Add Numeric.MarshalJSON

numeric.go

@@ -1,6 +1,7 @@
 package pgtype
 
 import (
+	"bytes"
 	"database/sql/driver"
 	"encoding/binary"
 	"fmt"
@@ -807,3 +808,41 @@ func (src Numeric) Value() (driver.Value, error) {
 
 	return string(buf), nil
 }
+
+func (src Numeric) MarshalJSON() ([]byte, error) {
+	if !src.Valid {
+		return []byte("null"), nil
+	}
+
+	if src.NaN {
+		return []byte(`"NaN"`), nil
+	}
+
+	intStr := src.Int.String()
+	buf := &bytes.Buffer{}
+	exp := int(src.Exp)
+	if exp > 0 {
+		buf.WriteString(intStr)
+		for i := 0; i < exp; i++ {
+			buf.WriteByte('0')
+		}
+	} else if exp < 0 {
+		if len(intStr) <= -exp {
+			buf.WriteString("0.")
+			leadingZeros := -exp - len(intStr)
+			for i := 0; i < leadingZeros; i++ {
+				buf.WriteByte('0')
+			}
+			buf.WriteString(intStr)
+		} else if len(intStr) > -exp {
+			dpPos := len(intStr) + exp
+			buf.WriteString(intStr[:dpPos])
+			buf.WriteByte('.')
+			buf.WriteString(intStr[dpPos:])
+		}
+	} else {
+		buf.WriteString(intStr)
+	}
+
+	return buf.Bytes(), nil
+}

numeric_test.go

@@ -1,6 +1,8 @@
 package pgtype_test
 
 import (
+	"context"
+	"encoding/json"
 	"math"
 	"math/big"
 	"math/rand"
@@ -9,6 +11,7 @@ import (
 
 	"github.com/jackc/pgtype"
 	"github.com/jackc/pgtype/testutil"
+	"github.com/stretchr/testify/require"
 )
 
 // For test purposes only. Note that it does not normalize values. e.g. (Int: 1, Exp: 3) will not equal (Int: 1000, Exp: 0)
@@ -410,3 +413,35 @@ func TestNumericEncodeDecodeBinary(t *testing.T) {
 		}
 	}
 }
+
+func TestNumericMarshalJSON(t *testing.T) {
+	conn := testutil.MustConnectPgx(t)
+	defer testutil.MustCloseContext(t, conn)
+
+	for i, tt := range []struct {
+		decString string
+	}{
+		{"NaN"},
+		{"0"},
+		{"1"},
+		{"-1"},
+		{"1000000000000000000"},
+		{"1234.56789"},
+		{"1.56789"},
+		{"0.00000000000056789"},
+		{"0.00123000"},
+		{"123e-3"},
+		{"243723409723490243842378942378901237502734019231380123e23790"},
+		{"3409823409243892349028349023482934092340892390101e-14021"},
+	} {
+		var num pgtype.Numeric
+		var pgJSON string
+		err := conn.QueryRow(context.Background(), `select $1::numeric, to_json($1::numeric)`, tt.decString).Scan(&num, &pgJSON)
+		require.NoErrorf(t, err, "%d", i)
+
+		goJSON, err := json.Marshal(num)
+		require.NoErrorf(t, err, "%d", i)
+
+		require.Equal(t, pgJSON, string(goJSON))
+	}
+}