fix(sio): isolate recovery offsets across child namespaces

[xingsy97]

The kind of change this PR does introduce

• a bug fix
• a new feature
• an update to the documentation
• a code change that improves performance
• other

Current behavior

With connection state recovery enabled, room-targeted parent broadcasts pass the same packet to every child adapter. Each child appends its recovery offset to the shared data array, also modifying events already cached by earlier children. A replayed event can therefore carry another child's offset, causing a subsequent session recovery to fail.

New behavior

Shallow-copy the packet and its data array for each child adapter. Recovery offsets remain isolated, while nested payload objects and Buffers retain their original references.

[darrachequesne]

Hi! Thanks for the pull request.

I wonder if it wouldn't be better to fix this in the addOffsetIfNecessary method here:

socket.io/packages/socket.io-adapter/lib/cluster-adapter.ts

Lines 471 to 473 in 3df3fed

	if (isEventPacket && withoutAcknowledgement && notVolatile) {
	packet.data.push(offset);
	}

This way, a new array will be created only if connection state recovery is enabled.

What do you think?

[xingsy97]

Hi! Thanks for the pull request.

I wonder if it wouldn't be better to fix this in the addOffsetIfNecessary method here:

socket.io/packages/socket.io-adapter/lib/cluster-adapter.ts

Lines 471 to 473 in 3df3fed

	if (isEventPacket && withoutAcknowledgement && notVolatile) {
	packet.data.push(offset);
	}

This way, a new array will be created only if connection state recovery is enabled.

What do you think?

Agreed, I updated accordingly. Thanks!