Make mux the source of truth for virtual channel prefix layout#63
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Make mux the source of truth for virtual channel prefix layout#63
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April 29, 2026 18:04
VirtualChannel already forwards SlotSize/NumSlots/GetFds to its mux because storage is owned by the mux, but it did not forward ChecksumSize, MetadataSize, or PrefixSize. As a result, HandleCreatePublisher's SetChecksumSize/ SetMetadataSize/SetPrefixSize calls landed on the virtual channel only, the consistency check at the same site validated against per-vchan fields, and HandleCreateSubscriber returned the virtual channel's (often default) sizes. Two virtual channels on the same mux could silently disagree on prefix layout while sharing storage. Mark the cs/ms/ps accessors and setters virtual on Channel and override them on VirtualChannel to delegate to the mux. Now the existing consistency check naturally rejects mismatched layouts across vchans on a mux, subscribers always receive the mux's authoritative sizes, and writes from any vchan handle update the shared mux. Made-with: Cursor
VirtualChannelMuxPrefixIsShared verifies that a publisher's checksum_size and metadata_size on one virtual channel propagate to the mux, that a subscriber on a sibling vchan sees those sizes (not the per-vchan defaults), that a matching second publisher on a sibling vchan succeeds, and that mismatched cs/ms on another sibling vchan is rejected. VirtualChannelMuxPrefixSubscriberFirst covers the placeholder-mux path: a subscriber creates the mux and a vchan first, then a publisher with non-default cs/ms arrives, and a subsequent subscriber on a sibling vchan sees the publisher's authoritative sizes via the mux. Both tests fail on the previous code (sibling vchans report PrefixSize=64 default) and pass after the layout-forwarding fix. Made-with: Cursor
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VirtualChannel already forwards SlotSize/NumSlots/GetFds to its mux because storage is owned by the mux, but it did not forward ChecksumSize, MetadataSize, or PrefixSize. As a result, HandleCreatePublisher's SetChecksumSize/ SetMetadataSize/SetPrefixSize calls landed on the virtual channel only, the consistency check at the same site validated against per-vchan fields, and HandleCreateSubscriber returned the virtual channel's (often default) sizes. Two virtual channels on the same mux could silently disagree on prefix layout while sharing storage.
Mark the cs/ms/ps accessors and setters virtual on Channel and override them on VirtualChannel to delegate to the mux. Now the existing consistency check naturally rejects mismatched layouts across vchans on a mux, subscribers always receive the mux's authoritative sizes, and writes from any vchan handle update the shared mux.
Made-with: Cursor