dont overallocate ram when reading blobs from disk

ReadFile checks the file size and allocates a bit more space than we
expect we'll need. ReadAll uses Go's standard resizing algo, which
doubles the underlying array each time you hit the end. So ReadAll
ends up allocating 4MB for a full blob, while ReadFile allocates
slightly over 2MB.

store/disk.go

@@ -58,17 +58,15 @@ func (d *DiskStore) Get(hash string) (stream.Blob, error) {
 		return nil, err
 	}
 
-	file, err := os.Open(d.path(hash))
+	blob, err := ioutil.ReadFile(d.path(hash))
 	if err != nil {
 		if os.IsNotExist(err) {
 			return nil, errors.Err(ErrBlobNotFound)
 		}
-		return nil, err
+		return nil, errors.Err(err)
 	}
-	defer file.Close()
 
-	blob, err := ioutil.ReadAll(file)
-	return blob, errors.Err(err)
+	return blob, nil
 }
 
 // Put stores the blob on disk

store/disk_test.go

@@ -0,0 +1,45 @@
+package store
+
+import (
+	"io/ioutil"
+	"os"
+	"path"
+	"path/filepath"
+	"testing"
+
+	"github.com/lbryio/lbry.go/v2/extras/errors"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestDiskStore_Get(t *testing.T) {
+	tmpDir, err := ioutil.TempDir("", "reflector_test_*")
+	require.NoError(t, err)
+	defer os.RemoveAll(tmpDir)
+	d := NewDiskStore(tmpDir, 2)
+
+	hash := "1234567890"
+	data := []byte("oyuntyausntoyaunpdoyruoyduanrstjwfjyuwf")
+
+	expectedPath := path.Join(tmpDir, hash[:2], hash)
+	err = os.MkdirAll(filepath.Dir(expectedPath), os.ModePerm)
+	require.NoError(t, err)
+	err = ioutil.WriteFile(expectedPath, data, os.ModePerm)
+	require.NoError(t, err)
+
+	blob, err := d.Get(hash)
+	assert.NoError(t, err)
+	assert.EqualValues(t, data, blob)
+}
+
+func TestDiskStore_GetNonexistentBlob(t *testing.T) {
+	tmpDir, err := ioutil.TempDir("", "reflector_test_*")
+	require.NoError(t, err)
+	defer os.RemoveAll(tmpDir)
+	d := NewDiskStore(tmpDir, 2)
+
+	blob, err := d.Get("nonexistent")
+	assert.Nil(t, blob)
+	assert.True(t, errors.Is(err, ErrBlobNotFound))
+}