adding generate image hash example

Author: vsoch

examples/reproducibility/generate_image_hash.py

@@ -0,0 +1,55 @@
+from glob import glob
+
+from singularity.reproduce import (
+    get_image_hash,
+    get_levels,
+    get_content_hashes,
+    get_image_file_hash    
+)
+
+image_files = glob("*.img")
+image_path = image_files[0]
+
+########################################################
+# Get Image Hash (Single Container --> Single Value)
+########################################################
+
+# This function will return a hash specific to a level of 
+# reproducibility, meaning a subset  of files within the 
+# image. You can see the levels for selection:
+
+levels = get_levels()
+
+levels.keys()
+# dict_keys(['IDENTICAL', 'BASE', 'REPLICATE', 'RECIPE', 'RUNSCRIPT', 'ENVIRONMENT', 'LABELS'])
+
+# or specify a different version:
+
+levels = get_levels(version=2.3)
+
+# We can, then generate an image hash, and by default the level "REPLICATION" will be used:
+
+get_image_hash(image_path)
+#'bf8e242931e25ae9496015868ab2e8cc8d156ffd'
+
+# But we can also specify a level that we want:
+get_image_hash(image_path,level="IDENTICAL")
+#'3f4dcf64b58d314ac9ef0c02f641cd2109a07d64'
+
+########################################################
+# Get Image Content Digest (One Container --> Multiple)
+########################################################
+
+
+# We might want to get a dictionary of content hashes for all files
+# of one container at one level!
+digest = get_content_hashes(image_path)
+digest['./usr/bin/pinky']
+# 'ee2b438c278011bdac1a3a927e2d37519a8ed9c7'
+
+# We can also get a hash of the entire image file, this is done on the
+# binary file and not contents inside.
+
+file_hash = get_image_file_hash(image_path)
+# '13775a83962ae60744d691eb7f7fd1e96599e656'
+