Re: BUG #16171: Potential malformed JSON in explain output - Mailing list pgsql-hackers

Daniel Gustafsson <daniel@yesql.se> writes:
> On 1 Feb 2020, at 20:37, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> 0002 attached isn't committable, because nobody would want the overhead
>> in production, but it seems like a good trick to keep up our sleeves.

> Thats a neat trick, I wonder if it would be worth maintaining a curated list of
> these tricks in a README under src/test to help others avoid/reduce wheel
> reinventing?

It occurred to me that as long as this is an uncommittable hack anyway,
we could feed the EXPLAIN data to jsonb_in and then hot-wire the jsonb
code to whine about duplicate keys.  So attached, for the archives' sake,
is an improved version that does that.  I still don't find any problems
(other than the one we're fixing here); though no doubt if I reverted
100136849 it'd complain about that.

            regards, tom lane

diff --git a/contrib/auto_explain/auto_explain.c b/contrib/auto_explain/auto_explain.c
index f69dde8..1945a77 100644
--- a/contrib/auto_explain/auto_explain.c
+++ b/contrib/auto_explain/auto_explain.c
@@ -18,6 +18,7 @@
 #include "commands/explain.h"
 #include "executor/instrument.h"
 #include "jit/jit.h"
+#include "utils/builtins.h"
 #include "utils/guc.h"

 PG_MODULE_MAGIC;
@@ -397,6 +398,10 @@ explain_ExecutorEnd(QueryDesc *queryDesc)
             {
                 es->str->data[0] = '{';
                 es->str->data[es->str->len - 1] = '}';
+
+                /* Verify that it's valid JSON by feeding to jsonb_in */
+                (void) DirectFunctionCall1(jsonb_in,
+                                           CStringGetDatum(es->str->data));
             }

             /*
diff --git a/src/backend/utils/adt/jsonb_util.c b/src/backend/utils/adt/jsonb_util.c
index edec657..b9038fa 100644
--- a/src/backend/utils/adt/jsonb_util.c
+++ b/src/backend/utils/adt/jsonb_util.c
@@ -1915,6 +1915,9 @@ uniqueifyJsonbObject(JsonbValue *object)
                 if (ptr != res)
                     memcpy(res, ptr, sizeof(JsonbPair));
             }
+            else
+                elog(WARNING, "dropping duplicate jsonb key %s",
+                     ptr->key.val.string.val);
             ptr++;
         }

diff --git a/src/test/regress/expected/jsonb.out b/src/test/regress/expected/jsonb.out
index a70cd0b..2db14e1 100644
--- a/src/test/regress/expected/jsonb.out
+++ b/src/test/regress/expected/jsonb.out
@@ -3488,6 +3488,9 @@ SELECT '{"ff":{"a":12,"b":16},"qq":123}'::jsonb;
 (1 row)

 SELECT '{"aa":["a","aaa"],"qq":{"a":12,"b":16,"c":["c1","c2"],"d":{"d1":"d1","d2":"d2","d1":"d3"}}}'::jsonb;
+WARNING:  dropping duplicate jsonb key d1
+LINE 1: SELECT '{"aa":["a","aaa"],"qq":{"a":12,"b":16,"c":["c1","c2"...
+               ^
                                               jsonb
 --------------------------------------------------------------------------------------------------
  {"aa": ["a", "aaa"], "qq": {"a": 12, "b": 16, "c": ["c1", "c2"], "d": {"d1": "d3", "d2": "d2"}}}
@@ -4021,6 +4024,8 @@ select jsonb_concat('{"d": "test", "a": [1, 2]}', '{"g": "test2", "c": {"c1":1,
 (1 row)

 select '{"aa":1 , "b":2, "cq":3}'::jsonb || '{"cq":"l", "b":"g", "fg":false}';
+WARNING:  dropping duplicate jsonb key baacq
+WARNING:  dropping duplicate jsonb key cq
                   ?column?
 ---------------------------------------------
  {"b": "g", "aa": 1, "cq": "l", "fg": false}
@@ -4033,6 +4038,7 @@ select '{"aa":1 , "b":2, "cq":3}'::jsonb || '{"aq":"l"}';
 (1 row)

 select '{"aa":1 , "b":2, "cq":3}'::jsonb || '{"aa":"l"}';
+WARNING:  dropping duplicate jsonb key aacq
            ?column?
 ------------------------------
  {"b": 2, "aa": "l", "cq": 3}