From bd82bb4fefead55610d771802bc13036c576b66f Mon Sep 17 00:00:00 2001
From: Holger Hans Peter Freyther <holger@moiji-mobile.com>
Date: Sun, 18 Dec 2016 12:25:35 +0100
Subject: [PATCH] Add utility to build a delta file with a single insert

For hijacking build a complete delta for a single insert. Need to
externalize the parameters. It could work for multiple files too.
---
 update-ec20/build_diff.py | 124 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 124 insertions(+)
 create mode 100644 update-ec20/build_diff.py

diff --git a/update-ec20/build_diff.py b/update-ec20/build_diff.py
new file mode 100644
index 0000000..c23293f
--- /dev/null
+++ b/update-ec20/build_diff.py
@@ -0,0 +1,124 @@
+#!/usr/bin/python3
+"""
+Build a single insert for RedBend OTA filesystem updates
+All rights reversed
+"""
+
+from PyCRC import CRC32
+import subprocess
+import os
+import io
+import struct
+
+permission_bytes = bytes.fromhex('1A 5F 72 65 64 62 65 6E 64 5F 30 34 30 37 35 35 3A 30 30 30 30 3A 30 30 30 30 00 1A 5F 72 65 64 62 65 6E 64 5F 30 34 31 37 37 37 3A 30 30 30 30 3A 30 30 30 30 00 1A 5F 72 65 64 62 65 6E 64 5F 30 34 32 37 35 35 3A 30 30 30 30 3A 30 30 30 30 00 1A 5F 72 65 64 62 65 6E 64 5F 31 30 30 36 34 34 3A 30 30 30 30 3A 30 30 30 30 00 1A 5F 72 65 64 62 65 6E 64 5F 31 30 30 37 35 35 3A 30 30 30 30 3A 30 30 30 30 00 1A 5F 72 65 64 62 65 6E 64 5F 31 30 30 37 37 37 3A 30 30 30 30 3A 30 30 30 30 00 1A 5F 72 65 64 62 65 6E 64 5F 31 30 34 37 35 35 3A 30 30 30 30 3A 30 30 30 30 00 1A 5F 72 65 64 62 65 6E 64 5F 31 32 30 37 37 37 3A 30 30 30 30 3A 30 30 30 30 00')
+general_bytes = bytes.fromhex('50 40 01 00 80 38 01 00 00 00 00')
+fs_bytes     = bytes.fromhex('80 80 02 00 00 ')
+
+# initialize tables only once
+crc32 = CRC32.CRC32()
+
+def compress(fname):
+    """I compress a file with LZMA and return the byte array"""
+    lzma_fname = fname + ".lzma"
+    print(lzma_fname)
+    ret = subprocess.call(["lzma", "e", fname, lzma_fname])
+    assert ret == 0
+    with open(lzma_fname, "rb") as f:
+        return f.read()
+
+def build_toc(fname, size, compr_size):
+    """I build the table of content for a single file and insert"""
+    wr = io.BytesIO()
+    # name + NUL
+    wr.write(fname.encode('utf8'))
+    wr.write(b'\0')
+    # permissions
+    wr.write(permission_bytes)
+    # FILE_SIZE  + D100 0000 (offset to permission) + COMPR_SIZE
+    off = len(wr.getvalue())
+    wr.write(struct.pack('<I', size))
+    wr.write(b'\xD1\x00\x00\x00')
+    wr.write(struct.pack('<I', compr_size))
+    return off, wr.getvalue()
+
+def build_delta(num_insert, toc, offset, data):
+    """I build the delta with the header, checksum, length, toc,
+    offsets and the data"""
+
+    hdr = io.BytesIO()
+    hdr.write(general_bytes)
+    hdr.write(fs_bytes)
+    hdr.write(b'\xc8\x00\x02\x00') # ram size
+    hdr.write(b'\x00\x00\x04\x00') # sector size
+    hdr.write(struct.pack('<I', offset))
+    hdr.write(struct.pack('<I', len(toc)))
+    hdr.write(b'\x22\x00\x02\x00') # min_alloc_ram_use | ext_info_sz
+    hdr.write(struct.pack('<H', 0)) # num_copy
+    hdr.write(struct.pack('<H', 0)) # num_diff
+
+    hdr.write(struct.pack('<H', num_insert)) # num_inser
+    hdr.write(struct.pack('<H', 0)) # num_delete
+
+    hdr.write(struct.pack('<H', 0)) # num_delete_dirs
+    hdr.write(struct.pack('<H', 0)) # num_dirs
+
+    hdr.write(struct.pack('<H', 0)) # num_del_link
+    hdr.write(struct.pack('<H', 0)) # num_link
+
+    hdr.write(struct.pack('<H', 0)) # num_cri_update
+    hdr.write(struct.pack('<H', num_insert)) # num_crit_insert
+
+    for i in range(0, num_insert):
+        hdr.write(b'\x33\xC3\xC3\x33') # crc of the target file?
+
+    combined = hdr.getvalue() + toc + data
+    wr = io.BytesIO()
+    wr.write(struct.pack("<I", len(combined) + 8))
+    wr.write(combined)
+
+    with_csum = io.BytesIO()
+    with_csum.write(struct.pack("<I", crc32.calculate(wr.getvalue())))
+    with_csum.write(wr.getvalue())
+    return with_csum.getvalue()
+
+def build_filenames(name):
+    """I build a filenames table including the name"""
+    wr = io.BytesIO()
+    wr.write(general_bytes)
+    wr.write(bytes.fromhex('00 00 03 00 00 01 00 00 00')) # never different
+    wr.write(struct.pack('<I', len(name) + 1))
+    wr.write(name.encode('utf8'))
+    wr.write(b'\x00')
+    wr.write(struct.pack('<I', 0))
+
+    hdr = io.BytesIO()
+    hdr.write(struct.pack("<I", len(wr.getvalue()) + 8))
+    hdr.write(wr.getvalue())
+
+    with_csum = io.BytesIO()
+    with_csum.write(struct.pack("<I", crc32.calculate(hdr.getvalue())))
+    with_csum.write(hdr.getvalue())
+    return with_csum.getvalue()
+
+def assemble(delta, filenames):
+    """I put delta and filenamestable together.. I might add padding
+    if the rule is understood correctly"""
+    return delta + filenames
+
+
+name = "system"
+fname = "/bin/hello_world.sh"
+fpath = "hello_world.sh"
+flen = os.stat(fpath).st_size
+fdata = compress(fpath)
+(offset,toc) = build_toc(fname, flen, len(fdata))
+with open("build_toc.bin", "wb") as f:
+    f.write(toc)
+toc_compr = compress("build_toc.bin")
+delta = build_delta(1, toc_compr, offset, fdata)
+namet = build_filenames(name)
+update = assemble(delta, namet)
+print(namet.hex())
+
+with open(name + ".diff", "wb") as f:
+    f.write(update)