net: send the subtracks user agent on every request

Only SubsonicClient tagged requests with 'subtracks/android'; playback (Media3 OkHttpDataSource), downloads (DownloadManager) and artwork (Coil/OkHttpArtworkFetcher) fell back to the OkHttp or platform default. Add a single UserAgent with the app version, apply it to the shared OkHttp client, the streaming data source factory and the DownloadManager request, and drop SubsonicClient's now-redundant header.

app/src/main/kotlin/com/subtracks/SubtracksApp.kt

@@ -14,7 +14,7 @@ import org.koin.core.context.startKoin
 import org.koin.core.context.stopKoin
 
 class SubtracksApp : Application() {
-    private val http = OkHttpClient()
+    private val http = OkHttpClient.Builder().addInterceptor(UserAgent.interceptor()).build()
 
     @OptIn(DelicateCoilApi::class)
     override fun onCreate() {

app/src/main/kotlin/com/subtracks/UserAgent.kt

@@ -0,0 +1,18 @@
+package com.subtracks
+
+import okhttp3.Interceptor
+
+object UserAgent {
+    val value: String = "subtracks/android (${BuildConfig.VERSION_NAME})"
+
+    fun interceptor(): Interceptor =
+        Interceptor { chain ->
+            chain.proceed(
+                chain
+                    .request()
+                    .newBuilder()
+                    .header("User-Agent", value)
+                    .build(),
+            )
+        }
+}

app/src/main/kotlin/com/subtracks/data/download/SystemDownloadEngine.kt

@@ -4,6 +4,7 @@ import android.app.DownloadManager
 import android.content.Context
 import android.os.Environment
 import androidx.core.net.toUri
+import com.subtracks.UserAgent
 import com.subtracks.data.model.DownloadError
 
 class SystemDownloadEngine(
@@ -16,6 +17,7 @@ class SystemDownloadEngine(
                 .setTitle(request.title)
                 .setDestinationInExternalFilesDir(context, Environment.DIRECTORY_MUSIC, request.path)
                 .setNotificationVisibility(DownloadManager.Request.VISIBILITY_HIDDEN)
+                .addRequestHeader("User-Agent", UserAgent.value)
                 // Wi-Fi only unless the preference allows a metered network, and roaming counts as
                 // one of those; the platform otherwise permits it by default.
                 .setAllowedOverMetered(request.allowMetered)

app/src/main/kotlin/com/subtracks/data/source/subsonic/SubsonicClient.kt

@@ -20,7 +20,6 @@ class SubsonicClient(
     private val password: String,
     useTokenAuth: Boolean,
     private val http: OkHttpClient,
-    private val userAgent: String = "subtracks/android",
     private val onTokenAuthUnsupported: () -> Unit = {},
 ) {
     @Volatile
@@ -76,7 +75,6 @@ class SubsonicClient(
             Request
                 .Builder()
                 .url(uri(method, params))
-                .header("User-Agent", userAgent)
                 .build()
         http.newCall(request).execute().use { response ->
             if (!response.isSuccessful) {

app/src/main/kotlin/com/subtracks/playback/PlaybackService.kt

@@ -29,6 +29,7 @@ import com.google.common.util.concurrent.Futures
 import com.google.common.util.concurrent.ListenableFuture
 import com.subtracks.MainActivity
 import com.subtracks.R
+import com.subtracks.UserAgent
 import com.subtracks.data.repo.LibraryRepository
 import com.subtracks.data.repo.SourceRepository
 import com.subtracks.data.source.StarType
@@ -104,7 +105,9 @@ class PlaybackService : MediaSessionService() {
                 .setMediaSourceFactory(
                     DefaultMediaSourceFactory(this)
                         .setEnableClippingInMediaPeriod(true)
-                        .setDataSourceFactory(mediaDataSourceFactory(this, OkHttpDataSource.Factory(streamingClient()))),
+                        .setDataSourceFactory(
+                            mediaDataSourceFactory(this, OkHttpDataSource.Factory(streamingClient()).setUserAgent(UserAgent.value)),
+                        ),
                 ).build()
         exoPlayer.addListener(
             object : Player.Listener {

app/src/test/kotlin/com/subtracks/UserAgentTest.kt

@@ -0,0 +1,24 @@
+package com.subtracks
+
+import okhttp3.OkHttpClient
+import okhttp3.Request
+import okhttp3.mockwebserver.MockResponse
+import okhttp3.mockwebserver.MockWebServer
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+class UserAgentTest {
+    @Test
+    fun addsTheSubtracksUserAgent() {
+        val server = MockWebServer()
+        server.enqueue(MockResponse())
+        server.start()
+        val client = OkHttpClient.Builder().addInterceptor(UserAgent.interceptor()).build()
+
+        client.newCall(Request.Builder().url(server.url("/")).build()).execute().close()
+        val header = server.takeRequest().getHeader("User-Agent")
+        server.shutdown()
+
+        assertEquals(UserAgent.value, header)
+    }
+}