Import orginal payload_dumper.py

 * Find on https://forum.xda-developers.com/nokia-7-plus/how-to/guide-how-to-extract-payload-bin-ota-t3830962
 * also on https://gist.github.com/ius/42bd02a5df2226633a342ab7a9c60f15
 * can't find original git repo and autor

.gitignore

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+# Ignore everything
+*
+
+# But not these files...
+!payload_dumper.py
+!requirements.txt
+!update_metadata_pb2.py
+!output/.gitkeep
+!README.md

README.md

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+# payload dumper
+Script work with Nokia 7 plus
+
+### System requirement
+
+- Python3, pip
+- google protobuf for python `pip install protobuf`
+
+### Guide
+
+- Make you sure you have Python 3.6 installed.
+- Download payload_dumper.py and update_metadata_pb2.py here.
+- Extract your OTA zip and place payload.bin in the same folder as these files.
+- Open PowerShell, Command Prompt, or Terminal depending on your OS.
+- Enter the following command: python -m pip install protobuf
+- When that’s finished, enter this command: python payload_dumper.py payload.bin
+- This will start to extract the images within the payload.bin file to the current folder you are in.

payload_dumper.py

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+#!/usr/bin/env python
+import struct
+import hashlib
+import bz2
+import sys
+
+try:
+    import lzma
+except ImportError:
+    from backports import lzma
+
+import update_metadata_pb2 as um
+
+flatten = lambda l: [item for sublist in l for item in sublist]
+
+def u32(x):
+    return struct.unpack('>I', x)[0]
+
+def u64(x):
+    return struct.unpack('>Q', x)[0]
+
+def verify_contiguous(exts):
+    blocks = 0
+
+    for ext in exts:
+        if ext.start_block != blocks:
+            return False
+
+        blocks += ext.num_blocks
+
+    return True
+
+def data_for_op(op):
+    p.seek(data_offset + op.data_offset)
+    data = p.read(op.data_length)
+
+    # assert hashlib.sha256(data).digest() == op.data_sha256_hash, 'operation data hash mismatch'
+
+    if op.type == op.REPLACE_XZ:
+        dec = lzma.LZMADecompressor()
+        data = dec.decompress(data) 
+    elif op.type == op.REPLACE_BZ:
+        dec = bz2.BZ2Decompressor()
+        data = dec.decompress(data) 
+
+    return data
+
+def dump_part(part):
+    print(part.partition_name)
+
+    out_file = open('output/%s.img' % part.partition_name, 'wb')
+    h = hashlib.sha256()
+
+    for op in part.operations:
+        data = data_for_op(op)
+        h.update(data)
+        out_file.write(data)
+
+    # assert h.digest() == part.new_partition_info.hash, 'partition hash mismatch'
+
+p = open(sys.argv[1], 'rb')
+
+magic = p.read(4)
+assert magic == b'CrAU'
+
+file_format_version = u64(p.read(8))
+assert file_format_version == 2
+
+manifest_size = u64(p.read(8))
+
+metadata_signature_size = 0
+
+if file_format_version > 1:
+    metadata_signature_size = u32(p.read(4))
+
+manifest = p.read(manifest_size)
+metadata_signature = p.read(metadata_signature_size)
+
+data_offset = p.tell()
+
+dam = um.DeltaArchiveManifest()
+dam.ParseFromString(manifest)
+
+for part in dam.partitions:
+    # for op in part.operations:
+    #     assert op.type in (op.REPLACE, op.REPLACE_BZ, op.REPLACE_XZ), \
+    #             'unsupported op'
+
+    # extents = flatten([op.dst_extents for op in part.operations])
+    # assert verify_contiguous(extents), 'operations do not span full image'
+
+    dump_part(part)

requirements.txt

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+protobuf==3.6.0
+six==1.11.0