fix(s3api): normalize checksum trailer header names (#9905)

Problem: SigV4 chunked upload checksum trailer parsing rejected mixed-case checksum header names even though HTTP header field names are case-insensitive.

Root cause: extractChecksumAlgorithm compared the x-amz-trailer value and trailer header key against exact lowercase strings.

Fix: Trim and lowercase checksum trailer header names before matching supported checksum algorithms.

Reproduction: go test ./weed/s3api -run TestExtractChecksumAlgorithmIsCaseInsensitive -count=1 with X-Amz-Checksum-Crc32; before the fix it returned unsupported checksum algorithm.

Validation: gofmt -w weed/s3api/chunked_reader_v4.go weed/s3api/chunked_reader_v4_test.go; git diff --check; go test ./weed/s3api -run TestExtractChecksumAlgorithmIsCaseInsensitive -count=1; go test ./weed/s3api -count=1

Co-authored-by: Codex <noreply@openai.com>

weed/s3api/chunked_reader_v4.go

@@ -31,6 +31,7 @@ import (
 	"hash/crc32"
 	"io"
 	"net/http"
+	"strings"
 	"time"
 
 	"github.com/seaweedfs/seaweedfs/weed/glog"
@@ -138,6 +139,7 @@ func (iam *IdentityAccessManagement) newChunkedReader(req *http.Request) (io.Rea
 
 func extractChecksumAlgorithm(amzTrailerHeader string) (ChecksumAlgorithm, error) {
 	// Extract checksum algorithm from the x-amz-trailer header.
+	amzTrailerHeader = strings.ToLower(strings.TrimSpace(amzTrailerHeader))
 	switch amzTrailerHeader {
 	case "x-amz-checksum-crc32":
 		return ChecksumAlgorithmCRC32, nil

weed/s3api/chunked_reader_v4_test.go

@@ -30,6 +30,16 @@ const (
 	defaultRegion          = "us-east-1"
 )
 
+func TestExtractChecksumAlgorithmIsCaseInsensitive(t *testing.T) {
+	got, err := extractChecksumAlgorithm("X-Amz-Checksum-Crc32")
+	if err != nil {
+		t.Fatalf("extractChecksumAlgorithm returned error: %v", err)
+	}
+	if got != ChecksumAlgorithmCRC32 {
+		t.Fatalf("extractChecksumAlgorithm() = %v, want %v", got, ChecksumAlgorithmCRC32)
+	}
+}
+
 func generateStreamingUnsignedPayloadTrailerPayload(includeFinalCRLF bool) string {
 	// This test will implement the following scenario:
 	// https://docs.aws.amazon.com/AmazonS3/latest/userguide/checking-object-integrity.html