From 525b38eee8fac48eb2a82fb78fa0a933a9eee2a4 Mon Sep 17 00:00:00 2001 From: aszlig Date: Sun, 13 Sep 2020 02:40:51 +0200 Subject: [PATCH] Fix unspecified behaviour in readStorePathCAMap 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 ':': /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 https://github.com/NixOS/nix/pull/3689, specifically in commit 66a62b3189c8c9b0965850e6b3c9b0fda0b50fd8. [1]: https://en.wikipedia.org/wiki/Unspecified_behavior#Order_of_evaluation_of_subexpressions Signed-off-by: aszlig --- src/libstore/remote-store.cc | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc index e4a4ef5af..8bcf92301 100644 --- a/src/libstore/remote-store.cc +++ b/src/libstore/remote-store.cc @@ -43,8 +43,11 @@ StorePathCAMap readStorePathCAMap(const Store & store, Source & from) { StorePathCAMap paths; auto count = readNum(from); - while (count--) - paths.insert_or_assign(store.parseStorePath(readString(from)), parseContentAddressOpt(readString(from))); + while (count--) { + auto path = store.parseStorePath(readString(from)); + auto ca = parseContentAddressOpt(readString(from)); + paths.insert_or_assign(path, ca); + } return paths; }