More general problem for .sqo files (Re: reading objects
bolot at cc.gatech.edu
Fri May 29 15:04:44 UTC 1998
I've made a 'quick-n-dirty' fix to the DataStream's behavior.
DataStream>>readString method uses PositionableStream>>nextString to do the
job. The latter only handles Strings that are shorter than 16384 bytes.
Further, it appears that when a String is saved, DataStream saves Strings
signature, and only then checks if it is longer than 16K. If so, it saves it
as a ByteArray.
I changed PositionableStream>>nextString method, and my program immediately
recovered seemingly lost data. The change is as follows: I read a byte that
designates length. If it is zero, I peek the next byte, if that one is zero
as well, I assume that this String is longer than 16K, thus 4 bytes comprise
the length byte. It has not been tested extensively with other applications
or Squeak itself (e.g., this could break if you legally had two consecutive
Please let me know if I am playing with fire.
---DO NOT FILE IT IN YET! LET'S HEAR WHAT SQUEAK CENTRAL SAYS---
"Read a string from the receiver. The first byte is the length of the
string, unless it is greater than 192, in which case the first two bytes
encode the length."
| aString char length|
length _ self next. "first byte."
length >= 192 ifTrue: [length _ (length - 192) * 256 + self next].
" I added these lines "
(length = 0 and: [self peek = 0])
ifTrue: [length _ (length bitShift: 24)
+ (self next bitShift: 16)
+ (self next bitShift: 8)
+ self next].
aString _ String new: length.
1 to: length do: [:i | aString at: i put: self next asCharacter].
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