store/nbs: s3_object_reader: Fix a regression which prevented loading large table files with the AWS NomsBlockStore backend.

Affects 1.50.0, 1.50.1 and 1.50.2.

go/store/nbs/s3_fake_test.go

@@ -235,14 +235,17 @@ func (m *fakeS3) GetObject(ctx context.Context, input *s3.GetObjectInput, opts .
 	if !present {
 		return nil, mockAWSError("NoSuchKey")
 	}
+	var outputRange *string
 	if input.Range != nil {
 		start, end := parseRange(*input.Range, len(obj))
+		outputRange = aws.String(*input.Range + "/" + strconv.Itoa(len(obj)))
 		obj = obj[start:end]
 	}
 
 	return &s3.GetObjectOutput{
 		Body:          io.NopCloser(bytes.NewReader(obj)),
 		ContentLength: aws.Int64(int64(len(obj))),
+		ContentRange:  outputRange,
 	}, nil
 }
 

go/store/nbs/s3_object_reader.go

@@ -185,10 +185,8 @@ func (s3or *s3ObjectReader) readS3ObjectFromEnd(ctx context.Context, name string
 			}
 			bs := p[start:end]
 			rangeStart := sz - uint64(len(p)) + uint64(start)
-			rangeEnd := sz - uint64(len(p)) + uint64(end) - 1
-			length := rangeEnd - rangeStart
 			eg.Go(func() error {
-				n, _, err := s3or.readRange(egctx, name, bs, httpRangeHeader(int64(rangeStart), int64(length)))
+				n, _, err := s3or.readRange(egctx, name, bs, httpRangeHeader(int64(rangeStart), int64(len(bs))))
 				if err != nil {
 					return err
 				}

go/store/nbs/s3_object_reader_test.go

@@ -0,0 +1,51 @@
+// Copyright 2025 Dolthub, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package nbs
+
+import (
+	"context"
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestS3ObjectReader(t *testing.T) {
+	t.Run("LargeReadFromObjectEnd", func(t *testing.T) {
+		ns := "5c2d1e52-e9bc-4779-881a-9087ad9a9f7b"
+		obj := "rhi4dnrr2ov6420h7j419lc4f72u7egf"
+		key := fmt.Sprintf("%s/%s", ns, obj)
+		s3client := makeFakeS3(t)
+		s3or := &s3ObjectReader{
+			s3client,
+			"dolthub-chunks-prod",
+			nil,
+			"5c2d1e52-e9bc-4779-881a-9087ad9a9f7b",
+		}
+		sz := maxS3ReadFromEndReqSize * 2 + maxS3ReadFromEndReqSize / 2
+		data := make([]byte, sz)
+		for i := range data {
+			data[i] = byte((i % 256))
+		}
+		rd := make([]byte, sz-256)
+		s3client.data[key] = data
+		n, rdSz, err := s3or.readS3ObjectFromEnd(context.Background(), obj, rd, &Stats{})
+		require.NoError(t, err)
+		assert.Equal(t, uint64(sz), rdSz)
+		assert.Equal(t, n, len(rd))
+		assert.Equal(t, data[256:], rd)
+	})
+}