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POUsing JSON-RPC call from Pyjamas/PyJs with a web.py backend
 

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  1. POUsing JSON-RPC call from Pyjamas/PyJs with a web.py backend
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    <p>This has already cost me many hours of Googling and I still cannot get it working, time to ask SO for help :-)</p> <p>I try to put together a simple test application where the frontend is written in Pyjamas, the backend is running on <a href="http://webpy.org" rel="nofollow">Web.py</a>. They are supposed to talk to each other via JSON-RPC. The desired functionality is to let the user enter a string which is then converted to uppercase. </p> <p>There is a description in the Pyjamas online book <a href="http://pyjs.org/book/Bookreader.html#Rest%20of%20the%20World" rel="nofollow">"Rest of the World"</a> on how to use JSON-RPC which presents various technologies mixed together and is therefore difficult to parse. By looking at hints e.g. from <a href="http://amundblog.blogspot.co.at/2008/12/ajax-with-python-combining-pyjs-and.html" rel="nofollow">Amund Tveit's blog</a> etc. I cobbled together the following:</p> <p>1) The <strong>server script</strong> which is really simple:</p> <pre><code>import web import json import os urls = ( '/json', 'JSONHandler', '/json/', 'JSONHandler', ) app = web.application(urls, globals()) class JSONHandler: def json_upper(self,args): return [args[0].upper()] def json_markdown(self,args): return [args[0].lower()] def POST(self): args = json.loads(web.data()) print args json_func = getattr(self, 'json_%s' % args[u"method"]) json_params = args[u"params"] json_method_id = args[u"id"] result = json_func(json_params) # reuse args to send result back args.pop(u"method") args["result"] = result[0] args["error"] = None # IMPORTANT!! web.header("Content-Type","text/html; charset=utf-8") return json.dumps(args) if __name__ == "__main__": app.run() </code></pre> <p>and it <strong>definitely works</strong>, tested with a simple query script (not shown) that relies on <a href="https://github.com/joshmarshall/jsonrpclib" rel="nofollow">Josh Marshall's JSON-RPC library</a>.</p> <p>2) The <strong>client-script for Pyjamas</strong> which is also straightforward:</p> <pre><code># Client example from Amund Tveit's blog # http://amundblog.blogspot.co.at/2008/12/ajax-with-python-combining-pyjs-and.html # note: ui and JSONService were not prefixed with pyjamas, but that's needed from pyjamas.ui import RootPanel, TextArea, Label, Button, HTML, VerticalPanel, HorizontalPanel, ListBox from pyjamas.JSONService import JSONProxy class Client: def onModuleLoad(self): self.TEXT_WAITING = "Waiting for response..." self.TEXT_ERROR = "Server Error" # This is the remote service self.remote_server = UpperService() self.status=Label() self.text_area = TextArea() self.text_area.setText(r"Please uppercase this string") self.text_area.setCharacterWidth(80) self.text_area.setVisibleLines(8) self.button_py = Button("Send to Python Service", self) buttons = HorizontalPanel() buttons.add(self.button_py) buttons.setSpacing(8) info = r'Upper-case a string using JSON-RPC' panel = VerticalPanel() panel.add(HTML(info)) panel.add(self.text_area) panel.add(buttons) panel.add(self.status) RootPanel().add(panel) def onClick(self, sender): self.status.setText(self.TEXT_WAITING) text = self.text_area.getText() # (data, response_class): if the latter is 'self', then # the response is handled by the self.onRemoteResponse() method if self.remote_server.upper(self.text_area.getText(), self) &lt; 0: self.status.setText(self.TEXT_ERROR) def onRemoteResponse(self, response, request_info): self.status.setText(response) def onRemoteError(self, code, message, request_info): self.status.setText("Server Error or Invalid Response: ERROR " + code + " - " + message) # AJAX calls must come from the same server, only the path is given here class UpperService(JSONProxy): def __init__(self): JSONProxy.__init__(self, "/json/", ["upper"]) </code></pre> <p>I compiled it with PyJs, renamed the default <code>output</code> directory to <code>static</code> so that web.py can serve it, edited <code>static/Client.html</code> so that the internal references point to <code>static</code>:</p> <pre><code>&lt;html&gt; &lt;!-- auto-generated html - You should consider editing and adapting this to suit your requirements. No doctype used here to force quirks mode; see wiki for details: http://pyjs.org/wiki/csshellandhowtodealwithit/ --&gt; &lt;head&gt; &lt;title&gt;Client (Pyjamas Auto-Generated HTML file)&lt;/title&gt; &lt;meta name="pygwt:module" content="/static/Client"&gt; &lt;!-- was content="Client" --&gt; &lt;/head&gt; &lt;body style="background-color:white"&gt; &lt;script type="text/javascript" src="/static/bootstrap.js"&gt;&lt;/script&gt; &lt;!-- was src="bootstrap.js" --&gt; &lt;iframe id="__pygwt_historyFrame" style="display:none;"&gt;&lt;/iframe&gt; &lt;/body&gt; &lt;/html&gt; </code></pre> <p>... and then pointing the browser to <code>http://localhost:8080/static/Client.html</code>. All I get is a blank page, inspecting the page source shows <code>static/Client.html</code> above so it was indeed served to the browser. The server's log also shows that at least some pages have been served:</p> <pre><code>http://0.0.0.0:8080/ 127.0.0.1:61466 - - [14/Mar/2013 13:59:39] "HTTP/1.1 GET /static/Client.html" - 200 127.0.0.1:61466 - - [14/Mar/2013 13:59:40] "HTTP/1.1 GET /static/Client.nocache.html" - 200 127.0.0.1:61466 - - [14/Mar/2013 13:59:40] "HTTP/1.1 GET /static/Client.safari.cache.html" - 200 </code></pre> <p>No indication of what went wrong, however. Tried all sorts of other combinations of URLs, renaming directories, compiling the Pyjamas part with the -d option in the hope to get a debug stack trace ... to no avail. </p> <p>Has anyone succeeded in getting Pyjamas and Web.py working together? If yes, then please share how. Thanks.</p> <p>PS: I am using web.py V0.37 and the latest Pyjamas development release. (The current stable release V0.8.1 does not work either.)</p>
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