POST Request unable to receive the JSON respose in Salesforce - salesforce

Question

I am calling an API of FluidSurvey. when i make a POST request ... it post the request on the fluidSurvey but i didnt get the JSON response. rather it returns nothing. any suggestion??
my controller code
public class fluidSurvey{
public String tst{set;get;}
public String result{get;set;}
public PageReference chk() {
getData();
return null;
}
public void getData(){
String apiKey = 'xxxxxx';
String pwd = 'xxxxxx';
String u = 'https://app.fluidsurveys.com/api/v2/surveys/survey_id/responses/';
HttpRequest req = new HttpRequest();
Http http = new Http();
HTTPResponse res;
try{
req.setEndPoint(u);
req.setTimeout(2000);
req.setMethod('POST');
Blob headerValue = Blob.valueOf(apikey + ':' + pwd);
String authorizationHeader = 'Basic '+ EncodingUtil.base64Encode(headerValue);
req.setHeader('Authorization', authorizationHeader);
req.setHeader('Content-Type', 'application/json');
req.setHeader('Content-Length','31999');
res = http.send(req);
tst= res.toString();
catch(Exception e){
System.debug('Callout error: '+ e);
System.debug(tst+'--------'+res);
}
}
}
and the Apex page code is
<apex:page controller="fluidSurvey">
<apex:form >
<apex:pageBlock title="New Fluid Surveys API">
<apex:outputText value="{!tst}"></apex:outputText><br/>
<apex:pageBlockButtons location="bottom">
<apex:commandButton value="Submit" action="{!chk}"/>
</apex:pageBlockButtons>
</apex:pageBlock>
</apex:form>
and api documentation link is http://docs.fluidsurveys.com/api/surveys.html#getting-a-list-of-surveys..

Answer 1

FluidSurveys Dev here.
Looks like you're doing a POST request, which according to the docs is for creating a new response. But your function is named getData, so I'm assuming you want to get a list of responses?
Change the request type from GET to POST and it should start to work.
Also, the response type will be application/json, but you shouldn't be setting the request type to that encoding.
If I'm mistaken and you're looking to submit a new response, then this code wouldnt work because you're not actually passing any content.
As you can see by http://docs.fluidsurveys.com/api/surveys.html#submitting-a-new-response you need to actually pass a dictionary of question ids and answers. The best way to figure out what the ids are or what the format is, is to first look at the response returned from a GET request.

Answer 2

The problem with my code was that i setting a content-length header, but not setting any body,the server is diligently waiting for the 3199 byte body. so after using the setBody method my code properly returns a json response

Answer 3

I wanted to add to this answer in that I found that some messages from Apex being posted to external endpoints were getting dropped by firewalls on the other end due to intrusion detection rules.
Apparently, there are conditions where on the Apex end, outbound messages do not conform to certain construction rules that prevent man-in-the-middle attacks and some firewalls or IDS are blocking them. This will appear on the Apex side as a "Read Time Out".
The specific IDS rule is CVE-2009-3555 (http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2009-3555).
If you are experiencing read timeouts in Apex to external endpoints and can't isolate them to apex programming, you might do some logging on the destination firewall to see if this is the issue, and if it is, create an exception in that firewall for this type of case.