Re: [boost] buffer_size behavior in boost::iostreams::filtering_istream

Thanks very much for the replies on this post. Following Paul's advice, I did some thorough testing with version 1.74.0 (the latest boost version, as of this writing). The new version of boost seems to resolve the issue entirely. This latest version works without error regardless of how I set the buffering parameters. Regards, Justin On Sun, Sep 6, 2020 at 7:44 AM Paul A Bristow via Boost < boost@lists.boost.org> wrote:

It would be courteous (and probably wise) to update to latest Boost version before raising an issue?

Both 1.65 and 1.55 are way out of date.

Hundreds of bugs have been squashed since then!

Users of Boost should plan their development process to update Boost version regularly so as not to get too far behind like this.

Paul

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-----Original Message----- From: Boost On Behalf Of Richard Hodges via Boost Sent: 6 September 2020 08:55 To: boost@lists.boost.org List Cc: Richard Hodges Subject: Re: [boost] buffer_size behavior in boost::iostreams::filtering_istream

Perhaps file an issue here?

https://github.com/boostorg/iostreams/issues

On Sat, 5 Sep 2020 at 20:58, Justin McManus via Boost < boost@lists.boost.org> wrote:

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To follow up on my original post, I have two additional observations: 1.) I'm currently using boost version 1_65_1. In version 1_58_0, the code always read to the EOF without an issue, even with the default buffering. 2.) I tried making the buffer size arbitrarily large (1e8), but this had almost no effect at all on the behavior of the code. Since that buffer size is guaranteed to be large enough to hold any line in the input files I'm processing, it would seem that a limitation in the buffer size is not the underlying problem.

On Sat, Sep 5, 2020 at 2:23 PM Justin McManus wrote:

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I have some code that works as intended, but it requires setting a buffer_size parameter to zero on a std::ifstream pushed onto a filtering chain, and I'd like to understand why, to ensure I'm not introducing a bug or a hack.

I have essentially the following code:

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std::ifstream m_jf("json_filename", std::ios_base::in | std::ios_base::binary); std::locale utf8_locale("en_US.UTF-8"); m_jf.imbue(utf8_locale);

boost::iostreams::filtering_istream m_inbuf; m_inbuf.push(boost::iostreams::bzip2_decompressor()); m_inbuf.push(m_jf);

std::string m_line; while (std::getline(m_inbuf, m_line)) { // Process the current line from the JSON file }

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What I find is that the std::getline call will fail before the code

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reached the EOF. It will always fail at the same line in a given JSON file, but it will fail on different lines in different JSON files. It's

has perfectly

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reproducible.

However, if I change lines 4 and 5 to m_inbuf.push(boost::iostreams::bzip2_decompressor(), *0*); m_inbuf.push(m_jf, *0*); then the problem goes away.

My question is, Why does setting the buffer_size parameter to zero solve the issue? What does this do, exactly? I saw the suggestion to set

---------------------------------------------------------------------------------------------------- ---- the

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buffer size this way from an old post in 2009, and it appears to work, but I'd like a deeper understanding of what's happening under the hood. If the buffer size is set to zero, what does the underlying implementation do, and how might this influence whether std::getline fails before the EOF?

Thanks very much, Justin

-- Justin McManus, Ph.D. Principal Scientist Lead Computational Biologist and Statistical Geneticist Kallyope, Inc. 430 East 29th Street, Suite 1050 New York, NY 10016

-- Justin McManus, Ph.D. Principal Scientist Lead Computational Biologist and Statistical Geneticist Kallyope, Inc. 430 East 29th Street, Suite 1050 New York, NY 10016 (646) 596-3471

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-- Richard Hodges hodges.r@gmail.com office: +442032898513 home: +376841522 mobile: +376380212

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-- Justin McManus, Ph.D. Principal Scientist Lead Computational Biologist and Statistical Geneticist Kallyope, Inc. 430 East 29th Street, Suite 1050 New York, NY 10016 (646) 596-3471