[Core] Clean up array-like msgspec structs (#32688)

experimental/sgl-router/src/policies/kv_events/wire.rs

@@ -5,7 +5,7 @@
 //! `msgspec.msgpack`. Two struct families are involved:
 //!
 //! * `EventBatch` (the outer payload) — declared with
-//!   `array_like=True, omit_defaults=True, gc=False` (no tag).
+//!   `array_like=True, gc=False` (no tag).
 //! * `KVCacheEvent` (each inner event variant) — additionally declared
 //!   with `tag=True`.
 //!
@@ -17,9 +17,6 @@
 //!   of each inner event array, so an event is
 //!   `[class_name_str, field1, field2, ...]`. The outer `EventBatch`
 //!   array does **not** carry a tag prefix.
-//! * `omit_defaults=True` allows trailing fields whose values equal their
-//!   declared defaults to be dropped from the array. The decoder therefore
-//!   accepts variable-length sequences for each struct shape.
 //!
 //! This module deserializes those bytes into Rust types and exposes a single
 //! [`decode_event_batch`] entry point.
@@ -32,7 +29,7 @@ use serde::Deserialize;
 /// Top-level batch payload published by SGLang.
 ///
 /// Wire shape (`EventBatch`, `array_like`):
-/// `[ts: f64, events: [...], attn_dp_rank: int_or_nil_or_omitted]`.
+/// `[ts: f64, events: [...], attn_dp_rank: int_or_nil]`.
 /// SGLang declares `attn_dp_rank` as a Python `Optional[int]`; we decode
 /// it as `u32` since DP ranks are non-negative and bounded by the
 /// publisher's `dp_size`.
@@ -43,7 +40,8 @@ pub struct KvEventBatch {
     /// Ordered list of cache events in this batch.
     pub events: Vec<KvCacheEvent>,
     /// Optional DP-attention rank that produced this batch. `None` if the
-    /// publisher emitted nil or omitted the field via `omit_defaults`.
+    /// publisher emitted nil. The decoder also accepts an omitted field for
+    /// compatibility.
     pub attn_dp_rank: Option<u32>,
 }
 
@@ -332,8 +330,8 @@ impl<'de> Deserialize<'de> for BoundedU32Vec {
 
 // ---------------------------------------------------------------------------
 // Custom Deserialize impls — msgspec encodes these structs as msgpack arrays
-// (not maps), and `omit_defaults=True` means trailing optional fields may be
-// absent. We therefore implement `Deserialize` by hand against `SeqAccess`.
+// (not maps). The visitors also accept absent trailing optional fields for
+// compatibility.
 // ---------------------------------------------------------------------------
 
 impl<'de> Deserialize<'de> for KvEventBatch {
@@ -731,8 +729,7 @@ mod tests {
 
     #[test]
     fn attn_dp_rank_omitted_decodes_as_none() {
-        // msgspec's `omit_defaults=True` may drop attn_dp_rank entirely from
-        // the wire array when it equals its default of None.
+        // Accept a payload that omits the optional trailing rank field.
         let event = build_all_blocks_cleared_bytes();
         let bytes = build_batch_bytes(5.0, &[event], None, /* include_dp_field */ false);
 

python/sglang/srt/disaggregation/kv_events.py

@@ -61,7 +61,6 @@ def select_kv_publisher_dp_rank(
 class EventBatch(
     msgspec.Struct,
     array_like=True,  # type: ignore[call-arg]
-    omit_defaults=True,  # type: ignore[call-arg]
     gc=False,  # type: ignore[call-arg]
 ):
     ts: float
@@ -72,7 +71,6 @@ class EventBatch(
 class KVCacheEvent(
     msgspec.Struct,
     array_like=True,  # type: ignore[call-arg]
-    omit_defaults=True,  # type: ignore[call-arg]
     gc=False,  # type: ignore[call-arg]
     tag=True,
 ):

python/sglang/srt/sampling/sampling_params.py

@@ -72,7 +72,7 @@ def raise_if_tokenizer_required(
         )
 
 
-class SamplingParams(msgspec.Struct, kw_only=True, omit_defaults=True):
+class SamplingParams(msgspec.Struct, kw_only=True, array_like=True):
     """
     The sampling parameters.
 
@@ -106,10 +106,10 @@ class SamplingParams(msgspec.Struct, kw_only=True, omit_defaults=True):
     skip_special_tokens: bool = True
     spaces_between_special_tokens: bool = True
     no_stop_trim: bool = False
-    custom_params: Optional[Dict[str, CustomParamValue]] = None
     stream_interval: Optional[int] = None
     logit_bias: Optional[Dict[str, float]] = None
     sampling_seed: Optional[int] = None
+    custom_params: Optional[Dict[str, CustomParamValue]] = None
 
     # --- Internal fields (populated by __post_init__ or normalize(), not API-facing) ---
     stop_strs: Optional[Union[str, List[str]]] = None  # from stop
@@ -269,7 +269,7 @@ class SamplingParams(msgspec.Struct, kw_only=True, omit_defaults=True):
             tokenizer, self.stop_strs, self.stop_regex_strs, self.min_new_tokens
         )
 
-        # Clear API input aliases so omit_defaults=True drops them from the wire.
+        # Clear API input aliases after normalizing them into internal fields.
         self.stop = None
         self.stop_regex = None
         self.is_normalized = True

test/registered/unit/sampling/test_sampling_params.py

@@ -411,11 +411,6 @@ class TestSamplingParamsMsgspecStruct(CustomTestCase):
         self.assertTrue(sp.spaces_between_special_tokens)
         self.assertFalse(sp.no_stop_trim)
 
-    def test_msgpack_omits_default_fields(self):
-        encoded = msgspec.msgpack.encode(SamplingParams())
-
-        self.assertEqual(msgspec.msgpack.decode(encoded), {})
-
     def test_msgpack_round_trip_preserves_normalized_state(self):
         tokenizer = MagicMock()
         tokenizer.encode.side_effect = lambda s, add_special_tokens=False: {