Benoit Tellier created JAMES-3365:
-------------------------------------

             Summary: JMAP RFC-8621 : Back-reference resolution
                 Key: JAMES-3365
                 URL: https://issues.apache.org/jira/browse/JAMES-3365
             Project: James Server
          Issue Type: New Feature
          Components: JMAP
            Reporter: Benoit Tellier
            Assignee: Antoine Duprat


## Why

https://jmap.io/spec-core.html#references-to-previous-method-results

To allow clients to make more efficient use of the network and avoid round 
trips, an argument to one method can be taken from the result of a previous 
method call in the same request.

Example:

{code:java}
[[ "Foo/changes", {
    "accountId": "A1",
    "sinceState": "abcdef"
}, "t0" ],
[ "Foo/get", {
    "accountId": "A1",
    "#ids": {
        "resultOf": "t0",
        "name": "Foo/changes",
        "path": "/created"
    }
}, "t1" ]]
{code}

`back references` that mean server will reuse the result of a previous method 
call in the same request.
Process is:
- When processing a method call, the server MUST first check the arguments 
object for any names beginning with **#**.
- If found, the result reference should be resolved and the value used as the 
“real” argument.
- If any result reference fails to resolve, the whole method MUST be rejected 
with an **invalidResultReference** error.
- If an arguments object contains the same argument name in normal and 
referenced form (e.g., foo and #foo), the method MUST return an 
**invalidArguments** error.

A **ResultReference** object has the following properties:
- **resultOf**: String The method call id (see Section 3.1.1) of a previous 
method call in the current request.
- **name**: String The required name of a response to that method call.
- **path**: String A pointer into the arguments of the response selected via 
the name and resultOf properties. This is a JSON Pointer, except it also allows 
the use of * to map through an array (see the description below).

## How

https://github.com/linagora/james-project/pull/3683 demonstrated a proof of 
concept doing JSON substitution within the method arguments (relying on 
play-JSON JSON transformers) before the actual processing start

This makes back-reference resolution completly orthogonal to the Methods being 
written.

## Definition of Done

Write some simple memory integration tests demonstrating back-references are 
resolved. Also test back-reference resolution failure.




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