Nginx Redirect if GET request only

Question

I have a redirect (add trailing slash if there's not one) in nginx that I only want to run on GET requests in order to maintain POSTed data. Checking the if is evil article it seems like this setup is OK?:

location / {
  if ($request_method = GET) {
    rewrite ^([^.]*[^/])$ $1/ permanent;
  }
  try_files $uri $uri/ /index.php?$query_string;
}

However this rule appears to get me a 404 error on every request, before actually loading the content (because my 404 handler also goes through index.php I guess?). This is a Craft CMS site.

This doesn't seem to be an issue with the redirection part, this works fine (if I have no slash it redirects) it's when a trailing slash is hit that the 404 happens, so I presume it's something with the try_files part that's wrong somehow? However, weirdly, if I comment out the whole if statement (so it just runs the try_files) I don't get the 404.

If it helps here are the rest of the location blocks etc. in the config (these all follow the location / block shown above)

location = /favicon.ico { access_log off; log_not_found off; }
location = /robots.txt  { access_log off; log_not_found off; }

access_log off;
error_log  /var/log/nginx/mysite.com-error.log error;

error_page 404 /index.php;

location ~ \.php$ {
    fastcgi_split_path_info ^(.+\.php)(/.+)$;
    fastcgi_pass unix:/var/run/php/php7.3-fpm.sock;
    fastcgi_index index.php;
    include fastcgi_params;
}

location ~* \.(css|js|gif|png|ico|svg)$ {
    try_files $uri $uri/ /index.php?p=$uri&$args;
    expires 7d;
}

location ~* \.(jpg|jpeg)$ {
    expires 7d;
}

location ~ /\.ht {
    deny all;
}

location ~ /\.(?!well-known).* {
    deny all;
}

Answer 1

The problem is that the if context processes all of the GET requests.

Assuming that the POST requests should be handled by /index.php , you could use the if block to handle all POST requests instead.

For example:

location / {
    if ($request_method = POST) {
        rewrite ^ /index.php last;
    }
    rewrite ^([^.]*[^/])$ $1/ permanent;
    try_files $uri $uri/ /index.php?$query_string;
}