pgtype.JSON(B).Value now returns []byte

Allows scanning jsonb column into *json.RawMessage.

fixes #409

CHANGELOG.md

@@ -12,6 +12,13 @@
 * Fix StartReplication() syntax (steampunkcoder)
 * Fix precision loss for test format geometric types
 
+## Changes
+
+* pgtype.JSON(B).Value now returns []byte instead of string. This allows
+  database/sql to scan json(b) into \*json.RawMessage. This is a tiny behavior
+  change, but database/sql Scan should automatically convert []byte to string, so
+  there shouldn't be any incompatibility.
+
 # 3.1.0 (January 15, 2018)
 
 ## Features

pgtype/json.go

@@ -152,7 +152,7 @@ func (dst *JSON) Scan(src interface{}) error {
 func (src *JSON) Value() (driver.Value, error) {
 	switch src.Status {
 	case Present:
-		return string(src.Bytes), nil
+		return src.Bytes, nil
 	case Null:
 		return nil, nil
 	default:

stdlib/sql.go

@@ -495,6 +495,10 @@ func (r *Rows) Next(dest []driver.Value) error {
 				r.values[i] = &pgtype.Int4{}
 			case pgtype.Int8OID:
 				r.values[i] = &pgtype.Int8{}
+			case pgtype.JSONOID:
+				r.values[i] = &pgtype.JSON{}
+			case pgtype.JSONBOID:
+				r.values[i] = &pgtype.JSONB{}
 			case pgtype.OIDOID:
 				r.values[i] = &pgtype.OIDValue{}
 			case pgtype.TimestampOID:

stdlib/sql_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"database/sql"
+	"encoding/json"
 	"fmt"
 	"math"
 	"reflect"
@@ -1466,3 +1467,22 @@ func TestSimpleQueryLifeCycle(t *testing.T) {
 
 	ensureConnValid(t, db)
 }
+
+// https://github.com/jackc/pgx/issues/409
+func TestScanJSONIntoJSONRawMessage(t *testing.T) {
+	db := openDB(t)
+	defer closeDB(t, db)
+
+	var msg json.RawMessage
+
+	err := db.QueryRow("select '{}'::jsonb").Scan(&msg)
+	if err != nil {
+		t.Fatalf("QueryRow / Scan failed: %v", err)
+	}
+
+	if bytes.Compare([]byte("{}"), []byte(msg)) != 0 {
+		t.Fatalf("Expected %v, got %v", []byte("{}"), msg)
+	}
+
+	ensureConnValid(t, db)
+}

values.go

@@ -31,6 +31,32 @@ func convertSimpleArgument(ci *pgtype.ConnInfo, arg interface{}) (interface{}, e
 	}
 
 	switch arg := arg.(type) {
+
+	// https://github.com/jackc/pgx/issues/409 Changed JSON and JSONB to surface
+	// []byte to database/sql instead of string. But that caused problems with the
+	// simple protocol because the driver.Valuer case got taken before the
+	// pgtype.TextEncoder case. And driver.Valuer needed to be first in the usual
+	// case because of https://github.com/jackc/pgx/issues/339. So instead we
+	// special case JSON and JSONB.
+	case *pgtype.JSON:
+		buf, err := arg.EncodeText(ci, nil)
+		if err != nil {
+			return nil, err
+		}
+		if buf == nil {
+			return nil, nil
+		}
+		return string(buf), nil
+	case *pgtype.JSONB:
+		buf, err := arg.EncodeText(ci, nil)
+		if err != nil {
+			return nil, err
+		}
+		if buf == nil {
+			return nil, nil
+		}
+		return string(buf), nil
+
 	case driver.Valuer:
 		return callValuerValue(arg)
 	case pgtype.TextEncoder: