Salesforce HTTP RESTful Webservice stopped working at some point

Question

We are using a HTTP Restful Outbound Webservice which was working fine for 2 years but suddenly stopped working which we are not able to understand the reason. It's giving below error.

System.CalloutException: Unable to tunnel through proxy. Proxy returns "HTTP/1.0 404 Not Found"

It looks like Firewall issue to us, but our internal Network team is claiming that, the inbound request from Salesforce is not reaching our Firewall as per logs though IP's provided by Salesforce are correctly whitelisted. But this is working in Sandboxes so we don't think it's Salesforce issue. I would like to know if there is a tool or by any means, can we ping our ESB servers from Salesforce instance?

public class postCall(String siebelId ){

        Http h = new Http();
        HttpRequest req = new HttpRequest();
     req.setEndpoint('https://esb.ent.abc.org/ServiceRequest');
        req.setMethod('POST');
        req.setBody('{"ocl:accountId":"'+siebelId+'"}');
        req.setHeader('Token', '9fdb3ab5-efc8-473f-bc5e-a474b0b9d1e2');
         HttpResponse res = h.send(req);
        System.debug(res.getBody());
 }

Answer 1

From the Salesforce instance, you can use a script which mimics this request in a VF or lightning component:

Before any Visualforce page, Apex callout, or JavaScript code using XmlHttpRequest in an s-control or custom button can call an external site, that site must be registered in the Remote Site Settings page, or the call fails.

To enable corresponding access for Lightning components, create a CSP Trusted Site.

For example:

var request = new Request('https://esb.ent.abc.org/ServiceRequest');

fetch(request, {
    mode: 'cors', 
    method: 'POST',
    body: '{"ocl:accountId":"'+siebelId+'"}'
    credentials: 'include',
    headers: {
             'Authorization': 'Bearer TOKEN'
             'Token': '9fdb3ab5-efc8-473f-bc5e-a474b0b9d1e2'
             }
}).then(function(response) {
    document.title = JSON.stringify(response);
}).catch(function(error) {
    document.title = 'Request failed:  ' + JSON.stringify(error)
});

You need to setup CORS headers on your endpoint for this to work.

References

• Configure Remote Site Settings

• Create CSP Trusted Sites to Access Third-Party APIs

• Cross-Origin Resource Sharing (CORS) | MDN

• Fetch directive | MDN

• Javascript Fetch API Example Tutorial From Scratch