feat(firmware): implement OTA download, ECDSA verify, and flash

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

firmware/lib/ota_updater/ota_updater.cpp

@@ -49,6 +49,14 @@ bool ota_verify_signature_with_key(const uint8_t hash32[32], const uint8_t sig64
 // ── device-only code ───────────────────────────────────────────────────────
 #ifndef NATIVE_TEST
 
+#include <Arduino.h>
+#include <HTTPClient.h>
+#include <WiFi.h>
+#include <ArduinoJson.h>
+#include <esp_ota_ops.h>
+#include <mbedtls/sha256.h>
+#include <mbedtls/base64.h>
+#include "hmac.h"
 #include "ota_pubkey.h"
 #include "version.h"
 
@@ -71,6 +79,148 @@ void ota_updater_init(const char* server_base, const char* device_id,
     s_last_check_ms = 0; // force first check on next call
 }
 
-bool ota_updater_check_and_apply() { return false; } // filled in Task 8
+static void add_hmac_headers(HTTPClient& http, const char* method, const char* path) {
+    uint32_t ts = (uint32_t)(esp_timer_get_time() / 1000000ULL);
+    String sig = hmac_sign(s_hmac_secret, method, path, ts, "");
+    if (sig.isEmpty()) {
+        log_e("[OTA] HMAC sign failed");
+        return;
+    }
+    http.addHeader("X-Device-Id",      s_device_id);
+    http.addHeader("X-Timestamp",      String(ts));
+    http.addHeader("X-HMAC-Signature", sig);
+}
+
+static bool download_and_flash(const char* fw_url, size_t expected_size,
+                                const uint8_t sig64[64]) {
+    const esp_partition_t* target = esp_ota_get_next_update_partition(nullptr);
+    if (!target) {
+        log_e("[OTA] No update partition found");
+        return false;
+    }
+
+    esp_ota_handle_t handle;
+    if (esp_ota_begin(target, OTA_WITH_SEQUENTIAL_WRITES, &handle) != ESP_OK) {
+        log_e("[OTA] esp_ota_begin failed");
+        return false;
+    }
+
+    mbedtls_sha256_context sha_ctx;
+    mbedtls_sha256_init(&sha_ctx);
+    mbedtls_sha256_starts(&sha_ctx, 0);  // 0 = SHA-256
+
+    HTTPClient http;
+    http.begin(fw_url);
+    add_hmac_headers(http, "GET", "/ota/firmware");
+    int code = http.GET();
+    if (code != HTTP_CODE_OK) {
+        log_e("[OTA] Firmware fetch failed: HTTP %d", code);
+        http.end();
+        mbedtls_sha256_free(&sha_ctx);
+        esp_ota_abort(handle);
+        return false;
+    }
+
+    WiFiClient* stream = http.getStreamPtr();
+    uint8_t buf[4096];
+    size_t  written = 0;
+
+    while (written < expected_size) {
+        size_t want = min((size_t)sizeof(buf), expected_size - written);
+        int got = stream->readBytes(buf, want);
+        if (got <= 0) break;
+        esp_ota_write(handle, buf, (size_t)got);
+        mbedtls_sha256_update(&sha_ctx, buf, (size_t)got);
+        written += (size_t)got;
+    }
+    http.end();
+
+    uint8_t hash[32];
+    mbedtls_sha256_finish(&sha_ctx, hash);
+    mbedtls_sha256_free(&sha_ctx);
+
+    if (written != expected_size) {
+        log_e("[OTA] Download truncated (%zu/%zu bytes)", written, expected_size);
+        esp_ota_abort(handle);
+        return false;
+    }
+
+    if (!ota_verify_signature_with_key(hash, sig64, kOtaPublicKey)) {
+        log_e("[OTA] SIGNATURE INVALID — staying on current firmware");
+        esp_ota_abort(handle);
+        return false;
+    }
+
+    if (esp_ota_end(handle) != ESP_OK ||
+        esp_ota_set_boot_partition(target) != ESP_OK) {
+        log_e("[OTA] Commit failed");
+        return false;
+    }
+
+    log_i("[OTA] Firmware verified and committed — rebooting");
+    esp_restart();
+    return true;  // unreachable
+}
+
+bool ota_updater_check_and_apply() {
+    if (!s_server_base || !s_device_id || !s_hmac_secret) return false;
+    if (s_last_check_ms != 0 &&
+        (uint32_t)(millis() - s_last_check_ms) < s_interval_ms) {
+        return false;
+    }
+    s_last_check_ms = millis();
+
+    char check_path[128];
+    snprintf(check_path, sizeof(check_path), "/ota/check?version=%s", FW_VERSION);
+    char check_url[256];
+    snprintf(check_url, sizeof(check_url), "%s%s", s_server_base, check_path);
+
+    HTTPClient http;
+    http.begin(check_url);
+    add_hmac_headers(http, "GET", check_path);
+    int code = http.GET();
+    if (code != HTTP_CODE_OK) {
+        log_w("[OTA] Check failed: HTTP %d", code);
+        http.end();
+        return false;
+    }
+
+    JsonDocument doc;
+    DeserializationError err = deserializeJson(doc, http.getStream());
+    http.end();
+    if (err) {
+        log_w("[OTA] JSON parse error: %s", err.c_str());
+        return false;
+    }
+
+    if (!doc["update"].as<bool>()) {
+        log_i("[OTA] Firmware up to date (%s)", FW_VERSION);
+        return false;
+    }
+
+    const char* remote_ver = doc["version"] | "";
+    size_t      fw_size    = doc["size"]    | 0;
+    const char* sig_b64    = doc["sig_b64"] | "";
+
+    if (fw_size == 0 || strlen(sig_b64) == 0) {
+        log_e("[OTA] Invalid update manifest");
+        return false;
+    }
+
+    log_i("[OTA] Update: %s → %s (%zu bytes)", FW_VERSION, remote_ver, fw_size);
+
+    uint8_t sig64[64];
+    size_t  sig_len = 0;
+    if (mbedtls_base64_decode(sig64, sizeof(sig64), &sig_len,
+                              (const uint8_t*)sig_b64, strlen(sig_b64)) != 0 ||
+        sig_len != 64) {
+        log_e("[OTA] Bad signature encoding (len=%zu)", sig_len);
+        return false;
+    }
+
+    char fw_url[256];
+    snprintf(fw_url, sizeof(fw_url), "%s/ota/firmware", s_server_base);
+    return download_and_flash(fw_url, fw_size, sig64);
+}
 
 #endif // NATIVE_TEST