From 9ab37d15fdb2b3a8efbf29da42de8872c2feb0ee Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Stanis=C5=82aw=20Chmiela?= <sjchmiela@gmail.com>
Date: Wed, 28 Jan 2026 21:59:54 +0100
Subject: [PATCH] Add support for cuttlefish config

---
 .../steps/functions/startCuttlefishDevice.ts  | 55 +++++++++++++++++--
 1 file changed, 51 insertions(+), 4 deletions(-)

diff --git a/packages/build-tools/src/steps/functions/startCuttlefishDevice.ts b/packages/build-tools/src/steps/functions/startCuttlefishDevice.ts
index 95d62c08..db454c13 100644
--- a/packages/build-tools/src/steps/functions/startCuttlefishDevice.ts
+++ b/packages/build-tools/src/steps/functions/startCuttlefishDevice.ts
@@ -1,9 +1,42 @@
+import fs from 'node:fs';
+import os from 'node:os';
+import path from 'node:path';
+
 import { BuildFunction, BuildStepInput, BuildStepInputValueTypeName } from '@expo/steps';
 import spawn from '@expo/turtle-spawn';
 import { asyncResult } from '@expo/results';
 
 import { sleepAsync } from '../../utils/retry';
 
+// Needs to conform to https://github.com/google/android-cuttlefish/blob/928026d2833b3e326d9d3b4a9a477e522b37b825/base/cvd/cuttlefish/host/commands/cvd/cli/parser/load_config.proto#L29-L36.
+// See example: https://github.com/google/android-cuttlefish/blob/928026d2833b3e326d9d3b4a9a477e522b37b825/base/cvd/cuttlefish/host/cvd_test_configs/main_phone.json
+const CVD_CONFIG_JSON = {
+  common: {
+    host_package: '@ab/aosp-android-latest-release/aosp_cf_x86_64_only_phone-userdebug',
+  },
+  instances: [
+    {
+      '@import': 'phone',
+      graphics: {
+        displays: [
+          // Pixel 5
+          {
+            dpi: 432,
+            height: 2340,
+            width: 1080,
+          },
+        ],
+      },
+      vm: {
+        memory_mb: 4096,
+      },
+      disk: {
+        default_build: '@ab/aosp-main/aosp_cf_x86_64_phone-trunk_staging-userdebug',
+      },
+    },
+  ],
+};
+
 export function createStartCuttlefishDeviceBuildFunction(): BuildFunction {
   return new BuildFunction({
     namespace: 'eas',
@@ -79,10 +112,24 @@ export function createStartCuttlefishDeviceBuildFunction(): BuildFunction {
       }
 
       logger.info('Creating CVD');
-      await spawn('cvdr', ['create', ...(count > 1 ? ['--num_instances', String(count)] : [])], {
-        env,
-        logger,
-      });
+
+      const args = [];
+
+      const cvdConfigJson = env.CVD_CONFIG_JSON ?? JSON.stringify(CVD_CONFIG_JSON);
+      if (cvdConfigJson) {
+        const configJsonDirectory = await fs.promises.mkdtemp(
+          path.join(os.tmpdir(), 'start_cuttlefish-')
+        );
+        const configJsonPath = path.join(configJsonDirectory, 'config.json');
+        await fs.promises.writeFile(configJsonPath, cvdConfigJson);
+        args.push(configJsonPath);
+      }
+
+      if (count > 1) {
+        args.push('--num_instances', String(count));
+      }
+
+      await spawn('cvdr', ['create', ...args], { env, logger });
 
       logger.info('Listing adb devices...');
       await spawn('adb', ['devices'], { env, logger });