use builder pattern for txs

examples/local_signer.rs

@@ -1,6 +1,5 @@
 use ethers::{types::TransactionRequest, HttpProvider, MainnetWallet};
 use std::convert::TryFrom;
-use std::str::FromStr;
 
 #[tokio::main]
 async fn main() -> Result<(), failure::Error> {
@@ -8,28 +7,17 @@ async fn main() -> Result<(), failure::Error> {
     let provider = HttpProvider::try_from("http://localhost:8545")?;
 
     // create a wallet and connect it to the provider
-    let client = MainnetWallet::from_str(
-        "15c42bf2987d5a8a73804a8ea72fb4149f88adf73e98fc3f8a8ce9f24fcb7774",
-    )?
+    let client = "15c42bf2987d5a8a73804a8ea72fb4149f88adf73e98fc3f8a8ce9f24fcb7774"
+        .parse::<MainnetWallet>()?
         .connect(&provider);
 
-    // get the account's nonce (we abuse the Deref to access the provider's functions)
-    let nonce = client.get_transaction_count(client.address(), None).await?;
-    dbg!(nonce);
-
     // craft the transaction
-    let tx = TransactionRequest {
-        from: None,
-        to: Some("986eE0C8B91A58e490Ee59718Cca41056Cf55f24".parse().unwrap()),
-        gas: Some(21000.into()),
-        gas_price: Some(100_000.into()),
-        value: Some(10000.into()),
-        data: Some(vec![].into()),
-        nonce: Some(nonce),
-    };
+    let tx = TransactionRequest::new()
+        .send_to_str("986eE0C8B91A58e490Ee59718Cca41056Cf55f24")?
+        .value(10000);
 
     // send it!
-    let tx = client.sign_and_send_transaction(tx).await?;
+    let tx = client.sign_and_send_transaction(tx, None).await?;
 
     // get the mined tx
     let tx = client.get_transaction(tx.hash).await?;

examples/transfer_eth.rs

@@ -12,15 +12,10 @@ async fn main() -> Result<(), failure::Error> {
     let from = accounts[0];
 
     // craft the tx
-    let tx = TransactionRequest {
-        from: Some(from),
-        to: Some("9A7e5d4bcA656182e66e33340d776D1542143006".parse()?),
-        value: Some(1000u64.into()),
-        gas: None,
-        gas_price: None,
-        data: None,
-        nonce: None,
-    };
+    let tx = TransactionRequest::new()
+        .send_to_str("9A7e5d4bcA656182e66e33340d776D1542143006")?
+        .value(1000)
+        .from(from); // specify the `from` field so that the client knows which account to use
 
     let balance_before = provider.get_balance(from, None).await?;
 

src/providers/mod.rs

@@ -46,6 +46,29 @@ impl<P: JsonRpcClient> Provider<P> {
         }
     }
 
+    // Cost related
+
+    /// Gets the current gas price as estimated by the node
+    pub async fn get_gas_price(&self) -> Result<U256, P::Error> {
+        self.0.request("eth_gasPrice", None::<()>).await
+    }
+
+    /// Tries to estimate the gas for the transaction
+    pub async fn estimate_gas(
+        &self,
+        tx: &TransactionRequest,
+        block: Option<BlockNumber>,
+    ) -> Result<U256, P::Error> {
+        let tx = utils::serialize(tx);
+
+        let args = match block {
+            Some(block) => vec![tx, utils::serialize(&block)],
+            None => vec![tx],
+        };
+
+        self.0.request("eth_estimateGas", Some(args)).await
+    }
+
     /// Gets the accounts on the node
     pub async fn get_accounts(&self) -> Result<Vec<Address>, P::Error> {
         self.0.request("eth_accounts", None::<()>).await
@@ -65,6 +88,8 @@ impl<P: JsonRpcClient> Provider<P> {
         self.0.request("eth_getTransactionByHash", Some(hash)).await
     }
 
+    // State mutations
+
     /// Broadcasts the transaction request via the `eth_sendTransaction` API
     pub async fn send_transaction(&self, tx: TransactionRequest) -> Result<TxHash, P::Error> {
         self.0.request("eth_sendTransaction", Some(tx)).await

src/signers/client.rs

@@ -1,7 +1,7 @@
 use crate::{
     providers::{JsonRpcClient, Provider},
     signers::Signer,
-    types::{Address, Transaction, TransactionRequest},
+    types::{Address, BlockNumber, Transaction, TransactionRequest},
 };
 
 use std::ops::Deref;
@@ -17,8 +17,30 @@ impl<'a, S: Signer, P: JsonRpcClient> Client<'a, S, P> {
     /// API
     pub async fn sign_and_send_transaction(
         &self,
-        tx: TransactionRequest,
+        mut tx: TransactionRequest,
+        block: Option<BlockNumber>,
     ) -> Result<Transaction, P::Error> {
+        // TODO: Convert to join'ed futures
+        // get the gas price
+        if tx.gas_price.is_none() {
+            tx.gas_price = Some(self.provider.get_gas_price().await?);
+        }
+
+        // estimate the gas
+        if tx.gas.is_none() {
+            tx.from = Some(self.address());
+            tx.gas = Some(self.provider.estimate_gas(&tx, block).await?);
+        }
+
+        // set our nonce
+        if tx.nonce.is_none() {
+            tx.nonce = Some(
+                self.provider
+                    .get_transaction_count(self.address(), block)
+                    .await?,
+            );
+        }
+
         // sign the transaction
         let signed_tx = self.signer.sign_transaction(tx).unwrap(); // TODO
 

src/types/keys.rs

@@ -59,13 +59,18 @@ impl PrivateKey {
         self.sign_with_eip155(&sig_message, None)
     }
 
-    /// RLP encodes and then signs the stransaction. If no chain_id is provided, then EIP-155 is
-    /// not used.
+    /// RLP encodes and then signs the stransaction.
+    ///
+    /// If no chain_id is provided, then EIP-155 is not used.
+    ///
+    /// This will return an error if called if any of the `nonce`, `gas_price` or `gas`
+    /// fields are not populated.
     pub fn sign_transaction(
         &self,
         tx: TransactionRequest,
         chain_id: Option<U64>,
     ) -> Result<Transaction, TxError> {
+        // Calling `
         let nonce = tx.nonce.ok_or(TxError::NonceMissing)?;
         let gas_price = tx.gas_price.ok_or(TxError::NonceMissing)?;
         let gas = tx.gas.ok_or(TxError::NonceMissing)?;

src/types/transaction.rs

@@ -5,9 +5,10 @@ use crate::{
 };
 use rlp::RlpStream;
 use serde::{Deserialize, Serialize};
+use std::str::FromStr;
 
 /// Parameters for sending a transaction
-#[derive(Clone, Serialize, Deserialize, PartialEq, Eq, Debug)]
+#[derive(Clone, Default, Serialize, Deserialize, PartialEq, Eq, Debug)]
 pub struct TransactionRequest {
     /// Sender address or ENS name
     #[serde(skip_serializing_if = "Option::is_none")]
@@ -41,27 +42,89 @@ pub struct TransactionRequest {
 }
 
 impl TransactionRequest {
-    fn rlp_base(&self, rlp: &mut RlpStream) {
-        rlp_opt(rlp, self.nonce);
-        rlp_opt(rlp, self.gas_price);
-        rlp_opt(rlp, self.gas);
-        rlp_opt(rlp, self.to);
-        rlp_opt(rlp, self.value);
-        rlp_opt(rlp, self.data.as_ref().map(|d| &d.0[..]));
+    /// Creates an empty transaction request with all fields left empty
+    pub fn new() -> Self {
+        Self::default()
     }
 
-    pub fn hash(&self, chain_id: Option<U64>) -> H256 {
+    /// Convenience function for sending a new payment transaction to the receiver. The
+    /// `gas`, `gas_price` and `nonce` fields are left empty, to be populated
+    pub fn pay<T: Into<Address>, V: Into<U256>>(to: T, value: V) -> Self {
+        TransactionRequest {
+            from: None,
+            to: Some(to.into()),
+            gas: None,
+            gas_price: None,
+            value: Some(value.into()),
+            data: None,
+            nonce: None,
+        }
+    }
+
+    // Builder pattern helpers
+
+    /// Sets the `from` field in the transaction to the provided value
+    pub fn from<T: Into<Address>>(mut self, from: T) -> Self {
+        self.from = Some(from.into());
+        self
+    }
+
+    /// Sets the `to` field in the transaction to the provided value
+    pub fn send_to_str(mut self, to: &str) -> Result<Self, rustc_hex::FromHexError> {
+        self.to = Some(Address::from_str(to)?);
+        Ok(self)
+    }
+
+    /// Sets the `to` field in the transaction to the provided value
+    pub fn to<T: Into<Address>>(mut self, to: T) -> Self {
+        self.to = Some(to.into());
+        self
+    }
+
+    /// Sets the `gas` field in the transaction to the provided value
+    pub fn gas<T: Into<U256>>(mut self, gas: T) -> Self {
+        self.gas = Some(gas.into());
+        self
+    }
+
+    /// Sets the `gas_price` field in the transaction to the provided value
+    pub fn gas_price<T: Into<U256>>(mut self, gas_price: T) -> Self {
+        self.gas_price = Some(gas_price.into());
+        self
+    }
+
+    /// Sets the `value` field in the transaction to the provided value
+    pub fn value<T: Into<U256>>(mut self, value: T) -> Self {
+        self.value = Some(value.into());
+        self
+    }
+
+    /// Sets the `data` field in the transaction to the provided value
+    pub fn data<T: Into<Bytes>>(mut self, data: T) -> Self {
+        self.data = Some(data.into());
+        self
+    }
+
+    /// Sets the `nonce` field in the transaction to the provided value
+    pub fn nonce<T: Into<U256>>(mut self, nonce: T) -> Self {
+        self.nonce = Some(nonce.into());
+        self
+    }
+
+    /// Hashes the transaction's data with the provided chain id
+    pub fn hash<T: Into<U64>>(&self, chain_id: Option<T>) -> H256 {
         let mut rlp = RlpStream::new();
         rlp.begin_list(9);
         self.rlp_base(&mut rlp);
 
-        rlp.append(&chain_id.unwrap_or_else(U64::zero));
+        rlp.append(&chain_id.map(|c| c.into()).unwrap_or_else(U64::zero));
         rlp.append(&0u8);
         rlp.append(&0u8);
 
         keccak256(rlp.out().as_ref()).into()
     }
 
+    /// Produces the RLP encoding of the transaction with the provided signature
     pub fn rlp_signed(&self, signature: &Signature) -> Bytes {
         let mut rlp = RlpStream::new();
         rlp.begin_list(9);
@@ -73,6 +136,15 @@ impl TransactionRequest {
 
         rlp.out().into()
     }
+
+    fn rlp_base(&self, rlp: &mut RlpStream) {
+        rlp_opt(rlp, self.nonce);
+        rlp_opt(rlp, self.gas_price);
+        rlp_opt(rlp, self.gas);
+        rlp_opt(rlp, self.to);
+        rlp_opt(rlp, self.value);
+        rlp_opt(rlp, self.data.as_ref().map(|d| &d.0[..]));
+    }
 }
 
 fn rlp_opt<T: rlp::Encodable>(rlp: &mut RlpStream, opt: Option<T>) {