types: Dec.MarshalJSON now marshals as a normal decimal string

Closes cosmos#2475

PENDING.md

@@ -72,6 +72,8 @@ BREAKING CHANGES
     * [x/stake] \#2412 Added an unbonding validator queue to EndBlock to automatically update validator.Status when finished Unbonding
     * [x/stake] \#2500 Block conflicting redelegations until we add an index
     * [x/params] Global Paramstore refactored
+    * [types] \#2506 sdk.Dec MarshalJSON now marshals as a normal Decimal, with 10 digits of decimal precision
+
 
 * Tendermint
   * Update tendermint version from v0.23.0 to v0.25.0, notable changes

types/decimal.go

@@ -407,17 +407,36 @@ func (d *Dec) UnmarshalAmino(text string) (err error) {
 	return nil
 }
 
-// MarshalJSON defines custom encoding scheme
+// MarshalJSON marshals the decimal
 func (d Dec) MarshalJSON() ([]byte, error) {
 	if d.Int == nil {
 		return nilJSON, nil
 	}
-
 	bz, err := d.Int.MarshalText()
 	if err != nil {
 		return nil, err
 	}
-	return json.Marshal(string(bz))
+	var bzWDec []byte
+	// TODO: Remove trailing zeros
+	// case 1, pure decimal
+	if len(bz) <= 10 {
+		bzWDec = make([]byte, 12)
+		// 0. prefix
+		bzWDec[0] = byte('0')
+		bzWDec[1] = byte('.')
+		// set relevant digits to 0
+		for i := 0; i < 10-len(bz); i++ {
+			bzWDec[i+2] = byte('0')
+		}
+		// set last few digits
+		copy(bzWDec[2+(10-len(bz)):], bz)
+	} else {
+		bzWDec = make([]byte, len(bz)+1)
+		copy(bzWDec, bz[:len(bz)-10])
+		bzWDec[len(bz)-10] = byte('.')
+		copy(bzWDec[len(bz)-9:], bz[len(bz)-10:])
+	}
+	return json.Marshal(string(bzWDec))
 }
 
 // UnmarshalJSON defines custom decoding scheme
@@ -431,7 +450,13 @@ func (d *Dec) UnmarshalJSON(bz []byte) error {
 	if err != nil {
 		return err
 	}
-	return d.Int.UnmarshalText([]byte(text))
+	// TODO: Reuse dec allocation
+	newDec, err := NewDecFromStr(text)
+	if err != nil {
+		return err
+	}
+	d.Int = newDec.Int
+	return nil
 }
 
 //___________________________________________________________________________________

types/decimal_test.go

@@ -4,6 +4,8 @@ import (
 	"math/big"
 	"testing"
 
+	"github.com/stretchr/testify/assert"
+
 	"github.com/cosmos/cosmos-sdk/codec"
 	"github.com/stretchr/testify/require"
 )
@@ -248,6 +250,44 @@ func TestToLeftPadded(t *testing.T) {
 
 var cdc = codec.New()
 
+func TestDecMarshalJSON(t *testing.T) {
+	decimal := func(i int64) Dec {
+		d := NewDec(0)
+		d.Int = new(big.Int).SetInt64(i)
+		return d
+	}
+	tests := []struct {
+		name    string
+		d       Dec
+		want    string
+		wantErr bool // if wantErr = false, will also attempt unmarshaling
+	}{
+		{"zero", decimal(0), "\"0.0000000000\"", false},
+		{"one", decimal(1), "\"0.0000000001\"", false},
+		{"ten", decimal(10), "\"0.0000000010\"", false},
+		{"12340", decimal(12340), "\"0.0000012340\"", false},
+		{"zeroInt", NewDec(0), "\"0.0000000000\"", false},
+		{"oneInt", NewDec(1), "\"1.0000000000\"", false},
+		{"tenInt", NewDec(10), "\"10.0000000000\"", false},
+		{"12340Int", NewDec(12340), "\"12340.0000000000\"", false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := tt.d.MarshalJSON()
+			if (err != nil) != tt.wantErr {
+				t.Errorf("Dec.MarshalJSON() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if !tt.wantErr {
+				assert.Equal(t, tt.want, string(got), "incorrect marshalled value")
+				unmarshalledDec := NewDec(0)
+				unmarshalledDec.UnmarshalJSON(got)
+				assert.Equal(t, tt.d, unmarshalledDec, "incorrect unmarshalled value")
+			}
+		})
+	}
+}
+
 func TestZeroDeserializationJSON(t *testing.T) {
 	d := Dec{new(big.Int)}
 	err := cdc.UnmarshalJSON([]byte(`"0"`), &d)