined('AA_MAX_TIME')) define('AA_MAX_TIME',  60);
 
// max time for socket reads
if(!@defined('AA_RECV_TIME')) define('AA_RECV_TIME', 30);
 
// max time for socket connect
if(!@defined('AA_CONN_TIME')) define('AA_CONN_TIME', 5);
 
// linebreak
if(!@defined('AA_LF')) define('AA_LF', chr(13).chr(10));
 
// ignore TCP RST i.e. browser stop button
@ignore_user_abort(1);
 
// set the script execution time
@set_time_limit(AA_MAX_TIME);
 
// set the default socket timeout value
@ini_set("default_socket_timeout",AA_RECV_TIME);
 
// output implicitly
@ob_implicit_flush(1);
 
// for binary freads
@set_magic_quotes_runtime(0);
 
// keep track of script execution time
$aa_time=time();
 
// download each of these urls using fsockopen
aa_dl('http://httpd.apache.org');
aa_dl('http://www.w3.org');
aa_dl('http://www.google.com');
aa_dl('http://www.freebsd.org/cgi/man.cgi?query=connect&sektion=2&apropos=0&manpath=FreeBSD+7.0-RELEASE');
aa_dl('http://www.askapache.com/htaccess/htaccess.html');
aa_dl('http://www.php.net');
aa_dl('http://en.wikipedia.org/wiki/Main_Page');
 
/*  returns a socket pointer if valid or displays an error message
    sets stream timeout, starts the clock to check for socket read time */
function askapache_get_sock($target,$port){
  global $aa_time_start;
  $aa_time_start=time();
  if(false===($fp = @fsockopen($target,$port,$errno,$errstr,AA_CONN_TIME))||!is_resource($fp))
    return askapache_sock_strerror($errno,$errstr);
  @stream_set_timeout($fp, AA_RECV_TIME);
  return $fp;
}
 
/*  writes request, then reads response until EOF, script max, or socket max
    returns response on success.  Uses buffer to allow size>100megs */
function askapache_txrx($fp,$request,$chunk=1024){
  $rec=$buf='';
  if(!@fwrite($fp, $request, strlen($request)))die('fwrite error');
  while ( !@feof($fp) && askapache_time_ok(askapache_time_passed())){
    $buf = @fread($fp, $chunk);
    $rec .= $buf;
  }
  if(!@fclose($fp))die('fclose error');
  return $rec;
}
 
/* initiates the socket and download for the passed url.
   automatically handles gzip, chunked, both, and plain downloads.
   uses the long2ip/ip2long for ip validation, uses gethostbyname to
   get the ipv4 address which saves fsockopen from having to do the lookup
   final data is saved to $rbody but currently only displays headers.*/
function aa_dl($url=NULL){
  global $aa_time;
  $ub = @parse_url($url);
  if(!isset($ub['host'])||empty($ub['host'])) die("bad url $url");
  $proto   = ($ub['scheme']=='https')?'ssl://':'';
  $port   = (isset($ub['port'])&&!empty($ub['port'])) ? $ub['port']:($proto!='')?443:80;
  $path   = (isset($ub['path'])&&!empty($ub['path'])) ? $ub['path']:'/';
  $query   = (isset($ub['query'])&&!empty($ub['query'])) ? '?'.$ub['query'] : '';
  $host   = $ub['host'];
  $ipp     = @gethostbyname($host);
  $ip     = ($ipp!=$host) ? long2ip(ip2long($ipp)) : $host;
 
  $headers=array(
   "GET {$path}{$query} HTTP/1.1",
   "Host: {$host}",
   'User-Agent: Mozilla/5.0 (AskApache/; +http://www.askapache.com/)',
   'Accept: text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,*/*;q=0.5',
   'Accept-Language: en-us,en;q=0.5',
   'Accept-Encoding: gzip,deflate',
   'Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7',
   'Connection: close','Referer: http://www.askapache.com'
  );
  $request=join(AA_LF,$headers).AA_LF.AA_LF;
 
  $fp=askapache_get_sock($proto.$ip, $port);
  if($fp){
    $rbody=$rec='';$resp_headers=array();
    $rec=askapache_txrx($fp,$request);
    list($resp_headers, $rbody) = explode(AA_LF.AA_LF, trim($rec), 2);
  echo "n<p>$request</p>n<p>$resp_headers</p>n";
    $gzip2=(stripos($resp_headers,'Content-Encoding')!==false &&
        stripos($resp_headers,'gzip')!==false)?1:0;
    $chunk=(stripos($resp_headers,'Transfer-Encoding')!==false &&
        stripos($resp_headers,'chunked')!==false)?1:0;
    $rbody=aa_decode_body($rbody,$chunk,$gzip2);
    unset($rbody);
  }
}
 
/* based on http://us.php.net/manual/en/function.fsockopen.php#75175
   ungzips and/or re-assembles transfer-encoded:chunked responses
   returns the good response on success */
function aa_decode_body ($str, $chunked, $gzipped){
  if($gzipped && !$chunked) return aa_gzdecode($str);
  if(!$gzipped && !$chunked) return $str;
  $tmp = $str; $str = '';
  do {
    $tmp = ltrim($tmp);
    $pos = strpos($tmp,AA_LF);
    $len = hexdec(substr($tmp, 0, $pos));
    if($gzipped) $str .= gzinflate(substr($tmp,($pos+12),$len));
    else $str .=substr($tmp,($pos+2),$len);
    $tmp = substr($tmp,($len+$pos+2));
  $chk=trim($tmp);
  } while (!empty($chk));
  return $str;
}
 
/*  based on http://us2.php.net/manual/en/function.gzencode.php#82520
  saves the gzipped data to a tempfile, then outputs the decoded
  data to the output buffer using readgzfile, returning the decoded
  buffer and deleting the tempfile on success */
function aa_gzdecode($data){
  $g=tempnam('/tmp','ff');
  @file_put_contents($g,$data);
  ob_start(); readgzfile($g); $d=ob_get_clean(); @unlink($g);
  return $d;
}
 
/*  very cool!  this is run during socket reads and checks whether the script
  execution time limit or the socket read time limit has been met, killing
  the script if so, otherwise returns true.  Run with a cron-like process */
function askapache_time_ok($sock_time=0) {
  global $aa_time;
  if (time()-$aa_time>AA_MAX_TIME)
    die('killed script.. time exceeded '.AA_MAX_TIME.' Total: '.$total);
  if ($sock_time>AA_RECV_TIME)
    die('Killed socket.. time exceeded '.AA_RECV_TIME.' Total: '.$sock_time);
  return true;
}
 
/* input for askapache_time_ok to keep track of each socket read time time. */
function askapache_time_passed() {
  global $aa_time_start;
  return (time() - $aa_time_start);
}
 
/*  handles fsockopen errors, printing them out though you may want to die on err */
function askapache_sock_strerror($errno,$errstr){
  switch($errno){
    case -3:  $err="Socket creation failed"; break;
    case -4:  $err="DNS lookup failure"; break;
    case -5:  $err="Connection refused or timed out"; break;
    case 111: $err="Connection refused"; break;
    case 113: $err="No route to host"; break;
    case 110: $err="Connection timed out"; break;
    case 104: $err="Connection reset by client"; break;
    default:  $err="Connection failed"; break;
  }
  echo '<p>Fsockopen failed!'."n[".$errno."] ".$err." (".$errstr.")</p>";
  return false;
}
?>

Debugging Fsockopen

If you really want to know more about fsockopen, you can do what I did and read all the relevant php source files, your OS sys, lib, and user files relevant to fsockopen, and of course you can always trace php using the fsockopen function to get an under-the-hood look at what in the world fsockopen is doing. Personally, I was trying to find more error codes and error strings to display when an fsockopen call failed, and I ended up finding over 50..

fsockopen Errors

function fsockopen_err($errnum)
{
   static $fsockopen_errors;
   is_null($fsockopen_errors) && $fsockopen_errors = array(
  0 => 'Success',
  1 => 'Operation not permitted',
  2 => 'No such file or directory',
  3 => 'No such process',
  4 => 'Interrupted system call - DNS lookup failure',
  5 => 'Input/output error - Connection refused or timed out',
  6 => 'No such device or address',
  7 => 'Argument list too long',
  8 => 'Exec format error',
  9 => 'Bad file descriptor',
  10 => 'No child processes',
  11 => 'Resource temporarily unavailable',
  12 => 'Cannot allocate memory',
  13 => 'Permission denied',
  14 => 'Bad address',
  15 => 'Block device required',
  16 => 'Device or resource busy',
  17 => 'File exists',
  18 => 'Invalid cross-device link',
  19 => 'No such device',
  20 => 'Not a directory',
  21 => 'Is a directory',
  22 => 'Invalid argument',
  23 => 'Too many open files in system',
  24 => 'Too many open files',
  25 => 'Inappropriate ioctl for device',
  26 => 'Text file busy',
  27 => 'File too large',
  28 => 'No space left on device',
  29 => 'Illegal seek',
  30 => 'Read-only file system',
  31 => 'Too many links',
  32 => 'Broken pipe',
  33 => 'Numerical argument out of domain',
  34 => 'Numerical result out of range',
  35 => 'Resource deadlock avoided',
  36 => 'File name too long',
  37 => 'No locks available',
  38 => 'Function not implemented',
  39 => 'Directory not empty',
  40 => 'Too many levels of symbolic links',
  41 => 'Unknown error 41',
  42 => 'No message of desired type',
  43 => 'Identifier removed',
  44 => 'Channel number out of range',
  45 => 'Level 2 not synchronized',
  46 => 'Level 3 halted',
  47 => 'Level 3 reset',
  48 => 'Link number out of range',
  49 => 'Protocol driver not attached',
  50 => 'No CSI structure available',
  51 => 'Level 2 halted',
  52 => 'Invalid exchange',
  53 => 'Invalid request descriptor',
  54 => 'Exchange full',
  55 => 'No anode',
  56 => 'Invalid request code',
  57 => 'Invalid slot',
  58 => 'Unknown error 58',
  59 => 'Bad font file format',
  60 => 'Device not a stream',
  61 => 'No data available',
  62 => 'Timer expired',
  63 => 'Out of streams resources',
  64 => 'Machine is not on the network',
  65 => 'Package not installed',
  66 => 'Object is remote',
  67 => 'Link has been severed',
  68 => 'Advertise error',
  69 => 'Srmount error',
  70 => 'Communication error on send',
  71 => 'Protocol error',
  72 => 'Multihop attempted',
  73 => 'RFS specific error',
  74 => 'Bad message',
  75 => 'Value too large for defined data type',
  76 => 'Name not unique on network',
  77 => 'File descriptor in bad state',
  78 => 'Remote address changed',
  79 => 'Can not access a needed shared library',
  80 => 'Accessing a corrupted shared library',
  81 => '.lib section in a.out corrupted',
  82 => 'Attempting to link in too many shared libraries',
  83 => 'Cannot exec a shared library directly',
  84 => 'Invalid or incomplete multibyte or wide character',
  85 => 'Interrupted system call should be restarted',
  86 => 'Streams pipe error',
  87 => 'Too many users',
  88 => 'Socket operation on non-socket',
  89 => 'Destination address required',
  90 => 'Message too long',
  91 => 'Protocol wrong type for socket',
  92 => 'Protocol not available',
  93 => 'Protocol not supported',
  94 => 'Socket type not supported',
  95 => 'Operation not supported',
  96 => 'Protocol family not supported',
  97 => 'Address family not supported by protocol',
  98 => 'Address already in use',
  99 => 'Cannot assign requested address',
  100 => 'Network is down',
  101 => 'Network is unreachable',
  102 => 'Network dropped connection on reset',
  103 => 'Software caused connection abort',
  104 => 'Connection reset by peer',
  105 => 'No buffer space available',
  106 => 'Transport endpoint is already connected',
  107 => 'Transport endpoint is not connected',
  108 => 'Cannot send after transport endpoint shutdown',
  109 => 'Too many references: cannot splice',
  110 => 'Connection timed out',
  111 => 'Connection refused',
  112 => 'Host is down',
  113 => 'No route to host',
  114 => 'Operation already in progress',
  115 => 'Operation now in progress',
  116 => 'Stale NFS file handle',
  117 => 'Structure needs cleaning',
  118 => 'Not a XENIX named type file',
  119 => 'No XENIX semaphores available',
  120 => 'Is a named type file',
  121 => 'Remote I/O error',
  122 => 'Disk quota exceeded',
  123 => 'No medium found',
  124 => 'Wrong medium type',
  125 => 'Operation canceled'
  );
    return (isset($fsockopen_errors[$errnum])) ? $fsockopen_errors[$errnum] : $errnum;
}

If you would like to see all the errors on your particular machine:

for($i=0, $s=""; $i<250; $s=socket_strerror($i), $i++)
  !empty($s) && ('Unknown error' != (substr($s,0,13)) ) && print "{$i} => {$s}n";

Which outputs:

1 => Success
2 => Operation not permitted
3 => No such file or directory
4 => No such process
5 => Interrupted system call
6 => Input/output error
7 => No such device or address
8 => Argument list too long
9 => Exec format error
10 => Bad file descriptor
11 => No child processes
12 => Resource temporarily unavailable
13 => Cannot allocate memory
14 => Permission denied
15 => Bad address
16 => Block device required
17 => Device or resource busy
18 => File exists
19 => Invalid cross-device link
20 => No such device
21 => Not a directory
22 => Is a directory
23 => Invalid argument
24 => Too many open files in system
25 => Too many open files
26 => Inappropriate ioctl for device
27 => Text file busy
28 => File too large
29 => No space left on device
30 => Illegal seek
31 => Read-only file system
32 => Too many links
33 => Broken pipe
34 => Numerical argument out of domain
35 => Numerical result out of range
36 => Resource deadlock avoided
37 => File name too long
38 => No locks available
39 => Function not implemented
40 => Directory not empty
41 => Too many levels of symbolic links
43 => No message of desired type
44 => Identifier removed
45 => Channel number out of range
46 => Level 2 not synchronized
47 => Level 3 halted
48 => Level 3 reset
49 => Link number out of range
50 => Protocol driver not attached
51 => No CSI structure available
52 => Level 2 halted
53 => Invalid exchange
54 => Invalid request descriptor
55 => Exchange full
56 => No anode
57 => Invalid request code
58 => Invalid slot
60 => Bad font file format
61 => Device not a stream
62 => No data available
63 => Timer expired
64 => Out of streams resources
65 => Machine is not on the network
66 => Package not installed
67 => Object is remote
68 => Link has been severed
69 => Advertise error
70 => Srmount error
71 => Communication error on send
72 => Protocol error
73 => Multihop attempted
74 => RFS specific error
75 => Bad message
76 => Value too large for defined data type
77 => Name not unique on network
78 => File descriptor in bad state
79 => Remote address changed
80 => Can not access a needed shared library
81 => Accessing a corrupted shared library
82 => .lib section in a.out corrupted
83 => Attempting to link in too many shared libraries
84 => Cannot exec a shared library directly
85 => Invalid or incomplete multibyte or wide character
86 => Interrupted system call should be restarted
87 => Streams pipe error
88 => Too many users
89 => Socket operation on non-socket
90 => Destination address required
91 => Message too long
92 => Protocol wrong type for socket
93 => Protocol not available
94 => Protocol not supported
95 => Socket type not supported
96 => Operation not supported
97 => Protocol family not supported
98 => Address family not supported by protocol
99 => Address already in use
100 => Cannot assign requested address
101 => Network is down
102 => Network is unreachable
103 => Network dropped connection on reset
104 => Software caused connection abort
105 => Connection reset by peer
106 => No buffer space available
107 => Transport endpoint is already connected
108 => Transport endpoint is not connected
109 => Cannot send after transport endpoint shutdown
110 => Too many references: cannot splice
111 => Connection timed out
112 => Connection refused
113 => Host is down
114 => No route to host
115 => Operation already in progress
116 => Operation now in progress
117 => Stale NFS file handle
118 => Structure needs cleaning
119 => Not a XENIX named type file
120 => No XENIX semaphores available
121 => Is a named type file
122 => Remote I/O error
123 => Disk quota exceeded
124 => No medium found
125 => Wrong medium type
126 => Operation canceled

Tracing fsockopen using Strace

Once you save the above file on your site, you can use the strace tool to debug it. This is a tad overboard but way cool nevertheless!

strace -e trace=connect php -nef fsockopen-test.php

connect(3, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("66.33.216.129")}, 28) = 0
connect(3, {sa_family=AF_INET, sin_port=htons(80), sin_addr=inet_addr("192.87.106.226")}, 16) = -1 EINPROGRESS (Operation now in progress)

strace -e trace=network php -nef fsockopen-test.php

socket(PF_FILE, SOCK_STREAM, 0)         = 3
connect(3, {sa_family=AF_FILE, path="/var/run/.nscd_socket"}, 110) = -1 ENOENT (No such file or directory)
socket(PF_INET, SOCK_DGRAM, IPPROTO_IP) = 3
connect(3, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("66.33.216.129")}, 28) = 0
send(3, "2742211
httpd6apache3org
"..., 34, 0) = 34
recvfrom(3, "274221201200

httpd6apache3org"..., 1024, 0, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("66.33.216.129")}, [16]) = 50
socket(PF_INET6, SOCK_DGRAM, IPPROTO_IP) = -1 EAFNOSUPPORT (Address family not supported by protocol)
socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 3
connect(3, {sa_family=AF_INET, sin_port=htons(80), sin_addr=inet_addr("192.87.106.226")}, 16) = -1 EINPROGRESS (Operation now in progress)
getsockopt(3, SOL_SOCKET, SO_ERROR, [0], [4]) = 0
send(3, "GET / HTTP/1.1rnHost: httpd.apac"..., 356, MSG_DONTWAIT) = 356
recv(3, "HTTP/1.1 200 OKrnDate: Wed, 02 J"..., 8192, MSG_DONTWAIT) = 2609
recv(3, "", 8192, MSG_DONTWAIT)         = 0

strace -q -e trace=all php -nef fsockopen-test.php

mmap2(NULL, 266240, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb76ba000
munmap(0xb76ba000, 266240)              = 0
socket(PF_FILE, SOCK_STREAM, 0)         = 3
connect(3, {sa_family=AF_FILE, path="/var/run/.nscd_socket"}, 110) = -1 ENOENT (No such file or directory)
close(3)                                = 0
open("/etc/hosts", O_RDONLY)            = 3
fcntl64(3, F_GETFD)                     = 0
fcntl64(3, F_SETFD, FD_CLOEXEC)         = 0
fstat64(3, {st_mode=S_IFREG|0644, st_size=948, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7f6e000
read(3, "# /etc/hosts - dh2 generatedn127"..., 4096) = 948
read(3, "", 4096)                       = 0
close(3)                                = 0
munmap(0xb7f6e000, 4096)                = 0
socket(PF_INET, SOCK_DGRAM, IPPROTO_IP) = 3
connect(3, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("66.33.216.129")}, 28) = 0
send(3, "X~1
entwikipedia3org
"..., 34, 0) = 34
gettimeofday({1214998196, 656179}, NULL) = 0
poll([{fd=3, events=POLLIN, revents=POLLIN}], 1, 5000) = 1
ioctl(3, FIONREAD, [100])               = 0
recvfrom(3, "X~201200
entwikipedia3org
"..., 1024, 0, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("66.33.216.129")}, [16]) = 100
close(3)                                = 0
time(NULL)                              = 1214998196
gettimeofday({1214998196, 656754}, NULL) = 0
socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 3
fcntl64(3, F_GETFL)                     = 0x2 (flags O_RDWR)
fcntl64(3, F_SETFL, O_RDWR|O_NONBLOCK)  = 0
connect(3, {sa_family=AF_INET, sin_port=htons(80), sin_addr=inet_addr("208.80.152.2")}, 16) = -1 EINPROGRESS (Operation now in progress)
poll([{fd=3, events=POLLIN|POLLOUT|POLLERR|POLLHUP, revents=POLLOUT}], 1, 10000) = 1
getsockopt(3, SOL_SOCKET, SO_ERROR, [0], [4]) = 0
fcntl64(3, F_SETFL, O_RDWR)             = 0
send(3, "GET /wiki/Main_Page HTTP/1.1rnHo"..., 370, MSG_DONTWAIT) = 370
poll([{fd=3, events=POLLIN|POLLPRI|POLLERR|POLLHUP}], 1, 0) = 0
time(NULL)                              = 1214998196
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP, revents=POLLIN}], 1, 30000) = 1
recv(3, "HTTP/1.0 200 OKrnDate: Wed, 02 J"..., 8192, MSG_DONTWAIT) = 2896
time(NULL)                              = 1214998196
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP, revents=POLLIN}], 1, 30000) = 1
recv(3, "214!337i30733623w253wy21526EL227;227253261"..., 8192, MSG_DONTWAIT) = 5792
time(NULL)                              = 1214998196
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP, revents=POLLIN}], 1, 30000) = 1
recv(3, "420127321417yI347257371373344332330227245"..., 8192, MSG_DONTWAIT) = 7487
time(NULL)                              = 1214998197
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP, revents=POLLIN}], 1, 30000) = 1
recv(3, "", 8192, MSG_DONTWAIT)         = 0
close(3)                                = 0
write(1, "n<pre>GET /wiki/Main_Page HTTP/1"..., 1300

More Fsockopen Info

TCP Multiplexing

RFC 793: To allow for many processes within a single Host to use TCP communication facilities simultaneously, the TCP provides a set of addresses or ports within each host. Concatenated with the network and host addresses from the internet communication layer, this forms a socket. A pair of sockets uniquely identifies each connection. That is, a socket may be simultaneously used in multiple connections.

The binding of ports to processes is handled independently by each Host. However, it proves useful to attach frequently used processes (e.g., a "logger" or timesharing service) to fixed sockets which are made known to the public. These services can then be accessed through the known addresses. Establishing and learning the port addresses of other processes may involve more dynamic mechanisms.

TCP Connections

The reliability and flow control mechanisms described above require that TCPs initialize and maintain certain status information for each data stream. The combination of this information, including sockets, sequence numbers, and window sizes, is called a connection. Each connection is uniquely specified by a pair of sockets identifying its two sides.

When two processes wish to communicate, their TCP's must first establish a connection (initialize the status information on each side). When their communication is complete, the connection is terminated or closed to free the resources for other uses.

Since connections must be established between unreliable hosts and over the unreliable internet communication system, a handshake mechanism with clock-based sequence numbers is used to avoid erroneous initialization of connections.

Fsockopen Practical Uses

• Download Web Pages, Files, etc.
• Upload a file
• Send POST data to a form
• Emulate cron
• Download plugin updates
• Scan sites for exploits
• Auto Login to Google
• Pass wp-nonces via cookie headers, and more

Transfer-Encoding

RFC 2068

19.4.6 Introduction of Transfer-Encoding
 
   HTTP/1.1 introduces the Transfer-Encoding header field (section
   14.40).  Proxies/gateways MUST remove any transfer coding prior to
   forwarding a message via a MIME-compliant protocol.
 
   A process for decoding the "chunked" transfer coding (section 3.6)
   can be represented in pseudo-code as:
 
          length := 0
          read chunk-size, chunk-ext (if any) and CRLF
          while (chunk-size > 0) {
             read chunk-data and CRLF
             append chunk-data to entity-body
             length := length + chunk-size
             read chunk-size and CRLF
          }
          read entity-header
          while (entity-header not empty) {
             append entity-header to existing header fields
             read entity-header
          }
          Content-Length := length
          Remove "chunked" from Transfer-Encoding

Socket-Related Man Pages

DESCRIPTION
This  manual  page  describes the Linux networking socket layer user interface. The BSD compatible sockets are the uniform interface between
the user process and the network protocol stacks in the kernel.  The protocol modules are  grouped  into  protocol  families  like  PF_INET,
PF_IPX, PF_PACKET and socket types like SOCK_STREAM or SOCK_DGRAM.  See socket(2) for more information on families and types.
 
SOCKET LAYER FUNCTIONS
These  functions  are  used by the user process to send or receive packets and to do other socket operations. For more information see their
respective manual pages.
 
socket(2) creates a socket, connect(2) connects a socket to a remote socket address, the bind(2) function binds a socket to a  local  socket
address,  listen(2)  tells  the socket that new connections shall be accepted, and accept(2) is used to get a new socket with a new incoming
connection.  socketpair(2) returns two connected anonymous sockets (only implemented for a few local families like PF_UNIX)
 
send(2), sendto(2), and sendmsg(2) send data over a socket, and recv(2), recvfrom(2), recvmsg(2) receive data from a  socket.   poll(2)  and
select(2)  wait  for  arriving  data  or a readiness to send data.  In addition, the standard I/O operations like write(2), writev(2), send-
file(2), read(2), and readv(2) can be used to read and write data.
 
getsockname(2) returns the local socket address and getpeername(2) returns the remote socket address.  getsockopt(2) and  setsockopt(2)  are
used to set or get socket layer or protocol options.  ioctl(2) can be used to set or read some other options.
 
close(2) is used to close a socket.  shutdown(2) closes parts of a full duplex socket connection.
 
Seeking, or calling pread(2) or pwrite(2) with a non-zero position is not supported on sockets.
 
It  is possible to do non-blocking IO on sockets by setting the O_NONBLOCK flag on a socket file descriptor using fcntl(2).  Then all opera-
tions that would block will (usually) return with EAGAIN (operation should be retried later); connect(2) will return EINPROGRESS error.  The
user can then wait for various events via poll(2) or select(2).

From the FreeBSD man page for socket(2)

Sockets of type SOCK_STREAM are full-duplex byte streams, similar to
pipes.  A stream socket must be in a connected state before any data may
be sent or received on it.  A connection to another socket is created
with a connect(2) system call.  Once connected, data may be transferred
using read(2) and write(2) calls or some variant of the send(2) and
recv(2) functions.  (Some protocol families, such as the Internet family,
support the notion of an ``implied connect'', which permits data to be
sent piggybacked onto a connect operation by using the sendto(2) system
call.)  When a session has been completed a close(2) may be performed.
Out-of-band data may also be transmitted as described in send(2) and
received as described in recv(2).
 
The communications protocols used to implement a SOCK_STREAM insure that
data is not lost or duplicated.  If a piece of data for which the peer
protocol has buffer space cannot be successfully transmitted within a
reasonable length of time, then the connection is considered broken and
calls will indicate an error with -1 returns and with ETIMEDOUT as the
specific code in the global variable errno.  The protocols optionally
keep sockets ``warm'' by forcing transmissions roughly every minute in
the absence of other activity.  An error is then indicated if no response
can be elicited on an otherwise idle connection for an extended period
(e.g. 5 minutes).  A SIGPIPE signal is raised if a process sends on a
broken stream; this causes naive processes, which do not handle the sig-
nal, to exit.

Have Fun ;)

define ('SOCKET_EPERM', 1);
define ('SOCKET_ENOENT', 2);
define ('SOCKET_EINTR', 4);
define ('SOCKET_EIO', 5);
define ('SOCKET_ENXIO', 6);
define ('SOCKET_E2BIG', 7);
define ('SOCKET_EBADF', 9);
define ('SOCKET_EAGAIN', 11);
define ('SOCKET_ENOMEM', 12);
define ('SOCKET_EACCES', 13);
define ('SOCKET_EFAULT', 14);
define ('SOCKET_ENOTBLK', 15);
define ('SOCKET_EBUSY', 16);
define ('SOCKET_EEXIST', 17);
define ('SOCKET_EXDEV', 18);
define ('SOCKET_ENODEV', 19);
define ('SOCKET_ENOTDIR', 20);
define ('SOCKET_EISDIR', 21);
define ('SOCKET_EINVAL', 22);
define ('SOCKET_ENFILE', 23);
define ('SOCKET_EMFILE', 24);
define ('SOCKET_ENOTTY', 25);
define ('SOCKET_ENOSPC', 28);
define ('SOCKET_ESPIPE', 29);
define ('SOCKET_EROFS', 30);
define ('SOCKET_EMLINK', 31);
define ('SOCKET_EPIPE', 32);
define ('SOCKET_ENAMETOOLONG', 36);
define ('SOCKET_ENOLCK', 37);
define ('SOCKET_ENOSYS', 38);
define ('SOCKET_ENOTEMPTY', 39);
define ('SOCKET_ELOOP', 40);
define ('SOCKET_EWOULDBLOCK', 11);
define ('SOCKET_ENOMSG', 42);
define ('SOCKET_EIDRM', 43);
define ('SOCKET_ECHRNG', 44);
define ('SOCKET_EL2NSYNC', 45);
define ('SOCKET_EL3HLT', 46);
define ('SOCKET_EL3RST', 47);
define ('SOCKET_ELNRNG', 48);
define ('SOCKET_EUNATCH', 49);
define ('SOCKET_ENOCSI', 50);
define ('SOCKET_EL2HLT', 51);
define ('SOCKET_EBADE', 52);
define ('SOCKET_EBADR', 53);
define ('SOCKET_EXFULL', 54);
define ('SOCKET_ENOANO', 55);
define ('SOCKET_EBADRQC', 56);
define ('SOCKET_EBADSLT', 57);
define ('SOCKET_ENOSTR', 60);
define ('SOCKET_ENODATA', 61);
define ('SOCKET_ETIME', 62);
define ('SOCKET_ENOSR', 63);
define ('SOCKET_ENONET', 64);
define ('SOCKET_EREMOTE', 66);
define ('SOCKET_ENOLINK', 67);
define ('SOCKET_EADV', 68);
define ('SOCKET_ESRMNT', 69);
define ('SOCKET_ECOMM', 70);
define ('SOCKET_EPROTO', 71);
define ('SOCKET_EMULTIHOP', 72);
define ('SOCKET_EBADMSG', 74);
define ('SOCKET_ENOTUNIQ', 76);
define ('SOCKET_EBADFD', 77);
define ('SOCKET_EREMCHG', 78);
define ('SOCKET_ERESTART', 85);
define ('SOCKET_ESTRPIPE', 86);
define ('SOCKET_EUSERS', 87);
define ('SOCKET_ENOTSOCK', 88);
define ('SOCKET_EDESTADDRREQ', 89);
define ('SOCKET_EMSGSIZE', 90);
define ('SOCKET_EPROTOTYPE', 91);
define ('SOCKET_ENOPROTOOPT', 92);
define ('SOCKET_EPROTONOSUPPORT', 93);
define ('SOCKET_ESOCKTNOSUPPORT', 94);
define ('SOCKET_EOPNOTSUPP', 95);
define ('SOCKET_EPFNOSUPPORT', 96);
define ('SOCKET_EAFNOSUPPORT', 97);
define ('SOCKET_EADDRINUSE', 98);
define ('SOCKET_EADDRNOTAVAIL', 99);
define ('SOCKET_ENETDOWN', 100);
define ('SOCKET_ENETUNREACH', 101);
define ('SOCKET_ENETRESET', 102);
define ('SOCKET_ECONNABORTED', 103);
define ('SOCKET_ECONNRESET', 104);
define ('SOCKET_ENOBUFS', 105);
define ('SOCKET_EISCONN', 106);
define ('SOCKET_ENOTCONN', 107);
define ('SOCKET_ESHUTDOWN', 108);
define ('SOCKET_ETOOMANYREFS', 109);
define ('SOCKET_ETIMEDOUT', 110);
define ('SOCKET_ECONNREFUSED', 111);
define ('SOCKET_EHOSTDOWN', 112);
define ('SOCKET_EHOSTUNREACH', 113);
define ('SOCKET_EALREADY', 114);
define ('SOCKET_EINPROGRESS', 115);
define ('SOCKET_EISNAM', 120);
define ('SOCKET_EREMOTEIO', 121);
define ('SOCKET_EDQUOT', 122);
define ('SOCKET_ENOMEDIUM', 123);
define ('SOCKET_EMEDIUMTYPE', 124);

• Hypertext Transfer Protocol — HTTP/1.1, RFC 2616. R. Fielding et al.
• Hypertext ransport Protocol HTTP/1.1. J. Gettys. (slides)
• What's wrong with HTTP (and why it doesn't matter).J. C. Mogul. (PDF slides)
• Network Performance Effects of HTTP/1.1, CSS1, and PNG.H. F. Nielsen, J. Gettys et al.
• Mozilla's HTTP/1.1 Pipelining FAQ. D. Fisher.
• Wikipedia: HTTP proxy.

July 2nd, 2008

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