Thread: [Cppcms-users] JSON-RPC dispatching together with Normal Web Page

I am setting up a basic webcomic site which uses a class:

class webcomic : cppcms::application { /*...*/ };

for delivering the webcomic functionality, and a class:

class json_service : public cppcms::rpc::json_rpc_server { /*...*/ };

to deliver additional widget based content in a widgets panel. But now I
can't figure out how to properly dispatch the '/rpc' call that is supposed
to be sent to the rpc server in my overloaded webcomic::main function.

The source code for the implementing chat using json-rpc was... somewhat
helpful, but also confusing, as I couldn't see any other class in there
that inherited from cppcms::application. I'm kind of at a loss for how to
do this.

Please help me. And thank you for your time.

I feel like I'm missing a piece of the picture but I'll give it a go:

Typically to mount an application in the URL space you do something like
this in the program's main():

    cppcms::service srv(argc,argv);
    srv.applications_pool().mount(
        cppcms::create_pool<rpc_app_class>(),
        cppcms::mount_point("/rpc")
    );

Or you can mount it in another applications URL space with attach() like
this inside a cppcms::application constructor:

    attach( new rpc_app_class(s),
        "rpc",
        "/rpc{1}",
        "/rpc((/.*)?)",1);

And technically you can use dispatcher() and mapper() directly to dispatch
from one app class to another. Just create the additional app object in the
constructor of a parent app object. Then map/dispatch in the traditional
way, but supply the child object to dispatcher. Something like this in the
parent's (app1) constructor:

        mapper().assign("rpc", "/rpc");
    dispatcher().assign("/rpc", &app2_child::handler, app2);

Obviously the app2 object has to be constructed as a member of app1 in the
usual manner. And don't forget to make sure the object gets destroyed too.

Lastly you can call one app from another through the top most
application::main(). You would need to construct the child app yourself, as
above. But since main() gets the URL you can customize the URL handling to
dispatch the call however you see fit.

I'm sure this is "clear as mud". So ask questions and provide more detail
and I'll see if I can't lend a hand.

- Jon


On 11/05/2020 06:00 AM, Varstray Pl wrote:
> I am setting up a basic webcomic site which uses a class:
>
> class webcomic : cppcms::application { /*...*/ };
>
> for delivering the webcomic functionality, and a class:
>
> class json_service : public cppcms::rpc::json_rpc_server { /*...*/ };
>
> to deliver additional widget based content in a widgets panel. But now I
> can't figure out how to properly dispatch the '/rpc' call that is
> supposed to be sent to the rpc server in my overloaded webcomic::main
> function.
>
> The source code for the implementing chat using json-rpc was... somewhat
> helpful, but also confusing, as I couldn't see any other class in there
> that inherited from cppcms::application. I'm kind of at a loss for how to
> do this.
>
> Please help me. And thank you for your time.
>
>
>
>
> _______________________________________________
> Cppcms-users mailing list
> Cpp...@li...
> https://lists.sourceforge.net/lists/listinfo/cppcms-users

-- 
Sent from my Devuan Linux workstation -- https://devuan.org/
"Init Freedom", Yeah!

Jon Foster
JF Possibilities, Inc.
jo...@jf...

Ah! Ok. So this is actually very helpful!

I've decided to go with mounting the rpc server in the webcomic's url space
using the attach method you described above. The code for my webcomic page
constructor is as follows:
* * *
webcomic::webcomic(cppcms::service &srv) : cppcms::application(srv){
    attach(new json_service(srv), "rpc", "/rpc{1}", "/rpc(/(.*))?", 1);
    //.. various dispatcher and mapper calls.
};
***
The browser now appears to be successfully calling the rpc server! Yay!
Unfortunately (there's always an unfortunately, isn't there? xD), I think I
haven't set up the handling of the rpc request properly within the server,
because instead of a proper response, the widgets panel is simply filled
with the text "Invalid JSON-RPC". I'm not sure where in the pipeline things
are going wrong, but here is how I've set up the rpc server. Maybe you can
see what I'm doing wrong?

First, the basic class definition:
* * *
class json_service: public cppcms::rpc::json_rpc_server{
public:
    json_service(cppcms::service &srv);

    // Ajax Methods
    void widgets();
};
* * *

And then the implementation of the server constructor and the widgets
method:
* * *
json_service::json_service(cppcms::service &srv) :
cppcms::rpc::json_rpc_server(srv)
{
    bind("widgets", cppcms::rpc::json_method(&json_service::widgets,
this),method_role);
}

void json_service::widgets()
{
    return_result("widgets via AJAX-RPC!!! Cool!");
}
* * *

Finally, this is how the request is set up on the client side via
javascript:
* * *
function getWidgets() {
    var xhr = new XMLHttpRequest();
    xhr.open("post", '/rpc');

    // Required by JSON-RPC over HTTP
    xhr.setRequestHeader("Content-Type","application/json");

    // Configure JSON-RPC request.
    var request = '{"method":"widgets"}';

    // Define our callback function.
    xhr.onreadystatechange = function(){
        if (xhr.readyState === 4){
            var response;

            if (xhr.status === 200){
                response = xhr.responseText;
            } else {
                response = 'Invalid Status: ' + xhr.status;
            }

            document.getElementById('widgets').innerHTML = response;
        }
    }

    xhr.send(request);
    return false;
}
* * *
The javascript method is pretty much taken from the json-rpc tutorial on
the cppcms.com website. Although because this method doesn't take any
parameters(yet), I *think* perhaps the issue lies somewhere in the
modifications I made for sending a request for a non-parameter method,
whereas the tutorial method does take parameters. Also, up till this point,
diagnostic information on stderr and stdout has been very helpful, but now
there doesn't appear to be any stderr output at all, lol.

I *can* verify that on the browser end the rpc call is actually being sent
to the rpc server, and because 'Invalid RPC-JSON' is different from
'Invalid Status: bla bla', I think that the getWidgets() method is actually
getting a proper response from the rpc server. It's just clearly there's
something else going wrong somewhere.
* * *

Thank you for your help, Jon, and sorry for any additional trouble. I'll
also keep searching on my end for an answer as well. ^^;

<html>
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    <p>Glad to hear it. I've never actually used the C++CMS JSON RPC
      server class because the docs leave too much unsaid, making it far
      simpler to write my own handler. I think you might have to dig
      through the source to see what its actually doing. I put together
      a test environment made from the "clippings" you sent along and
      I'm not sure I made it as far as you did. :-) What I'm seeing is
      the call dying in the CORS authentication phase (OPTIONS req) my
      C++CMS app failing to respond with the appropriate "allowed"
      response, in fact it says nothing and FF just drops the request.</p>
    <p>"CORS" is fairly recent pseudo-security feature. Its possible
      that C++CMS is not prepared for it and a simple extension to the
      JSON RPC server class may be needed. But I could be getting ahead
      of myself.</p>
    <p>The primary thing you need to do is fire up your browser's "dev
      tools". The "console" section will allow you to call your
      javascript function, to manually trigger requests to the server
      side. It should also log the requests and responses made to your
      server. All XHR requests should come in two phases the "OPTIONS"
      request to ask the server for permission, followed by the actual
      JSON request you made, which would be a "POST" transaction. Check
      the request and response to make sure your getting what you
      expect. Often times what you see there will reveal the issue.</p>
    <p>I don't know your experience level so this page from MDN might be
      useful in understanding CORS:
      <a class="moz-txt-link-freetext" href="https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS">https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS</a></p>
    <p>Anyhow I have client needs to attend to or I'd drill the rest of
      the way down. Use your browser's debugger and sprinkle "std::cerr
      &lt;&lt; ..." stuff liberally in your server side code to get a
      picture of what its doing. On my setup I can call the RPC url with
      a generic client (browser, wget, curl, ...) and get "invalid
      content type" so I know the request is getting dispatched to the
      RPC handler. Yet an override of main() fails to show an URL hit
      the application so the call must be getting blocked further up in
      the class. maybe init()? Or I fat-fingered something? Like I said
      I'd have to drill down on the source to figure out what its up to.</p>
    <p>I'll try to help out as I can.</p>
    <p>- Jon<br>
    </p>
    <br>
    <div class="moz-cite-prefix">On 11/09/2020 09:29 AM, Varstray Pl
      wrote:<br>
    </div>
    <blockquote
cite="mid:CAN...@ma..."
      type="cite">
      <div dir="ltr">
        <div>Ah! Ok. So this is actually very helpful!</div>
        <div><br>
        </div>
        <div>I've decided to go with mounting the rpc server in the
          webcomic's url space using the attach method you described
          above. The code for my webcomic page constructor is as
          follows:</div>
        <div>* * *<br>
        </div>
        <div><span style="font-family:monospace">webcomic::webcomic(cppcms::service
            &amp;srv) : cppcms::application(srv){<br>
            attach(new json_service(srv), "rpc", "/rpc{1}",
            "/rpc(/(.*))?", 1);</span></div>
        <div><span style="font-family:monospace"> //.. various
            dispatcher and mapper calls.<br>
          </span></div>
        <div><span style="font-family:monospace">};</span></div>
        <div><span style="font-family:monospace">***<br>
          </span></div>
        <div><span style="font-family:monospace"><font
              face="arial,sans-serif">The browser now appears to be
              successfully calling the rpc server! Yay! Unfortunately
              (there's always an unfortunately, isn't there? xD), I
              think I haven't set up the handling of the rpc request
              properly within the server, because instead of a proper
              response, the widgets panel is simply filled with the text
              "Invalid JSON-RPC"</font>. <span
              style="font-family:arial,sans-serif">I'm not sure where in
              the pipeline things are going wrong, but here is how I've
              set up the rpc server. Maybe you can see what I'm doing
              wrong?</span></span></div>
        <div><span style="font-family:monospace"><span
              style="font-family:arial,sans-serif"><br>
            </span></span></div>
        <div><span style="font-family:monospace"><span
              style="font-family:arial,sans-serif">First, the basic
              class definition:</span></span></div>
        <div><span style="font-family:monospace"><span
              style="font-family:arial,sans-serif">* * *</span></span></div>
        <div><span style="font-family:monospace">class json_service:
            public cppcms::rpc::json_rpc_server{<br>
            public:<br>
            json_service(cppcms::service &amp;srv);<br>
            <br>
            // Ajax Methods<br>
            void widgets();<br>
            };</span></div>
        <div><span style="font-family:monospace"><span
              style="font-family:arial,sans-serif">* * *</span></span></div>
        <div><span style="font-family:monospace"><span
              style="font-family:arial,sans-serif"><br>
            </span></span></div>
        <div><span style="font-family:monospace"><span
              style="font-family:arial,sans-serif">And then the
              implementation of the server constructor and the widgets
              method:</span></span></div>
        <div><span style="font-family:monospace"><span
              style="font-family:arial,sans-serif">* * *</span></span></div>
        <div><span style="font-family:monospace">json_service::json_service(cppcms::service
            &amp;srv) : cppcms::rpc::json_rpc_server(srv)<br>
            {<br>
            bind("widgets",
            cppcms::rpc::json_method(&amp;json_service::widgets,
            this),method_role);<br>
            }<br>
            <br>
            void json_service::widgets()<br>
            {<br>
            return_result("widgets via AJAX-RPC!!! Cool!");<br>
            }</span></div>
        <div><span style="font-family:monospace"><span
              style="font-family:arial,sans-serif">* * *</span></span></div>
        <div><span style="font-family:monospace"><span
              style="font-family:arial,sans-serif"><br>
            </span></span></div>
        <div><span style="font-family:monospace"><span
              style="font-family:arial,sans-serif">Finally, this is how
              the request is set up on the client side via javascript:</span></span></div>
        <div><span style="font-family:monospace"><span
              style="font-family:arial,sans-serif">* * *</span></span></div>
        <div><span style="font-family:monospace"><span
              style="font-family:arial,sans-serif"><span
                style="font-family:monospace">function getWidgets() { <br>
                var xhr = new XMLHttpRequest(); <br>
                xhr.open("post", '/rpc');<br>
                <br>
                // Required by JSON-RPC over HTTP <br>
                xhr.setRequestHeader("Content-Type","application/json");<br>
                <br>
                // Configure JSON-RPC request.<br>
                var request = '{"method":"widgets"}';<br>
                <br>
                // Define our callback function.<br>
                xhr.onreadystatechange = function(){<br>
                if (xhr.readyState === 4){<br>
                var response;<br>
                <br>
                if (xhr.status === 200){<br>
                response = xhr.responseText;<br>
                } else {<br>
                response = 'Invalid Status: ' + xhr.status;<br>
                }<br>
                <br>
                document.getElementById('widgets').innerHTML = response;<br>
                }<br>
                }<br>
                <br>
                xhr.send(request);<br>
                return false;<br>
                } </span><br>
            </span></span></div>
        <div><span style="font-family:monospace"><span
              style="font-family:arial,sans-serif">* * *<br>
            </span></span></div>
        <div><span style="font-family:monospace"><span
              style="font-family:arial,sans-serif">The javascript method
              is pretty much taken from the json-rpc tutorial on the <a
                moz-do-not-send="true" href="http://cppcms.com">cppcms.com</a>
              website. Although because this method doesn't take any
              parameters(yet), I *think* perhaps the issue lies
              somewhere in the modifications I made for sending a
              request for a non-parameter method, whereas the tutorial
              method does take parameters. Also, up till this point,
              diagnostic information on stderr and stdout has been very
              helpful, but now there doesn't appear to be any stderr
              output at all, lol.</span></span></div>
        <div><span style="font-family:monospace"><span
              style="font-family:arial,sans-serif"><br>
            </span></span></div>
        <div><span style="font-family:monospace"><span
              style="font-family:arial,sans-serif">I *can* verify that
              on the browser end the rpc call is actually being sent to
              the rpc server, and because 'Invalid RPC-JSON' is
              different from 'Invalid Status: bla bla', I think that the
              getWidgets() method is actually getting a proper response
              from the rpc server. It's just clearly there's something
              else going wrong somewhere.</span></span></div>
        <div><span style="font-family:monospace"><span
              style="font-family:arial,sans-serif">* * *</span></span></div>
        <div><span style="font-family:monospace"><span
              style="font-family:arial,sans-serif"><br>
            </span></span></div>
        <div><span style="font-family:monospace"><span
              style="font-family:arial,sans-serif">Thank you for your
              help, Jon, and sorry for any additional trouble. I'll also
              keep searching on my end for an answer as well. ^^;<br>
            </span></span></div>
        <div><span style="font-family:monospace"><span
              style="font-family:arial,sans-serif"><br>
            </span></span></div>
        <div><span style="font-family:monospace"><span
              style="font-family:arial,sans-serif"></span><br>
          </span></div>
      </div>
      <br>
      <fieldset class="mimeAttachmentHeader"></fieldset>
      <br>
      <br>
      <fieldset class="mimeAttachmentHeader"></fieldset>
      <br>
      <pre wrap="">_______________________________________________
Cppcms-users mailing list
<a class="moz-txt-link-abbreviated" href="mailto:Cpp...@li...">Cpp...@li...</a>
<a class="moz-txt-link-freetext" href="https://lists.sourceforge.net/lists/listinfo/cppcms-users">https://lists.sourceforge.net/lists/listinfo/cppcms-users</a>
</pre>
    </blockquote>
    <br>
    <pre class="moz-signature" cols="75">-- 
Sent from my Devuan Linux workstation -- <a class="moz-txt-link-freetext" href="https://devuan.org/">https://devuan.org/</a>
"Init Freedom", Yeah!

Jon Foster
JF Possibilities, Inc.
<a class="moz-txt-link-abbreviated" href="mailto:jo...@jf...">jo...@jf...</a>
</pre>
  </body>
</html>

Wow! Ok, so I took your information and ran with it, Jon. The information
on CORS was definitely useful. Originally I thought I was going to have to
set the necessary cors-compliant response headers in my webcomic.cpp code
itself, but something was bugging me about it. My test environment is
essentially from localhost:8080/webcomic, whereas the url given in the
widgets.js getWidgets() method was just simply '/rpc'. So, to make
absolutely sure that I wasn't engaging in any cross site scripting, I set
the xmlhttprequest url to "http:localhost:8080/webcomic/rpc"
.
The response was actually a 404 status code, lol. Verifying the actual url
that the browser tried to contact shed some light on the issue: It was
"http:localhost:8080/webcomic/http:localhost:8080/webcomic/rpc". Aha! So
the xml request was reaching the json_server backend after all! I didn't
actually have much experience with the firefox developer console, but your
information regarding how to manually trigger the getWidgets() method and
view the response set me on the right track quickly. I was able to verify
that the "Invalid JSON-RPC" string was actually coming from the response
payload, indicating an issue in the CppCMS codebase itself.

A quick bash command:
for fd in `ls $SRCDIR`; do echo "In file: $fd" ; cat ./$fd | grep -e
"JSON-RPC" ; done

Revealed:
In file: rpc_json.cpp
throw call_error("Invalid JSON-RPC");
BOOSTER_DEBUG("cppcms") << "JSON-RPC Method call:" << method();
throw cppcms_error("JSON-RPC Request is not assigned to class");

Which led me to this snippet of code in rpc_json.cpp:
if( request.type("method")!=json::is_string
|| request.type("params")!=json::is_array
|| request.type("id")==json::is_undefined)
{
throw call_error("Invalid JSON-RPC");
}

Boom. That was the issue. My JSON request was originally
{"method":"widgets"}, but it needed to be
{"method":"widgets","params":[],"id":1}.
Making the appropriate change and also updating the XMLHttpRequest url to
"/webcomic/rpc" solved the issue 100%!

Whew! Thank you very much for your help on this, Jon! I am DEEPLY grateful
for all of this!

Sincerely,
VarstrayPl.

On Mon, Nov 9, 2020 at 1:52 PM Jon Foster <jon...@jf...>
wrote:

> Glad to hear it. I've never actually used the C++CMS JSON RPC server class
> because the docs leave too much unsaid, making it far simpler to write my
> own handler. I think you might have to dig through the source to see what
> its actually doing. I put together a test environment made from the
> "clippings" you sent along and I'm not sure I made it as far as you did.
> :-) What I'm seeing is the call dying in the CORS authentication phase
> (OPTIONS req) my C++CMS app failing to respond with the appropriate
> "allowed" response, in fact it says nothing and FF just drops the request.
>
> "CORS" is fairly recent pseudo-security feature. Its possible that C++CMS
> is not prepared for it and a simple extension to the JSON RPC server class
> may be needed. But I could be getting ahead of myself.
>
> The primary thing you need to do is fire up your browser's "dev tools".
> The "console" section will allow you to call your javascript function, to
> manually trigger requests to the server side. It should also log the
> requests and responses made to your server. All XHR requests should come in
> two phases the "OPTIONS" request to ask the server for permission, followed
> by the actual JSON request you made, which would be a "POST" transaction.
> Check the request and response to make sure your getting what you expect.
> Often times what you see there will reveal the issue.
>
> I don't know your experience level so this page from MDN might be useful
> in understanding CORS:
> https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS
>
> Anyhow I have client needs to attend to or I'd drill the rest of the way
> down. Use your browser's debugger and sprinkle "std::cerr << ..." stuff
> liberally in your server side code to get a picture of what its doing. On
> my setup I can call the RPC url with a generic client (browser, wget, curl,
> ...) and get "invalid content type" so I know the request is getting
> dispatched to the RPC handler. Yet an override of main() fails to show an
> URL hit the application so the call must be getting blocked further up in
> the class. maybe init()? Or I fat-fingered something? Like I said I'd have
> to drill down on the source to figure out what its up to.
>
> I'll try to help out as I can.
>
> - Jon
>
> On 11/09/2020 09:29 AM, Varstray Pl wrote:
>
> Ah! Ok. So this is actually very helpful!
>
> I've decided to go with mounting the rpc server in the webcomic's url
> space using the attach method you described above. The code for my webcomic
> page constructor is as follows:
> * * *
> webcomic::webcomic(cppcms::service &srv) : cppcms::application(srv){
> attach(new json_service(srv), "rpc", "/rpc{1}", "/rpc(/(.*))?", 1);
> //.. various dispatcher and mapper calls.
> };
> ***
> The browser now appears to be successfully calling the rpc server! Yay!
> Unfortunately (there's always an unfortunately, isn't there? xD), I think I
> haven't set up the handling of the rpc request properly within the server,
> because instead of a proper response, the widgets panel is simply filled
> with the text "Invalid JSON-RPC". I'm not sure where in the pipeline
> things are going wrong, but here is how I've set up the rpc server. Maybe
> you can see what I'm doing wrong?
>
> First, the basic class definition:
> * * *
> class json_service: public cppcms::rpc::json_rpc_server{
> public:
> json_service(cppcms::service &srv);
>
> // Ajax Methods
> void widgets();
> };
> * * *
>
> And then the implementation of the server constructor and the widgets
> method:
> * * *
> json_service::json_service(cppcms::service &srv) :
> cppcms::rpc::json_rpc_server(srv)
> {
> bind("widgets", cppcms::rpc::json_method(&json_service::widgets,
> this),method_role);
> }
>
> void json_service::widgets()
> {
> return_result("widgets via AJAX-RPC!!! Cool!");
> }
> * * *
>
> Finally, this is how the request is set up on the client side via
> javascript:
> * * *
> function getWidgets() {
> var xhr = new XMLHttpRequest();
> xhr.open("post", '/rpc');
>
> // Required by JSON-RPC over HTTP
> xhr.setRequestHeader("Content-Type","application/json");
>
> // Configure JSON-RPC request.
> var request = '{"method":"widgets"}';
>
> // Define our callback function.
> xhr.onreadystatechange = function(){
> if (xhr.readyState === 4){
> var response;
>
> if (xhr.status === 200){
> response = xhr.responseText;
> } else {
> response = 'Invalid Status: ' + xhr.status;
> }
>
> document.getElementById('widgets').innerHTML = response;
> }
> }
>
> xhr.send(request);
> return false;
> }
> * * *
> The javascript method is pretty much taken from the json-rpc tutorial on
> the cppcms.com website. Although because this method doesn't take any
> parameters(yet), I *think* perhaps the issue lies somewhere in the
> modifications I made for sending a request for a non-parameter method,
> whereas the tutorial method does take parameters. Also, up till this point,
> diagnostic information on stderr and stdout has been very helpful, but now
> there doesn't appear to be any stderr output at all, lol.
>
> I *can* verify that on the browser end the rpc call is actually being sent
> to the rpc server, and because 'Invalid RPC-JSON' is different from
> 'Invalid Status: bla bla', I think that the getWidgets() method is actually
> getting a proper response from the rpc server. It's just clearly there's
> something else going wrong somewhere.
> * * *
>
> Thank you for your help, Jon, and sorry for any additional trouble. I'll
> also keep searching on my end for an answer as well. ^^;
>
>
>
>
>
>
> _______________________________________________
> Cppcms-users mailing lis...@li...://lists.sourceforge.net/lists/listinfo/cppcms-users
>
>
> --
> Sent from my Devuan Linux workstation -- https://devuan.org/
> "Init Freedom", Yeah!
>
> Jon Foster
> JF Possibilities, In...@jf...
>
> _______________________________________________
> Cppcms-users mailing list
> Cpp...@li...
> https://lists.sourceforge.net/lists/listinfo/cppcms-users
>

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    <p>Splendid! Good job! It seems everyone implements their JSON based
      APIs/RPCs differently. Looks like Artyom implements the
      JSON-RPC-1.0 spec pretty strictly, which is probably a good thing.
      Get to know those in-browser debugging tools. They can save a ton
      of time!<br>
    </p>
    <p>@Artyom, if you read this I wanted to let you know: the link to
      the spec is broken. Probably should go here:
      <a class="moz-txt-link-freetext" href="https://www.jsonrpc.org/specification_v1">https://www.jsonrpc.org/specification_v1</a>. Also RPC is transposed
      at least once on your tutorial page.</p>
    <p>Congratulations,<br>
      Jon<br>
    </p>
    <br>
    <div class="moz-cite-prefix">On 11/10/2020 02:32 PM, Varstray Pl
      wrote:<br>
    </div>
    <blockquote
cite="mid:CAN...@ma..."
      type="cite">
      <div dir="ltr">Wow! Ok, so I took your information and ran with
        it, Jon. The information on CORS was definitely useful.
        Originally I thought I was going to have to set the necessary
        cors-compliant response headers in my webcomic.cpp code itself,
        but something was bugging me about it. My test environment is
        essentially from localhost:8080/webcomic, whereas the url given
        in the widgets.js getWidgets() method was just simply '/rpc'.
        So, to make absolutely sure that I wasn't engaging in any cross
        site scripting, I set the xmlhttprequest url to
        <a class="moz-txt-link-rfc2396E" href="http:localhost:8080/webcomic/rpc">"http:localhost:8080/webcomic/rpc"</a><br>
        <div>.</div>
        <div>The response was actually a 404 status code, lol. Verifying
          the actual url that the browser tried to contact shed some
          light on the issue: It was
          <a class="moz-txt-link-rfc2396E" href="http:localhost:8080/webcomic/http:localhost:8080/webcomic/rpc">"http:localhost:8080/webcomic/http:localhost:8080/webcomic/rpc"</a>.
          Aha! So the xml request was reaching the json_server backend
          after all! I didn't actually have much experience with the
          firefox developer console, but your information regarding how
          to manually trigger the getWidgets() method and view the
          response set me on the right track quickly. I was able to
          verify that the "Invalid JSON-RPC" string was actually coming
          from the response payload, indicating an issue in the CppCMS
          codebase itself.</div>
        <div><br>
        </div>
        <div>A quick bash command:</div>
        <div><span style="font-family:monospace">for fd in `ls $SRCDIR`;
            do echo "In file: $fd" ; cat ./$fd | grep -e "JSON-RPC" ;
            done</span></div>
        <div><span style="font-family:monospace"><font
              face="arial,sans-serif"><br>
            </font></span></div>
        <div><span style="font-family:monospace"><font
              face="arial,sans-serif">Revealed:</font></span></div>
        <div><span style="font-family:monospace">In file: rpc_json.cpp<br>
            throw call_error("Invalid JSON-RPC");<br>
            BOOSTER_DEBUG("cppcms") &lt;&lt; "JSON-RPC Method call:"
            &lt;&lt; method();<br>
            throw cppcms_error("JSON-RPC Request is not assigned to
            class");<br>
          </span></div>
        <div><span style="font-family:monospace"><br>
          </span></div>
        <div><span style="font-family:monospace"><font
              face="arial,sans-serif">Which led me to this snippet of
              code in rpc_json.cpp:</font></span></div>
        <div><span style="font-family:monospace"> if(
            request.type("method")!=json::is_string <br>
            || request.type("params")!=json::is_array<br>
            || request.type("id")==json::is_undefined)<br>
            {<br>
            throw call_error("Invalid JSON-RPC");<br>
            }</span></div>
        <div><span style="font-family:monospace"><br>
          </span></div>
        <div><span style="font-family:monospace"><font
              face="arial,sans-serif">Boom. That was the issue. My JSON
              request was originally <span
                style="font-family:monospace">{"method":"widgets"}</span>,
              but it needed to be <span style="font-family:monospace">{"method":"widgets","params":[],"id":1}</span></font>.</span></div>
        <div><span style="font-family:monospace"><font
              face="arial,sans-serif">Making the appropriate change and
              also updating the XMLHttpRequest url to "/webcomic/rpc"
              solved the issue 100%!</font></span></div>
        <div><span style="font-family:monospace"><font
              face="arial,sans-serif"><br>
            </font></span></div>
        <div><span style="font-family:monospace"><font
              face="arial,sans-serif">Whew! Thank you very much for your
              help on this, Jon! I am DEEPLY grateful for all of this!</font></span></div>
        <div><span style="font-family:monospace"><font
              face="arial,sans-serif"><br>
            </font></span></div>
        <div><span style="font-family:monospace"><font
              face="arial,sans-serif">Sincerely,</font></span></div>
        <div><span style="font-family:monospace"><font
              face="arial,sans-serif">VarstrayPl.<br>
            </font></span></div>
      </div>
      <br>
      <div class="gmail_quote">
        <div dir="ltr" class="gmail_attr">On Mon, Nov 9, 2020 at 1:52 PM
          Jon Foster &lt;<a moz-do-not-send="true"
            href="mailto:jon...@jf...">jon...@jf...</a>&gt;
          wrote:<br>
        </div>
        <blockquote class="gmail_quote" style="margin:0px 0px 0px
          0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
          <div bgcolor="#FFFFFF">
            <p>Glad to hear it. I've never actually used the C++CMS JSON
              RPC server class because the docs leave too much unsaid,
              making it far simpler to write my own handler. I think you
              might have to dig through the source to see what its
              actually doing. I put together a test environment made
              from the "clippings" you sent along and I'm not sure I
              made it as far as you did. :-) What I'm seeing is the call
              dying in the CORS authentication phase (OPTIONS req) my
              C++CMS app failing to respond with the appropriate
              "allowed" response, in fact it says nothing and FF just
              drops the request.</p>
            <p>"CORS" is fairly recent pseudo-security feature. Its
              possible that C++CMS is not prepared for it and a simple
              extension to the JSON RPC server class may be needed. But
              I could be getting ahead of myself.</p>
            <p>The primary thing you need to do is fire up your
              browser's "dev tools". The "console" section will allow
              you to call your javascript function, to manually trigger
              requests to the server side. It should also log the
              requests and responses made to your server. All XHR
              requests should come in two phases the "OPTIONS" request
              to ask the server for permission, followed by the actual
              JSON request you made, which would be a "POST"
              transaction. Check the request and response to make sure
              your getting what you expect. Often times what you see
              there will reveal the issue.</p>
            <p>I don't know your experience level so this page from MDN
              might be useful in understanding CORS: <a
                moz-do-not-send="true"
                href="https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS"
                target="_blank">https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS</a></p>
            <p>Anyhow I have client needs to attend to or I'd drill the
              rest of the way down. Use your browser's debugger and
              sprinkle "std::cerr &lt;&lt; ..." stuff liberally in your
              server side code to get a picture of what its doing. On my
              setup I can call the RPC url with a generic client
              (browser, wget, curl, ...) and get "invalid content type"
              so I know the request is getting dispatched to the RPC
              handler. Yet an override of main() fails to show an URL
              hit the application so the call must be getting blocked
              further up in the class. maybe init()? Or I fat-fingered
              something? Like I said I'd have to drill down on the
              source to figure out what its up to.</p>
            <p>I'll try to help out as I can.</p>
            <p>- Jon<br>
            </p>
            <br>
            <div>On 11/09/2020 09:29 AM, Varstray Pl wrote:<br>
            </div>
            <blockquote type="cite">
              <div dir="ltr">
                <div>Ah! Ok. So this is actually very helpful!</div>
                <div><br>
                </div>
                <div>I've decided to go with mounting the rpc server in
                  the webcomic's url space using the attach method you
                  described above. The code for my webcomic page
                  constructor is as follows:</div>
                <div>* * *<br>
                </div>
                <div><span style="font-family:monospace">webcomic::webcomic(cppcms::service
                    &amp;srv) : cppcms::application(srv){<br>
                    attach(new json_service(srv), "rpc", "/rpc{1}",
                    "/rpc(/(.*))?", 1);</span></div>
                <div><span style="font-family:monospace"> //.. various
                    dispatcher and mapper calls.<br>
                  </span></div>
                <div><span style="font-family:monospace">};</span></div>
                <div><span style="font-family:monospace">***<br>
                  </span></div>
                <div><span style="font-family:monospace"><font
                      face="arial,sans-serif">The browser now appears to
                      be successfully calling the rpc server! Yay!
                      Unfortunately (there's always an unfortunately,
                      isn't there? xD), I think I haven't set up the
                      handling of the rpc request properly within the
                      server, because instead of a proper response, the
                      widgets panel is simply filled with the text
                      "Invalid JSON-RPC"</font>. <span
                      style="font-family:arial,sans-serif">I'm not sure
                      where in the pipeline things are going wrong, but
                      here is how I've set up the rpc server. Maybe you
                      can see what I'm doing wrong?</span></span></div>
                <div><span style="font-family:monospace"><span
                      style="font-family:arial,sans-serif"><br>
                    </span></span></div>
                <div><span style="font-family:monospace"><span
                      style="font-family:arial,sans-serif">First, the
                      basic class definition:</span></span></div>
                <div><span style="font-family:monospace"><span
                      style="font-family:arial,sans-serif">* * *</span></span></div>
                <div><span style="font-family:monospace">class
                    json_service: public cppcms::rpc::json_rpc_server{<br>
                    public:<br>
                    json_service(cppcms::service &amp;srv);<br>
                    <br>
                    // Ajax Methods<br>
                    void widgets();<br>
                    };</span></div>
                <div><span style="font-family:monospace"><span
                      style="font-family:arial,sans-serif">* * *</span></span></div>
                <div><span style="font-family:monospace"><span
                      style="font-family:arial,sans-serif"><br>
                    </span></span></div>
                <div><span style="font-family:monospace"><span
                      style="font-family:arial,sans-serif">And then the
                      implementation of the server constructor and the
                      widgets method:</span></span></div>
                <div><span style="font-family:monospace"><span
                      style="font-family:arial,sans-serif">* * *</span></span></div>
                <div><span style="font-family:monospace">json_service::json_service(cppcms::service
                    &amp;srv) : cppcms::rpc::json_rpc_server(srv)<br>
                    {<br>
                    bind("widgets",
                    cppcms::rpc::json_method(&amp;json_service::widgets,
                    this),method_role);<br>
                    }<br>
                    <br>
                    void json_service::widgets()<br>
                    {<br>
                    return_result("widgets via AJAX-RPC!!! Cool!");<br>
                    }</span></div>
                <div><span style="font-family:monospace"><span
                      style="font-family:arial,sans-serif">* * *</span></span></div>
                <div><span style="font-family:monospace"><span
                      style="font-family:arial,sans-serif"><br>
                    </span></span></div>
                <div><span style="font-family:monospace"><span
                      style="font-family:arial,sans-serif">Finally, this
                      is how the request is set up on the client side
                      via javascript:</span></span></div>
                <div><span style="font-family:monospace"><span
                      style="font-family:arial,sans-serif">* * *</span></span></div>
                <div><span style="font-family:monospace"><span
                      style="font-family:arial,sans-serif"><span
                        style="font-family:monospace">function
                        getWidgets() { <br>
                        var xhr = new XMLHttpRequest(); <br>
                        xhr.open("post", '/rpc');<br>
                        <br>
                        // Required by JSON-RPC over HTTP <br>
xhr.setRequestHeader("Content-Type","application/json");<br>
                        <br>
                        // Configure JSON-RPC request.<br>
                        var request = '{"method":"widgets"}';<br>
                        <br>
                        // Define our callback function.<br>
                        xhr.onreadystatechange = function(){<br>
                        if (xhr.readyState === 4){<br>
                        var response;<br>
                        <br>
                        if (xhr.status === 200){<br>
                        response = xhr.responseText;<br>
                        } else {<br>
                        response = 'Invalid Status: ' + xhr.status;<br>
                        }<br>
                        <br>
                        document.getElementById('widgets').innerHTML =
                        response;<br>
                        }<br>
                        }<br>
                        <br>
                        xhr.send(request);<br>
                        return false;<br>
                        } </span><br>
                    </span></span></div>
                <div><span style="font-family:monospace"><span
                      style="font-family:arial,sans-serif">* * *<br>
                    </span></span></div>
                <div><span style="font-family:monospace"><span
                      style="font-family:arial,sans-serif">The
                      javascript method is pretty much taken from the
                      json-rpc tutorial on the <a
                        moz-do-not-send="true" href="http://cppcms.com"
                        target="_blank">cppcms.com</a> website. Although
                      because this method doesn't take any
                      parameters(yet), I *think* perhaps the issue lies
                      somewhere in the modifications I made for sending
                      a request for a non-parameter method, whereas the
                      tutorial method does take parameters. Also, up
                      till this point, diagnostic information on stderr
                      and stdout has been very helpful, but now there
                      doesn't appear to be any stderr output at all,
                      lol.</span></span></div>
                <div><span style="font-family:monospace"><span
                      style="font-family:arial,sans-serif"><br>
                    </span></span></div>
                <div><span style="font-family:monospace"><span
                      style="font-family:arial,sans-serif">I *can*
                      verify that on the browser end the rpc call is
                      actually being sent to the rpc server, and because
                      'Invalid RPC-JSON' is different from 'Invalid
                      Status: bla bla', I think that the getWidgets()
                      method is actually getting a proper response from
                      the rpc server. It's just clearly there's
                      something else going wrong somewhere.</span></span></div>
                <div><span style="font-family:monospace"><span
                      style="font-family:arial,sans-serif">* * *</span></span></div>
                <div><span style="font-family:monospace"><span
                      style="font-family:arial,sans-serif"><br>
                    </span></span></div>
                <div><span style="font-family:monospace"><span
                      style="font-family:arial,sans-serif">Thank you for
                      your help, Jon, and sorry for any additional
                      trouble. I'll also keep searching on my end for an
                      answer as well. ^^;<br>
                    </span></span></div>
                <div><span style="font-family:monospace"><span
                      style="font-family:arial,sans-serif"><br>
                    </span></span></div>
                <div><span style="font-family:monospace"><span
                      style="font-family:arial,sans-serif"></span><br>
                  </span></div>
              </div>
              <br>
              <fieldset></fieldset>
              <br>
              <br>
              <fieldset></fieldset>
              <br>
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            <br>
            <pre cols="75">-- 
Sent from my Devuan Linux workstation -- <a moz-do-not-send="true" href="https://devuan.org/" target="_blank">https://devuan.org/</a>
"Init Freedom", Yeah!

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JF Possibilities, Inc.
<a moz-do-not-send="true" href="mailto:jo...@jf..." target="_blank">jo...@jf...</a>
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    <pre class="moz-signature" cols="75">-- 
Sent from my Devuan Linux workstation -- <a class="moz-txt-link-freetext" href="https://devuan.org/">https://devuan.org/</a>
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