Fix unspecified behaviour in readStorePathCAMap #4008
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When deploying a Hydra instance with current Nix master, most builds would not run because of errors like this: queue monitor: error: --- Error --- hydra-queue-runner error: --- UsageError --- nix-daemon not a content address because it is not in the form '<prefix>:<rest>': /nix/store/...-somedrv The last error message is from parseContentAddress, which expects a colon-separated string, however what we got here is a store path. Looking at the worker protocol, the following message sent to the Nix daemon caused the error above: 0x1E -> wopQuerySubstitutablePathInfos 0x01 -> Number of paths 0x16 -> Length of string "/nix/store/...-somedrv" 0x00 -> Length of string "" Looking at writeStorePathCAMap, the store path is indeed the first field that's transmitted. However, readStorePathCAMap expects it to be the *second* field *on my machine*, since expression evaluation order is a classic form of unspecified behaviour[1] in C++. This has been introduced in NixOS#3689, specifically in commit 66a62b3. [1]: https://en.wikipedia.org/wiki/Unspecified_behavior#Order_of_evaluation_of_subexpressions Signed-off-by: aszlig <aszlig@nix.build>
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Cc: @matthewbauer in case the notification via commit referencing didn't work |
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Thanks! |
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Ah, I should have fixed this myself after we hit this exact same thing on another branch where it was slightly changed. Thanks! |
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When deploying a Hydra instance with current Nix master, most builds would not run because of errors like this:
The last error message is from
parseContentAddress, which expects a colon-separated string, however what we got here is a store path.Looking at the worker protocol, the following message sent to the Nix daemon caused the error above:
/nix/store/...-somedrvLooking at
writeStorePathCAMap, the store path is indeed the first field that's transmitted. However,readStorePathCAMapexpects it to be the second field on my machine, since expression evaluation order is a classic form of unspecified behaviour in C++.This has been introduced in #3689, specifically in commit 66a62b3.