adding json support for constraints and version

this change adds support to marshal and unmarshal version constraints
and versions to JSON.

constraint.go

@@ -1,6 +1,7 @@
 package version
 
 import (
+	"encoding/json"
 	"fmt"
 	"reflect"
 	"regexp"
@@ -202,3 +203,24 @@ func constraintPessimistic(v, c *Version) bool {
 	// If nothing has rejected the version by now, it's valid
 	return true
 }
+
+// MarshalJSON implements the json.Marshaler interface
+func (c *Constraints) MarshalJSON() ([]byte, error) {
+	return json.Marshal(c.String())
+}
+
+// UnmarshalJSON implements the json.Unmarshaler interface
+func (c *Constraints) UnmarshalJSON(data []byte) error {
+	var csStr string
+	if err := json.Unmarshal(data, &csStr); err != nil {
+		return err
+	}
+
+	nc, err := NewConstraint(csStr)
+	if err != nil {
+		return err
+	}
+	*c = nc
+
+	return nil
+}

constraint_test.go

@@ -1,6 +1,7 @@
 package version
 
 import (
+	"encoding/json"
 	"testing"
 )
 
@@ -124,3 +125,58 @@ func TestConstraintsString(t *testing.T) {
 		}
 	}
 }
+
+func TestConstraintsMarshalJSON(t *testing.T) {
+	cases := []struct {
+		constraint string
+		result     string
+	}{
+		{">= 1.0, < 1.2", `"\u003e= 1.0, \u003c 1.2"`},
+		{"~> 1.0.7", `"~\u003e 1.0.7"`},
+	}
+
+	for _, tc := range cases {
+		c, err := NewConstraint(tc.constraint)
+		if err != nil {
+			t.Fatalf("err: %s", err)
+		}
+
+		actual, err := json.Marshal(&c)
+		if err != nil {
+			t.Fatalf("err: %s", err)
+		}
+
+		expected := tc.result
+		if string(actual) != expected {
+			t.Fatalf("Constraint: %s\nExpected: %s\nActual: %s",
+				tc.constraint, expected, actual)
+		}
+	}
+}
+
+func TestConstraintsUnmarshalJSON(t *testing.T) {
+	cases := []struct {
+		constraint string
+		result     string
+	}{
+		{`">= 1.0, < 1.2"`, ">= 1.0, < 1.2"},
+		{`"~> 1.0.7"`, "~> 1.0.7"},
+	}
+
+	for _, tc := range cases {
+		var actual Constraints
+		if err := json.Unmarshal([]byte(tc.constraint), &actual); err != nil {
+			t.Fatalf("err: %s", err)
+		}
+
+		expected, err := NewConstraint(tc.result)
+		if err != nil {
+			t.Fatalf("err: %s", err)
+		}
+
+		if actual.String() != expected.String() {
+			t.Fatalf("Constraint: %s\nExpected: %s\nActual: %s",
+				tc.result, expected, actual)
+		}
+	}
+}

version.go

@@ -2,6 +2,7 @@ package version
 
 import (
 	"bytes"
+	"encoding/json"
 	"fmt"
 	"reflect"
 	"regexp"
@@ -382,3 +383,24 @@ func (v *Version) String() string {
 func (v *Version) Original() string {
 	return v.original
 }
+
+// MarshalJSON implements the json.Marshaler interface
+func (v *Version) MarshalJSON() ([]byte, error) {
+	return json.Marshal(v.original)
+}
+
+// UnmarshalJSON implements the json.Unmarshaler interface
+func (v *Version) UnmarshalJSON(data []byte) error {
+	var vStr string
+	if err := json.Unmarshal(data, &vStr); err != nil {
+		return err
+	}
+
+	nv, err := NewVersion(vStr)
+	if err != nil {
+		return err
+	}
+	*v = *nv
+
+	return nil
+}

version_test.go

@@ -1,6 +1,7 @@
 package version
 
 import (
+	"encoding/json"
 	"reflect"
 	"testing"
 )
@@ -622,3 +623,58 @@ func TestLessThanOrEqual(t *testing.T) {
 		}
 	}
 }
+
+func TestVersionMarshalJSON(t *testing.T) {
+	cases := []struct {
+		version string
+		result  string
+	}{
+		{"1.7rc2", `"1.7rc2"`},
+		{"1.2.0", `"1.2.0"`},
+	}
+
+	for _, tc := range cases {
+		v, err := NewVersion(tc.version)
+		if err != nil {
+			t.Fatalf("err: %s", err)
+		}
+
+		actual, err := json.Marshal(&v)
+		if err != nil {
+			t.Fatalf("err: %s", err)
+		}
+
+		expected := tc.result
+		if string(actual) != expected {
+			t.Fatalf("Version: %s\nExpected: %s\nActual: %s",
+				tc.version, expected, actual)
+		}
+	}
+}
+
+func TestVersionUnmarshalJSON(t *testing.T) {
+	cases := []struct {
+		version string
+		result  string
+	}{
+		{`"1.7rc2"`, "1.7rc2"},
+		{`"1.2.0"`, "1.2.0"},
+	}
+
+	for _, tc := range cases {
+		var actual Version
+		if err := json.Unmarshal([]byte(tc.version), &actual); err != nil {
+			t.Fatalf("err: %s", err)
+		}
+
+		expected, err := NewVersion(tc.result)
+		if err != nil {
+			t.Fatalf("err: %s", err)
+		}
+
+		if !reflect.DeepEqual(&actual, expected) {
+			t.Fatalf("Constraint: %s\nExpected: %#v\nActual: %#v",
+				tc.result, expected, actual)
+		}
+	}
+}