Move os and arch detection to downloader, add checksum verification.

packages/safe-chain/src/installation/downloadAgent.js

@@ -1,9 +1,25 @@
-import { createWriteStream } from "fs";
+import { createWriteStream, createReadStream } from "fs";
+import { createHash } from "crypto";
 import { pipeline } from "stream/promises";
 import fetch from "make-fetch-happen";
 
 const ULTIMATE_VERSION = "v0.2.0";
 
+const DOWNLOAD_URLS = {
+  win32: {
+    x64: {
+      url: "https://github.com/AikidoSec/safechain-internals/releases/download/v0.2.0/SafeChainAgent-windows-amd64.msi",
+      checksum:
+        "sha256:c699f74a3666d85b70b8ede076a2192a6a023f1b395e8e6c7556927ee698a020",
+    },
+    arm64: {
+      url: "https://github.com/AikidoSec/safechain-internals/releases/download/v0.2.0/SafeChainAgent-windows-arm64.msi",
+      checksum:
+        "sha256:5b08dd4749c8befe5379bc01f7a8a5ac1d6a35b6bee37c6c72a4ba8744c3b052",
+    },
+  },
+};
+
 /**
  * Builds the download URL for the SafeChain Agent installer.
  * @param {string} fileName
@@ -31,3 +47,67 @@ export async function downloadFile(url, destPath) {
 export function getAgentVersion() {
   return ULTIMATE_VERSION;
 }
+
+/**
+ * Returns download info (url, checksum) for the current OS and architecture.
+ * @returns {{ url: string, checksum: string } | null}
+ */
+export function getDownloadInfoForCurrentPlatform() {
+  const platform = process.platform;
+  const arch = process.arch;
+
+  if (!Object.hasOwn(DOWNLOAD_URLS, platform)) {
+    return null;
+  }
+  const platformUrls =
+    DOWNLOAD_URLS[/** @type {keyof typeof DOWNLOAD_URLS} */ (platform)];
+
+  if (!Object.hasOwn(platformUrls, arch)) {
+    return null;
+  }
+
+  return platformUrls[/** @type {keyof typeof platformUrls} */ (arch)];
+}
+
+/**
+ * Verifies the checksum of a file.
+ * @param {string} filePath
+ * @param {string} expectedChecksum - Format: "algorithm:hash" (e.g., "sha256:abc123...")
+ * @returns {Promise<boolean>}
+ */
+async function verifyChecksum(filePath, expectedChecksum) {
+  const [algorithm, expected] = expectedChecksum.split(":");
+
+  const hash = createHash(algorithm);
+
+  if (filePath.includes("..")) throw new Error("Invalid file path");
+  const stream = createReadStream(filePath);
+
+  for await (const chunk of stream) {
+    hash.update(chunk);
+  }
+
+  const actual = hash.digest("hex");
+  return actual === expected;
+}
+
+/**
+ * Downloads the SafeChain agent for the current OS/arch and verifies its checksum.
+ * @param {string} fileName - Destination file path
+ * @returns {Promise<string | null>} The file path if successful, null if no download URL for current platform
+ */
+export async function downloadAgentToFile(fileName) {
+  const info = getDownloadInfoForCurrentPlatform();
+  if (!info) {
+    return null;
+  }
+
+  await downloadFile(info.url, fileName);
+
+  const isValid = await verifyChecksum(fileName, info.checksum);
+  if (!isValid) {
+    throw new Error("Checksum verification failed");
+  }
+
+  return fileName;
+}