Add Base64 field for encoding byte slices (uber-go#103)

field.go

@@ -21,6 +21,7 @@
 package zap
 
 import (
+	"encoding/base64"
 	"fmt"
 	"math"
 	"time"
@@ -57,6 +58,13 @@ func Skip() Field {
 	return Field{fieldType: skipType}
 }
 
+// Base64 constructs a field that encodes the given value as a
+// padded base64 string. The byte slice is converted to a base64
+// string immediately.
+func Base64(key string, val []byte) Field {
+	return String(key, base64.StdEncoding.EncodeToString(val))
+}
+
 // Bool constructs a Field with the given key and value.
 func Bool(key string, val bool) Field {
 	var ival int64

field_test.go

@@ -172,6 +172,13 @@ func TestNestField(t *testing.T) {
 	assertCanBeReused(t, nest)
 }
 
+func TestBase64Field(t *testing.T) {
+	assertFieldJSON(t, `"foo":"YWIxMg=="`,
+		Base64("foo", []byte("ab12")),
+	)
+	assertCanBeReused(t, Base64("foo", []byte("bar")))
+}
+
 func TestLogMarshalerFunc(t *testing.T) {
 	assertFieldJSON(t, `"foo":{"name":"phil"}`,
 		Marshaler("foo", LogMarshalerFunc(fakeUser{"phil"}.MarshalLog)))