Sven,
I tested your change with the file and filter (our own way of defining
csv mappings by the end users) which used to send our application into
an endless loop.
And voila: we get an exception instead of a frozen image! I will give
the conversion errors a test drive tomorrow.
I am absolutely happy with your change. Thank you very much.
Joachim
P.S: I even learned a little bit about Iceberg. I am not really sure
each of my mouse clicks made sense, but I had your commit in the image
and could test it and port the deltas over to my Smalltalk dialect...
Am 05.01.21 um 19:52 schrieb jtuc...@objektfabrik.de:
Hi Sven,
all I can say is: wow. I have no words.
I will have to learn a bit about Pharo and github real quick now in
order to try your changes....
Thank you very much. I'll give you feedback as fast as I can.
(And forget my questions about #readAtEndOrEndOfLine. I somhow didn't
understand it is expected to return a Boolean. Not sure why. I thought
of 'read' as a command, not a question in simple past..., so I thought
its job should be to read the rest of the line if we're not there yet)
Joachim
Am 05.01.21 um 17:49 schrieb Sven Van Caekenberghe:
Hi Joachim,
Have a look at the following commit:
https://github.com/svenvc/NeoCSV/commit/a3d6258c28138fe3b15aa03ae71cf1e077096d39
and specifically the added unit tests. These should help clarify the
new behaviour.
If anything is not clear, please ask.
HTH,
Sven
On 5 Jan 2021, at 08:49, jtuc...@objektfabrik.de wrote:
Sven,
first of all thanks a lot for taking your time with this!
Your test case is so beautifully small I can't believe it ;-)
While I think some kind of validation could help with parsing CSV, I
remember reading your comment on this in some other discussion long
ago. You wrote you don't see it as a responsibility of a parser and
that you wouldn't want to add this to NeoCSV. I must say I tend to
agree mostly. Whatever you do at parsing can only cover part of the
problems related to validation. There will be checks that require
access to other fields from the same line, or some object that will
be the owner of the Collection that you are just importing, so a lot
of validation must be done after parsing anyways.
So I think we can mostly ignore the validation part. Whatever a
reader will do, it will not be good enough.
A nice way of exposing conversion errors for fields created with
#addField:converter: would help a lot, however.
I am glad you agree on the underflow bug. This is more a question of
well-formedness than of validation. If a reader finds out it doesn't
fit for a file structure, it should tell the user/developer about it
or at least gracefully return some more or less incomplete object
resembling what it could parse. But it shouldn't cross line borders
and return a wrong number of objects.
I will definitely continue my hunt for the endless loop. It is not
an ideal situation if one user of our Seaside Application completely
blocks an image that may be serving a few other users by just using
a CVS parser that doesn't fit with the file. I suspect this has to
do with #readEndOfLine in some special case of the underflow bug,
but cannot prove it yet. But I have a file and parser that reliably
goes into an endless loop. I just need to isolate the bare CSV
parsing from the whole machinery we've build around NeoCSV reader
for these user-defined mappings... I wouldn't be surprised if it is
a problem buried somewhere in our preparations in building a parser
from user-defined data... I will report my progress here, I promise!
One question I keep thinking about in NeoCSV: You implemented a
method called #peekChar, but it doesn't #peek. It buffers a
character and does read the #next character. I tried replacing the
#next with #peek, but that is definitely a shortcut to 100% CPU,
because #peekChar is used a lot, not only for consuming an "unmapped
remainder" of a line... I somehow have the feeling that at least in
#readEndOfLine the next char should bee peeked instead of consumed
in order to find out if it's workload or part of the crlf/lf...
Shouldn't a reader step forward by using #peek to see whether there
is more data after all fieldAccessors have been applied to the line
(see #readNextRecordAsObject)? Otoh, at one point the reader has to
skip to the next line, so I am not sure if peek has any place
here... I need to debug a little more to understand...
Joachim
Am 04.01.21 um 20:57 schrieb Sven Van Caekenberghe:
Hi Joachim,
Thanks for the detailed feedback. This is most helpful. I need to
think more about this and experiment a bit. This is what I came up
with in a Workspace/Playground:
input := 'foo,1
bar,2
foobar,3'.
(NeoCSVReader on: input readStream) upToEnd.
(NeoCSVReader on: input readStream) addField; upToEnd.
(NeoCSVReader on: input readStream) addField; addField; addField;
upToEnd.
(NeoCSVReader on: input readStream) recordClass: Dictionary;
addField: [ :obj :str | obj at: #one put: str]; upToEnd.
(NeoCSVReader on: input readStream) recordClass: Dictionary;
addField: [ :obj :str | obj at: #one put: str]; addField: [ :obj
:str | obj at: #two put: str]; addField: [ :obj :str | obj at:
#three put: str]; upToEnd.
(NeoCSVReader on: input readStream) recordClass: Dictionary;
emptyFieldValue: #passNil; addField: [ :obj :str | obj at: #one
put: str]; addField: [ :obj :str | obj at: #two put: str];
addField: [ :obj :str | obj at: #three put: str]; upToEnd.
In my opinion there are two distinct issues:
1. what to do when you define a specific number of fields to be
read and there are not enough of them in the input (underflow), or
there are too many of them in the input (overflow).
it is clear that the underflow case is wrong and a bug that has to
be fixed.
the overflow case seems OK (resulting in nil fields)
2. to validate the input (a functionality not yet present)
this would basically mean to signal an error in the under or
overflow case.
but wrong type conversions should be errors too.
I understand that you want to validate foreign input.
It is a pity that you cannot produce an infinite loop example, that
would also be useful.
That's it for now, I will come back to you.
Regards,
Sven
On 4 Jan 2021, at 14:46, jtuc...@objektfabrik.de wrote:
Please find attached a small test case to demonstrate what I mean.
There is just some nonsense Business Object class and a simple
test case in this fileout.
Am 04.01.21 um 14:36 schrieb jtuc...@objektfabrik.de:
Happy new year to all of you! May 2021 be an increasingly less
crazy year than 2020...
I have a question that sounds a bit strange, but we have two
effects with NeoCSVReader related to wrong definitions of the
reader.
One effect is that reading a Stream #upToEnd leads to an endless
loop, the other is that the Reader produces twice as many objects
as there are lines in the file that is being read.
In both scenarios, the reason is that the CSV Reader has a wrong
number of column definitions.
Of course that is my fault: why do I feed a "malformed" CSV file
to poor NeoCSVReader?
Let me explain: we have a few import interfaces which end users
can define using a more or less nice assistant in our
Application. The CSV files they upload to our App come from third
parties like payment providers, banks and other sources. These
change their file structures whenever they feel like it and never
tell anybody. So a CSV import that may have been working for
years may one day tear a whole web server image down because of a
wrong number of fieldAccessors. This is bad on many levels.
You can easily try the doubling effect at home: define a working
CSV Reader and comment out one of the addField: commands before
you use the NeoCSVReader to parse a CSV file. Say your CSV file
has 3 lines with 4 columns each. If you remove one of the
fieldAccessors, an #upToEnd will yoield an Array of 6 objects
rather than 3.
I haven't found the reason for the cases where this leads to an
endless loop, but at least this one is clear...
I *guess* this is due to the way #readEndOfLine is implemented.
It seems to not peek forward to the end of the line. I have the
gut feeling #peekChar should peek instead of reading the #next
character form the input Stream, but #peekChar has too many
senders to just go ahead and mess with it ;-)
So I wonder if there are any tried approaches to this problem.
One thing I might do is not use #upToEnd, but read each line
using PositionableStream>>#nextLine and first check each line if
the number of separators matches the number of fieldAccessors
minus 1 (and go through the hoops of handling separators in
quoted fields and such...). Only if that test succeeds, I would
then hand a Stream with the whole line to the reader and do a #next.
This will, however, mean a lot of extra cycles for large files.
Of course I could do this only for some lines, maybe just the
first one. Whatever.
But somehow I have the feeling I should get an exception telling
me the line is not compatible to the Reader's definition or such.
Or #readAtEndOrEndOfLine should just walk the line to the end and
ignore the rest of the line, returnong an incomplete object....
Maybe I am just missing the right setting or switch? What best
practices did you guys come up with for such problems?
Thanks in advance,
Joachim
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<NeoCSVEndlessLoopTest.st>
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Telefon: +49 7141 56 10 86 0 Fax: +49 7141 56 10 86 1
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Fliederweg 1 http://www.objektfabrik.de
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Telefon: +49 7141 56 10 86 0 Fax: +49 7141 56 10 86 1
