In the example at http://alx3apps.appspot.com/jsonrpc_example/ when I click the submit button, I notice (by using Firebug) that my browser submits the source:
{"params":["Hello ","Python!"],"method":"concat","id":1}
It's not posting a parameter (eg. json=[encoded string from above]), but rather just posting a raw string with the above value.
Is there an widely accepted way to replicated this via a GET request, or do I need to just urlencode the same string and include it as http://www.example.com/?json=%7b%22params%22%3a%5b%22Hello+%22%2c%22Python!%22%5d%2c%22method%22%3a%22concat%22%2c%22id%22%3a1%7d? I understand that some older browsers cannot handle a URI of more than 250 characters, but I'm OK with that.
A GET request doesn't usually transmit data in any other way besides headers, so you should pass the string encoded in the URL if you wish to use GET.
POST http://alx3apps.appspot.com/jsonrpc_example/json_service/ HTTP/1.1
Host: alx3apps.appspot.com
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-GB; rv:1.9.2.13) Gecko/20101203 Firefox/3.6.13
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-gb,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 115
Connection: keep-alive
Content-Type: application/json-rpc; charset=UTF-8
X-Requested-With: XMLHttpRequest
Referer: http://alx3apps.appspot.com/jsonrpc_example/
Content-Length: 55
Pragma: no-cache
Cache-Control: no-cache
{"params":["Howdy","Python!"],"method":"concat","id":1}
In a normal form post the header Content-Type: application/x-www-form-urlencoded lets the server know to expect the format in key=val format whereas the page you linked sends Content-Type: application/json-rpc; charset=UTF-8. After the headers (which are terminated with the blank line) the data follows in the specified format.
You are correct that only POST submits data separately from the URI. So urlencoding it into the querystring is the only way to go, if you must use GET. (Well, I suppose you could try setting custom request headers or using cookies, but the only "widely accepted" way is to use the querystring.)
