fix: allow missing-tag deser of tx envelope

crates/consensus/src/transaction/envelope.rs

@@ -87,18 +87,18 @@ impl TryFrom<u8> for TxType {
 /// [EIP-2718]: https://eips.ethereum.org/EIPS/eip-2718
 #[derive(Clone, Debug, PartialEq, Eq)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
-#[cfg_attr(feature = "serde", serde(tag = "type"))]
+#[cfg_attr(
+    feature = "serde",
+    serde(into = "serde_from::TaggedTxEnvelope", from = "serde_from::MaybeTaggedTxEnvelope")
+)]
 #[doc(alias = "TransactionEnvelope")]
 #[non_exhaustive]
 pub enum TxEnvelope {
     /// An untagged [`TxLegacy`].
-    #[cfg_attr(feature = "serde", serde(rename = "0x0", alias = "0x00"))]
     Legacy(Signed<TxLegacy>),
     /// A [`TxEip2930`] tagged with type 1.
-    #[cfg_attr(feature = "serde", serde(rename = "0x1", alias = "0x01"))]
     Eip2930(Signed<TxEip2930>),
     /// A [`TxEip1559`] tagged with type 2.
-    #[cfg_attr(feature = "serde", serde(rename = "0x2", alias = "0x02"))]
     Eip1559(Signed<TxEip1559>),
     /// A TxEip4844 tagged with type 3.
     /// An EIP-4844 transaction has two network representations:
@@ -107,10 +107,8 @@ pub enum TxEnvelope {
     ///
     /// 2 - The transaction with a sidecar, which is the form used to
     /// send transactions to the network.
-    #[cfg_attr(feature = "serde", serde(rename = "0x3", alias = "0x03"))]
     Eip4844(Signed<TxEip4844Variant>),
     /// A [`TxEip7702`] tagged with type 4.
-    #[cfg_attr(feature = "serde", serde(rename = "0x4", alias = "0x04"))]
     Eip7702(Signed<TxEip7702>),
 }
 
@@ -518,6 +516,77 @@ impl Transaction for TxEnvelope {
     }
 }
 
+#[cfg(feature = "serde")]
+mod serde_from {
+    //! NB: Why do we need this?
+    //!
+    //! Because the tag may be missing, we need an abstraction over tagged (with
+    //! type) and untagged (always legacy). This is [`MaybeTaggedTxEnvelope`].
+    //!
+    //! The tagged variant is [`TaggedTxEnvelope`], which always has a type tag.
+    //!
+    //! We serialize via [`TaggedTxEnvelope`] and deserialize via
+    //! [`MaybeTaggedTxEnvelope`].
+    use crate::{Signed, TxEip1559, TxEip2930, TxEip4844Variant, TxEip7702, TxLegacy};
+
+    use super::TxEnvelope;
+
+    #[derive(Debug, serde::Deserialize)]
+    #[serde(untagged)]
+    pub(crate) enum MaybeTaggedTxEnvelope {
+        Tagged(TaggedTxEnvelope),
+        Untagged(Signed<TxLegacy>),
+    }
+
+    #[derive(Debug, serde::Serialize, serde::Deserialize)]
+    #[serde(tag = "type")]
+    pub(crate) enum TaggedTxEnvelope {
+        #[serde(rename = "0x0", alias = "0x00")]
+        Legacy(Signed<TxLegacy>),
+        #[serde(rename = "0x1", alias = "0x01")]
+        Eip2930(Signed<TxEip2930>),
+        #[serde(rename = "0x2", alias = "0x02")]
+        Eip1559(Signed<TxEip1559>),
+        #[serde(rename = "0x3", alias = "0x03")]
+        Eip4844(Signed<TxEip4844Variant>),
+        #[serde(rename = "0x4", alias = "0x04")]
+        Eip7702(Signed<TxEip7702>),
+    }
+
+    impl From<MaybeTaggedTxEnvelope> for TxEnvelope {
+        fn from(value: MaybeTaggedTxEnvelope) -> Self {
+            match value {
+                MaybeTaggedTxEnvelope::Tagged(tagged) => tagged.into(),
+                MaybeTaggedTxEnvelope::Untagged(tx) => Self::Legacy(tx),
+            }
+        }
+    }
+
+    impl From<TaggedTxEnvelope> for TxEnvelope {
+        fn from(value: TaggedTxEnvelope) -> Self {
+            match value {
+                TaggedTxEnvelope::Legacy(signed) => Self::Legacy(signed),
+                TaggedTxEnvelope::Eip2930(signed) => Self::Eip2930(signed),
+                TaggedTxEnvelope::Eip1559(signed) => Self::Eip1559(signed),
+                TaggedTxEnvelope::Eip4844(signed) => Self::Eip4844(signed),
+                TaggedTxEnvelope::Eip7702(signed) => Self::Eip7702(signed),
+            }
+        }
+    }
+
+    impl From<TxEnvelope> for TaggedTxEnvelope {
+        fn from(value: TxEnvelope) -> Self {
+            match value {
+                TxEnvelope::Legacy(signed) => Self::Legacy(signed),
+                TxEnvelope::Eip2930(signed) => Self::Eip2930(signed),
+                TxEnvelope::Eip1559(signed) => Self::Eip1559(signed),
+                TxEnvelope::Eip4844(signed) => Self::Eip4844(signed),
+                TxEnvelope::Eip7702(signed) => Self::Eip7702(signed),
+            }
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;