feature: 백엔드 api 정의 및 프론트엔드 엔드포인트 전환

backend/Cargo.toml

@@ -10,6 +10,7 @@ path = "src/main.rs"
 [dependencies]
 # Web server
 axum = "0.7"
+tower-http = { version = "0.5", features = ["cors"] }
 
 # Solana
 solana-client = "1.18"
@@ -41,3 +42,5 @@ solana-account-decoder = "1.18"
 sha2      = "0.10"
 bincode   = "1"
 base64    = "0.22"
+tokio-stream = { version = "0.1", features = ["sync"] }
+futures-util = "0.3"

backend/src/cache.rs

@@ -0,0 +1,120 @@
+use std::{collections::HashMap, sync::Arc};
+
+use anyhow::Result;
+use tokio::{
+    sync::{broadcast, RwLock},
+    time::{sleep, Duration},
+};
+
+use crate::{
+    config::Config,
+    oracle::program_accounts::{scan_flight_policies, scan_master_policies},
+    solana::client::SolanaClient,
+};
+
+/// 단일 SSE 메시지 (event 타입 + JSON data)
+#[derive(Clone, Debug)]
+pub struct SseMessage {
+    pub event: String,
+    pub data: String,
+}
+
+/// 앱 전체에서 공유하는 캐시 + 브로드캐스트 채널
+pub struct CacheState {
+    pub master_policies: RwLock<Vec<crate::oracle::program_accounts::MasterPolicyInfo>>,
+    pub flight_policies: RwLock<Vec<crate::oracle::program_accounts::FlightPolicyInfo>>,
+    pub event_tx: broadcast::Sender<SseMessage>,
+}
+
+impl CacheState {
+    pub fn new() -> Self {
+        let (event_tx, _) = broadcast::channel(256);
+        Self {
+            master_policies: RwLock::new(Vec::new()),
+            flight_policies: RwLock::new(Vec::new()),
+            event_tx,
+        }
+    }
+}
+
+/// 백그라운드 캐시 갱신 루프.
+/// CACHE_POLL_INTERVAL_SEC (기본 5초)마다 Solana RPC 스캔 후
+/// 상태 변경 감지 시 SSE 브로드캐스트.
+pub async fn start(config: Arc<Config>, cache: Arc<CacheState>) -> Result<()> {
+    let poll_secs: u64 = std::env::var("CACHE_POLL_INTERVAL_SEC")
+        .ok()
+        .and_then(|v| v.parse().ok())
+        .unwrap_or(5);
+    let heartbeat_secs: u64 = std::env::var("SSE_HEARTBEAT_INTERVAL_SEC")
+        .ok()
+        .and_then(|v| v.parse().ok())
+        .unwrap_or(30);
+
+    let mut last_heartbeat = std::time::Instant::now();
+
+    loop {
+        let client = SolanaClient::new(&config.rpc_url);
+
+        // ── MasterPolicy 스캔 ──────────────────────────────────────────
+        match scan_master_policies(&client, &config.program_id) {
+            Ok(new_masters) => {
+                let mut guard = cache.master_policies.write().await;
+                // 이전 상태 맵: pubkey → status
+                let prev: HashMap<String, u8> =
+                    guard.iter().map(|m| (m.pubkey.clone(), m.status)).collect();
+
+                for m in &new_masters {
+                    let changed = prev.get(&m.pubkey).map(|&s| s != m.status).unwrap_or(true);
+                    if changed {
+                        if let Ok(data) = serde_json::to_string(m) {
+                            let _ = cache.event_tx.send(SseMessage {
+                                event: "master_policy_updated".to_string(),
+                                data,
+                            });
+                        }
+                    }
+                }
+                *guard = new_masters;
+            }
+            Err(e) => tracing::warn!("[cache] MasterPolicy 스캔 실패: {e}"),
+        }
+
+        // ── FlightPolicy 스캔 ─────────────────────────────────────────
+        match scan_flight_policies(&client, &config.program_id) {
+            Ok(new_flights) => {
+                let mut guard = cache.flight_policies.write().await;
+                let prev: HashMap<String, u8> =
+                    guard.iter().map(|f| (f.pubkey.clone(), f.status)).collect();
+
+                for f in &new_flights {
+                    let changed = prev.get(&f.pubkey).map(|&s| s != f.status).unwrap_or(true);
+                    if changed {
+                        if let Ok(data) = serde_json::to_string(f) {
+                            let _ = cache.event_tx.send(SseMessage {
+                                event: "flight_policy_updated".to_string(),
+                                data,
+                            });
+                        }
+                    }
+                }
+                *guard = new_flights;
+            }
+            Err(e) => tracing::warn!("[cache] FlightPolicy 스캔 실패: {e}"),
+        }
+
+        // ── Heartbeat ─────────────────────────────────────────────────
+        if last_heartbeat.elapsed().as_secs() >= heartbeat_secs {
+            let ts = std::time::SystemTime::now()
+                .duration_since(std::time::UNIX_EPOCH)
+                .unwrap_or_default()
+                .as_secs();
+            let _ = cache.event_tx.send(SseMessage {
+                event: "heartbeat".to_string(),
+                data: format!(r#"{{"ts":{ts}}}"#),
+            });
+            last_heartbeat = std::time::Instant::now();
+        }
+
+        sleep(Duration::from_secs(poll_secs)).await;
+    }
+}