After instantiating the reader and before doing the reading you can #readHeader and check that the reader field count and header field count match. Would that help? If the CSV doesn't use headers then you can process the "header" as the first record and then process the rest of the file. jtuchel 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

jtuchel@

:

...

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

-- ----------------------------------------------------------------------- Objektfabrik Joachim Tuchel mailto:

jtuchel@

Fliederweg 1 http://www.objektfabrik.de D-71640 Ludwigsburg http://joachimtuchel.wordpress.com Telefon: +49 7141 56 10 86 0 Fax: +49 7141 56 10 86 1

NeoCSVEndlessLoopTest.st (2K) <http://forum.world.st/attachment/5125853/0/NeoCSVEndlessLoopTest.st>;

-- Sent from: http://forum.world.st/Pharo-Smalltalk-Users-f1310670.html

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, jtuchel@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 jtuchel@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

-- ----------------------------------------------------------------------- Objektfabrik Joachim Tuchel mailto:jtuchel@objektfabrik.de Fliederweg 1 http://www.objektfabrik.de D-71640 Ludwigsburg http://joachimtuchel.wordpress.com Telefon: +49 7141 56 10 86 0 Fax: +49 7141 56 10 86 1

<NeoCSVEndlessLoopTest.st>

Hi Joachim, Have a look at the following commit: https://github.com/svenvc/NeoCSV/commit/a3d6258c28138fe3b15aa03ae71cf1e07709... 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, jtuchel@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, jtuchel@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 jtuchel@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

-- ----------------------------------------------------------------------- Objektfabrik Joachim Tuchel mailto:jtuchel@objektfabrik.de Fliederweg 1 http://www.objektfabrik.de D-71640 Ludwigsburg http://joachimtuchel.wordpress.com Telefon: +49 7141 56 10 86 0 Fax: +49 7141 56 10 86 1

<NeoCSVEndlessLoopTest.st>

-- ----------------------------------------------------------------------- Objektfabrik Joachim Tuchel mailto:jtuchel@objektfabrik.de Fliederweg 1 http://www.objektfabrik.de D-71640 Ludwigsburg http://joachimtuchel.wordpress.com Telefon: +49 7141 56 10 86 0 Fax: +49 7141 56 10 86 1

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 jtuchel@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/a3d6258c28138fe3b15aa03ae71cf1e07709...

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, jtuchel@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, jtuchel@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 jtuchel@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

-- -----------------------------------------------------------------------

Objektfabrik Joachim Tuchel mailto:jtuchel@objektfabrik.de Fliederweg 1 http://www.objektfabrik.de D-71640 Ludwigsburg http://joachimtuchel.wordpress.com Telefon: +49 7141 56 10 86 0         Fax: +49 7141 56 10 86 1

<NeoCSVEndlessLoopTest.st>

-- ----------------------------------------------------------------------- Objektfabrik Joachim Tuchel mailto:jtuchel@objektfabrik.de Fliederweg 1 http://www.objektfabrik.de D-71640 Ludwigsburg http://joachimtuchel.wordpress.com Telefon: +49 7141 56 10 86 0         Fax: +49 7141 56 10 86 1

-- ----------------------------------------------------------------------- Objektfabrik Joachim Tuchel mailto:jtuchel@objektfabrik.de Fliederweg 1 http://www.objektfabrik.de D-71640 Ludwigsburg http://joachimtuchel.wordpress.com Telefon: +49 7141 56 10 86 0 Fax: +49 7141 56 10 86 1

Joachim,

On 6 Jan 2021, at 11:21, jtuchel@objektfabrik.de wrote:

Hi Sven,

I must say I am really happy with your change. We get a nice exception whenever the number of fieldAccessor doesn't match with the number of defined fieldAccessors. So far it also seems the endless loops are gone as well. What a leap forward!

Thank you for your kind words. But thank you as well: it really helps to get constructive feedback from actual users, to improve the code for everyone.

I'm adding an issue on github about the conversion errors, I hope that is a convenient place for such comments/ideas?

Did you see NeoCSVReaderTests>>#testConversionErrors ? It is not perfect, but you do get an error when a number conversion fails, you could make your own conversions fail similarly. (NeoCSVReader on: 'a' readStream) addIntegerField; upToEnd. Like you said: some validation can be done at the CSV level, but certainly not everything. Sven

Joachim

Am 05.01.21 um 21:06 schrieb jtuchel@objektfabrik.de:

...

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 jtuchel@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/a3d6258c28138fe3b15aa03ae71cf1e07709...

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, jtuchel@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, jtuchel@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 jtuchel@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

-- ----------------------------------------------------------------------- Objektfabrik Joachim Tuchel mailto:jtuchel@objektfabrik.de Fliederweg 1 http://www.objektfabrik.de D-71640 Ludwigsburg http://joachimtuchel.wordpress.com Telefon: +49 7141 56 10 86 0 Fax: +49 7141 56 10 86 1

<NeoCSVEndlessLoopTest.st>

-- ----------------------------------------------------------------------- Objektfabrik Joachim Tuchel mailto:jtuchel@objektfabrik.de Fliederweg 1 http://www.objektfabrik.de D-71640 Ludwigsburg http://joachimtuchel.wordpress.com Telefon: +49 7141 56 10 86 0 Fax: +49 7141 56 10 86 1

-- ----------------------------------------------------------------------- Objektfabrik Joachim Tuchel mailto:jtuchel@objektfabrik.de Fliederweg 1 http://www.objektfabrik.de D-71640 Ludwigsburg http://joachimtuchel.wordpress.com Telefon: +49 7141 56 10 86 0 Fax: +49 7141 56 10 86 1

John I’m sorry to tell you that but you cannot write mail like that without telling us where is the code of CVSParser. You cannot basically discredit the work on Sven without providing code to compare. S.

On 6 Jan 2021, at 05:10, Richard O'Keefe <raoknz@gmail.com> wrote:

NeoCSVReader is described as efficient. What is that in comparison to? What benchmark data are used? Here are benchmark results measured today. (5,000 data line file, 9,145,009 characters). method time(ms) Just read characters 410 CSVDecoder>>next 3415 astc's CSV reader (defaults). 1.26 x CSVParser NeoCSVReader>>next 4798 NeoCSVReader (default state). 1.78 x CSVParser CSVParser>>next 2701 pared-to-the-bone CSV reader. 1.00 reference.

(10,000 data line file, 1,544,836 characters). method time(ms) Just read characters 93 CSVDecoder>>next 530 astc's CSV reader (defaults). 1.26 x CSVParser NeoCSVReader>>next 737 NeoCSVReader (default state). 1.75 x CSVParser CSVParser>>next 421 pared-to-the-bone CSV reader. 1.00 reference.

CSVParser is just 78 lines and is not customisable. It really is stripped to pretty much an absolute minimum. All of the parsers were configured (if that made sense) to return an Array of Strings. Many of the CSV files I've worked with use short records instead of ending a line with a lot of commas. Some of them also have the occasional stray comment off to the right, not mentioned in the header. I've also found it necessary to skip multiple lines at the beginning and/or end. (Really, some government agencies seem to have NO idea that anyone might want to do more with a CSV file than eyeball it in Excel.)

If there is a benchmark suite I can use to improve CSVDecoder, I would like to try it out.

On Tue, 5 Jan 2021 at 02:36, jtuchel@objektfabrik.de <mailto:jtuchel@objektfabrik.de> <jtuchel@objektfabrik.de <mailto:jtuchel@objektfabrik.de>> wrote: 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

-------------------------------------------- Stéphane Ducasse http://stephane.ducasse.free.fr / http://www.pharo.org 03 59 35 87 52 Assistant: Aurore Dalle FAX 03 59 57 78 50 TEL 03 59 35 86 16 S. Ducasse - Inria 40, avenue Halley, Parc Scientifique de la Haute Borne, Bât.A, Park Plaza Villeneuve d'Ascq 59650 France

Richard, I am not sure what point you are trying to make here. You have something cooler and faster? Great, how about sharing? You could make a faster one when it doesn't convert numbers and stuff? Great. I guess the time will be spent after parsing in 95% of the use cases. It depends. And that is exactly what you are saying. The word efficient means nothing without context. How is that related to this thread? I think this thread mostly shows the strength of a community, especially when there are members who are active, friendly and highly motivated. My problem git solved in blazing speed without me paying anything for it. Just because Sven thought my problem could be other people's problem as well. I am happy with NeoCSV's speed, even if there may be more lightweigt and faster solutions. Tbh, my main concern with NeoCSV is not speed, but how well I can understand problems and fix them. I care about data types on parsing. A non-configurable csv parser gives me a bunch of dictionaries and Strings. That could be a waste of cycles and memory once you need the data as objects. My use case is not importing trillions of records all day, and for a few hundred or maybe sometimes thousands, it is good/fast enough. Joachim Am 06.01.21 um 05:10 schrieb Richard O'Keefe:

NeoCSVReader is described as efficient.  What is that in comparison to? What benchmark data are used? Here are benchmark results measured today. (5,000 data line file, 9,145,009 characters).  method                time(ms)  Just read characters   410  CSVDecoder>>next      3415   astc's CSV reader (defaults). 1.26 x CSVParser  NeoCSVReader>>next    4798   NeoCSVReader (default state). 1.78 x CSVParser  CSVParser>>next       2701   pared-to-the-bone CSV reader. 1.00 reference.

(10,000 data line file, 1,544,836 characters).  method                time(ms)  Just read characters    93  CSVDecoder>>next       530   astc's CSV reader (defaults). 1.26 x CSVParser  NeoCSVReader>>next     737   NeoCSVReader (default state). 1.75 x CSVParser  CSVParser>>next        421   pared-to-the-bone CSV reader. 1.00 reference.

CSVParser is just 78 lines and is not customisable.  It really is stripped to pretty much an absolute minimum.  All of the parsers were configured (if that made sense) to return an Array of Strings. Many of the CSV files I've worked with use short records instead of ending a line with a lot of commas.  Some of them also have the occasional stray comment off to the right, not mentioned in the header. I've also found it necessary to skip multiple lines at the beginning and/or end.  (Really, some government agencies seem to have NO idea that anyone might want to do more with a CSV file than eyeball it in Excel.)

If there is a benchmark suite I can use to improve CSVDecoder, I would like to try it out.

On Tue, 5 Jan 2021 at 02:36, jtuchel@objektfabrik.de <mailto:jtuchel@objektfabrik.de> <jtuchel@objektfabrik.de <mailto:jtuchel@objektfabrik.de>> wrote:

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

-- ----------------------------------------------------------------------- Objektfabrik Joachim Tuchel mailto:jtuchel@objektfabrik.de Fliederweg 1 http://www.objektfabrik.de D-71640 Ludwigsburg http://joachimtuchel.wordpress.com Telefon: +49 7141 56 10 86 0 Fax: +49 7141 56 10 86 1

Richard, Am 07.01.21 um 07:15 schrieb Richard O'Keefe:

You aren't sure what point I was making?

exactly, the thread you answered was about a possible bug in NeoCSV parser. Your post was about your doubts about the claim of efficiency on the parser's web site. So you threw in some completely unrelated topic and started by sounding more or less destructive (maybe this is a word too harsh, but I am not a native english speaker... maybe "challenging" is a better word?). I cannot comment on the efficiency of NeoCSV, other than it is fast enough for my use case and it gives me the option of combining reading CSV and producing objects in one run, even if some checks, backpointering, whatever has to be done after the parsing. It has a nice API and is supported quite well. The thread and Sven's reaction underline this last statement quite impressively: my bug was fixed within hours.

How about the one I actually wrote down:   What test data was NeoCSV benchmarked with   and can I get my hands on it?

That is a valid question. It is off-topic in the thread, however. And maybe your tone was a bit less kind than it should be. Nevertheless, the discussion itself is worth its own thread. If the raw speed of reading lots of CSV data is of concern in a use case, we should look for and at alternatives. You are of course free to ask about alternatives, present your measurements or alternative implementation and ask for comments, ideas, all kinds of input. That's what yields progress.

THAT is the point. The data points I showed (and many others I have not) are not satisfactory to me.

Fine and absolutely worth discussing. Maybe in its own discussion thread and started with a friendly invitation for discussion. Your post was more like "Oh, and, by the way, NeoCSV sucks". Maybe unintended, but that is what I read.

I have been searching for CSV test collections. One site offered 6 files of which only one downloaded. I found a "benchmark suite" for CSV containing no actual CSV files. So where *else* should I look for benchmark data than associated with a parser people in this community are generally happy with that is described as "efficient"?

So you would like the developers of NeoCSV to provide test data that allows for benchmarking and comparison? A valid point.

Is it so unreasonable to suspect that my results might be a fluke?  Is it bad manners to assume that something described as efficient has tests showing that?

Well, no. It is absolutely okay to ask if a claim like "efficient" can be proven. You are free to present better choices and discuss your definition of efficiency. For me personally, your post sounded a bit like some earlier ones of yours which seemed to have no other point than "I have something better, but I won't show you". Hence my reaction. I may have read something into your post that you haven't written into it. Sorry for that. Joachim

On Wed, 6 Jan 2021 at 22:23, jtuchel@objektfabrik.de <mailto:jtuchel@objektfabrik.de> <jtuchel@objektfabrik.de <mailto:jtuchel@objektfabrik.de>> wrote:

Richard,

I am not sure what point you are trying to make here. You have something cooler and faster? Great, how about sharing? You could make a faster one when it doesn't convert numbers and stuff? Great. I guess the time will be spent after parsing in 95% of the use cases. It depends. And that is exactly what you are saying. The word efficient means nothing without context. How is that related to this thread?

I think this thread mostly shows the strength of a community, especially when there are members who are active, friendly and highly motivated. My problem git solved in blazing speed without me paying anything for it. Just because Sven thought my problem could be other people's problem as well.

I am happy with NeoCSV's speed, even if there may be more lightweigt and faster solutions. Tbh, my main concern with NeoCSV is not speed, but how well I can understand problems and fix them. I care about data types on parsing. A non-configurable csv parser gives me a bunch of dictionaries and Strings. That could be a waste of cycles and memory once you need the data as objects. My use case is not importing trillions of records all day, and for a few hundred or maybe sometimes thousands, it is good/fast enough.

Joachim

Am 06.01.21 um 05:10 schrieb Richard O'Keefe:

...

NeoCSVReader is described as efficient.  What is that in comparison to?  What benchmark data are used? Here are benchmark results measured today. (5,000 data line file, 9,145,009 characters).  method                time(ms)  Just read characters   410  CSVDecoder>>next      3415   astc's CSV reader (defaults). 1.26 x CSVParser  NeoCSVReader>>next    4798   NeoCSVReader (default state). 1.78 x CSVParser  CSVParser>>next       2701   pared-to-the-bone CSV reader. 1.00 reference.

(10,000 data line file, 1,544,836 characters).  method                time(ms)  Just read characters    93  CSVDecoder>>next       530   astc's CSV reader (defaults). 1.26 x CSVParser  NeoCSVReader>>next     737   NeoCSVReader (default state). 1.75 x CSVParser  CSVParser>>next        421   pared-to-the-bone CSV reader. 1.00 reference.

CSVParser is just 78 lines and is not customisable.  It really is stripped to pretty much an absolute minimum.  All of the parsers were configured (if that made sense) to return an Array of Strings. Many of the CSV files I've worked with use short records instead of ending a line with a lot of commas.  Some of them also have the occasional stray comment off to the right, not mentioned in the header. I've also found it necessary to skip multiple lines at the beginning and/or end. (Really, some government agencies seem to have NO idea that anyone might want to do more with a CSV file than eyeball it in Excel.)

If there is a benchmark suite I can use to improve CSVDecoder, I would like to try it out.

On Tue, 5 Jan 2021 at 02:36, jtuchel@objektfabrik.de <mailto:jtuchel@objektfabrik.de> <jtuchel@objektfabrik.de <mailto:jtuchel@objektfabrik.de>> wrote:

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

-- ----------------------------------------------------------------------- Objektfabrik Joachim Tuchelmailto:jtuchel@objektfabrik.de <mailto:jtuchel@objektfabrik.de> Fliederweg 1http://www.objektfabrik.de <http://www.objektfabrik.de> D-71640 Ludwigsburghttp://joachimtuchel.wordpress.com <http://joachimtuchel.wordpress.com> Telefon: +49 7141 56 10 86 0 Fax: +49 7141 56 10 86 1

-- ----------------------------------------------------------------------- Objektfabrik Joachim Tuchel mailto:jtuchel@objektfabrik.de Fliederweg 1 http://www.objektfabrik.de D-71640 Ludwigsburg http://joachimtuchel.wordpress.com Telefon: +49 7141 56 10 86 0 Fax: +49 7141 56 10 86 1

Hi Richard, Benchmarking is a can of worms, many factors have to be considered. But the first requirement is obviously to be completely open over what you are doing and what you are comparing. NeoCSV contains a simple benchmark suite called NeoCSVBenchmark, which was used during development. Note that it is a bit tricky to use: you need to run a write benchmark with a specific configuration before you can try read benchmarks. The core data is a 100.000 line file (2.5 MB) like this: 1,-1,99999 2,-2,99998 3,-3,99997 4,-4,99996 5,-5,99995 6,-6,99994 7,-7,99993 8,-8,99992 9,-9,99991 10,-10,99990 ... That parses in ~250ms on my machine. NeoCSV has quite a bit of features and handles various edge cases. Obviously, a minimal, custom implementation could be faster. NeoCSV is called efficient not just because it is reasonably fast, but because it can be configured to generate domain objects without intermediate structures and because it can convert individual fields (parse numbers, dates, times, ...) while parsing. Like you said, some generated CSV output out in the wild is very irregular. I try to stick with standard CSV as much as possible. Sven

On 6 Jan 2021, at 05:10, Richard O'Keefe <raoknz@gmail.com> wrote:

NeoCSVReader is described as efficient. What is that in comparison to? What benchmark data are used? Here are benchmark results measured today. (5,000 data line file, 9,145,009 characters). method time(ms) Just read characters 410 CSVDecoder>>next 3415 astc's CSV reader (defaults). 1.26 x CSVParser NeoCSVReader>>next 4798 NeoCSVReader (default state). 1.78 x CSVParser CSVParser>>next 2701 pared-to-the-bone CSV reader. 1.00 reference.

(10,000 data line file, 1,544,836 characters). method time(ms) Just read characters 93 CSVDecoder>>next 530 astc's CSV reader (defaults). 1.26 x CSVParser NeoCSVReader>>next 737 NeoCSVReader (default state). 1.75 x CSVParser CSVParser>>next 421 pared-to-the-bone CSV reader. 1.00 reference.

CSVParser is just 78 lines and is not customisable. It really is stripped to pretty much an absolute minimum. All of the parsers were configured (if that made sense) to return an Array of Strings. Many of the CSV files I've worked with use short records instead of ending a line with a lot of commas. Some of them also have the occasional stray comment off to the right, not mentioned in the header. I've also found it necessary to skip multiple lines at the beginning and/or end. (Really, some government agencies seem to have NO idea that anyone might want to do more with a CSV file than eyeball it in Excel.)

If there is a benchmark suite I can use to improve CSVDecoder, I would like to try it out.

On Tue, 5 Jan 2021 at 02:36, jtuchel@objektfabrik.de <jtuchel@objektfabrik.de> wrote: 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

As it happened, I ran into the exact same scenario as Joachim just the other day, that is, the external provider of my csv had added some new columns. In my case manifested itself in an error that an integer field was not an integer (because new columns were added in the middle). Reading through this whole thread leaves me with the feeling that no matter what Sven adds, there is still a risk for error. Nevertheless, my suggestion would be to add a functionality to #skipHeaders, or make a sister method: #assertAndSkipHeaders: numberOfColumns onFailDo: aBlock given the actual number of headers That would give me a way to handle the error up front. This will only be interesting if your data has headers of cause. Thanks for NeoCSV which I use all the time! Best, Kasper

I’m not doing any CSV processing at the moment, but have in the past - so was interested in this thread. @Kasper, can’t you just use #readHeader upfront, and do the assertion yourself, and then proceed to loop through your records? It would seem that the Neo caters for what you are suggesting - and if you want to add a helper method extension you have the building blocks to already do this? The only flaw I can think of, is if there is no header present then I can’t recall what Neo does - ideally throws an exception so you can decide what to do - potentially continue if the number of columns is what you expect and the data matches the columns - or you fail with an error that a header is required. But I think you would always need to do some basic initial checks when processing CSV due to the nature of the format? Tim On Fri, 22 Jan 2021, at 6:42 AM, Kasper Osterbye wrote:

As it happened, I ran into the exact same scenario as Joachim just the other day, that is, the external provider of my csv had added some new columns. In my case manifested itself in an error that an integer field was not an integer (because new columns were added in the middle).

Reading through this whole thread leaves me with the feeling that no matter what Sven adds, there is still a risk for error. Nevertheless, my suggestion would be to add a functionality to #skipHeaders, or make a sister method: #assertAndSkipHeaders: numberOfColumns onFailDo: aBlock given the actual number of headers That would give me a way to handle the error up front.

This will only be interesting if your data has headers of cause.

Thanks for NeoCSV which I use all the time!

Best,

Kasper

There is now the following commit: https://github.com/svenvc/NeoCSV/commit/0acc2270b382f52533c478f2f1585341e390... which should address a couple of issues.

On 22 Jan 2021, at 12:15, jtuchel@objektfabrik.de wrote:

Tim,

Am 22.01.21 um 10:22 schrieb Tim Mackinnon:

...

I’m not doing any CSV processing at the moment, but have in the past - so was interested in this thread.

@Kasper, can’t you just use #readHeader upfront, and do the assertion yourself, and then proceed to loop through your records? It would seem that the Neo caters for what you are suggesting - and if you want to add a helper method extension you have the building blocks to already do this?

This is a good idea. One caveat, however: #readHeader in its current implementation does 2 things:

• read the line respecting each field (thereby, respect line breaks within quoted fields - perfect for this purpose) • update the number of Columns for further reading (assuming #readHeader's purpose is to interpret the header line) This second thing is in our way, because it may influence the way the following lines will be interpreted. That is ecactly why I created an issue on github (https://github.com/svenvc/NeoCSV/issues/20). A method that reads a line without any side effects (other than pushing the position pointer forward to the next line) would come in handy for such scenarios. But you can always argue that this has nothing to do with CSV, because in CSV all lines have the same number of columns, each of them containing the same kind of information, and there may be exactly one header line. Anything else is just some file that may contain CSV-y stuff in it. So I am really not sure if NeoCSV should build lots of stuff for such files. I'd love to have this, but I'd understand if Sven refused to integrate it.... ;-)

...

The only flaw I can think of, is if there is no header present then I can’t recall what Neo does - ideally throws an exception so you can decide what to do - potentially continue if the number of columns is what you expect and the data matches the columns - or you fail with an error that a header is required. But I think you would always need to do some basic initial checks when processing CSV due to the nature of the format? Right. You'd always have to write some specific logic for this particular file format and make NeoCSV ignore the right stuff...

Joachim

...

Tim

On Fri, 22 Jan 2021, at 6:42 AM, Kasper Osterbye wrote:

...

As it happened, I ran into the exact same scenario as Joachim just the other day, that is, the external provider of my csv had added some new columns. In my case manifested itself in an error that an integer field was not an integer (because new columns were added in the middle).

Reading through this whole thread leaves me with the feeling that no matter what Sven adds, there is still a risk for error. Nevertheless, my suggestion would be to add a functionality to #skipHeaders, or make a sister method: #assertAndSkipHeaders: numberOfColumns onFailDo: aBlock given the actual number of headers That would give me a way to handle the error up front.

This will only be interesting if your data has headers of cause.

Thanks for NeoCSV which I use all the time!

Best,

Kasper

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