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Transform Traffic

Massage traffic before it is replayed


In order to replay properly, most apps require traffic to contain up to date JWTs, timestamps and more. Speedscale provides a general purpose data transformation system very similar to Unix pipes for this purpose.

Data is extracted, transformed and re-inserted into the RRPair

First, data is extracted from the RRPair using an Extractor. For example, an extractor might pull the value of a particular HTTP header in an request. Extractors always produce a string that can be further transformed. The extracted string is called a token throughout this documentation.

Next, the token is mutated or further isolated using a Transform. Transforms can do simple things like change the data to a hard coded text value. They can also do more complex things like parse and shift a date or insert a value selectively like a switch statement in a programming language. Transforms are always executed sequentially.

Transforms also have a data cache where variables can be stored. Variables function as named short term storage for the life of the request, just like in a programming language hashmap.

Last, the transformed data is re-inserted into the RRPair in exactly the same location. Each transform runs in reverse order to re-encode the new token and place it back in its correct place.


Concrete example of two transforms

As an example, let's assume we need to shift the date in an HTTP header. We would extract that header and apply a date offset. This is a complete transform chain.

For a second example, let's extract part of the request body and change a JSON key. That would also be a complete transform chain.

Each extractor and transform is detailed in the following subsections.