FWD » Core Development » Base Language

In FWD, the implementation of OpenEdge.Net.HTTP.Lib.ABLSockets.ABLSocketLibrary uses Apache HttpClient library.

In this library, some headers are not allowed (or emitted also by the HttpClient); see this test for Content-Length and Transfer-Encoding:

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.EntityBuilder;
import org.apache.http.client.methods.HttpUriRequest;
import org.apache.http.impl.client.HttpClientBuilder;

public class ReqTest
{
   public static void main(String[] args) throws IOException, InterruptedException {
      String file = "abcdef";
      org.apache.http.client.methods.RequestBuilder requestBuilder = org.apache.http.client.methods.RequestBuilder
               .create("POST").setUri("https://httpbin.org/anything");
      requestBuilder.addHeader("Content-Type", "application/pdf");
      requestBuilder.addHeader("Authorization", "Token token=xyz");
      // requestBuilder.addHeader("Transfer-Encoding", "chunked");
      // requestBuilder.addHeader("Content-Length", String.valueOf(file.length()));
      HttpEntity httpEntity = EntityBuilder.create().setText(file).build();
      requestBuilder.setEntity(httpEntity);

      HttpUriRequest request = requestBuilder.build();
      HttpClient client = HttpClientBuilder.create().build();
      HttpResponse response = client.execute(request);
      ByteArrayOutputStream bos = new ByteArrayOutputStream();
      InputStream is = response.getEntity().getContent();
      long len = response.getEntity().getContentLength();
      for (int i = 0 ; i < len; i++)
      {
         bos.write(is.read());
      }
      System.out.println(new String(bos.toByteArray()));
      System.out.println();
  }
}

• log any IO errors during the HTTP request execution
• do not set the Context-Length or Transfer-Encoding to the actual HTTP request for the Apache HttpClient call

Sergey found that some request are 'forbidden' to be set (and can't be controlled programmatically) - see https://developer.mozilla.org/en-US/docs/Glossary/Forbidden_request_header

• what other headers can not be set for a HTTP Request in FWD (even if 4GL allows it), as is assumed to be calculated/set by the HttpClient library
• what happens in 4GL if the http request 'breaks' - previously we were ignoring these IOException's; test:
  • set the Content-Length twice in the request or other 'forbidden' headers
  • terminate (if possible) the network connection between the caller and the target server, to trigger a kind of IOException

Constantin, I just linked https://developer.mozilla.org/en-US/docs/Glossary/Forbidden_request_header to this issue because this is a similar issue but for the browser user agent.