From 43e43771bc4b03a9e33be7261cc84dc7f65ae9ef Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Mon, 28 Oct 2019 12:21:13 -0400
Subject: [PATCH] Handle empty-string edge cases correctly in strpos().
Commit 9556aa01c rearranged the innards of text_position() in a way
that would make it not work for empty search strings. Which is fine,
because all callers of that code special-case an empty pattern in
some way. However, the primary use-case (text_position itself) got
special-cased incorrectly: historically it's returned 1 not 0 for
an empty search string. Restore the historical behavior.
Per complaint from Austin Drenski (via Shay Rojansky).
Back-patch to v12 where it got broken.
Discussion: https://postgr.es/m/CADT4RqAz7oN4vkPir86Kg1_mQBmBxCp-L_=9vRpgSNPJf0KRkw@mail.gmail.com
---
src/backend/utils/adt/varlena.c | 10 +++++++++-
src/test/regress/expected/strings.out | 18 ++++++++++++++++++
src/test/regress/sql/strings.sql | 6 ++++++
3 files changed, 33 insertions(+), 1 deletion(-)
diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index 299d8b5790d..1587b4ed02a 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -1118,7 +1118,12 @@ text_position(text *t1, text *t2, Oid collid)
TextPositionState state;
int result;
- if (VARSIZE_ANY_EXHDR(t1) < 1 || VARSIZE_ANY_EXHDR(t2) < 1)
+ /* Empty needle always matches at position 1 */
+ if (VARSIZE_ANY_EXHDR(t2) < 1)
+ return 1;
+
+ /* Otherwise, can't match if haystack is shorter than needle */
+ if (VARSIZE_ANY_EXHDR(t1) < VARSIZE_ANY_EXHDR(t2))
return 0;
text_position_setup(t1, t2, collid, &state);
@@ -1272,6 +1277,9 @@ text_position_setup(text *t1, text *t2, Oid collid, TextPositionState *state)
* Advance to the next match, starting from the end of the previous match
* (or the beginning of the string, on first call). Returns true if a match
* is found.
+ *
+ * Note that this refuses to match an empty-string needle. Most callers
+ * will have handled that case specially and we'll never see it here.
*/
static bool
text_position_next(TextPositionState *state)
diff --git a/src/test/regress/expected/strings.out b/src/test/regress/expected/strings.out
index 486c00b3b3e..54505d1cdaf 100644
--- a/src/test/regress/expected/strings.out
+++ b/src/test/regress/expected/strings.out
@@ -1371,6 +1371,24 @@ SELECT strpos('abcdef', 'xy') AS "pos_0";
0
(1 row)
+SELECT strpos('abcdef', '') AS "pos_1";
+ pos_1
+-------
+ 1
+(1 row)
+
+SELECT strpos('', 'xy') AS "pos_0";
+ pos_0
+-------
+ 0
+(1 row)
+
+SELECT strpos('', '') AS "pos_1";
+ pos_1
+-------
+ 1
+(1 row)
+
--
-- test replace
--
diff --git a/src/test/regress/sql/strings.sql b/src/test/regress/sql/strings.sql
index 5744c9f8007..6905b4d7c1a 100644
--- a/src/test/regress/sql/strings.sql
+++ b/src/test/regress/sql/strings.sql
@@ -479,6 +479,12 @@ SELECT strpos('abcdef', 'cd') AS "pos_3";
SELECT strpos('abcdef', 'xy') AS "pos_0";
+SELECT strpos('abcdef', '') AS "pos_1";
+
+SELECT strpos('', 'xy') AS "pos_0";
+
+SELECT strpos('', '') AS "pos_1";
+
--
-- test replace
--
--
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