fix nonce issues by locking populate and send transaction

Concurrent asynchronous population of transactions cause issues with nonces not being in sync with the transaction count for an account on chain. This was being mitigated by tracking a "last seen" nonce and locking inside of `populateTransaction` so that the nonce could be populated in a concurrent fashion. However, if there was an async cancellation before the transaction was sent, then the nonce would become out of sync. One solution was to decrease the nonce if a cancellation occurred. The other solution, in this commit, is simply to lock the populate and sendTransaction calls together, so that there will not be concurrent nonce discrepancies. This removes the need for "lastSeenNonce" and is overall more simple.

ethers/contract.nim

@@ -127,10 +127,17 @@ proc send(contract: Contract,
           overrides = TransactionOverrides()):
          Future[?TransactionResponse] {.async.} =
   if signer =? contract.signer:
-    let transaction = createTransaction(contract, function, parameters, overrides)
-    let populated = await signer.populateTransaction(transaction)
-    var txResp = await signer.sendTransaction(populated)
-    return txResp.some
+
+    var params: seq[string] = @[]
+    for param in parameters.fields:
+      params.add $param
+
+    withLock(signer):
+      let transaction = createTransaction(contract, function, parameters, overrides)
+      let populated = await signer.populateTransaction(transaction)
+      trace "sending contract transaction", function, params
+      let txResp = await signer.sendTransaction(populated)
+      return txResp.some
   else:
     await call(contract, function, parameters, overrides)
     return TransactionResponse.none

ethers/signer.nim

@@ -81,13 +81,19 @@ method getChainId*(
 method getNonce(
   signer: Signer): Future[UInt256] {.base, async: (raises: [SignerError, ProviderError]).} =
 
-  var nonce = await signer.getTransactionCount(BlockTag.pending)
+  return await signer.getTransactionCount(BlockTag.pending)
+
+template withLock*(signer: Signer, body: untyped) =
+  if signer.populateLock.isNil:
+    signer.populateLock = newAsyncLock()
+
+  await signer.populateLock.acquire()
+  try:
+    body
+  finally:
+    signer.populateLock.release()
 
-  if lastSeen =? signer.lastSeenNonce and lastSeen >= nonce:
-    nonce = (lastSeen + 1.u256)
-  signer.lastSeenNonce = some nonce
 
-  return nonce
 
 method updateNonce*(
   signer: Signer,
@@ -109,6 +115,10 @@ method populateTransaction*(
   signer: Signer,
   transaction: Transaction): Future[Transaction]
   {.base, async: (raises: [CancelledError, AsyncLockError, ProviderError, SignerError]).} =
+  ## Populates a transaction with sender, chainId, gasPrice, nonce, and gasLimit.
+  ## NOTE: to avoid async concurrency issues, this routine should be called with
+  ## a lock if it is followed by sendTransaction. For reference, see the `send`
+  ## function in contract.nim.
 
   var address: Address
   convertError:
@@ -119,20 +129,14 @@ method populateTransaction*(
   if chainId =? transaction.chainId and chainId != await signer.getChainId():
     raiseSignerError("chain id mismatch")
 
-  if signer.populateLock.isNil:
-    signer.populateLock = newAsyncLock()
-
-  await signer.populateLock.acquire()
-
   var populated = transaction
 
-  try:
-    if transaction.sender.isNone:
-      populated.sender = some(address)
-    if transaction.chainId.isNone:
-      populated.chainId = some(await signer.getChainId())
-    if transaction.gasPrice.isNone and (transaction.maxFee.isNone or transaction.maxPriorityFee.isNone):
-      populated.gasPrice = some(await signer.getGasPrice())
+  if transaction.sender.isNone:
+    populated.sender = some(address)
+  if transaction.chainId.isNone:
+    populated.chainId = some(await signer.getChainId())
+  if transaction.gasPrice.isNone and (transaction.maxFee.isNone or transaction.maxPriorityFee.isNone):
+    populated.gasPrice = some(await signer.getGasPrice())
 
     if transaction.nonce.isNone and transaction.gasLimit.isNone:
       # when both nonce and gasLimit are not populated, we must ensure getNonce is
@@ -149,14 +153,12 @@ method populateTransaction*(
         signer.decreaseNonce()
         raiseSignerError(e.msg)
 
-    else:
-      if transaction.nonce.isNone:
-        populated.nonce = some(await signer.getNonce())
-      if transaction.gasLimit.isNone:
-        populated.gasLimit = some(await signer.estimateGas(populated, BlockTag.pending))
-
-  finally:
-    signer.populateLock.release()
+  else:
+    if transaction.nonce.isNone:
+      let nonce = await signer.getNonce()
+      populated.nonce = some nonce
+    if transaction.gasLimit.isNone:
+      populated.gasLimit = some(await signer.estimateGas(populated, BlockTag.pending))
 
   return populated
 
@@ -172,7 +174,8 @@ method cancelTransaction*(
   without nonce =? tx.nonce:
     raiseSignerError "transaction must have nonce"
 
-  var cancelTx = Transaction(to: sender, value: 0.u256, nonce: some nonce)
-  convertError:
-    cancelTx = await signer.populateTransaction(cancelTx)
-    return await signer.sendTransaction(cancelTx)
+  withLock(signer):
+    convertError:
+      var cancelTx = Transaction(to: sender, value: 0.u256, nonce: some nonce)
+      cancelTx = await signer.populateTransaction(cancelTx)
+      return await signer.sendTransaction(cancelTx)