support add/read multiple arbitrary tx data (#189)

* support add/read multiple arbitrary tx  data

* fix clippy errors

* resolve pr issues

coins/monero/tests/add_data.rs

@@ -0,0 +1,79 @@
+use monero_serai::{rpc::Rpc, wallet::TransactionError, transaction::Transaction};
+
+mod runner;
+
+test!(
+  add_single_data_less_than_255,
+  (
+    |_, mut builder: Builder, addr| async move {
+      // make a data that is less than 255 bytes
+      let arbitrary_data = Vec::from("this is an arbitrary data less than 255 bytes");
+
+      // make sure we can add to tx
+      let result = builder.add_data(arbitrary_data.clone());
+      assert!(result.is_ok());
+
+      builder.add_payment(addr, 5);
+      (builder.build().unwrap(), (arbitrary_data,))
+    },
+    |rpc: Rpc, signed: Transaction, mut scanner: Scanner, state: (Vec<u8>,)| async move {
+      let tx = rpc.get_transaction(signed.hash()).await.unwrap();
+      let output = scanner.scan_transaction(&tx).not_locked().swap_remove(0);
+      assert_eq!(output.commitment().amount, 5);
+      assert_eq!(output.arbitrary_data()[0], state.0);
+    },
+  ),
+);
+
+test!(
+  add_multiple_data_less_than_255,
+  (
+    |_, mut builder: Builder, addr| async move {
+      // make a data that is less than 255 bytes
+      let arbitrary_data = Vec::from("this is an arbitrary data less than 255 bytes");
+
+      // add tx multiple times
+      for _ in 0 .. 5 {
+        let result = builder.add_data(arbitrary_data.clone());
+        assert!(result.is_ok());
+      }
+
+      builder.add_payment(addr, 5);
+      (builder.build().unwrap(), (arbitrary_data,))
+    },
+    |rpc: Rpc, signed: Transaction, mut scanner: Scanner, state: (Vec<u8>,)| async move {
+      let tx = rpc.get_transaction(signed.hash()).await.unwrap();
+      let output = scanner.scan_transaction(&tx).not_locked().swap_remove(0);
+      assert_eq!(output.commitment().amount, 5);
+      let data = output.arbitrary_data();
+      for i in 0 .. 5 {
+        assert_eq!(data[i], state.0);
+      }
+    },
+  ),
+);
+
+test!(
+  add_single_data_more_than_255,
+  (
+    |_, mut builder: Builder, addr| async move {
+      // make a data that is bigger than 255 bytes
+      let mut arbitrary_data = vec![];
+      for _ in 0 .. 256 {
+        arbitrary_data.push(b'a');
+      }
+
+      // make sure we get an error if we try to add it to tx
+      let mut result = builder.add_payment(addr, 5).add_data(arbitrary_data.clone());
+      assert_eq!(result, Err(TransactionError::TooMuchData));
+
+      // reduce data size and re-try
+      arbitrary_data.swap_remove(0);
+      result = builder.add_data(arbitrary_data);
+
+      assert!(result.is_ok());
+      (builder.build().unwrap(), ())
+    },
+    |_, _, _, _| async move {},
+  ),
+);