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Publish a labelled message's contract in a "contract" header - #97
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A message whose type carries SW.PrimitiveTypes.ContractAttribute is published with a "contract" header holding key@major, so a consumer can tell which shape the body has without relying on the class name. Types without the attribute, or with a malformed key, publish exactly as before: no header. The attribute is found by name, so the bus still depends on PrimitiveTypes 10.0.0 and applications that never label a message don't have to upgrade it (a raised floor would be a package-downgrade error for anyone pinning 10.0.0). Consumers only read the headers they know, so older consumers ignore it; the dead-letter copy keeps it.
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AhmadRAbuhussein
approved these changes
Oct 30, 2026
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What
When a published message's type carries
SW.PrimitiveTypes.ContractAttribute(PrimitiveTypes 10.0.2), e.g.[Contract("orders.msg.placed", Major = 2)], the message gets a headercontract: orders.msg.placed@2(BusOptions.ContractHeaderName). A consumer can then tell which shape the body has, and which major, without relying on the class name. Today a message is identified only by its type name, which is also its routing key.Backward compatibility
Most applications using the bus will never label a message, so this is built to change nothing for them:
IsWellFormedfalse): it's left out rather than failing the publish. The body, routing key, exchange and every other header are unchanged.SimplyWorks.PrimitiveTypes10.0.0 and finds the attribute by its full name with reflection, cached per type. Requiring 10.0.2 would turn into a package-downgrade error (NU1605) for any application that pins 10.0.0 directly. Only the integration test project references 10.0.2.ConsumerRunnerreads only the headers it knows by name (checked on currentmainand on 10.0.2), so older consumers ignore the new one. The dead-letter copy keeps all headers, so the contract survives into.bad.contractparameters are onBasicPublisher, which is internal. The only public addition is theBusOptions.ContractHeaderNameconstant.Publish(string messageTypeName, string message)) have no type, so they carry no header.Tests
ContractHeaderTestsagainst a real broker (Testcontainers):orders.msg.placed@2;