miniogw: set ListParts continuation token correctly

Previously ListParts made no effort to set the NextPartNumberMarker
continuation token correctly.  It's easy, it just the last part number
seen!

https://docs.aws.amazon.com/AmazonS3/latest/API/API_ListParts.html

Closes #53

Change-Id: I5fa7a2c07abb99ec0dd51963abdaac6b1ef83927

miniogw/multipart.go

@@ -8,7 +8,6 @@ import (
 	"errors"
 	"fmt"
 	"math"
-	"sort"
 
 	"github.com/zeebo/errs"
 
@@ -246,17 +245,17 @@ func (layer *gatewayLayer) ListObjectParts(ctx context.Context, bucket, object,
 	if list.Err() != nil {
 		return result, convertMultipartError(list.Err(), bucket, object, uploadID)
 	}
-
-	sort.Slice(parts, func(i, k int) bool {
-		return parts[i].PartNumber < parts[k].PartNumber
-	})
+	nextPartNumberMarker := partNumberMarker
+	if len(parts) > 0 {
+		nextPartNumberMarker = parts[len(parts)-1].PartNumber
+	}
 	return minio.ListPartsInfo{
 		Bucket:               bucket,
 		Object:               object,
 		UploadID:             uploadID,
-		StorageClass:         "",               // TODO
-		PartNumberMarker:     partNumberMarker, // Part number after which listing begins.
-		NextPartNumberMarker: partNumberMarker, // TODO Next part number marker to be used if list is truncated
+		StorageClass:         storageclass.STANDARD,
+		PartNumberMarker:     partNumberMarker,     // Part number after which listing begins.
+		NextPartNumberMarker: nextPartNumberMarker, // NextPartNum is really more like last part num.
 		MaxParts:             maxParts,
 		IsTruncated:          more,
 		Parts:                parts,

testsuite/miniogw/gateway_test.go

@@ -2910,6 +2910,40 @@ func TestListObjectParts(t *testing.T) {
 			assert.WithinDuration(t, now, listParts.Parts[i].LastModified, 5*time.Second)
 			assert.Equal(t, minioReaders[i].MD5CurrentHexString(), listParts.Parts[i].ETag)
 		}
+
+		// try batch of two
+		listParts, err = layer.ListObjectParts(ctx, testBucket, testFile, uploadID, 0, 2, minio.ObjectOptions{})
+		require.NoError(t, err)
+		require.Equal(t, testBucket, listParts.Bucket)
+		require.Equal(t, testFile, listParts.Object)
+		require.Equal(t, uploadID, listParts.UploadID)
+		require.Equal(t, 0, listParts.PartNumberMarker)
+		require.Equal(t, 0+2, listParts.NextPartNumberMarker)
+		require.Len(t, listParts.Parts, 2)
+		for i := 0; i < 2; i++ {
+			assert.Equal(t, i+1, listParts.Parts[i].PartNumber)
+			assert.Equal(t, minioReaders[i].Size(), listParts.Parts[i].Size)
+			assert.Equal(t, minioReaders[i].ActualSize(), listParts.Parts[i].ActualSize)
+			assert.WithinDuration(t, now, listParts.Parts[i].LastModified, 5*time.Second)
+			assert.Equal(t, minioReaders[i].MD5CurrentHexString(), listParts.Parts[i].ETag)
+		}
+
+		// try batch of remaining
+		listParts, err = layer.ListObjectParts(ctx, testBucket, testFile, uploadID, 2, 1000, minio.ObjectOptions{})
+		require.NoError(t, err)
+		require.Equal(t, testBucket, listParts.Bucket)
+		require.Equal(t, testFile, listParts.Object)
+		require.Equal(t, uploadID, listParts.UploadID)
+		require.Equal(t, 2, listParts.PartNumberMarker)
+		require.Equal(t, totalPartsCount, listParts.NextPartNumberMarker)
+		require.Len(t, listParts.Parts, totalPartsCount-2)
+		for i := 0; i < totalPartsCount-2; i++ {
+			assert.Equal(t, i+1+2, listParts.Parts[i].PartNumber)
+			assert.Equal(t, minioReaders[i].Size(), listParts.Parts[i].Size)
+			assert.Equal(t, minioReaders[i].ActualSize(), listParts.Parts[i].ActualSize)
+			assert.WithinDuration(t, now, listParts.Parts[i].LastModified, 5*time.Second)
+			assert.Equal(t, minioReaders[i].MD5CurrentHexString(), listParts.Parts[i].ETag)
+		}
 	})
 }