A problem:
The current struct.unpack api works well for unpacking C-structures where
everything is usually unpacked at once, but it
becomes inconvenient when unpacking binary files where things
often have to be unpacked field by field. Then one has to keep track
of offsets, slice the strings,call struct.calcsize(), etc...
Eg. with a current api unpacking of a record which consists of a
header followed by a variable number of items would go like this
hdr_fmt="iiii"
item_fmt="IIII"
item_size=calcsize(item_fmt)
hdr_size=calcsize(hdr_fmt)
hdr=unpack(hdr_fmt, rec[0:hdr_size]) #rec is the record to unpack
offset=hdr_size
for i in range(hdr[0]): #assume 1st field of header is a counter
item=unpack( item_fmt, rec[ offset: offset+item_size])
offset+=item_size
which is quite inconvenient...
A solution:
We could have an optional offset argument for
unpack(format, buffer, offset=None)
the offset argument is an object which contains a single integer field
which gets incremented inside unpack() to point to the next byte.
so with a new API the above code could be written as
offset=struct.Offset(0)
hdr=unpack("iiii", offset)
for i in range(hdr[0]):
item=unpack( "IIII", rec, offset)
When an offset argument is provided, unpack() should allow some bytes to
be left unpacked at the end of the buffer..
Does this suggestion make sense? Any better ideas?
Ilya
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