HTTP request to external web service

[kme...@minerva-group.com]

I have a HTTP server using mochiweb and I would like it to do an HTTP request to an external web service, wait for the result, do something with it, and then return a HTTP response.

How would you approach this situation in mochiweb?

In my case I would like to leverage data from the Amazon Advertising API, using the amazonproductapi library ( https://github.com/arjan/amazonproductapi )

[Bob Ippolito]

I think you've described the solution pretty well. Just use a HTTP client library to make the request to the external service and do whatever it is you need to do with the response. The fact that you're also using mochiweb is irrelevant. 

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[kme...@minerva-group.com]

When I am using the amazonproductapi to make a request, I am getting the following crash:

=CRASH REPORT==== 19-Jun-2013::17:32:50 ===

  crasher:

    initial call: mochiweb_acceptor:init/3

    pid: <0.104.0>

    registered_name: []

    exception exit: {noproc,

                     {gen_server,call,

                      [httpc_manager,

                       {request,

                        {request,undefined,<0.104.0>,0,http,

                         {"webservices.amazon.com",80},

                         "/onca/xml",

                         "?

                         get,

                         {http_request_h,undefined,"keep-alive",undefined,

                          undefined,undefined,undefined,undefined,undefined,

                          undefined,undefined,undefined,undefined,undefined,

                          undefined,undefined,undefined,

                          "webservices.amazon.com",undefined,undefined,

                          undefined,undefined,undefined,undefined,undefined,

                          undefined,undefined,[],undefined,undefined,

                          undefined,undefined,"0",undefined,undefined,

                          undefined,undefined,undefined,undefined,[]},

                         {[],[]},

                         {http_options,"HTTP/1.1",infinity,true,

                          {essl,[]},

                          undefined,false,infinity,false},

                         "http://webservices.amazon.com/onca/xml?

                         [],none,[],1371677570196,undefined,undefined,false}},

                       infinity]}}

      in function  gen_server:call/3 (gen_server.erl, line 188)

      in call from httpc:handle_request/9 (httpc.erl, line 584)

      in call from amazonproductapi:do_rest_call/4 (src/amazonproductapi.erl, line 65)

      in call from isbn_imageserver:handle_test/2 (src/isbn_imageserver.erl, line 86)

      in call from mochiweb_http:headers/5 (src/mochiweb_http.erl, line 101)

    ancestors: [mochiweb_http,isbn_imageserver_sup,<0.30.0>]

The line causing this is the following: https://github.com/kennym/amazonproductapi/blob/master/src/amazonproductapi.erl#L65

and the call was as following: amazonproductapi:itemSearch(Isbn, ?A_CONFIG) % where ?A_CONFIG is the API config object

This only happens when I run this inside of my mochiweb server, not when I run this from the console.

Do you have any ideas why this is happening? I cannot start a lot with the crash report.

On Tuesday, June 18, 2013 4:27:17 PM UTC-4, Bob Ippolito wrote:

I think you've described the solution pretty well. Just use a HTTP client library to make the request to the external service and do whatever it is you need to do with the response. The fact that you're also using mochiweb is irrelevant. 

On Tuesday, June 18, 2013, wrote:

I have a HTTP server using mochiweb and I would like it to do an HTTP request to an external web service, wait for the result, do something with it, and then return a HTTP response.

How would you approach this situation in mochiweb?

In my case I would like to leverage data from the Amazon Advertising API, using the amazonproductapi library ( https://github.com/arjan/amazonproductapi )

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[Jon Watte]

Mochiweb doesn't have a HTTP client library in itself. OTP does, though.

When using R13, the HTTP client available in OTP wasn't particularly robust -- it failed for our case (I think the problem was multiple overlapping requests got confused, IIRC.)

I don't know if that's been fixed since then, but we ended up implementing our own HTTP client for the kinds of requests we needed.

Sincerely,

jw

Sincerely,

Jon Watte


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[Kenny Meyer]

> I don't know if that's been fixed since then, but we ended up implementing our own HTTP client for the kinds of requests we needed.

How do you use it? Can you show me some code?

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Kenny Meyer <kme...@minerva-group.com>

[Bob Ippolito]

This is the error that you get from httpc if you haven't started the inets application. If you start the inets application, this will probably work just fine.

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[Kenny Meyer]

Thanks Bob, that fixed it. I have picked up Erlang a week ago, so there's still a lot I don't know.

Feeling much better now :)

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Kenny Meyer <kme...@minerva-group.com>

[Bob Ippolito]

It takes a little time to learn how to read those error messages. When I look at this error message I see a {noproc, {gen_server, call, _}} exit, which always means that you're trying to call a server that isn't currently running. This typically means that you haven't started all of the applications that your app depends on.