Motivation:
Since https://github.com/netty/netty/pull/9865 (Netty 4.1.44) the
default behavior of the HttpObjectDecoder has been to reject any HTTP
message that is found to have multiple Content-Length headers when
decoding. This behavior is well-justified as per the risks outlined in
https://github.com/netty/netty/issues/9861, however, we can see from the
cited RFC section that there are multiple possible options offered for
responding to this scenario:
> If a message is received that has multiple Content-Length header
> fields with field-values consisting of the same decimal value, or a
> single Content-Length header field with a field value containing a
> list of identical decimal values (e.g., "Content-Length: 42, 42"),
> indicating that duplicate Content-Length header fields have been
> generated or combined by an upstream message processor, then the
> recipient MUST either reject the message as invalid or replace the
> duplicated field-values with a single valid Content-Length field
> containing that decimal value prior to determining the message body
> length or forwarding the message.
https://tools.ietf.org/html/rfc7230#section-3.3.2
Netty opted for the first option (rejecting as invalid), which seems
like the safest, but the second option (replacing duplicate values with
a single value) is also valid behavior.
Modifications:
* Introduce "allowDuplicateContentLengths" parameter to
HttpObjectDecoder (defaulting to false).
* When set to true, will allow multiple Content-Length headers only if
they are all the same value. The duplicated field-values will be
replaced with a single valid Content-Length field.
* Add new parameterized test class for testing different variations of
multiple Content-Length headers.
Result:
This is a backwards-compatible change with no functional change to the
existing behavior.
Note that the existing logic would result in NumberFormatExceptions
for header values like "Content-Length: 42, 42". The new logic correctly
reports these as IllegalArgumentException with the proper error message.
Additionally note that this behavior is only applied to HTTP/1.1, but I
suspect that we may want to expand that to include HTTP/1.0 as well...
That behavior is not modified here to minimize the scope of this change.
f7fa9fce72