Add operation ‘nix-store --repair-path’

This operation allows fixing corrupted or accidentally deleted store
paths by redownloading them using substituters, if available.

Since the corrupted path cannot be replaced atomically, there is a
very small time window (one system call) during which neither the old
(corrupted) nor the new (repaired) contents are available.  So
repairing should be used with some care on critical packages like
Glibc.

1 files changed, 17 insertions, 0 deletions

diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
index d3a707f0d8..ce415ce4ae 100644
--- a/src/nix-store/nix-store.cc
+++ b/src/nix-store/nix-store.cc
@@ -734,6 +734,21 @@ static void opVerifyPath(Strings opFlags, Strings opArgs)
 }
 
 
+/* Repair the contents of the given path by redownloading it using a
+   substituter (if available). */
+static void opRepairPath(Strings opFlags, Strings opArgs)
+{
+    if (!opFlags.empty())
+        throw UsageError("no flags expected");
+
+    foreach (Strings::iterator, i, opArgs) {
+        Path path = followLinksToStorePath(*i);
+        printMsg(lvlTalkative, format("repairing path `%1%'...") % path);
+        ensureLocalStore().repairPath(path);
+    }
+}
+
+
 static void showOptimiseStats(OptimiseStats & stats)
 {
     printMsg(lvlError,
@@ -834,6 +849,8 @@ void run(Strings args)
             op = opVerify;
         else if (arg == "--verify-path")
             op = opVerifyPath;
+        else if (arg == "--repair-path")
+            op = opRepairPath;
         else if (arg == "--optimise")
             op = opOptimise;
         else if (arg == "--query-failed-paths")