[Fix] dsv4: Build the DSpark draft block metadata without host sequence lengths

python/sglang/srt/layers/attention/deepseek_v4_backend.py

@@ -2211,13 +2211,13 @@ def init_forward_metadata_dspark_draft_block(
         block_size: int,
         dspark_swa_buffers: Optional[Tuple[torch.Tensor, torch.Tensor]] = None,
     ) -> DSV4Metadata:
-        if seq_lens_cpu is None:
-            seq_lens_cpu_list = seq_lens.tolist()
-        else:
-            seq_lens_cpu_list = [int(x) for x in seq_lens_cpu.tolist()]
         lengths = compute_uniform_extend_lengths(
             seq_lens=seq_lens,
-            seq_lens_cpu=seq_lens_cpu_list,
+            seq_lens_cpu=(
+                None
+                if seq_lens_cpu is None
+                else [int(x) for x in seq_lens_cpu.tolist()]
+            ),
             extend_len=block_size,
         )
         extend_seq_lens = self._draft_block_extend_lens(lengths.extend_seq_lens_cpu)

python/sglang/srt/speculative/ragged_verify.py

@@ -278,7 +278,7 @@ def compute_target_verify_graph_key(
 
 class VerifyExtendLengths(msgspec.Struct, frozen=True):
     seq_lens_extended: torch.Tensor
-    seq_lens_cpu_extended: List[int]
+    seq_lens_cpu_extended: Optional[List[int]]
     extend_seq_lens_cpu: List[int]
     num_tokens: int
     extend_start_loc: Optional[torch.Tensor]
@@ -287,12 +287,14 @@ class VerifyExtendLengths(msgspec.Struct, frozen=True):
 def compute_uniform_extend_lengths(
     *,
     seq_lens: torch.Tensor,
-    seq_lens_cpu: List[int],
+    seq_lens_cpu: Optional[List[int]],
     extend_len: int,
 ) -> VerifyExtendLengths:
-    batch_size = len(seq_lens_cpu)
+    batch_size = seq_lens.shape[0]
     seq_lens_extended = seq_lens + extend_len
-    seq_lens_cpu_extended = [x + extend_len for x in seq_lens_cpu]
+    seq_lens_cpu_extended = (
+        None if seq_lens_cpu is None else [x + extend_len for x in seq_lens_cpu]
+    )
     extend_seq_lens_cpu = [extend_len] * batch_size
     num_tokens = extend_len * batch_size
     return VerifyExtendLengths(

test/registered/spec/dspark/test_ragged_verify.py

@@ -5,6 +5,7 @@
 from sglang.srt.speculative.ragged_verify import (
     RaggedVerifyLayout,
     build_ragged_target_verify_geometry,
+    compute_uniform_extend_lengths,
 )
 from sglang.test.ci.ci_register import register_cpu_ci
 from sglang.test.test_utils import CustomTestCase
@@ -32,6 +33,26 @@ def test_mixed_verify_lens_geometry(self):
         self.assertEqual(geometry.max_seq_len_q, 8)
 
 
+class TestUniformExtendLengths(CustomTestCase):
+    def test_without_host_seq_lens(self):
+        seq_lens = torch.tensor([10, 20, 30], dtype=torch.int32)
+        lengths = compute_uniform_extend_lengths(
+            seq_lens=seq_lens, seq_lens_cpu=None, extend_len=5
+        )
+        self.assertEqual(lengths.seq_lens_extended.tolist(), [15, 25, 35])
+        self.assertIsNone(lengths.seq_lens_cpu_extended)
+        self.assertEqual(lengths.extend_seq_lens_cpu, [5, 5, 5])
+        self.assertEqual(lengths.num_tokens, 15)
+
+    def test_with_host_seq_lens(self):
+        seq_lens = torch.tensor([10, 20], dtype=torch.int32)
+        lengths = compute_uniform_extend_lengths(
+            seq_lens=seq_lens, seq_lens_cpu=[10, 20], extend_len=5
+        )
+        self.assertEqual(lengths.seq_lens_cpu_extended, [15, 25])
+        self.assertEqual(lengths.num_tokens, 10)
+
+
 class TestPaddedRaggedVerifyGeometry(CustomTestCase):
     def test_padded_layout_grows_bs_and_fills_bucket(self):
         raw = RaggedVerifyLayout.from_verify_lens(