feat(android): RenderingControl get/set volume

android/app/src/main/java/com/fabledsword/minstrel/player/output/upnp/RenderingControlClient.kt

@@ -0,0 +1,44 @@
+package com.fabledsword.minstrel.player.output.upnp
+
+import okhttp3.HttpUrl
+
+/**
+ * RenderingControl service wrapper for hardware-volume routing while a
+ * UPnP route is active. GetVolume seeds an in-memory cache; SetVolume
+ * is invoked by NowPlayingScreen's volume-key interceptor. Clamps to
+ * the UPnP-standard 0..100 range.
+ */
+class RenderingControlClient(
+    private val soap: SoapClient,
+    private val controlUrl: HttpUrl,
+) {
+    suspend fun getVolume(channel: String = "Master"): Int {
+        val args = soap.call(
+            controlUrl = controlUrl,
+            serviceType = SERVICE_TYPE,
+            action = "GetVolume",
+            args = mapOf("InstanceID" to "0", "Channel" to channel),
+        )
+        return args["CurrentVolume"]?.toIntOrNull() ?: 0
+    }
+
+    suspend fun setVolume(volume: Int, channel: String = "Master") {
+        val clamped = volume.coerceIn(VOLUME_MIN, VOLUME_MAX)
+        soap.call(
+            controlUrl = controlUrl,
+            serviceType = SERVICE_TYPE,
+            action = "SetVolume",
+            args = mapOf(
+                "InstanceID" to "0",
+                "Channel" to channel,
+                "DesiredVolume" to clamped.toString(),
+            ),
+        )
+    }
+
+    private companion object {
+        const val SERVICE_TYPE = "urn:schemas-upnp-org:service:RenderingControl:1"
+        const val VOLUME_MIN = 0
+        const val VOLUME_MAX = 100
+    }
+}

android/app/src/test/java/com/fabledsword/minstrel/player/output/upnp/RenderingControlClientTest.kt

@@ -0,0 +1,56 @@
+package com.fabledsword.minstrel.player.output.upnp
+
+import kotlinx.coroutines.test.runTest
+import okhttp3.OkHttpClient
+import okhttp3.mockwebserver.MockResponse
+import okhttp3.mockwebserver.MockWebServer
+import org.junit.jupiter.api.AfterEach
+import org.junit.jupiter.api.BeforeEach
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+class RenderingControlClientTest {
+
+    private lateinit var server: MockWebServer
+    private lateinit var client: RenderingControlClient
+
+    @BeforeEach
+    fun setUp() {
+        server = MockWebServer()
+        server.start()
+        client = RenderingControlClient(SoapClient(OkHttpClient()), server.url("/RC"))
+    }
+
+    @AfterEach
+    fun tearDown() { server.shutdown() }
+
+    @Test
+    fun `getVolume parses CurrentVolume`() = runTest {
+        server.enqueue(MockResponse().setBody(
+            """<?xml version="1.0"?>
+               <s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
+                 <s:Body>
+                   <u:GetVolumeResponse xmlns:u="urn:schemas-upnp-org:service:RenderingControl:1">
+                     <CurrentVolume>42</CurrentVolume>
+                   </u:GetVolumeResponse>
+                 </s:Body>
+               </s:Envelope>""".trimIndent()))
+        assertEquals(42, client.getVolume())
+    }
+
+    @Test
+    fun `setVolume clamps and sends DesiredVolume`() = runTest {
+        server.enqueue(MockResponse().setBody(
+            """<?xml version="1.0"?>
+               <s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
+                 <s:Body>
+                   <u:SetVolumeResponse
+                       xmlns:u="urn:schemas-upnp-org:service:RenderingControl:1"/>
+                 </s:Body>
+               </s:Envelope>""".trimIndent()))
+        client.setVolume(150)
+        val body = server.takeRequest().body.readUtf8()
+        assertTrue(body.contains("<DesiredVolume>100</DesiredVolume>")) { body }
+    }
+}