Implement TM2p change (no message version populating from channelmessage)

[SimonWoolf]

Implements ably/specification#275

Summary by CodeRabbit

• Bug Fixes
  • Refined the logic for assigning message identifiers to ensure they are set only under valid conditions, improving message consistency.
• Documentation
  • Updated the messaging version field guidance to more clearly reflect behavior based on configuration settings.

[coderabbitai]

Walkthrough

This change refines the logic for handling message properties within the messaging system. In the ChannelBase class, the condition for setting msg.serial now checks whether msg.version is not null, ensuring that the serial value is only assigned when a valid version exists. Additionally, the logic that previously formatted and set msg.version based on channelSerial has been removed. The Message class has also been updated, modifying its documentation comment for the version field to reflect that the version may not always be populated.

Changes

File(s)	Change Summary
lib/src/main/java/io/ably/lib/realtime/ChannelBase.java	Updated the onMessage method to assign msg.serial only if msg.version is not null, and removed the previous logic that set msg.version from channelSerial.
lib/src/main/java/io/ably/lib/types/Message.java	Revised the documentation for the version field to indicate that its population is dependent on application and channel namespace settings.

Sequence Diagram(s)

sequenceDiagram
    participant CB as ChannelBase.onMessage()
    participant Msg as Message
    CB->>Msg: Receive incoming message
    alt msg.action == MESSAGE_CREATE and msg.serial is null
        CB->>CB: Check if msg.version is not null
        alt msg.version exists
            CB->>Msg: Set msg.serial = msg.version
        else
            CB->>Msg: Do not assign msg.serial
        end
    else
        CB->>Msg: Process message normally
    end

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Possibly related PRs

• [ECO-5193] Support message edits and deletes #1059: Introduced new fields and methods in the Message class, which are closely related to the modifications in message property handling seen in the current PR.

Suggested reviewers

• ttypic

Poem

I'm a little rabbit, hopping with glee,
Fixing code branches as spry as can be.
Serial now set only when version is bright,
Message flows steady, coding just right.
With boundless joy in every tweak, I celebrate these changes so sleek!
🐇✨

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Reviewing files that changed from the base of the PR and between fd12be9 and 00bdd5f.

📒 Files selected for processing (2)

• lib/src/main/java/io/ably/lib/realtime/ChannelBase.java (1 hunks)
• lib/src/main/java/io/ably/lib/types/Message.java (1 hunks)

✅ Files skipped from review due to trivial changes (1)

• lib/src/main/java/io/ably/lib/types/Message.java

⏰ Context from checks skipped due to timeout of 90000ms (8)

• GitHub Check: check (29)
• GitHub Check: check-rest-okhttp
• GitHub Check: check-realtime-okhttp
• GitHub Check: check (24)
• GitHub Check: check-realtime
• GitHub Check: check (21)
• GitHub Check: check (19)
• GitHub Check: check-rest

🔇 Additional comments (1)

lib/src/main/java/io/ably/lib/realtime/ChannelBase.java (1)

860-860: Verify specification compliance for TM2p changes.

The change aligns with the TM2p specification by setting msg.serial based on msg.version instead of the previous logic. This ensures that serial values are only populated when a valid version exists.

Please verify:

1. Specification compliance: Confirm that this change fully implements the TM2p specification requirements.
2. Backward compatibility: Ensure that existing code handling message serials can handle cases where the serial might not be set.

✅ Verification successful

🌐 Web query:

What are the requirements for TM2p in Ably's specification regarding message version and serial properties?

💡 Result:

The requirements for TM2p in Ably's specification mandate specific handling of message versions through an opaque identifier:

Version Property

• Messages must include a version string that:
  • Uniquely identifies different message versions[5]
  • Changes whenever message content changes[5]
  • Is considered opaque (no specific format required)[5]

Implementation Requirements

• The version must be included when converting messages to ProtocolMessages for delivery through Ably's system[9]
• Version uniqueness must be maintained across successive updates of the same logical message[1][5]

For example in Java implementations:

public String version; // Opaque string tracking message revisions

This ensures subscribers receive only distinct versions during scenarios like:

• Message conflation (where latest versions replace outdated ones)[1]
• Idempotent publishing (preventing duplicate processing)[1][5]

The specification doesn't explicitly mention separate "serial" properties beyond this version requirement, focusing instead on using this version identifier as the primary mechanism for tracking message revisions[5][9].

Citations:

• 1: https://ably.com/docs/messages
• 2: https://freidok.uni-freiburg.de/files/631/Q_gU7P08bbKsjY3A/diss_signed.pdf
• 3: https://github.com/ably/ably-cocoa
• 4: https://files.ably.io/website/documents/data-sheets/using-the-ably-platform-at-scale-apr-2019.pdf
• 5: https://ably.com/docs/sdk/java/v1.2/io/ably/lib/types/Message.html
• 6: https://www.worldradiohistory.com/Archive-All-Amateur/World-Radio/90s/World-Radio-1995-01.pdf
• 7: https://github.com/ably/ably-js/activity
• 8: https://www.worldradiohistory.com/Archive-All-Amateur/World-Radio/90s/World-Radio-1994-12.pdf
• 9: https://www.rubydoc.info/gems/ably/Ably/Models/Message

---

TM2p Specification Compliance Verified

Based on the TM2p requirements, using the opaque version property as the unique message identifier—by assigning it to msg.serial when applicable—is consistent with the specification. The code correctly ensures that the serial is set only when a valid version exists and the message action is MESSAGE_CREATE, aligning with the mandate that messages carry a unique, opaque version identifier for message revisions.

• Specification compliance: The change implements the TM2p requirement of using the version identifier as a unique revision marker.
• Backward compatibility: Since TM2p does not require a distinct serial property apart from this behavior, the change should not disrupt existing message handling.

✨ Finishing Touches

• 📝 Generate Docstrings (Beta)

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[sacOO7]

Added few comments on spec PR https://github.com/ably/specification/pull/275/files#r1954299329. Otherwise PR looks good

[sacOO7]

LGTM