dockerTools: Fix the layer order

The layer order was not correct when a parent image was used: parent
image layers were above the new created layer.

This commits simplifies the code related to layer ordering. In
particular, layers in `layer-list` are ordered from bottom-most to
top-most. This is also the order of layers in the `rootfs.diff_ids`
attribute of the image configuration.

1 files changed, 11 insertions, 10 deletions

diff --git a/pkgs/build-support/docker/default.nix b/pkgs/build-support/docker/default.nix
index 11945e7b6f7..57e40069003 100644
--- a/pkgs/build-support/docker/default.nix
+++ b/pkgs/build-support/docker/default.nix
@@ -216,7 +216,7 @@ rec {
         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=$lowerdir''${lowerdir:+:}image/$extractionID/layer
+        lowerdir=image/$extractionID/layer''${lowerdir:+:}$lowerdir
       done
 
       mkdir work
@@ -585,9 +585,9 @@ rec {
           layerID=$(sha256sum "$layer/json" | cut -d ' ' -f 1)
           ln -s "$layer" "./image/$layerID"
 
-          manifestJson=$(echo "$manifestJson" | jq ".[0].Layers |= [\"$layerID/layer.tar\"] + .")
-          imageJson=$(echo "$imageJson" | jq ".history |= [{\"created\": \"$(jq -r .created ${configJson})\"}] + .")
-          imageJson=$(echo "$imageJson" | jq ".rootfs.diff_ids |= [\"sha256:$layerChecksum\"] + .")
+          manifestJson=$(echo "$manifestJson" | jq ".[0].Layers |= . + [\"$layerID/layer.tar\"]")
+          imageJson=$(echo "$imageJson" | jq ".history |= . + [{\"created\": \"$(jq -r .created ${configJson})\"}]")
+          imageJson=$(echo "$imageJson" | jq ".rootfs.diff_ids |= . + [\"sha256:$layerChecksum\"]")
         done
         imageJsonChecksum=$(echo "$imageJson" | sha256sum | cut -d ' ' -f1)
         echo "$imageJson" > "image/$imageJsonChecksum.json"
@@ -779,23 +779,24 @@ rec {
         # Use the temp folder we've been working on to create a new image.
         mv temp image/$layerID
 
-        # Add the new layer ID to the beginning of the layer list
+        # Add the new layer ID to the end of the layer list
         (
+          cat layer-list
           # originally this used `sed -i "1i$layerID" layer-list`, but
           # would fail if layer-list was completely empty.
           echo "$layerID/layer.tar"
-          cat layer-list
         ) | ${pkgs.moreutils}/bin/sponge layer-list
 
         # Create image json and image manifest
         imageJson=$(cat ${baseJson} | jq ". + {\"rootfs\": {\"diff_ids\": [], \"type\": \"layers\"}}")
         manifestJson=$(jq -n "[{\"RepoTags\":[\"$imageName:$imageTag\"]}]")
 
-        for layerTar in $(tac ./layer-list); do
+        for layerTar in $(cat ./layer-list); do
           layerChecksum=$(sha256sum image/$layerTar | cut -d ' ' -f1)
-          imageJson=$(echo "$imageJson" | jq ".history |= [{\"created\": \"$(jq -r .created ${baseJson})\"}] + .")
-          imageJson=$(echo "$imageJson" | jq ".rootfs.diff_ids |= [\"sha256:$layerChecksum\"] + .")
-          manifestJson=$(echo "$manifestJson" | jq ".[0].Layers |= [\"$layerTar\"] + .")
+          imageJson=$(echo "$imageJson" | jq ".history |= . + [{\"created\": \"$(jq -r .created ${baseJson})\"}]")
+          # diff_ids order is from the bottom-most to top-most layer
+          imageJson=$(echo "$imageJson" | jq ".rootfs.diff_ids |= . + [\"sha256:$layerChecksum\"]")
+          manifestJson=$(echo "$manifestJson" | jq ".[0].Layers |= . + [\"$layerTar\"]")
         done
 
         imageJsonChecksum=$(echo "$imageJson" | sha256sum | cut -d ' ' -f1)