[erlang-questions] Server Sent Events

Gattu shiva krishna <>
Thu Aug 24 07:53:41 CEST 2017


Hi,

         when i'm using below function

         Data = yaws_sse:data( [ "button1", "button2" ] ),

         the result value of that function is

         [<<"data:">>, [ "button1", "button2" ], <<"\n">>]

         when i'm trying to send this data to client side using below 
function

         yaws_sse:send_events(A#arg.clisock, Data)

         but in client side iam unable to retrieve the data, Is there 
any solution for this.

----------------------------------------------------------------------------------------------------------------------------------------------

         when i'm trying to use this  function ( yaws_sse:send_events/2 
)manually in yaws shell.

         for example :

         1> yaws_sse:send_events( '#port<0.3333>', [<<"data:">>,[ 
"button1", "button2" ],<<"\n">>]).

         It is giving some error like this :

         ** exception error: no function clause matching
                     gen_tcp:send('#port<0.3333>',
                                  [[<<"data:">>,
                                    [ "button1", "button2" ],
                                    <<"\n">>],
                                   <<"\n">>]) (gen_tcp.erl, line 261)

     What is the format of arguments that need to be given to this function.

On Wednesday 23 August 2017 04:08 PM, Jesper Louis Andersen wrote:
> Here is what I think is going wrong, though I'm not entirely sure:
>
> The Yaws yaws_sse:data/1,2 functions assume the data you give them are 
> so-called iodata(). So when you write something like
>
> ["Button1", "Button2"]
>
> and send it, it is effectively flattened into a binary
>
> <<"Button1Button2">>
>
> The iodata() system is really nice for doing scatter/gatter (typo 
> intended) IO, but you have to invent some kind of framing in which you 
> run.
>
> For example, we could use JSON:
>
> X = [<<"Button1">>, <<"Button"2>>],
> Data = yaws_sse:data(jsx:encode(X)),
> ...
>
> which encodes the data into a JSON structure which we can handle on 
> the client side.
>
> Also, look up the iodata() concept. It is pretty nice. There is an old 
> post by James Hague on it:
>
> http://prog21.dadgum.com/70.html
>
>
> On Wed, Aug 23, 2017 at 12:27 PM Gattu shiva krishna 
> < <mailto:>> wrote:
>
>     Hi all,
>
>              I'm learning to use yaws web-server and I came across server
>     sent events which is used to send data to the client. To send data to
>     the client I'm using the function yaws_sse:send_events(A#arg.clisock,
>     Data). What is the format of arguments that need to be given to this
>     function. I've googled enough and didn't get any satisfactory results.
>     Below is a sample application where I'm trying to experiment on
>     server-sent-events.
>
>          Here in code I'm trying to create buttons dynamically in client
>     side based on data that comes from server side.
>
>     ---------------------------------------------------------------------------------------------------------------------------------------
>
>     SERVER SIDE CODE:
>
>       <erl>
>              out(A) ->
>                  Data = yaws_sse:data(["Button1",
>     "Button2","Button3","Button4"]),
>
>                  yaws_sse:send_events(A#arg.clisock, Data).
>          </erl>
>
>     ---------------------------------------------------------------------------------------------------------------------------------------
>
>     CLIENT SIDE CODE:
>
>     <script type="text/javascript">
>            var source = new EventSource("button.yaws");
>            source.onmessage = function(event) {
>                  var i, buttonsToCreate,buttonContainer, newButton;
>
>              buttonsToCreate = event.data;
>                  buttonContainer =
>     document.getElementById('this_element_contains_my_buttons');
>              for (i = 0; i <= buttonsToCreate.length ; i++)
>              {
>                    newButton = document.createElement('input');
>                    newButton.type = 'button';
>                    newButton.value = buttonsToCreate[i];
>                    newButton.id = buttonsToCreate[i];
>                    buttonContainer.appendChild(newButton);
>              }
>          };
>
>          </script>
>
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