[WIP] New ETag Commands Syntax + ETag Object Support

[TalZaccai]

<<This PR is still a work in progress>>

This PR introduces a notion of "meta commands" - commands that "envelop" existing data commands.
The meta commands introduced in this PR are ETag related - EXECWITHETAG (execute a command and add the dest key's etag to the output), as well as EXECIFMATCH, EXECIFNOTMATCH, EXECIFGREATER (conditionally-execute a command based on the dest key's ETag in relation to the ETag meta-argument).

These command are able to replace the existing etag-related commands and command arguments, and in-turn support many more (including object commands).
For example:
DELIFGREATER key etag -> EXECIFGREATER etag DEL key
GETIFNOTMATCH key etag -> EXECIFNOTMATCH etag GET key
GETWITHETAG key -> EXECWITHETAG GET key
SETIFMATCH key value etag -> EXECIFMATCH etag SET key value

To achieve this logic, we parse the meta command and its meta-arguments into the SessionParseState. Currently this logic supports a constant number of meta-arguments which is defined in the Arity property in the meta-command's RespCommandInfo (arg count = arity - 1).
When the parse state gets handed to the appropriate ISessionFunctions method, the method decides whether the operation should get executed (in the case of conditional-execution) and to what value should the record's ETag advance (if at all).
The "special output" (in case the ETag needs to be written along with the command output) is handled by the ISessionFunctions method in the main and unified case, and in the IGarnetObject.Operate method in the object case.

To-do:

• Add new supported meta-commands, remove existing etag commands and command arguments & update usages
• Implement meta-command and meta-argument parsing in the RESP command parser.
• Update SessionParseState to parse and hold meta-arguments
• Update InputHeader to include meta-command and update commands
• Implement ETag-related meta-command handling in ISessionFunctions for all 3 contexts
• Implement meta-command-based ETag output for all object commands
• Handle ETags in operations that do not call into ISessionFunctions (internal transactions)
• Handle ETags in custom operations
• Further clean-up of ETag logic in ISessionFunctions
• Introduce leaner AOF serialization for commands with single long meta-argument
• Support programmatic commands supplying long etag without serializing to parse state

Testing & Benchmarking:

• Expand existing main-store ETag tests to include all meta-commands
• Verify all write commands result in ETag advancement
• Verify ETag output added to all commands when meta-command present
• Verify running meta-commands within transactions
• Verify ETag advancement + ETag output with custom commands
• Verify benchmarking numbers on commands without ETags
• Consider adding benchmarking logic for meta-commands with basic commands / basic commands with ETags

[Copilot]

Pull request overview

This PR introduces a new "meta command" architecture for ETag operations in Garnet. Instead of separate commands like GETWITHETAG, SETIFMATCH, etc., the PR implements wrapper commands (EXECWITHETAG, EXECIFMATCH, EXECIFNOTMATCH, EXECIFGREATER) that can envelop any data command. This provides a more unified and extensible approach to ETag handling across both main store and object store operations.

Key changes include:

• Introduction of meta command parsing infrastructure that supports nested command execution
• Replacement of standalone ETag commands with meta command wrappers
• Extension of ETag support to object store operations (particularly sorted sets)

Reviewed changes

Copilot reviewed 80 out of 80 changed files in this pull request and generated 15 comments.

Show a summary per file

File	Description
test/Garnet.test/*.cs	Updated test files to use new meta command syntax (e.g., EXECWITHETAG SET instead of SET...WITHETAG)
libs/server/Resp/Parser/SessionParseState.cs	Added meta argument tracking with separate buffer pointers and count
libs/server/Resp/Parser/RespCommand.cs	Implemented meta command parsing with nested command detection
libs/server/Storage/Functions/**/VarLenInputMethods.cs	Updated field info methods to use MetaCmd.IsEtagCommand() instead of flag checks
libs/server/Storage/Functions/**/RMWMethods.cs	Refactored ETag handling to use GetUpdatedEtag() utility and support conditional execution
libs/server/Storage/Functions/SessionFunctionsUtils.cs	Added helper methods for ETag computation and conditional execution checks
playground/CommandInfoUpdater/*.json	Updated command metadata to reflect removed/added commands
samples/ETag/*.cs	Updated sample code to use new meta command syntax

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[badrishc]

add comments on what execOp and updatedEtag mean. ideally Operate and calls like it should not accept arguments about etags specifically. they just receive a meta command and its arguments.

[TalZaccai]

I agree, that irks me too, the issue here is that Operate sets the output of the command which may need to include the etag (and there are different scenarios depending on the Operate logic, for instance it may need to only output an error without the etag even when one is requested).

[badrishc]

meta command could be 0 by default, to simplify the common cases where nobody cares about meta commands.

[TalZaccai]

I wanted to err on the side of caution here, I didn't want it to be easy to just forget to input the meta command. If you want to ignore it, you should do so explicitly.

[badrishc]

it is unclear whether parseState here contains the wrapping command as well. ideally we have a parse state for the actual command that is no different from before, and an optional extra parse state for the outer wrapper shell.

[TalZaccai]

parseState contains both, and they are seperately accessed. The meta-parameters preceed the "standard" parameters on the buffer. You would access the standard parameters as you would before (indexes unchanged) and you access the meta-parameters by explicitly specifying isMetaArg: true.