Forum: Ruby trouble reading a gzipped xml-file

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guido.de-melo (Guest)
on 2005-11-14 17:05
(Received via mailing list)
Hi,

I'm trying to read a gzipped xml-file into rexml, but I don't quite
succeed. Perhaps someone can help me. Till now I tried this:

#!/usr/bin/ruby -w

require 'zlib'
require 'rexml/document'

Zlib::GzipReader.open('file.dia') {|gz|
   print gz.read
}
# this prints everything nicely and it works

f = Zlib::GzipReader.open("file.dia")
s = f.read
p s

# now the ungzipped contents are in s, they look like this however:
# "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<dia:diagram
# xmlns:dia=\"http://www.lysator.liu.se/~alla/dia/\">\n
# <dia:diagramdata>\n    <dia:attribute name=\"background\">\n
# all in one line and encapsulated in ""
# so of course the next command fails

xmldoc = REXML::Document.new s
p xmldoc
# gives: <UNDEFINED> ... </>

Any ideas on this? This can't be too difficult, I think...
Guido
bob.news (Guest)
on 2005-11-14 17:20
(Received via mailing list)
Guido de Melo wrote:
> Zlib::GzipReader.open('file.dia') {|gz|
>    print gz.read
> }
> # this prints everything nicely and it works
>
> f = Zlib::GzipReader.open("file.dia")
> s = f.read
> p s

You're not closing f here.

> # now the ungzipped contents are in s, they look like this however:
> # "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<dia:diagram
> # xmlns:dia=\"http://www.lysator.liu.se/~alla/dia/\">\n
> # <dia:diagramdata>\n    <dia:attribute name=\"background\">\n
> # all in one line and encapsulated in ""
> # so of course the next command fails

I'm not so sure that it fails just because of this.

> xmldoc = REXML::Document.new s
> p xmldoc
> # gives: <UNDEFINED> ... </>
>
> Any ideas on this? This can't be too difficult, I think...
> Guido

Did you try this?

xmldoc = Zlib::GzipReader.open('file.dia') {|gz| REXML::Document.new gz}

Kind regards

    robert
guido.de-melo (Guest)
on 2005-11-14 17:29
(Received via mailing list)
Robert K. wrote:
> You're not closing f here.
>
[...]
>
> I'm not so sure that it fails just because of this.

It shouldn't, because ruby will determine the end of the file by itself
and close the handle on exiting.

> Did you try this?
>
> xmldoc = Zlib::GzipReader.open('file.dia') {|gz| REXML::Document.new gz}

irb(main):003:0> xmldoc = Zlib::GzipReader.open('file.dia') {|gz|
REXML::Document.new gz}
RuntimeError: Zlib::GzipReader is not a valid input stream.  It must be
either a String, IO, StringIO or Source.

This doesn't work either, I'm afraid...
Guido
bob.news (Guest)
on 2005-11-14 17:44
(Received via mailing list)
Guido de Melo wrote:
> Robert K. wrote:
>> You're not closing f here.
>>
> [...]
>>
>> I'm not so sure that it fails just because of this.
>
> It shouldn't, because ruby will determine the end of the file by
> itself and close the handle on exiting.

I didn't mean to say that it fails because of the open file.  My point
with the first remark was that it's a good habit to open files for only
as
long as they are actually used.  The block form is the idiom of choice
here: it's not much longer as a simple File.open() or File.new() and it
ensures the file is always properly closed.

> This doesn't work either, I'm afraid...
I guess this is because GzipReader doesn't inherit IO:

>> Zlib::GzipReader.ancestors
=> [Zlib::GzipReader, Enumerable, Zlib::GzipFile, Object, Kernel]

But you can do this

xmldoc = Zlib::GzipReader.open('file.dia') {|gz| REXML::Document.new(
gz.read )}

Btw, you see differing output because you use different printing
methods:

Zlib::GzipReader.open('file.dia') {|gz|
   print gz.read
}

vs.

p s

If there is no exception during GZIP reading I guess there might be a
bug
somewhere.  As a test I'd write the gunzipped content to another file
and
do a diff on the plain xml and this output to see whether GzipReader
actually yields the same content.

Btw, did you actually try to make REXML read the first variant?  Maybe
you
have a problem in your XML file.

Kind regards

    robert
guido.de-melo (Guest)
on 2005-11-14 18:08
(Received via mailing list)
Thank you very much! You solved it!

Robert K. wrote:
> here: it's not much longer as a simple File.open() or File.new() and it
> ensures the file is always properly closed.

You are right of course, I will try to do this in the future.

> But you can do this
>
> xmldoc = Zlib::GzipReader.open('file.dia') {|gz| REXML::Document.new(
> gz.read )}

And this worked perfect for me :-)

> If there is no exception during GZIP reading I guess there might be a bug
> somewhere.  As a test I'd write the gunzipped content to another file and
> do a diff on the plain xml and this output to see whether GzipReader
> actually yields the same content.

They do

> Btw, did you actually try to make REXML read the first variant?  Maybe you
> have a problem in your XML file.

Thank goodness the XML produced by dia is sound :-)

Kind regards,
Guido
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