[PATCH] hstore_to_json: empty hstores must return empty json objects

hstore_to_json used to return an empty string for empty hstores, but
that is not correct as an empty string is not valid json and calling
row_to_json() on rows which have empty hstores will generate invalid
json for the entire row. The right thing to do is to return an empty
json object.

Signed-off-by: Oskari Saarenmaa <os(at)ohmu(dot)fi>
---
This should probably be applied to 9.3 tree as well as master.

# select row_to_json(r.*) from (select ''::hstore as d) r;
{"d":}

# select hstore_to_json('')::text::json;
ERROR: invalid input syntax for type json

contrib/hstore/expected/hstore.out | 12 ++++++++++++
contrib/hstore/hstore_io.c | 8 ++++----
contrib/hstore/sql/hstore.sql | 2 ++
3 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/contrib/hstore/expected/hstore.out b/contrib/hstore/expected/hstore.out
index 2114143..3280b5e 100644
--- a/contrib/hstore/expected/hstore.out
+++ b/contrib/hstore/expected/hstore.out
@@ -1472,6 +1472,18 @@ select hstore_to_json_loose('"a key" =>1, b => t, c => null, d=> 12345, e => 012
{"b": true, "c": null, "d": 12345, "e": "012345", "f": 1.234, "g": 2.345e+4, "a key": 1}
(1 row)

+select hstore_to_json('');
+ hstore_to_json
+----------------
+ {}
+(1 row)
+
+select hstore_to_json_loose('');
+ hstore_to_json_loose
+----------------------
+ {}
+(1 row)
+
create table test_json_agg (f1 text, f2 hstore);
insert into test_json_agg values ('rec1','"a key" =>1, b => t, c => null, d=> 12345, e => 012345, f=> 1.234, g=> 2.345e+4'),
('rec2','"a key" =>2, b => f, c => "null", d=> -12345, e => 012345.6, f=> -1.234, g=> 0.345e-4');
diff --git a/contrib/hstore/hstore_io.c b/contrib/hstore/hstore_io.c
index d3e67dd..3781a71 100644
--- a/contrib/hstore/hstore_io.c
+++ b/contrib/hstore/hstore_io.c
@@ -1241,8 +1241,8 @@ hstore_to_json_loose(PG_FUNCTION_ARGS)

if (count == 0)
{
- out = palloc(1);
- *out = '\0';
+ out = palloc(3);
+ memcpy(out, "{}", 3);
PG_RETURN_TEXT_P(cstring_to_text(out));
}

@@ -1370,8 +1370,8 @@ hstore_to_json(PG_FUNCTION_ARGS)

if (count == 0)
{
- out = palloc(1);
- *out = '\0';
+ out = palloc(3);
+ memcpy(out, "{}", 3);
PG_RETURN_TEXT_P(cstring_to_text(out));
}

diff --git a/contrib/hstore/sql/hstore.sql b/contrib/hstore/sql/hstore.sql
index 68b74bf..47cbfad 100644
--- a/contrib/hstore/sql/hstore.sql
+++ b/contrib/hstore/sql/hstore.sql
@@ -335,6 +335,8 @@ select count(*) from testhstore where h = 'pos=>98, line=>371, node=>CBA, indexe
select hstore_to_json('"a key" =>1, b => t, c => null, d=> 12345, e => 012345, f=> 1.234, g=> 2.345e+4');
select cast( hstore '"a key" =>1, b => t, c => null, d=> 12345, e => 012345, f=> 1.234, g=> 2.345e+4' as json);
select hstore_to_json_loose('"a key" =>1, b => t, c => null, d=> 12345, e => 012345, f=> 1.234, g=> 2.345e+4');
+select hstore_to_json('');
+select hstore_to_json_loose('');

create table test_json_agg (f1 text, f2 hstore);
insert into test_json_agg values ('rec1','"a key" =>1, b => t, c => null, d=> 12345, e => 012345, f=> 1.234, g=> 2.345e+4'),
--
1.8.3.1