pgsql: Optimize escaping of JSON strings

Optimize escaping of JSON strings

There were quite a few places where we either had a non-NUL-terminated
string or a text Datum which we needed to call escape_json() on. Many of
these places required that a temporary string was created due to the fact
that escape_json() needs a NUL-terminated cstring. For text types, those
first had to be converted to cstring before calling escape_json() on them.

Here we introduce two new functions to make escaping JSON more optimal:

escape_json_text() can be given a text Datum to append onto the given
buffer. This is more optimal as it foregoes the need to convert the text
Datum into a cstring. A temporary allocation is only required if the text
Datum needs to be detoasted.

escape_json_with_len() can be used when the length of the cstring is
already known or the given string isn't NUL-terminated. Having this
allows various places which were creating a temporary NUL-terminated
string to just call escape_json_with_len() without any temporary memory
allocations.

Discussion: https://postgr.es/m/CAApHDvpLXwMZvbCKcdGfU9XQjGCDm7tFpRdTXuB9PVgpNUYfEQ@mail.gmail.com
Reviewed-by: Melih Mutlu, Heikki Linnakangas

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/17a5871d9d58ea639b6d1ba4f0ce58462d55a33c

Modified Files
--------------
contrib/hstore/hstore_io.c | 41 ++++-----
src/backend/backup/backup_manifest.c | 2 +-
src/backend/utils/adt/json.c | 156 +++++++++++++++++++++++------------
src/backend/utils/adt/jsonb.c | 2 +-
src/backend/utils/adt/jsonfuncs.c | 34 ++++----
src/backend/utils/adt/jsonpath.c | 15 +++-
src/include/utils/json.h | 2 +
7 files changed, 151 insertions(+), 101 deletions(-)