Add an ECH sample

samples/android/README.md

@@ -0,0 +1,20 @@
+# Android ECH sample
+
+This instrumentation test makes HTTPS requests with Encrypted Client Hello (ECH). The sample keeps
+OkHttp's API 21 minimum and only enables ECH on Android 17 (API 37) or newer. The tests are skipped
+on older devices.
+
+The important pieces are:
+
+* [`EchClient.kt`](src/androidTest/kotlin/okhttp3/sample/ech/EchClient.kt), which configures OkHttp
+  with either Android's resolver or DNS over HTTPS, makes a sample request, and tests the result.
+* [`network_security_config.xml`](src/main/res/xml/network_security_config.xml), which opts the
+  sample domain into enabled ECH. Older Android versions ignore the unsupported element.
+
+Run the test from the repository root:
+
+```shell
+./gradlew :samples:android:connectedDebugAndroidTest
+```
+
+The test checks that Cloudflare reports `sni=encrypted`.

samples/android/build.gradle.kts

@@ -0,0 +1,40 @@
+@file:Suppress("UnstableApiUsage")
+
+plugins {
+  id("okhttp.base-conventions")
+  id("com.android.library")
+}
+
+android {
+  namespace = "okhttp3.sample.ech"
+
+  compileSdk {
+    version = release(37)
+  }
+
+  defaultConfig {
+    minSdk = 21
+    testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
+  }
+
+  testOptions {
+    targetSdk = 37
+  }
+
+  compileOptions {
+    sourceCompatibility = JavaVersion.VERSION_17
+    targetCompatibility = JavaVersion.VERSION_17
+  }
+
+  lint {
+    abortOnError = true
+  }
+}
+
+dependencies {
+  androidTestImplementation(projects.okhttp)
+  androidTestImplementation(projects.okhttpDnsoverhttps)
+  androidTestImplementation(libs.androidx.junit)
+  androidTestImplementation(libs.androidx.test.runner)
+  androidTestImplementation(libs.assertk)
+}

samples/android/src/androidTest/kotlin/okhttp3/sample/ech/EchClient.kt

@@ -0,0 +1,119 @@
+/*
+ * Copyright (c) 2026 OkHttp Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package okhttp3.sample.ech
+
+import android.os.Build
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import androidx.test.filters.SdkSuppress
+import assertk.assertThat
+import assertk.assertions.contains
+import assertk.assertions.isTrue
+import okhttp3.Dns
+import okhttp3.HttpUrl.Companion.toHttpUrl
+import okhttp3.OkHttpClient
+import okhttp3.Request
+import okhttp3.android.EchAwareDns
+import okhttp3.dnsoverhttps.DnsOverHttps
+import org.junit.Test
+import org.junit.runner.RunWith
+
+@RunWith(AndroidJUnit4::class)
+@SdkSuppress(minSdkVersion = 37)
+class EchClientTest {
+  @Test
+  fun androidDns() {
+    testEch(Resolver.AndroidDns)
+  }
+
+  @Test
+  fun dnsOverHttps() {
+    testEch(Resolver.DnsOverHttps)
+  }
+
+  private fun testEch(resolver: Resolver) {
+    val client = echClient(resolver)
+
+    client.newCall(ECH_CHECK_REQUEST).execute().use { response ->
+      assertThat(response.isSuccessful).isTrue()
+      assertThat(response.body.string()).contains("sni=encrypted")
+    }
+  }
+}
+
+private enum class Resolver {
+  AndroidDns,
+  DnsOverHttps,
+}
+
+private fun echClient(resolver: Resolver): OkHttpClient {
+  return OkHttpClient
+    .Builder()
+    .apply {
+      if (Build.VERSION.SDK_INT >= 37) {
+        dns(
+          when (resolver) {
+            Resolver.AndroidDns -> EchAwareDns()
+            Resolver.DnsOverHttps -> echAwareDnsOverHttps()
+          },
+        )
+      }
+    }.build()
+}
+
+private fun echAwareDnsOverHttps(): Dns {
+  val bootstrapClient = OkHttpClient()
+  val dnsUrl = "https://1.1.1.1/dns-query".toHttpUrl()
+
+  fun dns(includeServiceMetadata: Boolean): DnsOverHttps =
+    DnsOverHttps
+      .Builder()
+      .client(bootstrapClient)
+      .url(dnsUrl)
+      .includeServiceMetadata(includeServiceMetadata)
+      .build()
+
+  return EchAwareDns(
+    echDns = dns(includeServiceMetadata = true),
+    addressOnlyDns = dns(includeServiceMetadata = false),
+  )
+}
+
+/*
+DNS record: cloudflare-ech.com/104.18.10.118
+DNS record: cloudflare-ech.com/104.18.11.118
+DNS record: cloudflare-ech.com/2606:4700::6812:a76
+DNS record: cloudflare-ech.com/2606:4700::6812:b76
+DNS record: ServiceMetadata{
+  cloudflare-ech.com,
+  alpnIds=[h3, h2, http/1.1],
+  ipAddressHints=[104.18.10.118, 104.18.11.118, 2606:4700::6812:a76, 2606:4700::6812:b76],
+  echConfigList=0045fe0d0041da002000201e8ee5aa34c64a7439d45dfd1157ab774e2f70abccceef4cd24ae0998286cc760004000100010012636c6f7564666c6172652d6563682e636f6d0000
+}
+Parsed ECHConfigList:
+  config[0]:
+    version: 0xfe0d
+    contents length: 65
+    config ID: 218
+    KEM ID: 0x0020
+    public key: 1e8ee5aa34c64a7439d45dfd1157ab774e2f70abccceef4cd24ae0998286cc76
+    maximum name length: 0
+    public name: cloudflare-ech.com
+    cipher suites:
+      KDF 0x0001, AEAD 0x0001
+    extensions:
+*/
+private val ECH_CHECK_REQUEST =
+  Request("https://cloudflare-ech.com/cdn-cgi/trace".toHttpUrl())

samples/android/src/main/AndroidManifest.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+          xmlns:tools="http://schemas.android.com/tools">
+
+  <uses-permission android:name="android.permission.INTERNET" />
+
+  <application
+    android:networkSecurityConfig="@xml/network_security_config"
+    tools:targetApi="n" />
+
+</manifest>

samples/android/src/main/res/xml/network_security_config.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8"?>
+<network-security-config>
+  <base-config cleartextTrafficPermitted="false" />
+  <domain-config>
+    <domain includeSubdomains="true">cloudflare-ech.com</domain>
+    <domainEncryption mode="enabled" />
+  </domain-config>
+</network-security-config>

settings.gradle.kts

@@ -86,6 +86,7 @@ val sdkDir = localProperties.getProperty("sdk.dir")
 if (androidHome != null || sdkDir != null) {
   include(":android-test")
   include(":android-test-app")
+  include(":samples:android")
 }
 
 enableFeaturePreview("TYPESAFE_PROJECT_ACCESSORS")