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From: Matthew DeVore <matvore@comcast.net>
To: Junio C Hamano <gitster@pobox.com>
Cc: Matthew DeVore <matvore@google.com>,
	git@vger.kernel.org, jonathantanmy@google.com, jrn@google.com,
	dstolee@microsoft.com, jeffhost@microsoft.com,
	jrnieder@gmail.com, pclouds@gmail.com, emilyshaffer@google.com
Subject: Re: [PATCH v2 6/9] list-objects-filter-options: make filter_spec a strbuf
Date: Tue, 11 Jun 2019 11:44:27 -0700	[thread overview]
Message-ID: <20190611184426.GB58112@comcast.net> (raw)
In-Reply-To: <xmqqtvcwkowx.fsf@gitster-ct.c.googlers.com>

On Tue, Jun 11, 2019 at 10:33:18AM -0700, Junio C Hamano wrote:
> Matthew DeVore <matvore@comcast.net> writes:
> 
> >> convention, and it may even be a useful one (i.e. it allows you to
> >> calloc() a structure with an embedded strbuf in it and the "if
> >> .buf==NULL, call strbuf_init() lazily" can become an established
> >> pattern), but at the same time it feels a bit brittle.  
> >
> > Is it brittle because a strbuf may be initialized to non-zero memory, and so
> > the "if (buf.buf == NULL)" may evaluate to false, and then go on treating
> > garbage like a valid buffer?
> 
> It is brittle because callers are bound to forget doing "if
> (!x->buf.buf) lazy_init(&x->buf)" at some point, and blindly use an
> uninitialized x->buf.  Making sure x->buf is always initialized

A corallary proposition would be to make this particular strbuf a "struct
strbuf *" rather than an inline strbuf. It should then be rather clear to users
that it may be null. Then whoever allocates the memory can also do the
strbuf_init one-liner. The free'ing logic of list_objects_filter_options then
only becomes trivially more complicated than it was before. Does that sound
like a good compromise to you?

> before any caller touches is the only way to solve it, and as you
> said, there are two possible ways to make that happen.  One way that
> does not violate the current API contract is to make sure whoever
> allocates and/or initializes the surrounding struct that embeds a
> strbuf does strbuf_init(&x->buf) before any user sees the struct.

The thing I don't like about that is that the non-zeroness of its
initialization percolates upward to whatever the top-level struct is, which
means implementation details leak a lot. This seems quite brittle as well,
since anyone can forget to initialize some struct in the nested line.

> 
> Another would be to update strbuf API so that strbuf_init() does not
> even have to use slopbuf.  But that is a much larger change that
> potentially breaks existing users of strbuf API.  When you have a
> strbuf that has been prepared to be usable, the current API contract
> allows its users to expect buf.buf is never NULL, so they assume
> that they can safely write "if (!buf.buf)", so auditing strbuf.c and
> making sure a strbuf with buf==NULL gets lazily initialized is not
> enough.

That's true. I didn't think it matters in the case of filter_spec in
particular, since users of list_objects_filter_options are supposed to use an
accessor and not touch the strbuf directly, but looking at it like a more
general API change, it seems risky.

  reply	other threads:[~2019-06-11 18:45 UTC|newest]

Thread overview: 74+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-01  0:35 [PATCH v2 0/9] Filter combination Matthew DeVore
2019-06-01  0:35 ` [PATCH v2 1/9] list-objects-filter: make API easier to use Matthew DeVore
2019-06-01  0:35 ` [PATCH v2 2/9] list-objects-filter: put omits set in filter struct Matthew DeVore
2019-06-01  0:35 ` [PATCH v2 3/9] list-objects-filter-options: always supply *errbuf Matthew DeVore
2019-06-01  0:35 ` [PATCH v2 4/9] list-objects-filter: implement composite filters Matthew DeVore
2019-06-03 21:51   ` Jeff Hostetler
2019-06-06 22:32     ` Matthew DeVore
2019-06-07 17:58       ` Jeff Hostetler
2019-06-01  0:35 ` [PATCH v2 5/9] list-objects-filter-options: move error check up Matthew DeVore
2019-06-01  0:36 ` [PATCH v2 6/9] list-objects-filter-options: make filter_spec a strbuf Matthew DeVore
2019-06-10 20:13   ` Junio C Hamano
2019-06-11  0:34     ` Matthew DeVore
2019-06-11 17:33       ` Junio C Hamano
2019-06-11 18:44         ` Matthew DeVore [this message]
2019-06-11 21:34           ` Matthew DeVore
2019-06-11 21:48           ` Junio C Hamano
2019-06-12  0:37             ` Matthew DeVore
2019-06-12 14:55               ` Matthew DeVore
2019-06-01  0:36 ` [PATCH v2 7/9] list-objects-filter-options: allow mult. --filter Matthew DeVore
2019-06-01  0:36 ` [PATCH v2 8/9] list-objects-filter-options: clean up use of ALLOC_GROW Matthew DeVore
2019-06-03 22:07   ` Jacob Keller
2019-06-03 22:39     ` Matthew DeVore
2019-06-04  3:16       ` Jacob Keller
2019-06-01  0:36 ` [PATCH v2 9/9] list-objects-filter-options: make parser void Matthew DeVore
2019-06-03 21:35 ` [PATCH v2 0/9] Filter combination Jeff Hostetler
2019-06-13 21:51 ` [PATCH v3 00/10] " Matthew DeVore
2019-06-13 21:51   ` [PATCH v3 01/10] list-objects-filter: make API easier to use Matthew DeVore
2019-06-13 21:51   ` [PATCH v3 02/10] list-objects-filter: put omits set in filter struct Matthew DeVore
2019-06-13 21:51   ` [PATCH v3 03/10] list-objects-filter-options: always supply *errbuf Matthew DeVore
2019-06-13 21:51   ` [PATCH v3 04/10] list-objects-filter: implement composite filters Matthew DeVore
2019-06-13 21:51   ` [PATCH v3 05/10] list-objects-filter-options: move error check up Matthew DeVore
2019-06-13 21:51   ` [PATCH v3 06/10] list-objects-filter-options: make filter_spec a string_list Matthew DeVore
2019-06-13 21:51   ` [PATCH v3 07/10] strbuf: give URL-encoding API a char predicate fn Matthew DeVore
2019-06-13 21:51   ` [PATCH v3 08/10] list-objects-filter-options: allow mult. --filter Matthew DeVore
2019-06-13 21:51   ` [PATCH v3 09/10] list-objects-filter-options: clean up use of ALLOC_GROW Matthew DeVore
2019-06-13 21:51   ` [PATCH v3 10/10] list-objects-filter-options: make parser void Matthew DeVore
2019-06-14 19:50   ` [PATCH v3 00/10] Filter combination Junio C Hamano
2019-06-15  0:40 ` [PATCH v4 " Matthew DeVore
2019-06-15  0:40   ` [PATCH v4 01/10] list-objects-filter: make API easier to use Matthew DeVore
2019-06-21 22:58     ` Jonathan Tan
2019-06-27  0:46       ` Matthew DeVore
2019-06-15  0:40   ` [PATCH v4 02/10] list-objects-filter: put omits set in filter struct Matthew DeVore
2019-06-15  0:40   ` [PATCH v4 03/10] list-objects-filter-options: always supply *errbuf Matthew DeVore
2019-06-15  0:40   ` [PATCH v4 04/10] list-objects-filter: implement composite filters Matthew DeVore
2019-06-18  8:42     ` Johannes Schindelin
2019-06-18 20:22       ` Matthew DeVore
2019-06-21 18:17         ` Johannes Schindelin
2019-06-22  0:26     ` Jonathan Tan
2019-06-27 21:12       ` Matthew DeVore
2019-06-15  0:40   ` [PATCH v4 05/10] list-objects-filter-options: move error check up Matthew DeVore
2019-06-15  0:40   ` [PATCH v4 06/10] list-objects-filter-options: make filter_spec a string_list Matthew DeVore
2019-06-22  0:37     ` Jonathan Tan
2019-06-27 21:17       ` Matthew DeVore
2019-06-15  0:40   ` [PATCH v4 07/10] strbuf: give URL-encoding API a char predicate fn Matthew DeVore
2019-06-15  0:40   ` [PATCH v4 08/10] list-objects-filter-options: allow mult. --filter Matthew DeVore
2019-06-15  0:40   ` [PATCH v4 09/10] list-objects-filter-options: clean up use of ALLOC_GROW Matthew DeVore
2019-06-15  0:40   ` [PATCH v4 10/10] list-objects-filter-options: make parser void Matthew DeVore
2019-06-22  0:46     ` Jonathan Tan
2019-06-27 21:24       ` Matthew DeVore
2019-06-27 22:27         ` Matthew DeVore
2019-06-18  1:25   ` [PATCH v4 00/10] Filter combination Junio C Hamano
2019-06-27 22:54 ` [PATCH v5 " Matthew DeVore
2019-06-27 22:54   ` [PATCH v5 01/10] list-objects-filter: encapsulate filter components Matthew DeVore
2019-06-27 22:54   ` [PATCH v5 02/10] list-objects-filter: put omits set in filter struct Matthew DeVore
2019-06-27 22:54   ` [PATCH v5 03/10] list-objects-filter-options: always supply *errbuf Matthew DeVore
2019-06-27 22:54   ` [PATCH v5 04/10] list-objects-filter: implement composite filters Matthew DeVore
2019-06-27 22:54   ` [PATCH v5 05/10] list-objects-filter-options: move error check up Matthew DeVore
2019-06-27 22:54   ` [PATCH v5 06/10] list-objects-filter-options: make filter_spec a string_list Matthew DeVore
2019-06-27 22:54   ` [PATCH v5 07/10] strbuf: give URL-encoding API a char predicate fn Matthew DeVore
2019-06-27 22:54   ` [PATCH v5 08/10] list-objects-filter-options: allow mult. --filter Matthew DeVore
2019-06-27 22:54   ` [PATCH v5 09/10] list-objects-filter-options: clean up use of ALLOC_GROW Matthew DeVore
2019-06-27 22:54   ` [PATCH v5 10/10] list-objects-filter-options: make parser void Matthew DeVore
2019-06-28 16:05   ` [PATCH v5 00/10] Filter combination Junio C Hamano
2019-06-28 17:16   ` Jonathan Tan

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