Return {error, max_length} instead of exception in cowboy_req:body/2

[benbro]

When the request max length is larger than the limit, cowboy throws an exception error:function_clause.
Wouldn't it be better to catch this case and return {error, max_length} or something similar?

https://github.com/extend/cowboy/blob/master/src/cowboy_req.erl#L705

-spec read_body(non_neg_integer() | infinity, Req, binary())
    -> {ok, binary(), Req} | {error, atom()} when Req::req().
read_body(MaxLength, Req, Acc) when MaxLength > byte_size(Acc) ->
    case stream_body(Req) of
        {ok, Data, Req2} ->
            read_body(MaxLength, Req2, << Acc/binary, Data/binary >>);
        {done, Req2} ->
            {ok, Acc, Req2};
        {error, Reason} ->
            {error, Reason}
    end;
read_body(_MaxLength, _Req, _Acc)  -> {error, max_length}.

[dvv]

seconded

[essen]

Just wondering why you would have a MaxLength larger than the request body size though?

[dvv]

take a look at #309

[essen]

No answers there.

[essen]

I'm sorry to say that I'm thinking of removing this function entirely.

It's just too unsafe. Me and @dvv agree it's best handled in your own code, where you can choose to throw, or to handle it, by calling stream_body directly, and looping similarly to this. Problem is that Cowboy here has no way of doing it without introducing risks that you might end up with the wrong state depending on what you are doing with it.

I prefer removing and perhaps providing an example later on instead.

[essen]

Removed in 2690d12. Thanks!