math/big: add support for general encoding interfaces

TextMarshaller and TextUnmarshaller to ease transport of
unlimited precision rational numbers.

Fixes #7287.

Consists of encode and decode functions and two test
functions, one using JSON and one using XML. Each
verifies round trips for integers (rationals with
denominator == 1) and for fractional vaues.

LGTM=gri
R=gri, cookieo9, bradfitz, mtj
CC=golang-codereviews
https://golang.org/cl/61180043

diff --git a/src/pkg/math/big/rat.go b/src/pkg/math/big/rat.go
index 7faee61a465c64b67a8215357f711916ee307b0a..3cdb1d807f5dc4406eab1b9a70e4013a7396f45f 100644 (file)
--- a/src/pkg/math/big/rat.go
+++ b/src/pkg/math/big/rat.go
@@ -585,3 +585,16 @@ func (z *Rat) GobDecode(buf []byte) error {
        z.b.abs = z.b.abs.setBytes(buf[i:])
        return nil
 }
+
+// MarshalText implements the encoding.TextMarshaler interface
+func (r *Rat) MarshalText() (text []byte, err error) {
+       return []byte(r.RatString()), nil
+}
+
+// UnmarshalText implements the encoding.TextUnmarshaler interface
+func (r *Rat) UnmarshalText(text []byte) error {
+       if _, ok := r.SetString(string(text)); !ok {
+               return fmt.Errorf("math/big: cannot unmarshal %q into a *big.Rat", text)
+       }
+       return nil
+}

diff --git a/src/pkg/math/big/rat_test.go b/src/pkg/math/big/rat_test.go
index 0d432637ba19764d65d7ef4f138d72bd652c1c84..414a67d419d68383455e5ae09e0785a5f79f2b3b 100644 (file)
--- a/src/pkg/math/big/rat_test.go
+++ b/src/pkg/math/big/rat_test.go
@@ -7,6 +7,8 @@ package big
 import (
        "bytes"
        "encoding/gob"
+       "encoding/json"
+       "encoding/xml"
        "fmt"
        "math"
        "strconv"
@@ -433,6 +435,69 @@ func TestGobEncodingNilRatInSlice(t *testing.T) {
        }
 }
 
+var ratNums = []string{
+       "-141592653589793238462643383279502884197169399375105820974944592307816406286",
+       "-1415926535897932384626433832795028841971",
+       "-141592653589793",
+       "-1",
+       "0",
+       "1",
+       "141592653589793",
+       "1415926535897932384626433832795028841971",
+       "141592653589793238462643383279502884197169399375105820974944592307816406286",
+}
+
+var ratDenoms = []string{
+       "1",
+       "718281828459045",
+       "7182818284590452353602874713526624977572",
+       "718281828459045235360287471352662497757247093699959574966967627724076630353",
+}
+
+func TestRatJSONEncoding(t *testing.T) {
+       for _, num := range ratNums {
+               for _, denom := range ratDenoms {
+                       var tx Rat
+                       tx.SetString(num + "/" + denom)
+                       b, err := json.Marshal(&tx)
+                       if err != nil {
+                               t.Errorf("marshaling of %s failed: %s", &tx, err)
+                               continue
+                       }
+                       var rx Rat
+                       if err := json.Unmarshal(b, &rx); err != nil {
+                               t.Errorf("unmarshaling of %s failed: %s", &tx, err)
+                               continue
+                       }
+                       if rx.Cmp(&tx) != 0 {
+                               t.Errorf("JSON encoding of %s failed: got %s want %s", &tx, &rx, &tx)
+                       }
+               }
+       }
+}
+
+func TestRatXMLEncoding(t *testing.T) {
+       for _, num := range ratNums {
+               for _, denom := range ratDenoms {
+                       var tx Rat
+                       tx.SetString(num + "/" + denom)
+                       b, err := xml.Marshal(&tx)
+                       if err != nil {
+                               t.Errorf("marshaling of %s failed: %s", &tx, err)
+                               continue
+                       }
+                       var rx Rat
+                       if err := xml.Unmarshal(b, &rx); err != nil {
+                               t.Errorf("unmarshaling of %s failed: %s", &tx, err)
+                               continue
+                       }
+                       if rx.Cmp(&tx) != 0 {
+                               t.Errorf("XML encoding of %s failed: got %s want %s", &tx, &rx, &tx)
+                       }
+               }
+       }
+}
+
 func TestIssue2379(t *testing.T) {
        // 1) no aliasing
        q := NewRat(3, 2)