From d3158f339f7580ce7eeb71a6f2da0b1813aa3684 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Mon, 20 Feb 2012 00:52:42 -0500 Subject: [PATCH] Fix regex back-references that are directly quantified with *. The syntax "\n*", that is a backref with a * quantifier directly applied to it, has never worked correctly in Spencer's library. This has been an open bug in the Tcl bug tracker since 2005: https://sourceforge.net/tracker/index.php?func=detail&aid=1115587&group_id=10894&atid=110894 The core of the problem is in parseqatom(), which first changes "\n*" to "\n+|" and then applies repeat() to the NFA representing the backref atom. repeat() thinks that any arc leading into its "rp" argument is part of the sub-NFA to be repeated. Unfortunately, since parseqatom() already created the arc that was intended to represent the empty bypass around "\n+", this arc gets moved too, so that it now leads into the state loop created by repeat(). Thus, what was supposed to be an "empty" bypass gets turned into something that represents zero or more repetitions of the NFA representing the backref atom. In the original example, in place of ^([bc])\1*$ we now have something that acts like ^([bc])(\1+|[bc]*)$ At runtime, the branch involving the actual backref fails, as it's supposed to, but then the other branch succeeds anyway. We could no doubt fix this by some rearrangement of the operations in parseqatom(), but that code is plenty ugly already, and what's more the whole business of converting "x*" to "x+|" probably needs to go away to fix another problem I'll mention in a moment. Instead, this patch suppresses the *-conversion when the target is a simple backref atom, leaving the case of m == 0 to be handled at runtime. This makes the patch in regcomp.c a one-liner, at the cost of having to tweak cbrdissect() a little. In the event I went a bit further than that and rewrote cbrdissect() to check all the string-length-related conditions before it starts comparing characters. It seems a bit stupid to possibly iterate through many copies of an n-character backreference, only to fail at the end because the target string's length isn't a multiple of n --- we could have found that out before starting. The existing coding could only be a win if integer division is hugely expensive compared to character comparison, but I don't know of any modern machine where that might be true. This does not fix all the problems with quantified back-references. In particular, the code is still broken for back-references that appear within a larger expression that is quantified (so that direct insertion of the quantification limits into the BACKREF node doesn't apply). I think fixing that will take some major surgery on the NFA code, specifically introducing an explicit iteration node type instead of trying to transform iteration into concatenation of modified regexps. Back-patch to all supported branches. In HEAD, also add a regression test case for this. (It may seem a bit silly to create a regression test file for just one test case; but I'm expecting that we will soon import a whole bunch of regex regression tests from Tcl, so might as well create the infrastructure now.) --- src/backend/regex/regcomp.c | 8 +++- src/backend/regex/regexec.c | 73 +++++++++++++++++++++++-------------- 2 files changed, 52 insertions(+), 29 deletions(-) diff --git a/src/backend/regex/regcomp.c b/src/backend/regex/regcomp.c index bd4d4c3761..4dac8f5d3c 100644 --- a/src/backend/regex/regcomp.c +++ b/src/backend/regex/regcomp.c @@ -1087,8 +1087,12 @@ parseqatom(struct vars * v, NOERR(); } - /* it's quantifier time; first, turn x{0,...} into x{1,...}|empty */ - if (m == 0) + /* + * It's quantifier time. If the atom is just a BACKREF, we'll let it deal + * with quantifiers internally. Otherwise, the first step is to turn + * x{0,...} into x{1,...}|empty + */ + if (m == 0 && atomtype != BACKREF) { EMPTYARC(s2, atom->end); /* the bypass */ assert(PREF(qprefer) != 0); diff --git a/src/backend/regex/regexec.c b/src/backend/regex/regexec.c index 7dc0ddba29..3df859f368 100644 --- a/src/backend/regex/regexec.c +++ b/src/backend/regex/regexec.c @@ -719,7 +719,7 @@ cdissect(struct vars * v, case '|': /* alternation */ assert(t->left != NULL); return caltdissect(v, t, begin, end); - case 'b': /* back ref -- shouldn't be calling us! */ + case 'b': /* back reference */ assert(t->left == NULL && t->right == NULL); return cbrdissect(v, t, begin, end); case '.': /* concatenation */ @@ -976,12 +976,12 @@ cbrdissect(struct vars * v, chr *begin, /* beginning of relevant substring */ chr *end) /* end of same */ { - int i; int n = t->subno; - size_t len; - chr *paren; + size_t numreps; + size_t tlen; + size_t brlen; + chr *brstring; chr *p; - chr *stop; int min = t->min; int max = t->max; @@ -992,46 +992,65 @@ cbrdissect(struct vars * v, MDEBUG(("cbackref n%d %d{%d-%d}\n", t->retry, n, min, max)); + /* get the backreferenced string */ if (v->pmatch[n].rm_so == -1) return REG_NOMATCH; - paren = v->start + v->pmatch[n].rm_so; - len = v->pmatch[n].rm_eo - v->pmatch[n].rm_so; + brstring = v->start + v->pmatch[n].rm_so; + brlen = v->pmatch[n].rm_eo - v->pmatch[n].rm_so; /* no room to maneuver -- retries are pointless */ if (v->mem[t->retry]) return REG_NOMATCH; v->mem[t->retry] = 1; - /* special-case zero-length string */ - if (len == 0) + /* special cases for zero-length strings */ + if (brlen == 0) + { + /* + * matches only if target is zero length, but any number of + * repetitions can be considered to be present + */ + if (begin == end && min <= max) + { + MDEBUG(("cbackref matched trivially\n")); + return REG_OKAY; + } + return REG_NOMATCH; + } + if (begin == end) { - if (begin == end) + /* matches only if zero repetitions are okay */ + if (min == 0) + { + MDEBUG(("cbackref matched trivially\n")); return REG_OKAY; + } return REG_NOMATCH; } - /* and too-short string */ - assert(end >= begin); - if ((size_t) (end - begin) < len) + /* + * check target length to see if it could possibly be an allowed number of + * repetitions of brstring + */ + assert(end > begin); + tlen = end - begin; + if (tlen % brlen != 0) + return REG_NOMATCH; + numreps = tlen / brlen; + if (numreps < min || (numreps > max && max != INFINITY)) return REG_NOMATCH; - stop = end - len; - /* count occurrences */ - i = 0; - for (p = begin; p <= stop && (i < max || max == INFINITY); p += len) + /* okay, compare the actual string contents */ + p = begin; + while (numreps-- > 0) { - if ((*v->g->compare) (paren, p, len) != 0) - break; - i++; + if ((*v->g->compare) (brstring, p, brlen) != 0) + return REG_NOMATCH; + p += brlen; } - MDEBUG(("cbackref found %d\n", i)); - /* and sort it out */ - if (p != end) /* didn't consume all of it */ - return REG_NOMATCH; - if (min <= i && (i <= max || max == INFINITY)) - return REG_OKAY; - return REG_NOMATCH; /* out of range */ + MDEBUG(("cbackref matched\n")); + return REG_OKAY; } /* -- 2.40.0