use *os.File instead of file path

README.md

@@ -1,4 +1,4 @@
-# persist [![GoDoc](https://godoc.org/github.com/matryer/persist?status.png)](http://godoc.org/github.com/matryer/persist)
+# persist [![GoDoc](https://godoc.org/github.com/keks/persist?status.png)](http://godoc.org/github.com/keks/persist)
 Persist loads and saves Go objects to files
 
 ## Usage
@@ -13,7 +13,12 @@ Then save objects like this:
 
 ```
 var conf Config
-if err := persist.Save("./project.conf", &conf); err != nil {
+f, err := os.Create("./project.conf", 0x600)
+if err != nil {
+	log.Faralln("failed opening the persistent file:", err)
+}
+
+if err = persist.Save(f, &conf); err != nil {
 	log.Fatalln("failed to save config:", err)
 }
 ```
@@ -22,8 +27,10 @@ And load them like this:
 
 
 ```
+// f is still in scope
+
 var conf Config
-if err := persist.Load("./project.conf", &conf); err != nil {
+if err := persist.Load(f, &conf); err != nil {
 	log.Fatalln("failed to load config:", err)
 }
 ```

persist.go

@@ -1,60 +1,32 @@
 package persist
 
 import (
-	"bytes"
 	"encoding/json"
-	"io"
 	"os"
-	"sync"
-)
-
-var lock sync.Mutex
-
-// Marshal is a function that marshals the object into an
-// io.Reader.
-// By default, it uses the JSON marshaller.
-var Marshal = func(v interface{}) (io.Reader, error) {
-	b, err := json.MarshalIndent(v, "", "\t")
-	if err != nil {
-		return nil, err
-	}
-	return bytes.NewReader(b), nil
-}
 
-// Unmarshal is a function that unmarshals the data from the
-// reader into the specified value.
-// By default, it uses the JSON unmarshaller.
-var Unmarshal = func(r io.Reader, v interface{}) error {
-	return json.NewDecoder(r).Decode(v)
-}
+	"github.com/pkg/errors"
+)
 
 // Save saves a representation of v to the file at path.
-func Save(path string, v interface{}) error {
-	lock.Lock()
-	defer lock.Unlock()
-	f, err := os.Create(path)
+func Save(f *os.File, v interface{}) error {
+	data, err := json.MarshalIndent(v, "", "\t")
 	if err != nil {
-		return err
+		return errors.Wrapf(err, "error marshaling value of type %T", v)
 	}
-	defer f.Close()
-	r, err := Marshal(v)
+
+	_, err = f.Write(data)
 	if err != nil {
-		return err
+		return errors.Wrap(err, "error copying data into file")
 	}
-	_, err = io.Copy(f, r)
-	return err
+
+	_, err = f.Seek(0, 0)
+	return errors.Wrap(err, "error seeking to beginning of file")
 }
 
 // Load loads the file at path into v.
 // Use os.IsNotExist() to see if the returned error is due
 // to the file being missing.
-func Load(path string, v interface{}) error {
-	lock.Lock()
-	defer lock.Unlock()
-	f, err := os.Open(path)
-	if err != nil {
-		return err
-	}
-	defer f.Close()
-	return Unmarshal(f, v)
+func Load(f *os.File, v interface{}) error {
+	err := json.NewDecoder(f).Decode(v)
+	return errors.Wrap(err, "error decoding value")
 }

persist_test.go

@@ -6,7 +6,7 @@ import (
 	"time"
 
 	"github.com/cheekybits/is"
-	"github.com/matryer/persist"
+	"github.com/keks/persist"
 )
 
 type obj struct {
@@ -15,17 +15,11 @@ type obj struct {
 	When   time.Time
 }
 
-func TestNoFile(t *testing.T) {
-	is := is.New(t)
-
-	var v interface{}
-	err := persist.Load("no-such-file.conf", &v)
-	is.Equal(true, os.IsNotExist(err))
-
-}
-
 func TestPersist(t *testing.T) {
 	is := is.New(t)
+
+	f, err := os.Create("./file.tmp")
+	is.NoErr(err)
 	defer os.Remove("./file.tmp")
 
 	o := &obj{
@@ -35,16 +29,15 @@ func TestPersist(t *testing.T) {
 	}
 
 	// save it
-	err := persist.Save("./file.tmp", o)
+	err = persist.Save(f, o)
 	is.NoErr(err)
 
 	// load it
 	var o2 obj
-	err = persist.Load("./file.tmp", &o2)
+	err = persist.Load(f, &o2)
 	is.NoErr(err)
 
 	is.Equal(o.Name, o2.Name)
 	is.Equal(o.Number, o2.Number)
-	is.Equal(o.When, o2.When)
-
+	is.True(o.When.Equal(o2.When))
 }