400 bad request despite correct request handling

Question

I am having trouble getting an AJAX request to work. From this earlier thread it appears the request handler and hooks to register the handler are not the issue: Wordpress: Ajax request logs 400 Bad Request to console

The framework (wordpress) does send ajax requests (to the same target) with a "heartbeat" k/v pair every minute or so. I've copied my bad request and one of these good requests from the core below. What sticks out is the response header of text/html in my one. Could that cause a bad REQUEST ? If not what else might cause it?

Request Headers

// my bad request. Error code 400 "BAD REQUEST"
Request URL:http://localhost/wptest2/wp-admin/admin-ajax.php
Request method:POST
Remote address:127.0.0.1:80
Status code: 400
Version:HTTP/1.1

Response headers (177 B)    
Raw headers
Connection  close
Content-Length  165
Content-Type    text/html; charset=UTF-8
Date    Sun, 05 May 2019 04:58:48 GMT
Server  Apache/2.4.29 (Ubuntu)

Request headers (1.030 KB)  
Raw headers
Accept    application/json, text/javascript, */*; q=0.01
Accept-Encoding gzip, deflate
Accept-Language  en-US,en;q=0.5
Connection  keep-alive
Content-Length  30
Content-Type    application/json
Cookie    wordpress_69cb7e12fdbb27dfb560…2-1ebb-4ab4-ba67-14f7be9e4c98
Host    localhost
Referer http://localhost/wptest2/wp-ad…-general.php?page=fvc-settings
User-Agent  Mozilla/5.0 (X11; Ubuntu; Linu…) Gecko/20100101 Firefox/66.0
X-Requested-With    XMLHttpRequest


// A working request done automatically every minute or two by wordpress core
Request URL:http://localhost/wptest2/wp-admin/admin-ajax.php
Request method:POST
Remote address:127.0.0.1:80
Status code: 200
Version:HTTP/1.1

Response headers (605 B)    
Raw headers
Cache-Control     no-cache, must-revalidate, max-age=0
Connection  Keep-Alive
Content-Length   423
Content-Type     application/json; charset=UTF-8
Date    Sun, 05 May 2019 04:59:46 GMT
Expires Wed, 11 Jan 1984 05:00:00 GMT
Keep-Alive    timeout=5, max=100
Referrer-Policy strict-origin-when-cross-origin
Server  Apache/2.4.29 (Ubuntu)
X-Content-Type-Options  nosniff
X-Frame-Options SAMEORIGIN
X-QM-overview-memory    7,444 kB
X-QM-overview-memory_usage  5.7% of 131,072 kB limit
X-QM-overview-time_taken    0.5868
X-QM-overview-time_usage    2.0% of 30s limit
X-Robots-Tag    noindex

Request headers (1.062 KB)  
Raw headers
Accept    application/json, text/javascript, */*; q=0.01
Accept-Encoding gzip, deflate
Accept-Language en-US,en;q=0.5
Connection  keep-alive
Content-Length  99
Content-Type    application/x-www-form-urlencoded; charset=UTF-8
Cookie    wordpress_69cb7e12fdbb27dfb560…2-1ebb-4ab4-ba67-14f7be9e4c98
Host    localhost
Referer http://localhost/wptest2/wp-ad…-general.php?page=fvc-settings
User-Agent  Mozilla/5.0 (X11; Ubuntu; Linu…) Gecko/20100101 Firefox/66.0
X-Requested-With    XMLHttpRequest

Ajax Calls

Of course I only test one at a time.

jQuery(document).ready(function() {
      jQuery('#previousButton').click(function() {
        jQuery.ajax({
          type: "POST",
          url: ajaxurl,
          headers : {
            'Content-Type' : 'application/json'
          },
          dataType: "json",
          action: "selectTargetsWithOffset",
          data: {
            action: "selectTargetsWithOffset",
          },
          success: function() {
            console.log(response, `=====response from $.ajax}=====`);
          }
        });

      });

You are saying the datatype is json but the data you are passing is not a valid json. — Carlos Alves Jorge, May 07 '19 at 09:08
The comment of @CarlosAlvesJorge seems valid. Try this: `var data = { action: "selectTargetsWithOffset" };` and then in the `ajax` call use this: `data: JSON.stringify(data)` — Leron, May 07 '19 at 09:35
You can use this question for reference: https://stackoverflow.com/questions/12693947/how-to-send-json-instead-of-a-query-string-with-ajax — Leron, May 07 '19 at 09:38

score 2 · Answer 1 · answered May 07 '19 at 08:20

On first looking at your question, I thought your issue may have been a formatting issue - a large chunk of your file looks 'commented out'. If the commenting is intentional [and not a mistake in the SO post], I suggest you start by making a backup copy of the file and then delete any unnecessary parts of the file.

Then:

Clear your cookies; invalid/expired session cookies can sometimes cause a 400 error.
check that the url you're accessing is ok (no misspellings etc.)
Check the size of the file you're submitting is small enough to be accepted. files that are too large can be rejected by the server with a 400 error

Definitely check over your file for formatting errors and special characters. (why the ;q=0.01 before the Accept-Encoding?)

Hope this helps.

P.S. You may find this article helpful

400 bad request despite correct request handling

Request Headers

Ajax Calls

1 Answers1