# Is there a contract my HTTP filter must adhere to?¶

• During encoding/decoding of headers if a local reply wasn’t sent and a filter returns FilterHeadersStatus::StopIteration, the processing can be resumed if encodeData()/decodeData() return FilterDataStatus::Continue or by explicitly calling continueEncoding()/continueDecoding().

• During encoding/decoding of headers if a local reply wasn’t sent and a filter returns FilterHeadersStatus::StopAllIterationAndBuffer or FilterHeadersStatus::StopAllIterationAndWatermark, the processing can be resumed by calling continueEncoding()/continueDecoding().

• A filter’s decodeHeaders() implementation must not return FilterHeadersStatus::ContinueAndDontEndStream when called with end_stream set to false. In this case FilterHeadersStatus::Continue should be returned.

• A filter’s encode100ContinueHeaders() must return FilterHeadersStatus::Continue or FilterHeadersStatus::StopIteration.

• Data encoding/decoding

• During encoding/decoding of data if a local reply wasn’t sent and a filter returns FilterDataStatus::StopIterationAndBuffer, FilterDataStatus::StopIterationAndWatermark, or FilterDataStatus::StopIterationNoBuffer, the processing can be resumed if encodeData()/decodeData() return FilterDataStatus::Continue or by explicitly calling continueEncoding()/continueDecoding().

• Trailers encoding/decoding

• During encoding/decoding of trailers if a local reply wasn’t sent and a filter returns FilterTrailersStatus::StopIteration, the processing can be resumed by explicitly calling continueEncoding()/continueDecoding().

# Are there well-known headers that will appear in the given headers map of decodeHeaders()?¶

The first filter of the decoding filter chain will have the following headers in the map:

• Host

• Path (this might be omitted for CONNECT requests).

Although these headers may be omitted by one of the filters on the decoding filter chain, they should be reinserted before the terminal filter is triggered.