155 lines
5.7 KiB
Plaintext
155 lines
5.7 KiB
Plaintext
<?page
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title=>LiveJournal Protocol
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body<=
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<?h1 Introduction h1?>
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<?p
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The following information is intended for developers interested in writing their own
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LiveJournal clients to talk to the LiveJournal server. End users <I>do not</I> need
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to know any of this, and are probably better off not knowing it. ;)
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p?>
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<?h1 Prerequisites h1?>
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<?p
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Before reading this document, it is assumed you know at least some basics about network programming,
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at least the whole idea of opening sockets and reading/writing to them. If not, this might
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be kinda confusing.
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p?>
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<?h1 It's really HTTP h1?>
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<?p
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If you already know the HTTP protocol, this is going to be really easy. For those of you
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who don't know, HTTP is the protocol that web browsers talk to web servers with. For simplicity
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of writing the LiveJournal server, we've decided to just use HTTP as our protocol transport.
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This way, we can also go through proxies at schools and corporations really easily and
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without drawing any attention.
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p?>
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<?h1 The Basics h1?>
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<?p
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Basically, sending a LiveJournal request is like this:
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p?>
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<OL>
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<LI>Open a socket to <B>www.livejournal.com</B> on port <B>80</B>
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<LI>Send an HTTP POST request, containing the request variables (mode, user, password, etc...)
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<LI>Read the socket to get the response. The response is really easy to parse.
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<LI>Close the socket. Do any approriate action based on the server's response.
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</OL>
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<?h1 Encoding the request h1?>
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<?p
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As mentioned previously, the request is sent as an HTTP POST request. Open your socket, and send a request looking like:
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p?>
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<UL>
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<FONT COLOR=#0000FF><B>
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<XMP>
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POST /interface/flat HTTP/1.0
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Host: www.livejournal.com
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Content-type: application/x-www-form-urlencoded
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Content-length: 34
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mode=login&user=test&password=test
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</XMP>
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</B></FONT>
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</UL>
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As you can pretty easily see, the variables TO the webserver are encoded in the form <B>var1=val1&var2=val2&....</B>. Note
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that you <B>must quote all values</B> or the values can interfere with the encoding form. For example, what if somebody's
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password was "blah&=2+&something=yeah". It's an ugly password, sure, but somebody may have it. And if they do, it'll mess
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up the pretty format of the encoding format. So, here are the rules on how to encode values:
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<UL>
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<LI>Leave all values from a-z, A-Z, and 0-9 alone. These are fine.
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<LI>Convert spaces to a <B>+</B> sign.
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<LI>Convert everything else to <B>%<I>hh</I></B> where <I>hh</I> is the hex representation of the character's ASCII value.
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</UL>
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So, for example, the phrase "I'm going to the mall" could encoded as "I%27m+going+to+the+mall". There should
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be CGI libraries for all major languages which do this encoding for you. If not, it isn't that hard to do it yourself.
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<?p
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After you construct the big long ugly string of variables/values, find the length of it and send it in the
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<I>Content-length</I> field, as in the example above. Then send a blank line, then the big long ugly string.
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p?>
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<?p
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<B>Note about line endings: </B> Please note that the end of lines should be a carriage return (ASCII 13, 0x0D) and then a newline (ASCII 10, 0x0A).
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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
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it's generally better to send both.
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p?>
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<?p
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Here is a typical response from the web server after sending your request:
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<UL>
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<FONT COLOR=#0000FF><B>
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<XMP>
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HTTP/1.1 200 OK
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Date: Sat, 23 Oct 1999 21:32:35 GMT
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Server: Apache/1.3.4 (Unix)
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Connection: close
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Content-Type: text/plain
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name
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Mr. Test Account
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success
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OK
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message
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Hello Test Account!
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</XMP></B></FONT>
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</UL>
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The top stuff is headers from the HTTP request. There may be a lot of other stuff in there too.
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First thing to do is make sure the first lines <B>ends with "200 OK"</B>. If the first line
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does not end with 200 OK, tell the user that an error occured on the server and that it's not their fault.
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If you see 200 OK at the end, proceed with parsing the output. The format is as follows:
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<UL>
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<XMP>
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variable
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value
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someothervariable
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someothervalue
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</XMP>
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</UL>
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The ordering of the variable/value pairs does not matter. As you read them in, read them into a hash
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structure. (associative array, dictionary, collection... whatever it's called in your language. Just
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a data structure that links one string variable key to another string variable value.)
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p?>
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<?p
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After your hash is loaded, proceed with the logic of reporting errors if needed, as governed by the
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variables and logic above.
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p?>
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<?h1 Protocol modes h1?>
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<?p
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Of course, knowing all the above isn't useful unless you actually know what operations
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the server supports....
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p?>
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<P><CENTER>
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<A HREF="modelist.bml"><FONT SIZE=+1>Protocol Mode Documentation</FONT></A>
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</CENTER>
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<?h1 Proxies h1?>
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<?p
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As a final feature, once you get that stuff working, is to implement support for HTTP proxies. This
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is <I>very</I> easy. Give the user a checkbox if they want to use a proxy or not, and if so, ask
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the proxy host and proxy port. Now, if they selected to use a proxy, do not connect to
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www.livejournal.com and port 80, but instead connect to their proxy host on whatever proxy
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port they specified. The rest is basically the same, except for one difference. Instead of doing:
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<UL>
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<XMP>
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POST /interface/flat HTTP/1.0
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</XMP>
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</UL>
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<p>You would do...
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<UL>
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<FONT COLOR=#0000FF><B><XMP>
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POST http://www.livejournal.com/interface/flat HTTP/1.0
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</XMP></B></FONT>
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</UL>
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<p>That's it! That line tells the proxy what host it needs to connect to in order to make the real request.
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The rest of the HTTP you should leave just as you did before.
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This should be all you need to know to make a LiveJournal client.
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p?>
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<?h1 Need more help? h1?>
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<?p
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If anything is unclear, join the <?ljuser lj_clients ljuser?> community, where all the client authors hang out.
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p?>
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<=body
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page?>
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