add conditional put

bank/src/account.rs

@@ -1,3 +1,4 @@
+use std::collections::hash_map::DefaultHasher;
 use std::hash::{Hash, Hasher};
 
 use thiserror::Error;
@@ -25,6 +26,23 @@ pub struct Account {
     pub is_active: bool,
 }
 
+impl Account {
+    pub fn hash_string(&self) -> String {
+        let mut hasher = DefaultHasher::new();
+        self.hash(&mut hasher);
+        format!("{:x}", hasher.finish())
+    }
+}
+
+impl Hash for Account {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.number.hash(state);
+        self.owner.hash(state);
+        self.balance.to_string().hash(state);
+        self.is_active.hash(state);
+    }
+}
+
 impl Default for Account {
     fn default() -> Self {
         Account {
@@ -42,12 +60,6 @@ impl PartialEq for Account {
     }
 }
 
-impl Hash for Account {
-    fn hash<H: Hasher>(&self, state: &mut H) {
-        self.number.hash(state);
-    }
-}
-
 impl Account {
     #[cfg(test)]
     pub fn new() -> Self {

bank/src/bank.rs

@@ -13,11 +13,11 @@ impl Bank {
         Default::default()
     }
 
-    pub fn account_action<F: Fn(&mut Account) -> Result<f64, AccountError>>(
+    pub fn account_action<F: Fn(&mut Account) -> Result<R, AccountError>, R>(
         bank: RwLockReadGuard<'_, Bank>,
         nr: &str,
         action: F,
-    ) -> Result<f64, AccountError> {
+    ) -> Result<R, AccountError> {
         match bank.accounts.get(nr) {
             None => Err(AccountError::NotFound),
             Some(account) => {

http-client/src/api.rs

@@ -27,8 +27,14 @@ pub async fn fetch_account(host: &str, nr: &str) -> Result<JsonAccount, FetchErr
     }
 }
 
-pub async fn set_balance(host: &str, nr: &str, balance: f64) -> Result<(), FetchError> {
+pub async fn set_balance(
+    host: &str,
+    nr: &str,
+    balance: f64,
+    etag: String,
+) -> Result<(), FetchError> {
     let data = JsValue::from_str(&format!("amount={}", balance));
-    client::put(&format! {"{}/accounts/{}", host, nr}, data).await?;
+    client::put(&format! {"{}/accounts/{}", host, nr}, data, Some(etag)).await?;
+
     Ok(())
 }

http-client/src/client.rs

@@ -53,7 +53,7 @@ pub async fn get_json(url: &str) -> Result<Option<String>, FetchError> {
     Ok(text.as_string())
 }
 
-pub async fn put(url: &str, data: JsValue) -> Result<(), FetchError> {
+pub async fn put(url: &str, data: JsValue, if_match: Option<String>) -> Result<(), FetchError> {
     let mut opts = RequestInit::new();
     opts.method("PUT");
     opts.mode(RequestMode::Cors);
@@ -63,6 +63,11 @@ pub async fn put(url: &str, data: JsValue) -> Result<(), FetchError> {
     request
         .headers()
         .set("Content-Type", "application/x-www-form-urlencoded")?;
+
+    if let Some(etag) = if_match {
+        request.headers().set("If-match", &etag)?;
+    }
+
     self::send_request(request).await?;
 
     Ok(())

http-client/src/components/main.rs

@@ -77,8 +77,17 @@ impl Component for Main {
                 true
             }
             Event::SetBalance(balance, nr) => {
+                let acc = bank::account::Account {
+                    number: nr.clone(),
+                    owner: self.selected_owner.clone(),
+                    balance: self.selected_balance,
+                    is_active: true,
+                };
+
+                let hash = acc.hash_string();
+
                 ctx.link().send_future(async move {
-                    match api::set_balance("http://localhost:8000", &nr, balance).await {
+                    match api::set_balance("http://localhost:8000", &nr, balance, hash).await {
                         Err(e) => Event::ShowError(e.to_string()),
                         Ok(_) => Event::SelectAccountNr(nr),
                     }

http-server/src/handlers/update_account.rs

@@ -1,9 +1,7 @@
-use actix_web::{put, web, HttpResponse, Responder, Result};
+use actix_web::{put, web, HttpRequest, HttpResponse, Responder, Result};
 use bank::account::AccountError;
 use serde::Serialize;
 
-use bank::bank::Bank;
-
 use crate::handlers::error::HttpAccountError;
 use crate::handlers::AmountData;
 use crate::AppState;
@@ -18,6 +16,7 @@ pub async fn route(
     info: web::Path<String>,
     form: web::Form<AmountData>,
     data: web::Data<AppState>,
+    req: HttpRequest,
 ) -> Result<impl Responder> {
     let nr = info.into_inner();
     let amount = form.amount;
@@ -29,11 +28,22 @@ pub async fn route(
     info!("updating account {}...", nr);
 
     let bank = data.bank.read().unwrap();
-    match Bank::account_action(bank, &nr, |account| {
-        account.balance = amount;
-        Ok(amount)
-    }) {
-        Err(e) => Err(HttpAccountError(e).into()),
-        Ok(_) => Ok(HttpResponse::Ok().finish()),
+    match bank.accounts.get(&nr) {
+        None => Err(HttpAccountError(AccountError::NotFound).into()),
+        Some(account) => {
+            let mut account = account.write().unwrap();
+            let hash = account.hash_string();
+            if let Some(etag) = req.headers().get("If-Match") {
+                let etag = etag.to_str().unwrap_or("");
+                if etag != hash {
+                    Ok(HttpResponse::PreconditionFailed().finish())
+                } else {
+                    account.balance = amount;
+                    Ok(HttpResponse::Ok().finish())
+                }
+            } else {
+                Ok(HttpResponse::PreconditionRequired().finish())
+            }
+        }
     }
 }

http-server/src/main.rs

@@ -155,6 +155,30 @@ mod tests {
             .set_form(&payload)
             .to_request();
         let resp = test::call_service(&app, req).await;
+        assert_eq!(resp.status(), StatusCode::PRECONDITION_REQUIRED);
+
+        let payload = AmountData { amount: 10_f64 };
+        let req = test::TestRequest::put()
+            .uri(&format!("/accounts/{}", nr))
+            .append_header((actix_web::http::header::IF_MATCH, "I aspire to be an etag"))
+            .set_form(&payload)
+            .to_request();
+        let resp = test::call_service(&app, req).await;
+        assert_eq!(resp.status(), StatusCode::PRECONDITION_FAILED);
+
+        let acc = bank::account::Account {
+            number: nr.to_string(),
+            owner: "aaa".to_string(),
+            balance: 5_f64,
+            is_active: true
+        };
+        let payload = AmountData { amount: 10_f64 };
+        let req = test::TestRequest::put()
+            .uri(&format!("/accounts/{}", nr))
+            .append_header((actix_web::http::header::IF_MATCH, acc.hash_string()))
+            .set_form(&payload)
+            .to_request();
+        let resp = test::call_service(&app, req).await;
         assert!(resp.status().is_success());
 
         let req = test::TestRequest::put()