Tcl Source Code

In the following script, the $src gains two new characters at the end each
time a zlib transform is pushed and then popped:

<code><pre>
#! /usr/bin/env tclsh

set data hello
set src [file tempfile]
puts -nonewline $src $data
flush $src
chan configure $src -translation binary

set dst [file tempfile]
chan configure $dst -translation binary

for {set i 0} {$i < 10} {incr i} {
    # Determine size of src channel
    seek $src 0 end
    set size [chan tell $src]
    seek $src 0 start
    # Determine size of content in src channel
    set data [read $src]
    set size2 [string length $data]
    seek $src 0 start
    # Copy src over to dst, keep dst empty
    zlib push deflate $src -level 6
    chan truncate $dst 0
    chan copy $src $dst
    chan pop $src
    # Show sizes
    puts [list $size $size2]
}
close $src
close $dst

</pre></code>

OK, the "problem" is that you're applying a compressor to a channel being read (a case we don't handle) yet the channel is really read-write so the flush on close (or pop) writes the header to it. **Doing `zlib push deflate` creates a channel filter that activates on output.**

I'm not quite sure what to do about this yet.

This appears to be due to the compression header. For `deflate` that's two bytes. It's rather more for `compress` and `gzip`.

It's quite odd that you're compressing on reading data into Tcl. I wonder if that's related?

(This is now test `zlib-14.1`)