postgres.git / summary / log / commit / refs

commit    43e43771bc4b03a9e33be7261cc84dc7f65ae9ef
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Mon Oct 28 16:21:13 2019 +0000
First released in: 13.0, 12.1

    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
 --


[parent: b1ad895e12f0]