I have a simple FormFunction like this:

FormFunction[{"expr" -> ToExpression}, HTTPRequestData[] &]

When I use CloudDeploy, it works as normal. But when I use SocketListen and GenerateHTTPResponse to establish a server, my Chrome seems have submitted no data as I can't Find it in the results of HTTPRequestData.

I've tried remote server(instead of local), GenerateHTTPResponse(instead of any really existing server), #expr &(instead of HTTPRequestData[] &), none of them works. If I use APIFunction as the backend and URLRead as the client, everything is OK.

What's missing for the submission compared to the WolframCloud one?

Here I provide a minimal server code. When I run this code on my VPS and click the submit button on my Chrome, nothing was submitted in fact.

#!/usr/bin/env wolframscript
Respond[socketMsg_Association] := Module[
                client = socketMsg["SourceSocket"],
                data = socketMsg["Data"],
        request = ImportString[data, "HTTPRequest"];
        response = GenerateHTTPResponse[
                URLDispatcher@{"" -> EvaluationService}
        , request];
                ExportString[response, "HTTPResponse"]
EvaluationService = FormFunction[
        {"expr" -> <|"Interpreter" -> ToExpression, "Required"->False|>},
        #expr &
  • $\begingroup$ What are you trying to do with the form? $\endgroup$
    – kickert
    Jan 25, 2020 at 17:07
  • $\begingroup$ @kickert I just want to evaluate expressions via internet explorer etc.. $\endgroup$
    – bcegkmqs23
    Jan 26, 2020 at 5:23
  • $\begingroup$ @Kuba I've updated this question with a server code. The ToExpression usage is documented, here's a link: FormObject. In the "Details and Options", there's a tfun item listed below "Possible forms of type specifications are" $\endgroup$
    – bcegkmqs23
    Jan 28, 2020 at 9:03
  • $\begingroup$ Thanks for clarification, I was looking at Interpreter docs. btw, it boils down to the fact that HTTPRequest[...]["FormRules"] returns None. You could use this patch: requestFormRules = Rule @@@ Partition[#, 2] &@URLDecode@StringSplit[#, {"&", "="}] &@ StringTrim@FromCharacterCode[#["BodyBytes"], "UTF-8"] & but I am not sure how to apply it. $\endgroup$
    – Kuba
    Jan 28, 2020 at 10:38
  • 1
    $\begingroup$ It does not work because of HttpRequest generated from ImportString. Form values are missing even though they are in the body. I already reported this. $\endgroup$
    – Kuba
    Jan 28, 2020 at 16:25

1 Answer 1


As @Kuba had commented, ImportString[#, "HTTPRequest"]& does not turn POST parameters to rules. So the property "FormRules", which FormFunction utilizes, can't be generated.

Here is a function to finish this convertion when needed:

MakeFormRules[request_HTTPRequest] := With[
        makeFormRules = <|
            URLQueryDecode@StringTrim@FromCharacterCode[#, "UTF-8"]&
    If[AssociationQ@makeFormRules@request["Body"], MapAt[makeFormRules, {2, "Body"}]@request, request]

Using it to process HTTPRequest received, the example code given in the question works.

request = MakeFormRules@ImportString[data, "HTTPRequest"];

It seems that WolframCloud use a function not provided in CloudObject(I didn't find it by Names[something]) but in its backend, which deals with this example and multipart/formdata etc.


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