dockerTools: Preprocess layers list before unpack to handle repeated layers

1 files changed, 12 insertions, 3 deletions

diff --git a/pkgs/build-support/docker/default.nix b/pkgs/build-support/docker/default.nix
index 0e4011a532b..7fa5aeafc8e 100644
--- a/pkgs/build-support/docker/default.nix
+++ b/pkgs/build-support/docker/default.nix
@@ -229,6 +229,15 @@ rec {
           mount /dev/${vmTools.hd} disk
           cd disk
 
+          function dedup() {
+            declare -A seen
+            while read ln; do
+              if [[ -z "''${seen["$ln"]:-}" ]]; then
+                echo "$ln"; seen["$ln"]=1
+              fi
+            done
+          }
+
           if [[ -n "$fromImage" ]]; then
             echo "Unpacking base image..."
             mkdir image
@@ -245,7 +254,8 @@ rec {
               parentID="$(cat "image/manifest.json" | jq -r '.[0].Config | rtrimstr(".json")')"
             fi
 
-            cat ./image/manifest.json  | jq -r '.[0].Layers | .[]' > layer-list
+            # In case of repeated layers, unpack only the last occurrence of each
+            cat ./image/manifest.json  | jq -r '.[0].Layers | .[]' | tac | dedup | tac > layer-list
           else
             touch layer-list
           fi
@@ -259,14 +269,13 @@ rec {
 
             mkdir -p image/$extractionID/layer
             tar -C image/$extractionID/layer -xpf image/$layerTar
+            rm image/$layerTar
 
             find image/$extractionID/layer -name ".wh.*" -exec bash -c 'name="$(basename {}|sed "s/^.wh.//")"; mknod "$(dirname {})/$name" c 0 0; rm {}' \;
 
             # Get the next lower directory and continue the loop.
             lowerdir=image/$extractionID/layer''${lowerdir:+:}$lowerdir
           done
-          # Don't remove tarballs until all unpacked in case some are used more than once
-          awk '{print "image/"$0}' layer-list | xargs rm -f
 
           mkdir work
           mkdir layer