CLIPSockets

Write CLIPS code that can talk to the internet!

Forward

• This repository is for educational purposes only :)
• I have only tested this codebase in Ubuntu 23.10 so far
• the library is only built for linux-based systems for now
• Don't know CLIPS? Try the Tour of CLIPS I wrote to learn!

High-Level Functionality Provided

Create a server that listens, accepts, and reads a message from a client:

         CLIPS (Forge Alpha 5/12/24)
CLIPS> (create-socket AF_INET SOCK_STREAM)
3
CLIPS> (bind-socket 3 127.0.0.1 8889)
127.0.0.1:8889
CLIPS> (listen 3) ; NOTE: 127.0.0.1:8889 would work here, too
TRUE
CLIPS> (accept 3) ; NOTE: 127.0.0.1:8889 would work here, too
4
CLIPS> (get-socket-logical-name 4)
127.0.0.1:42616
CLIPS> (readline 127.0.0.1:42616)

A client that would connect to that server would look like this:

         CLIPS (Forge Alpha 5/12/24)
CLIPS> (create-socket AF_INET SOCK_STREAM)
3
CLIPS> (connect 3 127.0.0.1 8889)
127.0.0.1:8889
CLIPS> (printout 127.0.0.1:8889 "Hello, server :)" crlf)
CLIPS> (flush-connection 3) ; NOTE: 127.0.0.1:8889 would work here, too
TRUE

You should see the message from the client in the previously mentioned server's rules engine when the client flushes their connection!

Immediate Purpose

Provide low-level networking functions to CLIPS environments via socket file descriptors. Allows CLIPS-based applications to send and receive messages to/from other computers on a network via I/O Router¹-based reading and writing operations.

This library adds functions that let you create network servers and clients. That is: you can make CLIPS applications that receive network requests and make network requests.

It does not currently support DNS resolution: you'll need to know the IP/PORT combination or location of unix socket instead of the URL you use to get to a site in your browser for now.

Long-Term Goals

Educational purposes for now. I would like to get the quality of code in this repo ready for upstream merging into CLIPS someday. For now, it's so I can make some fun web applications using CLIPS!

Installation

The project can be built from the root directory with make:

make

This will create the binary clips file in the root directory. Use this to run the example server and client network applications provided by the files in the examples directory.

Example Servers

There are 4 example servers provided in this repository and 3 clients.

The simplest server receives a single tcp connection and then exits. The other can be used to serve multiple concurrent requests until it is ctrl+z and killed.

./clips -f2 examples/server-simple.bat

or

./clips -f2 examples/server-complex.bat

Example Client

./clips -f2 examples/client.bat

Other ways to test things out

You should now also be able to connect to 127.0.0.1:8888 via telnet, curl, or a browser.

curl

curl --http0.9 http://localhost:8888/

telnet

telnet localhost 8888

Browser

Visit http://localhost:8888 in the browser of your choice. The message displayed back is the first line of text that your browser sends to the webserver under the hood. This can be used to build web applications that let the users navigate to different "pages" in your web app. For example, if you try to go to http://localhost:8888/asdf-123, you'll see a slightly different message.

Notes for Developers

API

(accept ?socketfdOrLogicalName)

Accepts a connection on a socket file descriptor. Returns an integer representing the client's file descriptor or FALSE if it fails.

(bind-socket ?socketfd ?ipOrDir <?port>)

Binds a socket to a given IP/PORT or directory (in case of unix sockets). Returns an integer representing the client's file descriptor or FALSE if it fails.

(connect ?socketfd ?ipOrDir <?port>)

Connects a socket to a given IP/PORT or directory (in case of unix sockets). Returns the logical name of the connection that can be read/written, or FALSE if it fails.

(close-connection ?socketfdOrLogicalName)

Closes a socket bound or connected on a given IP/PORT or directory (in case of unix sockets). Returns TRUE if connection closed successfully, FALSE if it fails.

(create-socket ?domain ?type <?protocol>)

Binds a socket to a given IP/PORT or directory (in case of unix sockets). Returns an integer representing the client's file descriptor or FALSE if it fails.

The following domains are currently supported:

• AF_UNIX: used for unix sockets
• AF_INET: IPv4
• AF_INET6: IPv6

The following types are currently supported:

• SOCK_STREAM: typically used for TCP
• SOCK_DGRAM: typically used for UDP

Protocol is optional and can typically be left blank.

(empty-connection ?socketfdOrLogicalName)

Use this to "empty" the buffer of data received from the client. WARNING: If this is run on a blocking request, you may block indefinitely.

(errno) and (errno-sym)

Returns errno, a global variable set when errors occur with some socket functions. For example, if you try to bind twice on a socket:

$ ./clips                                                                                                  
         CLIPS (Forge Alpha 5/12/24)                                                                                                   
CLIPS> (errno)                                                                                                                                                                                                                                                                
0                                                                                                                                                                                                                                                                             
CLIPS> (errno-sym)                                                                                                                     
CLIPS> (create-socket AF_INET SOCK_STREAM)                                                                                                                                                                                                                                    
3                                                                                                                                                                                                                                                                             
CLIPS> (bind-socket 3 127.0.0.1 8889)                                                                                                                                                                                                                                         
127.0.0.1:8889                                                                                                                                                                                                                                                                
CLIPS> (bind-socket 3 127.0.0.1 8887)                                                                                                                                                                                                                                         
Could not bind 127.0.0.1                                                                                                                                                                                                                                                      
perror: Invalid argument                                                                                                                                                                                                                                                      
FALSE                                                                                                                                                                                                                                                                         
CLIPS> (errno)                                                                                                                                                                                                                                                                
22                                                                                                                                                                                                                                                                            
CLIPS> (errno-sym)                                                                                                                                                                                                                                                            
EINVAL

(fcntl-add-status-flags ?socketfdOrLogicalName $?flags)

(fcntl-remove-status-flags ?socketfdOrLogicalName $?flags)

Add/remove certain flags on a socket as specified after the socket fd or logical name.

The following flags are currently supported:

• O_NONBLOCK
• O_APPEND
• O_ASYNC

(flush-connection ?socketfdOrLogicalName)

Flushes the buffer to the recipient.

(get-socket-logical-name ?socketfd)

Converts an integer representing a socket file descriptor to a symbol representing the name of the I/O router. Use this name to read and write to the socket.

(get-timeout ?socketfdOrLogicalName)

(set-timeout ?socketfdOrLogicalName ?microseconds)

Gets or Sets the timeout on the socket in microseconds.

(listen ?socketfdOrLogicalName ?backlog)

Listens for connections on a socket. After running this, you can now (accept clients connecting to your server via the socket.

(poll ?socketfdOrLogicalName ?milliseconds $?optionalFlags)

Polls the socket for a number of milliseconds for any given number of flags.

Specify 0 as ?milliseconds so that it returns immediately.

Possible flags:

• POLLIN
• POLLOUT
• POLLERR
• POLLHUP
• POLLNVAL
• POLLPRI
• POLLRDNORM
• POLLRDBAND
• POLLWRNORM
• POLLWRBAND

Returns TRUE if it got the FLAG, FALSE if it did not before timeout expires.

(getsockopt ?socketfdOrLogicalName ?level ?optionName)

(setsockopt ?socketfdOrLogicalName ?level ?optionName ?value)

Gets or Sets options on the socket.

Possible values for ?level currently supported:

• SOL_SOCKET
• IPPROTO_TCP

Possible values for ?optionName currently supported:

• SO_REUSEADDR
• TCP_NODELAY

?value is an integer to set the flag to.

(set-fully-buffered ?socketfdOrLogicalName)

(set-not-buffered ?socketfdOrLogicalName)

(set-line-buffered ?socketfdOrLogicalName)

Changes the buffering style for a connection. As a means of example, stderr is "not buffered," stdout via your terminal is probably "line buffered," and files are normally "block buffered."

(shutdown-connection ?socketfdOrLogicalName ?optionalHow)

Shut down part or all of a full-duplex connection.

Possible values of ?optionalHow:

• SHUT_RD: further receptions will be disallowed
• SHUT_WR: further transmissions will be disallowed
• SHUT_RDWR: further receptions and transmissions will be disallowed

Debugging

In order to watch all activity on your computer's port 8888 (which the example server and client use by default), use tcpdump. You may need to run as root or with sudo:

tcpdump -nn -i any port 8888

Small technical braindump

This codebase is based on CLIPS 7.0.x released on 5/12/24. I added a socketrtr.h and socketrtr.c to support reading/writing to sockets. I add user defined functions (UDFs) to CLIPS environments compiled with this source code in userfunctions.c. I initialize the socket router in router.c inside of the function InitializeDefaultRouters.

Footnotes

1. See Section 9: I/O Routers of the CLIPS Advanced Programming Guide ↩