Auto-recover corrupt packfiles in packfile maintenance

GVFS/GVFS.Common/GVFSConstants.cs

@@ -44,6 +44,13 @@ public static class GitConfig
             public const string TrustPackIndexes = GVFSPrefix + "trust-pack-indexes";
             public const bool TrustPackIndexesDefault = true;
 
+            /* Kill switch for the destructive part of packfile-maintenance corruption recovery: when
+             * false, GVFS still detects and reports corrupt packs but does not delete them (or later
+             * prefetch packs) and does not request a restoring prefetch. Detection/telemetry is
+             * unaffected; the non-destructive multi-pack-index rewrite still runs. */
+            public const string EnablePackfileRecovery = GVFSPrefix + "enable-packfile-recovery";
+            public const bool EnablePackfileRecoveryDefault = true;
+
             public const string ShowHydrationStatus = GVFSPrefix + "show-hydration-status";
             public const bool ShowHydrationStatusDefault = false;
 

GVFS/GVFS.Common/Git/GitProcess.cs

@@ -784,6 +784,17 @@ public Result VerifyMultiPackIndex(string objectDir)
             return this.InvokeGitAgainstDotGitFolder("-c core.multiPackIndex=true multi-pack-index verify --object-dir=\"" + objectDir + "\" --no-progress");
         }
 
+        /// <summary>
+        /// Verifies the integrity of a single packfile via its .idx. Returns a failure exit code if the
+        /// pack is truncated or otherwise unreadable. Used by pack maintenance recovery to determine
+        /// which pack is corrupt - the "could not load pack N" ordinal reported by the multi-pack-index
+        /// is an internal position, not a filename, so it cannot be mapped to a file directly.
+        /// </summary>
+        public Result VerifyPack(string packIndexPath)
+        {
+            return this.InvokeGitAgainstDotGitFolder("verify-pack \"" + packIndexPath + "\"");
+        }
+
         public Result RemoteAdd(string remoteName, string url)
         {
             return this.InvokeGitAgainstDotGitFolder("remote add " + remoteName + " " + url);

GVFS/GVFS.Common/Maintenance/GitMaintenanceScheduler.cs

@@ -54,7 +54,9 @@ private void ScheduleRecurringSteps()
                 return;
             }
 
-            if (this.gitObjects.IsUsingCacheServer())
+            bool usingCacheServer = this.gitObjects.IsUsingCacheServer();
+
+            if (usingCacheServer)
             {
                 TimeSpan prefetchPeriod = TimeSpan.FromMinutes(15);
                 this.stepTimers.Add(new Timer(
@@ -70,8 +72,16 @@ private void ScheduleRecurringSteps()
                 dueTime: this.looseObjectsDueTime,
                 period: this.looseObjectsPeriod));
 
+            // When packfile-maintenance recovery removes a corrupt prefetch pack (and the later prefetch
+            // packs that depend on it), it needs a prefetch to re-download them and rebuild the
+            // commit-graph. This is only meaningful when a cache server is in use; otherwise the objects
+            // are restored on demand.
+            Action requestPrefetch = usingCacheServer
+                ? () => this.queue.TryEnqueue(new PrefetchStep(this.context, this.gitObjects))
+                : (Action)null;
+
             this.stepTimers.Add(new Timer(
-                (state) => this.queue.TryEnqueue(new PackfileMaintenanceStep(this.context)),
+                (state) => this.queue.TryEnqueue(new PackfileMaintenanceStep(this.context, requestPrefetch: requestPrefetch)),
                 state: null,
                 dueTime: this.packfileDueTime,
                 period: this.packfilePeriod));