docker: init fetchdocker nix code for docker2nix

This change adds granular, non-docker daemon docker image fetchers and
a docker image layer compositor to be used in conjunction with the
`docker2nix` utility provided by the `haskellPackages.hocker` package.

This change includes a hackage package version bump and updated sha256
for recent fixes released to `hocker` resulting from formulating this
patch.

1 files changed, 13 insertions, 0 deletions

diff --git a/pkgs/build-support/fetchdocker/fetchDockerLayer.nix b/pkgs/build-support/fetchdocker/fetchDockerLayer.nix
new file mode 100644
index 000000000000..869ba637429c
--- /dev/null
+++ b/pkgs/build-support/fetchdocker/fetchDockerLayer.nix
@@ -0,0 +1,13 @@
+pkgargs@{ stdenv, lib, haskellPackages, writeText, gawk }:
+let
+  generic-fetcher =
+    import ./generic-fetcher.nix pkgargs;
+in
+
+args@{ layerDigest, ... }:
+
+generic-fetcher ({
+  fetcher = "hocker-layer";
+  name    = "docker-layer-${layerDigest}.tar.gz";
+  tag     = "unused";
+} // args)