Implement the http variant of the bank server.

During that process, many shortcomings with the socket server and the
bank lib were fixed.

I am aware a massive commit like this is not ideal.

http-server/src/handlers/transfer.rs

@@ -0,0 +1,44 @@
+use actix_web::{post, web, HttpResponse, Responder, Result};
+use serde::{Deserialize, Serialize};
+
+use bank::account::AccountError;
+
+use crate::handlers::error::HttpAccountError;
+use crate::AppState;
+
+#[derive(Deserialize, Serialize)]
+pub struct TransferData {
+    pub(crate) from: String,
+    pub(crate) to: String,
+    pub(crate) amount: f64,
+}
+
+#[post("/transfer")]
+pub async fn route(
+    form: web::Form<TransferData>,
+    data: web::Data<AppState>,
+) -> Result<impl Responder> {
+    let from = form.from.clone();
+    let to = form.to.clone();
+    let amount = form.amount;
+
+    info!("transfering {} from {} to {}...", from, to, amount);
+
+    let bank = data.bank.read().unwrap();
+    let from_acc = bank
+        .accounts
+        .get(&from)
+        .ok_or(HttpAccountError(AccountError::NotFound))?;
+    let mut from_acc = from_acc.write().unwrap();
+
+    let to_acc = bank
+        .accounts
+        .get(&to)
+        .ok_or(HttpAccountError(AccountError::NotFound))?;
+    let mut to_acc = to_acc.write().unwrap();
+
+    match bank.transfer(&mut from_acc, &mut to_acc, amount) {
+        Err(e) => Err(HttpAccountError(e).into()),
+        Ok(_) => Ok(HttpResponse::Ok().finish()),
+    }
+}