Fix shim fully drain stdin on close IO#246
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Pull request overview
This PR updates the shim’s stdin forwarding logic to ensure that when CloseIO fires, any remaining bytes already buffered on the stdin reader are fully drained and forwarded before the shim sends an in-band EOF (CloseWrite) to the guest.
Changes:
- Replace the single “drain one read” behavior on
CloseIOwith a loop that continues reading/writing until the stdin reader returns EOF or an error. - Expand the in-code rationale to document why a single read can truncate stdin under backpressure (e.g., slow guest consumption / vsock credit).
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Signed-off-by: Austin Vazquez <austin.vazquez@docker.com>
Signed-off-by: Austin Vazquez <austin.vazquez@docker.com>
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Signed-off-by: Austin Vazquez <austin.vazquez@docker.com>
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| for draining := true; draining; { | ||
| select { | ||
| case res := <-readCh: | ||
| if res.n > 0 { | ||
| if _, err := sc.Write(buf[:res.n]); err != nil { | ||
| log.G(ctx).WithError(err).Warn("error writing stdin on CloseIO") | ||
| draining = false | ||
| break | ||
| } | ||
| } | ||
| if res.err != nil { | ||
| // EOF (write end closed) or read error: fully drained. | ||
| draining = false | ||
| break | ||
| } | ||
| // More may be buffered; continue to drain. | ||
| go read() | ||
| case <-time.After(stdinDrainGrace): | ||
| // Stalled draining the buffer; EOF not yet reached. | ||
| log.G(ctx).Warn("stdin drain stalled after CloseIO; signaling EOF without client write-end close") | ||
| f.Close() | ||
| <-readCh | ||
| draining = false | ||
| } | ||
| } |
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This change addresses an edge case where draining stdin on close will truncate data. Attempt to read until EOF and bind the read with a timeout (currently 2 seconds which should only occur for bad clients that trigger CloseIO without close the pipe's write end)
Ref: https://github.com/containerd/nerdbox/actions/runs/28613973997/job/84853144969?pr=245