Date: Thu, 24 Nov 2016 17:39:12 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Daniel Verite <daniel@manitou-mail.org>
Cc: Tomas Vondra <tomas.vondra@2ndquadrant.com>,
	Craig Ringer <craig@2ndquadrant.com>, Tom Lane <tgl@sss.pgh.pa.us>,
	Robert Haas <robertmhaas@gmail.com>,
	Jim Nasby <Jim.Nasby@bluetreble.com>,
	Ronan Dunklau <ronan.dunklau@dalibo.com>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: pg_dump / copy bugs with "big lines" ?
Message-ID: <20161124203912.iccqstd4doqsnyuh@alvherre.pgsql>
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Daniel Verite wrote:

> Here's an updated patch. Compared to the previous version:
> 
> - removed CopyStartSend (per comment #1 in review)
> 
> - renamed flag to allow_long (comment #2)
> 
> - resetStringInfo no longer resets the flag (comment #3).
> 
> - allowLongStringInfo() is removed (comment #3 and #5),
> makeLongStringInfo() and initLongStringInfo() are provided
> instead, as alternatives to makeStringInfo() and initStringInfo().
> 
> - StringInfoData.len is back to int type, 2GB max.
> (addresses comment #4 incidentally).
> This is safer because  many routines peeking
> into StringInfoData use int for offsets into the buffer,
> for instance most of the stuff in backend/libpq/pqformat.c
> Altough these routines are not supposed to be called on long
> buffers, this assertion was not enforced in the code, and
> with a 64-bit length effectively over 2GB, they would misbehave
> pretty badly.

Hmm, this looks a lot better I think.  One change we overlooked and I
just noticed is that we need to change appendStringInfoVA() to return
size_t rather than int.  This comment at the bottom of it gave that up:

	/*
	 * Return pvsnprintf's estimate of the space needed.  (Although this is
	 * given as a size_t, we know it will fit in int because it's not more
	 * than MaxAllocSize.)
	 */
	return (int) nprinted;

The parenthical comment is no longer true.

This means we need to update all its callers to match.  I suppose it
won't be a problem for most of them since they are not using long
stringinfos anyway, but it seems better to keep everything consistent.
I hope that callers that do not adjust the type of the declared variable
would get a compiler warning.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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