Round out the runtime

Ensures the block's size limit is respected.

Defines a policy for weights. While I'm unsure I want to commit to this
forever, I do want to acknowledge it's valid and well-defined.

Cleans up the `serai-runtime` crate a bit with further modules in the `wasm`
folder.

substrate/abi/src/block.rs

@@ -63,6 +63,11 @@ pub struct HeaderV1 {
   pub consensus_commitment: [u8; 32],
 }
 
+impl HeaderV1 {
+  /// The size of a serialized V1 header.
+  pub const SIZE: usize = 8 + 32 + 8 + 32 + 32 + 32;
+}
+
 /// A header for a block.
 #[derive(Clone, Copy, PartialEq, Eq, Debug, BorshSerialize, BorshDeserialize)]
 pub enum Header {
@@ -71,6 +76,9 @@ pub enum Header {
 }
 
 impl Header {
+  /// The size of a serialized header.
+  pub const SIZE: usize = 1 + HeaderV1::SIZE;
+
   /// Get the hash of the header.
   pub fn number(&self) -> u64 {
     match self {
@@ -109,8 +117,8 @@ impl Header {
 
 /// A block.
 ///
-/// This does not guarantee consistency. The header's `transactions_root` may not match the
-/// contained transactions.
+/// This does not guarantee consistency nor validity. The header's `transactions_root` may not
+/// match the contained transactions, among other ill effects.
 #[derive(Clone, PartialEq, Eq, Debug, BorshSerialize, BorshDeserialize)]
 pub struct Block {
   /// The block's header.
@@ -119,6 +127,13 @@ pub struct Block {
   pub transactions: Vec<Transaction>,
 }
 
+impl Block {
+  /// The size limit for a block.
+  ///
+  /// This is not enforced upon deserialization. Be careful accordingly.
+  pub const SIZE_LIMIT: usize = 1024 * 1024;
+}
+
 #[cfg(feature = "substrate")]
 mod substrate {
   use core::fmt::Debug;
@@ -133,7 +148,7 @@ mod substrate {
 
   use super::*;
 
-  // Add `serde` implementations which treat self as a `Vec<u8>`
+  // Add `serde` implementations which treat `self` as a `Vec<u8>`
   impl sp_core::serde::Serialize for Transaction {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where

substrate/abi/src/transaction.rs

@@ -279,12 +279,13 @@ mod substrate {
     /// The implicit context to verify transactions with.
     fn implicit_context() -> ImplicitContext;
 
+    /// The size of the current block.
+    fn current_block_size(&self) -> usize;
+
     /// If a block is present in the blockchain.
     fn block_is_present_in_blockchain(&self, hash: &BlockHash) -> bool;
     /// The time embedded into the current block.
-    ///
-    /// Returns `None` if the time has yet to be set.
-    fn current_time(&self) -> Option<u64>;
+    fn current_time(&self) -> u64;
     /// Get the next nonce for an account.
     fn next_nonce(&self, signer: &SeraiAddress) -> u32;
     /// If the signer can pay the SRI fee.
@@ -295,7 +296,7 @@ mod substrate {
     ) -> Result<(), TransactionValidityError>;
 
     /// Begin execution of a transaction.
-    fn start_transaction(&self);
+    fn start_transaction(&self, len: usize);
     /// Consume the next nonce for an account.
     ///
     /// This MUST NOT be called if the next nonce is `u32::MAX`. The caller MAY panic in that case.
@@ -390,9 +391,14 @@ mod substrate {
   impl<Context: TransactionContext> TransactionWithContext<Context> {
     fn validate_except_fee<V: ValidateUnsigned<Call = Context::RuntimeCall>>(
       &self,
+      len: usize,
       source: TransactionSource,
       mempool_priority_if_signed: u64,
     ) -> TransactionValidity {
+      if self.1.current_block_size().saturating_add(len) > crate::Block::SIZE_LIMIT {
+        Err(TransactionValidityError::Invalid(InvalidTransaction::ExhaustsResources))?;
+      }
+
       match &self.0 {
         Transaction::Unsigned { call } => {
           let ValidTransaction { priority: _, requires, provides, longevity: _, propagate: _ } =
@@ -417,13 +423,8 @@ mod substrate {
             Err(TransactionValidityError::Unknown(UnknownTransaction::CannotLookup))?;
           }
           if let Some(include_by) = *include_by {
-            if let Some(current_time) = self.1.current_time() {
-              if current_time >= u64::from(include_by) {
-                // Since this transaction has a time bound which has passed, error
-                Err(TransactionValidityError::Invalid(InvalidTransaction::Stale))?;
-              }
-            } else {
-              // Since this transaction has a time bound, yet we don't know the time, error
+            if self.1.current_time() >= u64::from(include_by) {
+              // Since this transaction has a time bound which has passed, error
               Err(TransactionValidityError::Invalid(InvalidTransaction::Stale))?;
             }
           }
@@ -471,7 +472,7 @@ mod substrate {
       &self,
       source: TransactionSource,
       info: &DispatchInfo,
-      _len: usize,
+      len: usize,
     ) -> TransactionValidity {
       let mempool_priority_if_signed = match &self.0 {
         Transaction::Unsigned { .. } => {
@@ -493,19 +494,19 @@ mod substrate {
           }
         }
       };
-      self.validate_except_fee::<V>(source, mempool_priority_if_signed)
+      self.validate_except_fee::<V>(len, source, mempool_priority_if_signed)
     }
 
     fn apply<V: ValidateUnsigned<Call = Context::RuntimeCall>>(
       self,
       _info: &DispatchInfo,
-      _len: usize,
+      len: usize,
     ) -> sp_runtime::ApplyExtrinsicResultWithInfo<PostDispatchInfo> {
       // We use 0 for the mempool priority, as this is no longer in the mempool so it's irrelevant
-      self.validate_except_fee::<V>(TransactionSource::InBlock, 0)?;
+      self.validate_except_fee::<V>(len, TransactionSource::InBlock, 0)?;
 
       // Start the transaction
-      self.1.start_transaction();
+      self.1.start_transaction(len);
 
       let transaction_hash = self.0.hash();