nixos/ec2-metadata-fetcher: add xz user-data decompression

Support decompressing XZ-compressed EC2 user data via xzcat.
Includes a corresponding NixOS test.

nixos/modules/virtualisation/amazon-image.nix

@@ -102,6 +102,7 @@ in
         file
         gzip
         mktemp
+        xz
       ];
       script = builtins.readFile ./ec2-metadata-fetcher.sh;
       serviceConfig.Type = "oneshot";

nixos/modules/virtualisation/ec2-metadata-fetcher.sh

@@ -70,6 +70,7 @@ try_decompress() {
   case $ftype in
     gzip*)  decompress_cmd=zcat ;;
     bzip2*) decompress_cmd=bzcat ;;
+    XZ*)    decompress_cmd=xzcat ;;
     *)      return ;;
   esac
   echo "decompressing: $1"

nixos/tests/ec2-image.nix

@@ -278,6 +278,11 @@ in
             test_data = b"#!/bin/bash\necho bzip2-decompression-test\n"
             test_userdata_decompression(machine, user_data_path, bz2.compress(test_data), "bzip2")
 
+        with subtest("Decompression of xz-compressed user-data"):
+            import lzma
+            test_data = b"#!/bin/bash\necho xz-decompression-test\n"
+            test_userdata_decompression(machine, user_data_path, lzma.compress(test_data), "xz")
+
     finally:
         machine.shutdown()
         temp_dir.cleanup()