ai-app/app/androidApp/build.gradle.kts

plugins {
    alias(libs.plugins.androidApplication)
    alias(libs.plugins.composeMultiplatform)
    alias(libs.plugins.composeCompiler)
}

// The CA this app pins is baked in at build time from the certificates on
// the machine doing the build -- `$XDG_CONFIG_HOME/ai-app/certs/ca.pem`,
// which the server generates on first start. AI_APP_CA overrides the path.
//
// Reading it rather than keeping a pasted copy in the source is what makes
// the trust boundary follow the build: an APK built on the backend host
// pins the host's CA and never sees any other, while one built in the dev
// VM pins that VM's throwaway CA and is only good for its emulator. There
// is no second trust anchor to get wrong, and no stale paste to notice
// three days later. It also means the private key never has to exist
// anywhere near this repo.
val pinnedCaPath: String = System.getenv("AI_APP_CA")
    ?: "${System.getenv("XDG_CONFIG_HOME") ?: "${System.getProperty("user.home")}/.config"}" +
    "/ai-app/certs/ca.pem"

abstract class GeneratePinnedCert : DefaultTask() {
    /** Where the certificate is looked for, reported in failures. */
    @get:Input
    abstract val caPath: Property<String>

    /**
     * The certificate itself, set only when it exists -- so a missing one
     * produces this task's own instructions rather than Gradle's "no such
     * input file", which doesn't say what to run.
     */
    @get:InputFile
    @get:Optional
    @get:PathSensitive(PathSensitivity.NONE)
    abstract val caCertificate: RegularFileProperty

    /** Wired by AGP through `addGeneratedSourceDirectory`. */
    @get:OutputDirectory
    abstract val outputDir: DirectoryProperty

    @TaskAction
    fun generate() {
        val path = caPath.get()
        val ca = File(path)
        if (!ca.isFile) {
            throw GradleException(
                "No CA certificate at $path.\n" +
                    "Start ai-server once on this machine first -- it generates the CA the " +
                    "app pins, and the certificate has to exist before an APK can embed it.\n" +
                    "Set AI_APP_CA=/path/to/ca.pem to build against a different one.",
            )
        }
        val pem = ca.readText().trim()
        if (!pem.startsWith("-----BEGIN CERTIFICATE-----")) {
            throw GradleException("$path is not a PEM certificate.")
        }
        val file = outputDir.get().file("PinnedCaCertificate.kt").asFile
        file.parentFile.mkdirs()
        // The PEM must start immediately after the opening quotes: a
        // leading newline makes Android's CertificateFactory stop
        // recognising the "-----BEGIN" preamble and try to parse the whole
        // thing as DER, which fails with an ASN.1 decode error at runtime
        // rather than anywhere near this file.
        file.writeText(
            """
            |// Generated from $path by the generatePinnedCert task. Do not edit.
            |package com.example.aiapp
            |
            |const val PINNED_CA_PEM = ""${'"'}$pem
            |""${'"'}
            |
            """.trimMargin(),
        )
    }
}

val generatePinnedCert = tasks.register<GeneratePinnedCert>("generatePinnedCert") {
    val ca = file(pinnedCaPath)
    caPath.set(pinnedCaPath)
    if (ca.isFile) {
        caCertificate.set(ca)
    }
}

android {
    namespace = "com.example.aiapp"
    compileSdk = 37

    defaultConfig {
        applicationId = "com.example.aiapp"
        minSdk = 24
        targetSdk = 37
        versionCode = 1
        versionName = "1.0"
    }
    packaging {
        resources {
            excludes += "/META-INF/{AL2.0,LGPL2.1}"
        }
    }
    buildTypes {
        getByName("release") {
            isMinifyEnabled = false
        }
    }
    compileOptions {
        sourceCompatibility = JavaVersion.VERSION_21
        targetCompatibility = JavaVersion.VERSION_21
        // minSdk is 24 and UsageScreen formats its countdown with
        // java.time, which the platform only has from 26. Without this it
        // is a NoClassDefFoundError on 24 and 25 -- an Error, so the
        // catch around that code does not stop it.
        isCoreLibraryDesugaringEnabled = true
    }
}

// AGP 9 wants generated sources registered through the variant API rather
// than added to a source set, so the task dependency is carried properly.
androidComponents {
    onVariants { variant ->
        variant.sources.java?.addGeneratedSourceDirectory(
            generatePinnedCert,
            GeneratePinnedCert::outputDir,
        )
    }
}

dependencies {
    // Not a library this code calls: it is what `isCoreLibraryDesugaring
    // Enabled` above rewrites java.time against, so API 24 and 25 have it.
    coreLibraryDesugaring(libs.desugar.jdk.libs)

    implementation(libs.compose.runtime)
    implementation(libs.compose.foundation)
    implementation(libs.compose.material3)
    implementation(libs.compose.ui)
    implementation(libs.androidx.activity.compose)
    implementation(libs.androidx.core.ktx)
    implementation(libs.zxing.embedded)
}