# Client / Server Protocol - Quick Reference

# Client / Server Protocol - Quick Reference

## Introduction to the Protocol

Before reading this document, it is assumed you know at least some basics about network programming, at least the whole idea of opening sockets and reading/writing to them. If not, this might be kinda confusing.

Basically, sending a LiveJournal request is like this:

### Handshake

1. Open a socket to www.livejournal.com on port 80

2. Send an HTTP POST request, containing the request variables (mode, user, password, etc...)

3. Read the socket to get the response. The response is really easy to parse.

4. Close the socket. Do any approriate action based on the server's response.

For example, your client would output a request:

    POST /interface/flat HTTP/1.0
    Host: www.livejournal.com
    Content-type: application/x-www-form-urlencoded
    Content-length: 34

    mode=login&user=test&password=test

All values must be quoted or the values can interfere with the encoding form. For example, if someone's password was blah&=2+&something=yeah, it could quite possibly ruin the encoding format. Here are some guidelines on how to encode values:

- Leave all values from a-z, A-Z, and 0-9 alone. These are fine.

- Convert spaces to a + (plus) sign.

- Convert everything else to %hh where hh is the hex representation of the character's ASCII value.

For example, the phrase I'm going to the mall could encoded as I%27m+going+to+the+mall. There should be CGI libraries for all major languages which do this encoding for you. If not, it isn't that hard to do it yourself.

After you construct the big long ugly string of variables/values, find the length of it and send it in the Content-length field, as in the example above. Then send a blank line, then the big long ugly string.

### Line Endings

Please note that the end of lines should be a carriage return (ASCII `13`, `0x0D`) and then a newline (ASCII `10`, `0x0A`). In Perl, C/C++ or Java this is \r\n. In Basic, this is `Chr(13)` & `Chr(10)`. Sending just the newline may work too, but it's generally better to send both.

A typical response would be:

    HTTP/1.1 200 OK
    Date: Sat, 23 Oct 1999 21:32:35 GMT
    Server: Apache/1.3.4 (Unix)
    Connection: close
    Content-Type: text/plain

    name
    Mr. Test Account
    success
    OK
    message
    Hello Test Account!

The top stuff is headers from the HTTP request. There may be a lot of other stuff in there too. First thing to do is make sure the first lines ends with `200 OK`. If the first line does not end with `200 OK`, tell the user that an error occurred on the server and that it's not their fault. If you see `200 OK` at the end, proceed with parsing the output. The format is as follows:

    variable
    value
    someothervariable
    someothervalue

The ordering of the variable/value pairs does not matter. As you read them in, read them into a hash structure (associative array, dictionary, collection…whatever it's called in your language. Just a data structure that links one string variable key to another string variable value.).

After your hash is loaded, proceed with the logic of reporting errors if needed, as governed by the variables and logic above.

## Working with Proxies

As a final feature, once you get that stuff working, is to implement support for HTTP proxies. This is very easy. Give the user a checkbox if they want to use a proxy or not, and if so, ask the proxy host and proxy port. Now, if they selected to use a proxy, do not connect to www.livejournal.com and port 80, but instead connect to their proxy host on whatever proxy port they specified. The rest is basically the same, except for one difference. Instead of doing:

    POST /interface/flat HTTP/1.0

You would do:

    POST http://www.livejournal.com/interface/flat HTTP/1.0

That line tells the proxy what host it needs to connect to in order to make the real request. The rest of the HTTP you should leave just as you did before.

## Client Developer Community

If you ever have any questions about building clients for LiveJournal, then you'd probably interested in the lj_clients community on LiveJournal.com