Re: [PATCH] mailinfo.c: move side-effects outside of assert

On 12/19/2016 12:38 PM, Kyle J. McKay wrote:

On Dec 19, 2016, at 12:03, Jeff King wrote:

quoted

On Sat, Dec 17, 2016 at 11:54:18AM -0800, Kyle J. McKay wrote:

quoted

Since 6b4b013f18 (mailinfo: handle in-body header continuations,
2016-09-20, v2.11.0) mailinfo.c has contained new code with an
assert of the form:

    assert(call_a_function(...))

Thanks for spotting this - I'm not sure how I missed that.

quoted

This is obviously an improvement, but it makes me wonder if we should be
doing:

 if (!check_header(mi, &mi->inbody_header_accum, mi->s_hdr_data))
    die("BUG: some explanation of why this can never happen");

which perhaps documents the intended assumptions more clearly. A comment
regarding the side effects might also be helpful.

I wondered exactly the same thing myself.  I was hoping Jonathan would
pipe in here with some analysis about whether this is:

  a) a super paranoid, just-in-case, can't really ever fail because by
the time we get to this code we've already effectively validated
everything that could cause check_header to return false in this case

-or-

  b) Yeah, it could fail in the real world and it should "die" (and
probably have a test added that triggers such death)

-or-

  c) Actually, if check_header does return false we can keep going
without problem

-or-

  d) Actually, if check_header does return false we can keep going by
making a minor change that should be in the patch

I assume that since Jonathan added the code he will just know the answer
as to which one it is and I won't have to rely on the results of my
imaginary analysis.  ;)

The answer is "a". The only time that mi->inbody_header_accum is appended to is in check_inbody_header, and appending onto a blank mi->inbody_header_accum always happens when is_inbody_header is true (which guarantees a prefix that causes check_header to always return true).

Peff's suggestion sounds reasonable to me, maybe with an error message like "BUG: inbody_header_accum, if not empty, must always contain a valid in-body header".