build-remote: truncate+hash store URI used in lockfile paths

Fixes: https://git.lix.systems/lix-project/lix/issues/157
Fixes: https://git.lix.systems/lix-project/lix/issues/221

Previously the entire escaped store URI was included. This would cause
build failures if a very long or deeply nested path was being used in
the store.

Now, we use the first 48 characters of the URL (escaped), then 16 bytes
of hash of the entire URL. This should never collide and limits the
length of the file name to a bit over 64, which is fine.

Change-Id: Ic1ba690a94e83749567c2c29460b8d1bcf2ac413

1 files changed, 16 insertions, 3 deletions

diff --git a/src/build-remote/build-remote.cc b/src/build-remote/build-remote.cc
index f7a159829..fb90403a0 100644
--- a/src/build-remote/build-remote.cc
+++ b/src/build-remote/build-remote.cc
@@ -3,6 +3,7 @@
 #include <algorithm>
 #include <set>
 #include <memory>
+#include <string_view>
 #include <tuple>
 #include <iomanip>
 #if __APPLE__
@@ -20,9 +21,9 @@
 #include "local-store.hh"
 #include "legacy.hh"
 #include "experimental-features.hh"
+#include "hash.hh"
 
 using namespace nix;
-using std::cin;
 
 static void handleAlarm(int sig) {
 }
@@ -35,9 +36,19 @@ std::string escapeUri(std::string uri)
 
 static std::string currentLoad;
 
+static std::string makeLockFilename(const std::string & storeUri) {
+    // We include 48 bytes of escaped URI to give an idea of what the lock
+    // is on, then 16 bytes of hash to disambiguate.
+    // This avoids issues with the escaped URI being very long and causing
+    // path too long errors, while also avoiding any possibility of collision
+    // caused by simple truncation.
+    auto hash = hashString(HashType::htSHA256, storeUri).to_string(Base::Base32, false);
+    return escapeUri(storeUri).substr(0, 48) + "-" + hash.substr(0, 16);
+}
+
 static AutoCloseFD openSlotLock(const Machine & m, uint64_t slot)
 {
-    return openLockFile(fmt("%s/%s-%d", currentLoad, escapeUri(m.storeUri), slot), true);
+    return openLockFile(fmt("%s/%s-%d", currentLoad, makeLockFilename(m.storeUri), slot), true);
 }
 
 static bool allSupportedLocally(Store & store, const std::set<std::string>& requiredFeatures) {
@@ -263,7 +274,9 @@ connected:
         auto inputs = readStrings<PathSet>(source);
         auto wantedOutputs = readStrings<StringSet>(source);
 
-        AutoCloseFD uploadLock = openLockFile(currentLoad + "/" + escapeUri(storeUri) + ".upload-lock", true);
+        auto lockFileName = currentLoad + "/" + makeLockFilename(storeUri) + ".upload-lock";
+
+        AutoCloseFD uploadLock = openLockFile(lockFileName, true);
 
         {
             Activity act(*logger, lvlTalkative, actUnknown, fmt("waiting for the upload lock to '%s'", storeUri));