Some refactoring to export json(b) conversion functions

This is to export datum_to_json(), datum_to_jsonb(), and
jsonb_from_cstring(), though the last one is exported as
jsonb_from_text().

A subsequent commit to add new SQL/JSON constructor functions will
need them for calling from the executor.

Discussion: https://postgr.es/m/20230720160252.ldk7jy6jqclxfxkq%40alvherre.pgsql

1 files changed, 37 insertions, 22 deletions

diff --git a/src/backend/utils/adt/json.c b/src/backend/utils/adt/json.c
index f6bef9c1484..e405791f5d8 100644
--- a/src/backend/utils/adt/json.c
+++ b/src/backend/utils/adt/json.c
@@ -91,9 +91,9 @@ static void array_dim_to_json(StringInfo result, int dim, int ndims, int *dims,
 							  bool use_line_feeds);
 static void array_to_json_internal(Datum array, StringInfo result,
 								   bool use_line_feeds);
-static void datum_to_json(Datum val, bool is_null, StringInfo result,
-						  JsonTypeCategory tcategory, Oid outfuncoid,
-						  bool key_scalar);
+static void datum_to_json_internal(Datum val, bool is_null, StringInfo result,
+								   JsonTypeCategory tcategory, Oid outfuncoid,
+								   bool key_scalar);
 static void add_json(Datum val, bool is_null, StringInfo result,
 					 Oid val_type, bool key_scalar);
 static text *catenate_stringinfo_string(StringInfo buffer, const char *addon);
@@ -173,9 +173,9 @@ json_recv(PG_FUNCTION_ARGS)
  * it's of an acceptable type, and force it to be quoted.
  */
 static void
-datum_to_json(Datum val, bool is_null, StringInfo result,
-			  JsonTypeCategory tcategory, Oid outfuncoid,
-			  bool key_scalar)
+datum_to_json_internal(Datum val, bool is_null, StringInfo result,
+					   JsonTypeCategory tcategory, Oid outfuncoid,
+					   bool key_scalar)
 {
 	char	   *outputstr;
 	text	   *jsontext;
@@ -421,8 +421,9 @@ array_dim_to_json(StringInfo result, int dim, int ndims, int *dims, Datum *vals,
 
 		if (dim + 1 == ndims)
 		{
-			datum_to_json(vals[*valcount], nulls[*valcount], result, tcategory,
-						  outfuncoid, false);
+			datum_to_json_internal(vals[*valcount], nulls[*valcount],
+								   result, tcategory,
+								   outfuncoid, false);
 			(*valcount)++;
 		}
 		else
@@ -549,7 +550,8 @@ composite_to_json(Datum composite, StringInfo result, bool use_line_feeds)
 			json_categorize_type(att->atttypid, false, &tcategory,
 								 &outfuncoid);
 
-		datum_to_json(val, isnull, result, tcategory, outfuncoid, false);
+		datum_to_json_internal(val, isnull, result, tcategory, outfuncoid,
+							   false);
 	}
 
 	appendStringInfoChar(result, '}');
@@ -584,7 +586,8 @@ add_json(Datum val, bool is_null, StringInfo result,
 		json_categorize_type(val_type, false,
 							 &tcategory, &outfuncoid);
 
-	datum_to_json(val, is_null, result, tcategory, outfuncoid, key_scalar);
+	datum_to_json_internal(val, is_null, result, tcategory, outfuncoid,
+						   key_scalar);
 }
 
 /*
@@ -704,7 +707,6 @@ to_json(PG_FUNCTION_ARGS)
 {
 	Datum		val = PG_GETARG_DATUM(0);
 	Oid			val_type = get_fn_expr_argtype(fcinfo->flinfo, 0);
-	StringInfo	result;
 	JsonTypeCategory tcategory;
 	Oid			outfuncoid;
 
@@ -716,11 +718,23 @@ to_json(PG_FUNCTION_ARGS)
 	json_categorize_type(val_type, false,
 						 &tcategory, &outfuncoid);
 
-	result = makeStringInfo();
+	PG_RETURN_DATUM(datum_to_json(val, tcategory, outfuncoid));
+}
 
-	datum_to_json(val, false, result, tcategory, outfuncoid, false);
+/*
+ * Turn a Datum into JSON text.
+ *
+ * tcategory and outfuncoid are from a previous call to json_categorize_type.
+ */
+Datum
+datum_to_json(Datum val, JsonTypeCategory tcategory, Oid outfuncoid)
+{
+	StringInfo	result = makeStringInfo();
 
-	PG_RETURN_TEXT_P(cstring_to_text_with_len(result->data, result->len));
+	datum_to_json_internal(val, false, result, tcategory, outfuncoid,
+						   false);
+
+	return PointerGetDatum(cstring_to_text_with_len(result->data, result->len));
 }
 
 /*
@@ -780,8 +794,8 @@ json_agg_transfn_worker(FunctionCallInfo fcinfo, bool absent_on_null)
 	/* fast path for NULLs */
 	if (PG_ARGISNULL(1))
 	{
-		datum_to_json((Datum) 0, true, state->str, JSONTYPE_NULL,
-					  InvalidOid, false);
+		datum_to_json_internal((Datum) 0, true, state->str, JSONTYPE_NULL,
+							   InvalidOid, false);
 		PG_RETURN_POINTER(state);
 	}
 
@@ -795,8 +809,8 @@ json_agg_transfn_worker(FunctionCallInfo fcinfo, bool absent_on_null)
 		appendStringInfoString(state->str, "\n ");
 	}
 
-	datum_to_json(val, false, state->str, state->val_category,
-				  state->val_output_func, false);
+	datum_to_json_internal(val, false, state->str, state->val_category,
+						   state->val_output_func, false);
 
 	/*
 	 * The transition type for json_agg() is declared to be "internal", which
@@ -1059,8 +1073,8 @@ json_object_agg_transfn_worker(FunctionCallInfo fcinfo,
 
 	key_offset = out->len;
 
-	datum_to_json(arg, false, out, state->key_category,
-				  state->key_output_func, true);
+	datum_to_json_internal(arg, false, out, state->key_category,
+						   state->key_output_func, true);
 
 	if (unique_keys)
 	{
@@ -1082,8 +1096,9 @@ json_object_agg_transfn_worker(FunctionCallInfo fcinfo,
 	else
 		arg = PG_GETARG_DATUM(2);
 
-	datum_to_json(arg, PG_ARGISNULL(2), state->str, state->val_category,
-				  state->val_output_func, false);
+	datum_to_json_internal(arg, PG_ARGISNULL(2), state->str,
+						   state->val_category,
+						   state->val_output_func, false);
 
 	PG_RETURN_POINTER(state);
 }