61 lines
1.8 KiB
Python
61 lines
1.8 KiB
Python
# Routines to fiddle with 'cfrg' (Code Fragment) metadata resources
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# These are required only because the code fragments
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# referenced by a cfrg are usually at specific offsets
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# in a data fork, rather than in a resource. When we
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# manipulate a data fork, any corresponding cfrg must be
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# adjusted accordingly. This un-Mac-like scheme originated
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# as a way to allow code fragments to be memory-mapped,
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# which is impossible in a frequently-repacked resource fork.
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import struct
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# Internal: where are the fields that must be edited?
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def get_dfrkoffset_field_positions(cfrg):
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# old-style cfrg only, seems to work fine...
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entry_cnt, = struct.unpack_from('>L', cfrg, 28)
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ctr = 32
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for i in range(entry_cnt):
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if len(cfrg) < ctr + 43: break
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if cfrg[ctr + 23] == 1: # kDataForkCFragLocator
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yield ctr + 24
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ctr += 42 + 1 + cfrg[ctr + 42]
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while ctr % 4: ctr += 1
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# Tell this resource that you moved the PEFs that it references in the data fork
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def adjust_dfrkoffset_fields(cfrg, delta):
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cfrg = bytearray(cfrg)
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for field in get_dfrkoffset_field_positions(cfrg):
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ofs, = struct.unpack_from('>L', cfrg, field)
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ofs += delta
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struct.pack_into('>L', cfrg, field, ofs)
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return bytes(cfrg)
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# Get the (start, stop) offset range of PEFs in the data fork
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def get_dfrk_range(cfrg_list, dfrk_len):
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left = dfrk_len
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right = 0
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for cfrg in cfrg_list:
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for field in get_dfrkoffset_field_positions(cfrg):
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my_left, = struct.unpack_from('>L', cfrg, field)
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left = min(my_left, left)
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my_right, = struct.unpack_from('>L', cfrg, field + 4)
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if my_right == 0:
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right = dfrk_len
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else:
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right = max(right, my_left + my_right)
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return left, right
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