From f4afaec9b5d83ad9ae9e2595f04abb4b95276adc Mon Sep 17 00:00:00 2001
From: Jarek Kowalski <jaak@jkowalski.net>
Date: Sun, 24 Nov 2019 18:48:18 -0800
Subject: [PATCH] object: fixed Seek() behavior for seeking to end of object

---
 repo/object/object_manager_test.go | 52 ++++++++++++++++++++++++++++++
 repo/object/object_reader.go       | 20 ++++++------
 2 files changed, 63 insertions(+), 9 deletions(-)

diff --git a/repo/object/object_manager_test.go b/repo/object/object_manager_test.go
index c2fd91ad0..994b64a8a 100644
--- a/repo/object/object_manager_test.go
+++ b/repo/object/object_manager_test.go
@@ -8,6 +8,7 @@
 	"encoding/hex"
 	"encoding/json"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"math/rand"
 	"runtime/debug"
@@ -349,3 +350,54 @@ func verify(ctx context.Context, t *testing.T, om *Manager, objectID ID, expecte
 		}
 	}
 }
+
+// nolint:gocyclo
+func TestSeek(t *testing.T) {
+	ctx := context.Background()
+	_, om := setupTest(t)
+
+	for _, size := range []int{0, 1, 500000, 15000000} {
+		randomData := make([]byte, size)
+		cryptorand.Read(randomData) //nolint:errcheck
+
+		writer := om.NewWriter(ctx, WriterOptions{})
+		if _, err := writer.Write(randomData); err != nil {
+			t.Errorf("write error: %v", err)
+		}
+
+		objectID, err := writer.Result()
+		if err != nil {
+			t.Fatalf("unable to write: %v", err)
+		}
+
+		r, err := om.Open(ctx, objectID)
+		if err != nil {
+			t.Fatalf("open error: %v", err)
+		}
+
+		if pos, err := r.Seek(0, io.SeekStart); err != nil || pos != 0 {
+			t.Errorf("invalid seek-start result %v %v", pos, err)
+		}
+
+		if pos, err := r.Seek(0, io.SeekCurrent); err != nil || pos != 0 {
+			t.Errorf("invalid seek-current at start result %v %v", pos, err)
+		}
+
+		if pos, err := r.Seek(0, io.SeekEnd); err != nil || pos != int64(size) {
+			t.Errorf("invalid seek-end result %v %v", pos, err)
+		}
+
+		if pos, err := r.Seek(0, io.SeekCurrent); err != nil || pos != int64(size) {
+			t.Errorf("invalid seek-current at end result %v %v, wanted %v", pos, err, size)
+		}
+
+		if pos, err := r.Seek(1, io.SeekCurrent); err != nil || pos != int64(size)+1 {
+			t.Errorf("unexpected result when seeking past end of file: %v, %v, wanted %v", pos, err, size+1)
+		}
+
+		buf := make([]byte, 5)
+		if n, err := r.Read(buf); n != 0 || err != io.EOF {
+			t.Errorf("unexpected read result %v %v", n, err)
+		}
+	}
+}
diff --git a/repo/object/object_reader.go b/repo/object/object_reader.go
index 4ac8fac95..99d1eda57 100644
--- a/repo/object/object_reader.go
+++ b/repo/object/object_reader.go
@@ -29,6 +29,10 @@ func (r *objectReader) Read(buffer []byte) (int, error) {
 	readBytes := 0
 	remaining := len(buffer)
 
+	if r.currentPosition >= r.totalLength {
+		return 0, io.EOF
+	}
+
 	for remaining > 0 {
 		if r.currentChunkData != nil {
 			toCopy := len(r.currentChunkData) - r.currentChunkPosition
@@ -114,20 +118,19 @@ func (r *objectReader) findChunkIndexForOffset(offset int64) (int, error) {
 }
 
 func (r *objectReader) Seek(offset int64, whence int) (int64, error) {
-	if whence == 1 {
+	if whence == io.SeekCurrent {
 		return r.Seek(r.currentPosition+offset, 0)
 	}
 
-	if whence == 2 {
+	if whence == io.SeekEnd {
 		return r.Seek(r.totalLength+offset, 0)
 	}
 
-	if offset < 0 {
-		return -1, errors.Errorf("invalid seek %v %v", offset, whence)
-	}
-
-	if offset > r.totalLength {
-		offset = r.totalLength
+	if offset >= r.totalLength {
+		r.currentChunkIndex = len(r.seekTable)
+		r.currentChunkData = nil
+		r.currentPosition = offset
+		return offset, nil
 	}
 
 	index, err := r.findChunkIndexForOffset(offset)
@@ -136,7 +139,6 @@ func (r *objectReader) Seek(offset int64, whence int) (int64, error) {
 	}
 
 	chunkStartOffset := r.seekTable[index].Start
-
 	if index != r.currentChunkIndex {
 		r.closeCurrentChunk()
 		r.currentChunkIndex = index