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Akka.IO: remove the unimplemented ResumeWriting / WritingResumed / useResumeWriting API - #8660
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Aaronontheweb merged 3 commits intoSep 29, 2026
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…eResumeWriting API Removes Tcp.ResumeWriting, Tcp.WritingResumed, the useResumeWriting parameter and UseResumeWriting property on Tcp.Register, and the useResumeWriting parameter on TcpMessage.Register / TcpMessage.ResumeWriting(). This NACK-style write-suspend/resume mode mirrors JVM Akka's message shapes but was never implemented in Akka.NET: TcpConnection never read Register.UseResumeWriting, never suspended writes, and ResumeWriting was a no-op handler. Updates the two Akka.Streams callers, a streams test helper, a commented-out test line, and the API approval baselines. Ack-based writes (Tcp.Write.Create(data, ack)) remain the backpressure model. Records the removal in BREAKING_CHANGES_V1.6.md.
…me-writing # Conflicts: # BREAKING_CHANGES_V1.6.md
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What
Removes Akka.IO's NACK-style write-suspend/resume API, which was never implemented:
Tcp.ResumeWritingandTcp.WritingResumeduseResumeWritingparameter andUseResumeWritingproperty onTcp.RegisteruseResumeWritingparameter onTcpMessage.Register(...)TcpMessage.ResumeWriting()Why
JVM Akka's
Register(useResumeWriting = true)makes the connection reject writes while one is pending, suspend later writes, and replyWritingResumedonce it can accept writes again. Akka.NET copied the message shapes but never wired up the behavior:TcpConnectionnever readRegister.UseResumeWriting, never suspended writes, and itsResumeWritinghandler was a no-op ("No special action needed — transport handles write buffering"). Akka.NET already buffers writes and uses ack-based backpressure (Tcp.Write.Create(data, ack)) as the real flow-control mechanism, so this API only misled callers into thinking a NACK mode existed. Discussed in #8646 / #8617; removing it outright rather than deprecating it.Changes
src/core/Akka/IO/Tcp.cs, and the no-opReceive<ResumeWriting>handler fromsrc/core/Akka/IO/TcpConnection.cs.Tcp.Register(..., useResumeWriting: false)call sites inAkka.Streams'sTcpStages.cs, plus a test helper and a stale commented-out line.Akka.API.Testsapproval baselines (CoreAPISpec.ApproveCore.DotNet.verified.txt/...Net.verified.txt).BREAKING_CHANGES_V1.6.md.Migration
Delete the
useResumeWritingargument from anyRegister/TcpMessage.Registercalls and anyResumeWritingsends. Use ack-based writes (Tcp.Write.Create(data, ack)) for backpressure.