There are several different approaches in different places:
- FileStream reads strings by default. #binary and #ascii switch between
formats. File streams use an internal buffer which is either a String (default)
or a ByteArray. It’s even possible to switch between binary and ascii midstream
without losing information (if done right) because it only affects the buffer.
- ReadStream and WriteStream cannot change their format. Their behavior is
determined by the underlying collection. Forcing conversions (e.g. by
#asString) can lead to loss of information
- RWBinaryOrTextStream (and other subclasses of ReadWriteStream) also support
the #binary #ascii method of switching format. Default is #ascii
- SocketStream uses the same #binary / #ascii mechanism. Default is #ascii
- ZnLimitedReadStream uses the same #binary / #ascii mechanism. Default is
#binary (implicit); depends on the underlying stream
I think the pattern to follow is clear: ReadStream and WriteStream should allow
switching format with #ascii and #binary, default should be #ascii. However, I
suspect there’s a reason that these classes don’t support switching, namely
that switching makes the implementation more complicated and also slower
because more checks need to be made.
The easiest solution I see would be to implement something like this:
ReadStream>>next
^ self isBinary
ifTrue: [ self basicNext asCharacter ]
ifFalse: [ self basicNext ]
However, #next et al. are implemented in a plugin and the primitive method
looks like this:
ReadStream>>next
<primitive: 65>
position >= readLimit
ifTrue: [^nil]
ifFalse: [^collection at: (position := position + 1)]
This means the collection instance variable has to hold either a binary or a
string collection.
I’ve found a solution which would work and I’ve whipped up a working way
(there’s space for improvement…):
ReadStream>>binary
collection isString ifFalse: [ ^ self ].
collection := (ByteArray new: collection size) copyReplaceFrom: 1 to:
collection size with: collection
ReadStrem>>ascii
collection isString ifTrue: [ ^ self ].
collection := (String new: collection size) copyReplaceFrom: 1 to:
collection size with: collection
@Damien
opposed to what I wrote earlier, #asString does *not* destroy non-printable
characters. Instead, every byte (from 0 to 255) is encoded as a character and
thus the string can be converted back to a ByteArray *without* loss of
information. Sorry about that.
With this change in place the 12259 would become obsolete.
Please let me know what you think. This is a pretty big change that might have
a lot of consequences in the image.
Cheers,
Max
On 04.12.2013, at 13:14, Max Leske <[email protected]> wrote:
> Let me see what I can come up with.
>
>
> On 03.12.2013, at 19:36, Damien Cassou <[email protected]> wrote:
>
>> Thanks Max for the report. Do you have an idea on how we could solve the
>> problem ? The previous behaviour was not acceptable either because the
>> streams that came out of a memory filesystem were the only ones with binary
>> content
>>
>> On Dec 3, 2013 5:35 PM, "Max Leske" <[email protected]> wrote:
>> Damien, Marcus
>>
>> this change breaks a lot of things in FileSystem-Git. I don’t disagree with
>> the idea that reading characters should be default (one could argue about
>> it…) but your change makes it IMPOSSIBLE to read bytes because unprintable
>> characters are discarded! So if my ByteArray is a NULL terminated string,
>> for instance, I can not check for the NULL termination anymore.
>>
>> Cheers,
>> Max
>
