docs: added cookbook entry to compute raw transaction (#1857).

docs.wrm/api/providers/types.wrm

@@ -266,7 +266,9 @@ The number of blocks that have been mined (including the initial block) since th
 transaction was mined.
 
 _property: transaction.raw => string<[[DataHexString]]>
-The serialized transaction.
+The serialized transaction. This may be null as some backends do not
+rpopulate it. If this is required, it can be computed from a **TransactionResponse**
+object using [this cookbook recipe](cookbook--compute-raw-transaction).
 
 _property: transaction.wait([ confirms = 1 ]) => Promise<[[providers-TransactionReceipt]]>
 Resolves to the [[providers-TransactionReceipt]] once the transaction

docs.wrm/cookbook/index.wrm

@@ -6,4 +6,5 @@ snippets of code that are in general useful.
 _toc:
 
   react-native
+  transactions
 

docs.wrm/cookbook/transactions.wrm

@@ -0,0 +1,24 @@
+_section: Transactions @<cookbook--transactions>
+
+_subsection: Compute the raw transaction @<cookbook--compute-raw-transaction>
+
+_code: @lang<javascript>
+
+function getRawTransaction(tx) {
+  function addKey(accum, key) {
+    if (tx[key]) { accum[key] = tx[key]; }
+    return accum;
+  }
+
+  // Extract the relevant parts of the transaction and signature
+  const txFields = "accessList chainId data gasPrice gasLimit maxFeePerGer maxPriorityFeePerGas nonce to type value".split(" ");
+  const sigFields = "v r s".split(" ");
+
+  // Seriailze the signed transaction
+  const raw = utils.serializeTransaction(txFields.reduce(addKey, { }), sigFields.reduce(addKey, { }));
+
+  // Double check things went well
+  if (utils.keccak256(raw) !== tx.hash) { throw new Error("serializing failed!"); }
+
+  return raw;
+}