Here's your opportunity to implement a couple of RESP commands in Garnet!

SDIFF

Syntax:
SDIFF key [key ...]

Command description:
Returns the members of the set resulting from the difference between the first set and all the successive sets.

For example:

key1 = {a,b,c,d}
key2 = {c}
key3 = {a,c,e}
SDIFF key1 key2 key3 = {b,d}

Keys that do not exist are considered to be empty sets.

Response:

Array reply: a list with members of the resulting set.

SDIFFSTORE

Syntax:
SDIFFSTORE destination key [key ...]

Command description:
This command is equal to SDIFF, but instead of returning the resulting set, it is stored in destination.

If destination already exists, it is overwritten.

Response:

Integer reply: the number of elements in the resulting set.

How to approach this task:

1. Add the new command info to the setCommandsInfoMap in the RespCommandsInfo class (Garnet.server/Resp/RespCommandsInfo.cs)
2. Add the new command string to the returned HashSet in the RespInfo.GetCommands method (Garnet.server/Resp/RespInfo.cs)
3. Add the appropriate fast parsing logic for the new command in the RespCommand.FastParseArrayCommand method (use other commands as reference) (Garnet.server/Resp/RespCommand.cs)
4. Implement the wrapper method to the storage layer in StorageSession (Garnet.server/Storage/Session/ObjectStore/SetOps.cs)
5. Define a new method in IGarnetAPI and implement it in GarnetApiObjectCommands, calling the method you have implemented in step #4 (Garnet.server/API/IGarnetAPI.cs, Garnet.server/API/GarnetApiObjectCommands.cs)
6. Add a new method to the RespServerSession class which will call the storage API and return the appropriate response (Garnet.server/Resp/Objects/SetCommands.cs)
7. Add a new method to SetObjImpl which will perform the required operation on the hash object (Garnet.server/Objects/Set/SetObjectImpl.cs)
8. Add a new enum value to SetOperation and add the appropriate case to the switch in SetObject.Operate, in which you will call the method defined in step #8 (Garnet.server/Objects/Set/SetObject.cs)
9. Add an appropriate case to the switch in TransactionManager.SetObjectKeys (Garnet.server/Transaction/TxnKeyManager.cs)
10. Add tests for the new command in the RespSetTests class (Garnet.test/RespSetTests.cs)

Tip: First add a simple test that calls the new command and use it to debug as you develop, it will make your life much easier!

If you have any questions, the Garnet team is here to help!