Next read after read full file returns EOF

GODRIVER-1013

Fix bug in DownloadStream and add RoundTrip tabular tests that test
these bugs

Change-Id: I73777b5b422fdf0bfdee344fb08c2f686940ccd8

Author: eppingere

mongo/gridfs/download_stream.go

@@ -8,9 +8,7 @@ package gridfs
 
 import (
 	"context"
-
 	"errors"
-
 	"io"
 	"math"
 	"time"
@@ -91,13 +89,16 @@ func (ds *DownloadStream) Read(p []byte) (int, error) {
 
 	bytesCopied := 0
 	var err error
-
 	for bytesCopied < len(p) {
 		if ds.bufferStart >= ds.bufferEnd {
 			// Buffer is empty and can load in data from new chunk.
 			err = ds.fillBuffer(ctx)
 			if err != nil {
 				if err == errNoMoreChunks {
+					if bytesCopied == 0 {
+						ds.done = true
+						return 0, io.EOF
+					}
 					return bytesCopied, nil
 				}
 				return bytesCopied, err

mongo/gridfs/gridfs_test.go

@@ -190,51 +190,93 @@ func TestGridFS(t *testing.T) {
 	})
 
 	t.Run("RoundTrip", func(t *testing.T) {
-		if !canRunRoundTripTest(t, db) {
-			t.Skip()
-		}
 
-		bucket, err := NewBucket(db, nil)
-		if err != nil {
-			t.Fatalf("Failed to create bucket: %v", err)
+		oneMeg := 1024 * 1024
+		smallBuffSize := 100
+
+		tests := []struct {
+			name      string
+			chunkSize int // make -1 for no capacity for no chunkSize
+			fileSize  int
+			bufSize   int // make -1 for no capacity for no bufSize
+		}{
+			{"RoundTrip: original", -1, UploadBufferSize, -1},
+			{"RoundTrip: chunk size multiple of file", oneMeg, UploadBufferSize, -1},
+			{"RoundTrip: chunk size is file size", oneMeg, oneMeg, -1},
+			{"RoundTrip: chunk size multiple of file size and with strict buffer size", oneMeg, UploadBufferSize, smallBuffSize},
+			{"RoundTrip: chunk size multiple of file size and buffer size", oneMeg, UploadBufferSize, UploadBufferSize},
+			{"RoundTrip: chunk size, file size, buffer size all the same", oneMeg, oneMeg, oneMeg},
 		}
 
-		timeout := 5 * time.Second
-		if israce.Enabled {
-			timeout = 20 * time.Second // race detector causes 2-20x slowdown
-		}
+		for _, test := range tests {
 
-		err = bucket.SetWriteDeadline(time.Now().Add(timeout))
-		if err != nil {
-			t.Fatalf("Failed to set write deadline: %v", err)
-		}
-		err = bucket.Drop()
-		if err != nil {
-			t.Fatalf("Drop failed: %v", err)
-		}
+			t.Run(test.name, func(t *testing.T) {
 
-		// Test that Upload works when the buffer to write is longer than the upload stream's internal buffer.
-		// This requires multiple calls to uploadChunks.
-		size := UploadBufferSize + 1000000
-		p := make([]byte, size)
-		for i := 0; i < size; i++ {
-			p[i] = byte(rand.Intn(100))
-		}
+				if !canRunRoundTripTest(t, db) {
+					t.Skip()
+				}
 
-		_, err = bucket.UploadFromStream("filename", bytes.NewReader(p))
-		if err != nil {
-			t.Fatalf("Upload failed: %v", err)
-		}
+				var chunkSize *int32
+				var temp int32
+				if test.chunkSize != -1 {
+					temp = int32(test.chunkSize)
+					chunkSize = &temp
+				}
 
-		w := bytes.NewBuffer(make([]byte, 0))
-		_, err = bucket.DownloadToStreamByName("filename", w)
-		if err != nil {
-			t.Fatalf("Download failed: %v", err)
-		}
+				bucket, err := NewBucket(db, &options.BucketOptions{
+					ChunkSizeBytes: chunkSize,
+				})
+				if err != nil {
+					t.Fatalf("Failed to create bucket: %v", err)
+				}
+
+				timeout := 5 * time.Second
+				if israce.Enabled {
+					timeout = 20 * time.Second // race detector causes 2-20x slowdown
+				}
+
+				err = bucket.SetWriteDeadline(time.Now().Add(timeout))
+				if err != nil {
+					t.Fatalf("Failed to set write deadline: %v", err)
+				}
+				err = bucket.Drop()
+				if err != nil {
+					t.Fatalf("Drop failed: %v", err)
+				}
+
+				// Test that Upload works when the buffer to write is longer than the upload stream's internal buffer.
+				// This requires multiple calls to uploadChunks.
+				size := test.fileSize
+				p := make([]byte, size)
+				for i := 0; i < size; i++ {
+					p[i] = byte(rand.Intn(100))
+				}
+
+				_, err = bucket.UploadFromStream("filename", bytes.NewReader(p))
+				if err != nil {
+					t.Fatalf("Upload failed: %v", err)
+				}
+
+				var w *bytes.Buffer
+				if test.bufSize == -1 {
+					w = bytes.NewBuffer(make([]byte, 0))
+				} else {
+					w = bytes.NewBuffer(make([]byte, 0, test.bufSize))
+				}
+
+				_, err = bucket.DownloadToStreamByName("filename", w)
+				if err != nil {
+					t.Fatalf("Download failed: %v", err)
+				}
+
+				if !bytes.Equal(p, w.Bytes()) {
+					t.Errorf("Downloaded file did not match p.")
+				}
+
+			})
 
-		if !bytes.Equal(p, w.Bytes()) {
-			t.Errorf("Downloaded file did not match p.")
 		}
+
 	})
 
 	err = client.Disconnect(ctx)