Replace SSE price stream with WebSocket, use separate Docker port

- Replace SSE endpoint (/api/price/stream) with WebSocket (/api/price/ws)
  using ring-undertow-adapter's built-in WebSocket support
- Change Docker internal port from 4100 to 4101 to avoid conflicts with
  local dev (make run still uses 4100)
- Add free-port.sh utility script

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -1,6 +1,6 @@
 # btcdata
 
-Bitcoin data backend — Clojure Kit application. Fetches BTC prices from Binance WebSocket and Kraken HTTP, stores in PostgreSQL, exposes a JSON API with SSE price stream.
+Bitcoin data backend — Clojure Kit application. Fetches BTC prices from Binance WebSocket and Kraken HTTP, stores in PostgreSQL, exposes a JSON API with WebSocket price stream.
 
 ## Build & Development Commands
 
@@ -44,7 +44,7 @@ Docker runs alongside local dev on different ports and databases:
 ## API Endpoints
 
 - `GET /api/health` — Health check
-- `GET /api/price/stream` — SSE stream with JSON price updates
+- `GET /api/price/ws` — WebSocket endpoint for live JSON price updates
 - `GET /api/price/latest` — Latest price as JSON
 
 ## Source Layout
@@ -67,6 +67,6 @@ src/clj/pmagnus/btcdata/
     │   ├── exception.clj # Exception handling
     │   └── formats.clj   # Content negotiation
     └── routes/
-        ├── api.clj       # /api routes (JSON + SSE)
+        ├── api.clj       # /api routes (JSON + WebSocket)
         └── utils.clj     # Route utilities
 ```

Dockerfile

@@ -10,8 +10,8 @@ FROM eclipse-temurin:21-jre-alpine
 
 COPY --from=build /build/target/btcdata-standalone.jar /btcdata/btcdata-standalone.jar
 
-EXPOSE 4100
+EXPOSE 4101
-ENV BTCDATA_PORT=4100
+ENV BTCDATA_PORT=4101
 ENV CORS_ORIGIN=http://localhost:4000
 ENV JDBC_URL=jdbc:postgresql://postgres:5432/btcprod
 

docker-compose.yml

@@ -3,9 +3,9 @@ services:
     build: .
     restart: unless-stopped
     ports:
-      - "4101:4100"
+      - "4101:4101"
     environment:
-      BTCDATA_PORT: "4100"
+      BTCDATA_PORT: "4101"
       JDBC_URL: "jdbc:postgresql://postgres:5432/btcprod?user=postgres&password=ratata,123"
       CORS_ORIGIN: "http://localhost:4041"
     extra_hosts:

free-port.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+# Free port 4100 by stopping Docker containers and killing local processes
+PORT=4100
+
+# Stop Docker containers bound to the port
+for cid in $(docker ps -q --filter "publish=$PORT" 2>/dev/null); do
+  name=$(docker inspect --format '{{.Name}}' "$cid" | sed 's|^/||')
+  echo "Stopping Docker container: $name ($cid)"
+  docker stop "$cid"
+done
+
+# Kill any local processes on the port
+if command -v fuser &>/dev/null; then
+  fuser -k "$PORT/tcp" 2>/dev/null && echo "Killed local process on port $PORT"
+fi
+
+# Verify
+sleep 1
+if ss -tlnp sport = :"$PORT" 2>/dev/null | grep -q "$PORT"; then
+  echo "WARNING: port $PORT still in use"
+  ss -tlnp sport = :"$PORT"
+  exit 1
+else
+  echo "Port $PORT is free"
+fi

src/clj/pmagnus/btcdata/web/routes/api.clj

@@ -1,7 +1,6 @@
 (ns pmagnus.btcdata.web.routes.api
   (:require
    [clojure.data.json :as json]
-   [clojure.string :as str]
    [integrant.core :as ig]
    [pmagnus.btcdata.web.controllers.health :as health]
    [pmagnus.btcdata.web.middleware.exception :as exception]
@@ -10,67 +9,45 @@
    [reitit.ring.coercion :as coercion]
    [reitit.ring.middleware.muuntaja :as muuntaja]
    [reitit.ring.middleware.parameters :as parameters]
-   [reitit.swagger :as swagger])
+   [reitit.swagger :as swagger]
+   [ring.adapter.undertow.websocket :as ws])
   (:import
    [io.undertow.server HttpServerExchange]
-   [io.undertow.util HttpString]
+   [io.undertow.websockets.core WebSockets WebSocketChannel]
-   [java.io BufferedWriter OutputStreamWriter]
    [java.util.concurrent LinkedBlockingQueue TimeUnit]))
 
-(defn- format-sse [event data]
-  (str "event: " event "\n"
-       (str/join "\n" (map #(str "data: " %) (str/split-lines data)))
-       "\n\n"))
-
 (defn- price->json [{:keys [price prev-price recorded-at]}]
   (json/write-str
    {:price       (str price)
     :prev_price  (when prev-price (str prev-price))
     :recorded_at (str recorded-at)}))
 
-(defn- run-sse-loop! [^HttpServerExchange exchange price-atom cors-origin]
+(defn- ws-price-handler [{:keys [binance]} req]
-  (let [headers (.getResponseHeaders exchange)]
-    (.setStatusCode exchange 200)
-    (.put headers (HttpString. "Content-Type") "text/event-stream")
-    (.put headers (HttpString. "Cache-Control") "no-cache")
-    (.put headers (HttpString. "X-Accel-Buffering") "no")
-    (.put headers (HttpString. "Access-Control-Allow-Origin") cors-origin)
-    (when-not (.isBlocking exchange)
-      (.startBlocking exchange))
-    (let [out    (.getOutputStream exchange)
-          writer (BufferedWriter. (OutputStreamWriter. out "UTF-8"))
-          queue  (LinkedBlockingQueue.)
-          wkey   (keyword (gensym "sse-"))]
-      (add-watch price-atom wkey
-        (fn [_ _ _ v] (.offer queue v)))
-      (when-let [v @price-atom]
-        (.offer queue v))
-      (try
-        (loop []
-          (if-let [v (.poll queue 15 TimeUnit/SECONDS)]
-            (do (.write writer (format-sse "price-update" (price->json v)))
-                (.flush writer))
-            (do (.write writer ": heartbeat\n\n")
-                (.flush writer)))
-          (recur))
-        (catch Exception _)
-        (finally
-          (remove-watch price-atom wkey)
-          (try (.close writer) (catch Exception _))
-          (when-not (.isComplete exchange)
-            (.endExchange exchange)))))))
-
-(defn- price-stream-handler [{:keys [binance]} req]
   (let [^HttpServerExchange exchange (:server-exchange req)
-        price-atom  (:latest-price binance)
+        price-atom (:latest-price binance)]
-        cors-origin (or (System/getenv "CORS_ORIGIN") "*")]
+    (ws/ws-request exchange nil
-    ;; Dispatch to a worker thread so the Ring adapter never processes
+      (ws/ws-callback
-    ;; the return value — Undertow handles the exchange lifecycle directly.
+        {:on-open
-    (.dispatch exchange
+         (fn [{:keys [^WebSocketChannel channel]}]
-      (reify io.undertow.server.HttpHandler
+           (let [queue (LinkedBlockingQueue.)
-        (handleRequest [_ ex]
+                 wkey  (keyword (gensym "ws-"))]
-          (run-sse-loop! ex price-atom cors-origin))))
+             (add-watch price-atom wkey
-    ;; Return nil; exchange is dispatched so adapter won't touch it.
+               (fn [_ _ _ v] (.offer queue v)))
+             (when-let [v @price-atom]
+               (.offer queue v))
+             (future
+               (try
+                 (loop []
+                   (when (.isOpen channel)
+                     (if-let [v (.poll queue 15 TimeUnit/SECONDS)]
+                       (WebSockets/sendTextBlocking (price->json v) channel)
+                       (WebSockets/sendTextBlocking "{\"ping\":true}" channel))
+                     (recur)))
+                 (catch Exception _)
+                 (finally
+                   (remove-watch price-atom wkey)
+                   (when (.isOpen channel)
+                     (try (.close channel) (catch Exception _))))))))}))
     nil))
 
 (defn- latest-price-handler [{:keys [binance]} _req]
@@ -91,8 +68,8 @@
            :handler (swagger/create-swagger-handler)}}]
    ["/health"
     {:get health/healthcheck!}]
-   ["/price/stream"
+   ["/price/ws"
-    {:get        (fn [req] (price-stream-handler opts req))
+    {:get        (fn [req] (ws-price-handler opts req))
      :no-doc     true
      :middleware []}]
    ["/price/latest"