Output timestamps in ISO 8601 format when rendering JSON.

Many JSON processors require timestamp strings in ISO 8601 format in
order to convert the strings. When converting a timestamp, with or
without timezone, to a JSON datum we therefore now use such a format
rather than the type's default text output, in functions such as
to_json().

This is a change in behaviour from 9.2 and 9.3, as noted in the release
notes.

doc/src/sgml/release-9.4.sgml

@@ -162,6 +162,24 @@
      </para>
     </listitem>
 
+    <listitem>
+     <para>
+      Values of type
+      <link linkend="datatype-datetime"><type>timestamp</></link>  and
+      <link linkend="datatype-datetime"><type>timestamptz</></link> are now
+      rendered in a string format compliant with ISO 8601 rather than the
+      default output format when converting to or used in
+      <link linkend="datatype-json"><type>JSON</type></link>.
+      (Andrew Dunstan)
+     </para>
+
+     <para>
+      Previously these were rendered in the default text output format
+      for the type, but many JSON processors require timestamps in ISO 8601
+      format.
+     </para>
+    </listitem>
+
     <listitem>
      <para>
       Rename <link linkend="SQL-EXPLAIN"><command>EXPLAIN

src/backend/utils/adt/json.c

@@ -24,6 +24,7 @@
 #include "parser/parse_coerce.h"
 #include "utils/array.h"
 #include "utils/builtins.h"
+#include "utils/formatting.h"
 #include "utils/lsyscache.h"
 #include "utils/json.h"
 #include "utils/jsonapi.h"
@@ -53,6 +54,8 @@ typedef enum					/* type categories for datum_to_json */
 	JSONTYPE_NULL,				/* null, so we didn't bother to identify */
 	JSONTYPE_BOOL,				/* boolean (built-in types only) */
 	JSONTYPE_NUMERIC,			/* numeric (ditto) */
+	JSONTYPE_TIMESTAMP,         /* we use special formatting for timestamp */
+	JSONTYPE_TIMESTAMPTZ,       /* ... and timestamptz */
 	JSONTYPE_JSON,				/* JSON itself (and JSONB) */
 	JSONTYPE_ARRAY,				/* array */
 	JSONTYPE_COMPOSITE,			/* composite */
@@ -60,6 +63,13 @@ typedef enum					/* type categories for datum_to_json */
 	JSONTYPE_OTHER				/* all else */
 } JsonTypeCategory;
 
+/*
+ * to_char formats to turn timestamps and timpstamptzs into json strings
+ * that are ISO 8601 compliant
+ */
+#define TS_ISO8601_FMT "\\\"YYYY-MM-DD\"T\"HH24:MI:SS.US\\\""
+#define TSTZ_ISO8601_FMT "\\\"YYYY-MM-DD\"T\"HH24:MI:SS.USOF\\\""
+
 static inline void json_lex(JsonLexContext *lex);
 static inline void json_lex_string(JsonLexContext *lex);
 static inline void json_lex_number(JsonLexContext *lex, char *s, bool *num_err);
@@ -1262,6 +1272,14 @@ json_categorize_type(Oid typoid,
 			*tcategory = JSONTYPE_NUMERIC;
 			break;
 
+		case TIMESTAMPOID:
+			*tcategory = JSONTYPE_TIMESTAMP;
+			break;
+
+		case TIMESTAMPTZOID:
+			*tcategory = JSONTYPE_TIMESTAMPTZ;
+			break;
+
 		case JSONOID:
 		case JSONBOID:
 			*tcategory = JSONTYPE_JSON;
@@ -1375,6 +1393,29 @@ datum_to_json(Datum val, bool is_null, StringInfo result,
 			}
 			pfree(outputstr);
 			break;
+		case JSONTYPE_TIMESTAMP:
+			/*
+			 * The timestamp format used here provides for quoting the string,
+			 * so no escaping is required.
+			 */
+			jsontext = DatumGetTextP(
+				DirectFunctionCall2(timestamp_to_char, val,
+									CStringGetTextDatum(TS_ISO8601_FMT)));
+			outputstr = text_to_cstring(jsontext);
+			appendStringInfoString(result, outputstr);
+			pfree(outputstr);
+			pfree(jsontext);
+			break;
+		case JSONTYPE_TIMESTAMPTZ:
+			/* same comment as for timestamp above */
+			jsontext = DatumGetTextP(
+				DirectFunctionCall2(timestamptz_to_char, val,
+									CStringGetTextDatum(TSTZ_ISO8601_FMT)));
+			outputstr = text_to_cstring(jsontext);
+			appendStringInfoString(result, outputstr);
+			pfree(outputstr);
+			pfree(jsontext);
+			break;
 		case JSONTYPE_JSON:
 			/* JSON and JSONB output will already be escaped */
 			outputstr = OidOutputFunctionCall(outfuncoid, val);

src/test/regress/expected/json.out

@@ -403,6 +403,29 @@ SELECT row_to_json(row((select array_agg(x) as d from generate_series(5,10) x)),
  {"f1":[5,6,7,8,9,10]}
 (1 row)
 
+-- to_json, timestamps
+select to_json(timestamp '2014-05-28 12:22:35.614298');
+           to_json            
+------------------------------
+ "2014-05-28T12:22:35.614298"
+(1 row)
+
+BEGIN;
+SET LOCAL TIME ZONE 10.5;
+select to_json(timestamptz '2014-05-28 12:22:35.614298-04');
+              to_json               
+------------------------------------
+ "2014-05-29T02:52:35.614298+10:30"
+(1 row)
+
+SET LOCAL TIME ZONE -8;
+select to_json(timestamptz '2014-05-28 12:22:35.614298-04');
+             to_json             
+---------------------------------
+ "2014-05-28T08:22:35.614298-08"
+(1 row)
+
+COMMIT;
 --json_agg
 SELECT json_agg(q)
   FROM ( SELECT $$a$$ || x AS b, y AS c,

src/test/regress/expected/json_1.out

@@ -403,6 +403,29 @@ SELECT row_to_json(row((select array_agg(x) as d from generate_series(5,10) x)),
  {"f1":[5,6,7,8,9,10]}
 (1 row)
 
+-- to_json, timestamps
+select to_json(timestamp '2014-05-28 12:22:35.614298');
+           to_json            
+------------------------------
+ "2014-05-28T12:22:35.614298"
+(1 row)
+
+BEGIN;
+SET LOCAL TIME ZONE 10.5;
+select to_json(timestamptz '2014-05-28 12:22:35.614298-04');
+              to_json               
+------------------------------------
+ "2014-05-29T02:52:35.614298+10:30"
+(1 row)
+
+SET LOCAL TIME ZONE -8;
+select to_json(timestamptz '2014-05-28 12:22:35.614298-04');
+             to_json             
+---------------------------------
+ "2014-05-28T08:22:35.614298-08"
+(1 row)
+
+COMMIT;
 --json_agg
 SELECT json_agg(q)
   FROM ( SELECT $$a$$ || x AS b, y AS c,

src/test/regress/sql/json.sql

@@ -100,6 +100,17 @@ FROM rows q;
 
 SELECT row_to_json(row((select array_agg(x) as d from generate_series(5,10) x)),false);
 
+-- to_json, timestamps
+
+select to_json(timestamp '2014-05-28 12:22:35.614298');
+
+BEGIN;
+SET LOCAL TIME ZONE 10.5;
+select to_json(timestamptz '2014-05-28 12:22:35.614298-04');
+SET LOCAL TIME ZONE -8;
+select to_json(timestamptz '2014-05-28 12:22:35.614298-04');
+COMMIT;
+
 --json_agg
 
 SELECT json_agg(q)