Add cancel on error during filling state

When calling fillSlot, any transaction errors that occur (possibly during estimate gas) will cause that tx to be replaced with a cancellation transaction (a 0-valued tx to ourselves).

codex/contracts/market.nim

@@ -110,7 +110,14 @@ method getActiveSlot*(market: OnChainMarket,
       return none Slot
     raise e
 
-method fillSlot(market: OnChainMarket,
+proc cancelTransaction(market: OnChainMarket, nonce: UInt256) {.async.} =
+  let address = await market.getSigner()
+  let cancelTx = Transaction(to: address, value: 0.u256, nonce: some nonce)
+  let populated = await market.signer.populateTransaction(cancelTx)
+  trace "cancelling transaction to prevent stuck transactions", nonce
+  discard market.signer.sendTransaction(populated)
+
+method fillSlot*(market: OnChainMarket,
                 requestId: RequestId,
                 slotIndex: UInt256,
                 proof: seq[byte],

codex/market.nim

@@ -76,6 +76,17 @@ method getActiveSlot*(
 
   raiseAssert("not implemented")
 
+method cancelTransaction(market: Market, nonce: UInt256) {.base, async.} =
+  raiseAssert("not implemented")
+
+template cancelOnError*(market: Market, body) =
+  try:
+    body
+  except JsonRpcProviderError as e:
+    if e.nonce.isSome:
+      # send a 0-valued transaction with the errored nonce to prevent stuck txs
+      await market.cancelTransaction(!e.nonce)
+
 method fillSlot*(market: Market,
                  requestId: RequestId,
                  slotIndex: UInt256,

codex/sales/states/filling.nim

@@ -36,5 +36,6 @@ method run(state: SaleFilling, machine: Machine): Future[?State] {.async.} =
     raiseAssert("no slot index assigned")
 
   debug "Filling slot", requestId = $data.requestId, slotIndex
-  await market.fillSlot(data.requestId, slotIndex, state.proof, collateral)
-  debug "Waiting for slot filled event...", requestId = $data.requestId, slotIndex
+  market.cancelOnError:
+    await market.fillSlot(data.requestId, slotIndex, state.proof, collateral)
+    debug "Waiting for slot filled event...", requestId = $data.requestId, slotIndex

tests/codex/helpers/mockmarket.nim

@@ -205,6 +205,9 @@ proc emitRequestFailed*(market: MockMarket, requestId: RequestId) =
        subscription.requestId.isNone:
       subscription.callback(requestId)
 
+proc cancelTransaction(market: Market, nonce: UInt256) {.async.} =
+  discard
+
 proc fillSlot*(market: MockMarket,
                requestId: RequestId,
                slotIndex: UInt256,