feat(kanban): upload pending command with retry

req: sync/004\nreq: sync/009\nreq: sync/010\nreq: sync/016\nreq: sync/017

examples/kanban/src/main.rs

@@ -9,13 +9,13 @@ use hemplate::Hemplate;
 use hemx::{Html, IntoEffect};
 use hemx_axum::{
     interactions, runtime_js, runtime_js_path, sse, DispatchRegistry, DispatchRejection,
-    EffectResponse, InteractionRequest, PageRequest,
+    EffectResponse, InteractionRequest, PageRequest, PageResponse,
 };
 use hemx_kanban_example::ui::board::{self as board};
 use hemx_kanban_example::ui::board_card as card_board;
 use hemx_kanban_example::ui::{self, board as board_ui};
 use serde::Serialize;
-use std::collections::BTreeMap;
+use std::collections::{BTreeMap, BTreeSet};
 use std::convert::Infallible;
 use std::net::SocketAddr;
 use std::sync::{Arc, Mutex};
@@ -34,6 +34,8 @@ struct SyncState {
     next_sequence: u64,
     acknowledgements: BTreeMap<CommandId, SyncAcknowledgement>,
     reconnects: BTreeMap<String, u64>,
+    fail_first_upload: bool,
+    transient_failures: BTreeSet<CommandId>,
 }
 
 #[derive(Clone, Debug, Eq, Ord, PartialEq, PartialOrd)]
@@ -68,6 +70,7 @@ struct SyncAcknowledgement {
 enum SyncRejection {
     BadRequest(&'static str),
     Conflict(&'static str),
+    Transient,
 }
 
 impl IntoResponse for SyncRejection {
@@ -75,6 +78,7 @@ impl IntoResponse for SyncRejection {
         let (status, error) = match self {
             Self::BadRequest(error) => (StatusCode::BAD_REQUEST, error),
             Self::Conflict(error) => (StatusCode::CONFLICT, error),
+            Self::Transient => (StatusCode::SERVICE_UNAVAILABLE, "transient sync failure"),
         };
         (status, Json(serde_json::json!({ "error": error }))).into_response()
     }
@@ -99,6 +103,11 @@ struct AppShell {
     body: Html,
 }
 
+#[derive(Hemplate)]
+struct SyncShell {
+    runtime_src: &'static str,
+}
+
 #[derive(Hemplate)]
 #[hemplate = "partials"]
 struct BoardColumns {
@@ -171,6 +180,7 @@ async fn main() {
         }),
         sync: Mutex::new(SyncState {
             next_sequence: 1,
+            fail_first_upload: std::env::var_os("HEMX_KANBAN_FAIL_FIRST_SYNC").is_some(),
             ..SyncState::default()
         }),
     });
@@ -178,6 +188,8 @@ async fn main() {
     let app = Router::new()
         .route("/", get(home).post(interact))
         .route("/events", get(events))
+        .route("/sync-demo", get(sync_demo))
+        .route("/sync.js", get(sync_js))
         .route("/sync/commands", post(sync_command))
         .route("/sync/acknowledgements", get(sync_acknowledgements))
         .route(runtime_js_path(), get(runtime))
@@ -204,6 +216,24 @@ async fn runtime() -> impl IntoResponse {
     runtime_js()
 }
 
+async fn sync_demo() -> impl IntoResponse {
+    PageResponse::full(
+        ui::page(&SyncShell {
+            runtime_src: runtime_js_path(),
+        })
+        .into_string(),
+    )
+    .title("hemx Kanban sync")
+    .fingerprint(ui::BUILD_FINGERPRINT)
+}
+
+async fn sync_js() -> impl IntoResponse {
+    (
+        [("content-type", "text/javascript; charset=utf-8")],
+        include_str!("../static/sync.js"),
+    )
+}
+
 async fn interact(
     State(state): State<Arc<AppState>>,
     request: InteractionRequest,
@@ -254,6 +284,9 @@ async fn sync_command(
         }
         return Ok(Json(existing.clone()));
     }
+    if sync.fail_first_upload && sync.transient_failures.insert(command_id.clone()) {
+        return Err(SyncRejection::Transient);
+    }
 
     let mut board = state.board.lock().unwrap();
     let card = board