fix: name the checksum algorithm in PutObject/UploadPart mismatch errors

hash.ChecksumMismatch now carries the requested algorithm (CRC32, CRC32C,
SHA1, SHA256, CRC64NVME), and toAPIError renders it S3-style:

  The CRC32 you specified did not match the calculated checksum.

instead of the generic "The provided 'x-amz-checksum' header does not match
what was computed.", for all four mismatch construction sites (streaming
reader, trailing-checksum decode, and both Checksum.Matches paths). Mirrors
the wording already shipped for CompleteMultipartUpload in #225.

Fixes #226

cmd/api-errors.go

@@ -2505,6 +2505,14 @@ func toAPIError(ctx context.Context, err error) APIError {
 	case errors.Is(err, errMissingPartChecksum):
 		apiErr.Description = strings.TrimPrefix(err.Error(), errMissingPartChecksum.Error()+": ")
 	}
+	// PutObject/UploadPart checksum mismatches name the algorithm in the
+	// message, matching S3 (e.g. "The CRC32 you specified did not match the
+	// calculated checksum."). Falls through to the generic table description
+	// when the algorithm is unknown.
+	var checksumMismatch hash.ChecksumMismatch
+	if errors.As(err, &checksumMismatch) && checksumMismatch.Algorithm != "" {
+		apiErr.Description = fmt.Sprintf("The %s you specified did not match the calculated checksum.", checksumMismatch.Algorithm)
+	}
 	switch apiErr.Code {
 	case "NotImplemented":
 		apiErr = APIError{

cmd/object-handlers-chunked-checksum_test.go

@@ -62,12 +62,13 @@ func testAPIPutObjectChunkedChecksum(obj ObjectLayer, instanceType, bucketName s
 	// A well-formed 4-byte value that does not match the content.
 	wrongCRC := base64.StdEncoding.EncodeToString([]byte{0x01, 0x02, 0x03, 0x04})
 
-	apiCode := func(rec *httptest.ResponseRecorder) string {
+	apiErrOf := func(rec *httptest.ResponseRecorder) APIErrorResponse {
 		var apiErr APIErrorResponse
 		b, _ := io.ReadAll(rec.Body)
 		_ = xml.Unmarshal(b, &apiErr)
-		return apiErr.Code
+		return apiErr
 	}
+	apiCode := func(rec *httptest.ResponseRecorder) string { return apiErrOf(rec).Code }
 
 	// newChunkedJavaForm builds a non-trailer signed chunked PutObject request that
 	// mirrors the AWS Java SDK v2 wire form: the checksum value sits in the header
@@ -131,8 +132,12 @@ func testAPIPutObjectChunkedChecksum(obj ObjectLayer, instanceType, bucketName s
 		if rec.Code != http.StatusBadRequest {
 			t.Fatalf("%s: chunked+wrong CRC32: expected 400, got %d", instanceType, rec.Code)
 		}
-		if code := apiCode(rec); code != "XAmzContentChecksumMismatch" {
+		gotErr := apiErrOf(rec)
-			t.Fatalf("%s: chunked+wrong CRC32: want XAmzContentChecksumMismatch, got %q", instanceType, code)
+		if gotErr.Code != "XAmzContentChecksumMismatch" {
+			t.Fatalf("%s: chunked+wrong CRC32: want XAmzContentChecksumMismatch, got %q", instanceType, gotErr.Code)
+		}
+		if gotErr.Message != "The CRC32 you specified did not match the calculated checksum." {
+			t.Fatalf("%s: chunked+wrong CRC32: message = %q, want S3 algorithm-specific wording", instanceType, gotErr.Message)
 		}
 	}
 }

internal/hash/checksum.go

@@ -584,6 +584,7 @@ func (c Checksum) Matches(content []byte, parts int) error {
 	sum := hasher.Sum(nil)
 	if c.WantParts > 0 && c.WantParts != parts {
 		return ChecksumMismatch{
+			Algorithm: c.Type.String(),
 			Want:      fmt.Sprintf("%s-%d", c.Encoded, c.WantParts),
 			Got:       fmt.Sprintf("%s-%d", base64.StdEncoding.EncodeToString(sum), parts),
 		}
@@ -591,6 +592,7 @@ func (c Checksum) Matches(content []byte, parts int) error {
 
 	if !bytes.Equal(sum, c.Raw) {
 		return ChecksumMismatch{
+			Algorithm: c.Type.String(),
 			Want:      c.Encoded,
 			Got:       base64.StdEncoding.EncodeToString(sum),
 		}

internal/hash/errors.go

@@ -74,6 +74,9 @@ func (e SizeMismatch) Error() string {
 
 // ChecksumMismatch - when content checksum does not match with what was sent from client.
 type ChecksumMismatch struct {
+	// Algorithm carries the requested checksum type (e.g. "CRC32") so API
+	// error rendering can name it, matching S3's wording.
+	Algorithm string
 	Want      string
 	Got       string
 }

internal/hash/reader.go

@@ -302,11 +302,12 @@ func (r *Reader) Read(p []byte) (int, error) {
 				r.contentHash.Encoded = r.trailer.Get(r.contentHash.Type.Key())
 				r.contentHash.Raw, err = base64.StdEncoding.DecodeString(r.contentHash.Encoded)
 				if err != nil || len(r.contentHash.Raw) == 0 {
-					return 0, ChecksumMismatch{Got: r.contentHash.Encoded}
+					return 0, ChecksumMismatch{Algorithm: r.contentHash.Type.String(), Got: r.contentHash.Encoded}
 				}
 			}
 			if sum := r.contentHasher.Sum(nil); !bytes.Equal(r.contentHash.Raw, sum) {
 				err := ChecksumMismatch{
+					Algorithm: r.contentHash.Type.String(),
 					Want:      r.contentHash.Encoded,
 					Got:       base64.StdEncoding.EncodeToString(sum),
 				}