Update: It’s GoCardless who moved
api.gocardless.comto Google Cloud. Google Cloud has behaved this way for years.
I think that Google App Engine may have recently started requiring every
POST request to have a
Content-Length header, even if there is no request body.
That will cause you problems if your library doesn’t add one for
POST requests that have no content. Perl’s HTTP::Request is one such library.
You might be experiencing this if an API has just started replying to you with:
Error 411 (Length Required)!!1
POST requests require a
(Yes, the title does contain “!!1”.)
You can fix it by adding the header yourself, e.g.:
my $ua = LWP::UserAgent->new; my $req = HTTP::Request->new( POST => 'https://api.example.com/things/$id/actions/fettle' ); $req->header('Accept' => 'application/json'); $req->content_type('application/json'); my $json; $json = JSON->new->utf8->canonical->encode($params) if $params; $req->content($json) if $json; # Explicitly set Content-Length to zero as HTTP::Request doesn't add one # when there's no content. $req->header( 'Content-Length' => 0 ) unless $json; my $res = $ua->request( $req );
This is a bit far outside of my comfort zone so I’m not sure if I’m 100% correct, but I do know that sending the header fixes things for me.
What happened? ^
Yesterday a BitFolk customer tried to cancel their Direct Debit mandate, and it didn’t work. The server logs contained the above message.
For Direct Debit payments we use the Perl module Business::GoCardless for integrating with GoCardless, but the additional HTML styling in the message (which I’ve left out for brevity) made clear that the message was coming from Google.
api.gocardless.com is hosted on Google App Engine (or some bit of Google cloud anyway).
After a bit of debugging I established that HTTP::Request was only setting a
Content-Length header when there was actually request content. The API for cancelling a Direct Debit mandate is to send an empty
Content-Length: 0 makes it work again.
When did it change? ^
There was a successful mandate cancellation on 25 October 2018, so some time between then and 12 December 2018. I haven’t looked for any change notice put out by Google as I’m not a Google Cloud user and wouldn’t know where to look.
Who’s to blame ^
I haven’t yet looked into whether the HTTP standard requires
POST requests to have a
Content-Length header. I welcome comments from someone who wants to do the digging.
Realistically even if it doesn’t and Google is just being overly strict, other servers might also be strict, so I guess HTTP::Request should always send the header.