Add method to get cover art.

As this call should return byte stream: I've introduced helper method
in client to do the actual call and parse possible json error response.

Signed-off-by: Yahor Berdnikau <egorr.berd@gmail.com>

subsonic-api/src/integrationTest/kotlin/org/moire/ultrasonic/api/subsonic/CommonFunctions.kt

@@ -25,11 +25,12 @@ val dateFormat by lazy(LazyThreadSafetyMode.NONE, {
 
 fun MockWebServerRule.enqueueResponse(resourceName: String) {
     this.mockWebServer.enqueue(MockResponse()
-            .setBody(loadJsonResponse(this, resourceName)))
+            .setBody(loadJsonResponse(resourceName))
+            .setHeader("Content-Type", "application/json;charset=UTF-8"))
 }
 
-private fun loadJsonResponse(rule: MockWebServerRule, name: String): String {
-    val source = Okio.buffer(Okio.source(rule.javaClass.classLoader.getResourceAsStream(name)))
+fun MockWebServerRule.loadJsonResponse(name: String): String {
+    val source = Okio.buffer(Okio.source(javaClass.classLoader.getResourceAsStream(name)))
     return source.readString(Charset.forName("UTF-8"))
 }
 
@@ -67,7 +68,7 @@ fun SubsonicResponse.assertBaseResponseOk() {
 
 fun MockWebServerRule.assertRequestParam(responseResourceName: String,
                                          expectedParam: String,
-                                         apiRequest: () -> Response<out SubsonicResponse>) {
+                                         apiRequest: () -> Response<out Any>) {
     this.enqueueResponse(responseResourceName)
     apiRequest()
 

subsonic-api/src/integrationTest/kotlin/org/moire/ultrasonic/api/subsonic/SubsonicApiGetCoverArtTest.kt

@@ -0,0 +1,74 @@
+package org.moire.ultrasonic.api.subsonic
+
+import okhttp3.mockwebserver.MockResponse
+import org.amshove.kluent.`should be`
+import org.amshove.kluent.`should equal to`
+import org.amshove.kluent.`should equal`
+import org.amshove.kluent.`should not be`
+import org.junit.Test
+
+/**
+ * Integration test for [SubsonicAPIClient] for [SubsonicAPIDefinition.getCoverArt] call.
+ */
+class SubsonicApiGetCoverArtTest : SubsonicAPIClientTest() {
+    @Test
+    fun `Should handle api error response`() {
+        mockWebServerRule.enqueueResponse("generic_error_response.json")
+
+        val response = client.getCoverArt("some-id")
+
+        with(response) {
+            stream `should be` null
+            requestErrorCode `should be` null
+            apiError `should equal` SubsonicError.GENERIC
+        }
+    }
+
+    @Test
+    fun `Should handle server error`() {
+        val httpErrorCode = 404
+        mockWebServerRule.mockWebServer.enqueue(MockResponse().setResponseCode(httpErrorCode))
+
+        val response = client.getCoverArt("some-id")
+
+        with(response) {
+            stream `should be` null
+            requestErrorCode `should equal` 404
+            apiError `should be` null
+        }
+    }
+
+    @Test
+    fun `Should return successful call stream`() {
+        mockWebServerRule.mockWebServer.enqueue(MockResponse()
+                .setBody(mockWebServerRule.loadJsonResponse("ping_ok.json")))
+
+        val response = client.getCoverArt("some-id")
+
+        with(response) {
+            requestErrorCode `should be` null
+            apiError `should be` null
+            stream `should not be` null
+            val expectedContent = mockWebServerRule.loadJsonResponse("ping_ok.json")
+            stream!!.bufferedReader().readText() `should equal to` expectedContent
+        }
+    }
+
+    @Test
+    fun `Should pass id as parameter`() {
+        val id = "ca123994"
+
+        mockWebServerRule.assertRequestParam("ping_ok.json", id) {
+            client.api.getCoverArt(id).execute()
+        }
+    }
+
+    @Test
+    fun `Should pass size as a parameter`() {
+        val size = 45600L
+
+        mockWebServerRule.assertRequestParam("ping_ok.json", size.toString()) {
+            client.api.getCoverArt("some-id", size).execute()
+        }
+    }
+}

subsonic-api/src/main/kotlin/org/moire/ultrasonic/api/subsonic/SubsonicAPIClient.kt

@@ -3,9 +3,14 @@ package org.moire.ultrasonic.api.subsonic
 import com.fasterxml.jackson.databind.DeserializationFeature
 import com.fasterxml.jackson.databind.ObjectMapper
 import com.fasterxml.jackson.module.kotlin.KotlinModule
+import com.fasterxml.jackson.module.kotlin.readValue
 import okhttp3.HttpUrl
 import okhttp3.OkHttpClient
+import okhttp3.ResponseBody
 import okhttp3.logging.HttpLoggingInterceptor
+import org.moire.ultrasonic.api.subsonic.response.StreamResponse
+import org.moire.ultrasonic.api.subsonic.response.SubsonicResponse
+import retrofit2.Response
 import retrofit2.Retrofit
 import retrofit2.converter.jackson.JacksonConverterFactory
 import java.lang.IllegalStateException
@@ -65,6 +70,35 @@ class SubsonicAPIClient(baseUrl: String,
 
     val api: SubsonicAPIDefinition = retrofit.create(SubsonicAPIDefinition::class.java)
 
+    /**
+     * Convenient method to get cover art from api using item [id] and optional maximum [size].
+     *
+     * It detects the response `Content-Type` and tries to parse subsonic error if there is one.
+     *
+     * Prefer this method over [SubsonicAPIDefinition.getCoverArt] as this handles error cases.
+     */
+    fun getCoverArt(id: String, size: Long? = null): StreamResponse = handleStreamResponse {
+        api.getCoverArt(id, size).execute()
+    }
+
+    private inline fun handleStreamResponse(apiCall: () -> Response<ResponseBody>): StreamResponse {
+        val response = apiCall()
+        return if (response.isSuccessful) {
+            val responseBody = response.body()
+            val contentType = responseBody.contentType()
+            if (contentType != null &&
+                    contentType.type().equals("application", true) &&
+                    contentType.subtype().equals("json", true)) {
+                val error = jacksonMapper.readValue<SubsonicResponse>(responseBody.byteStream())
+                StreamResponse(apiError = error.error)
+            } else {
+                StreamResponse(stream = responseBody.byteStream())
+            }
+        } else {
+            StreamResponse(requestErrorCode = response.code())
+        }
+    }
+
     private val salt: String by lazy {
         val secureRandom = SecureRandom()
         BigInteger(130, secureRandom).toString(32)

subsonic-api/src/main/kotlin/org/moire/ultrasonic/api/subsonic/SubsonicAPIDefinition.kt

@@ -1,5 +1,6 @@
 package org.moire.ultrasonic.api.subsonic
 
+import okhttp3.ResponseBody
 import org.moire.ultrasonic.api.subsonic.models.AlbumListType
 import org.moire.ultrasonic.api.subsonic.response.GetAlbumList2Response
 import org.moire.ultrasonic.api.subsonic.response.GetAlbumListResponse
@@ -24,6 +25,7 @@ import org.moire.ultrasonic.api.subsonic.response.SubsonicResponse
 import retrofit2.Call
 import retrofit2.http.GET
 import retrofit2.http.Query
+import retrofit2.http.Streaming
 
 /**
  * Subsonic API calls.
@@ -160,4 +162,9 @@ interface SubsonicAPIDefinition {
 
     @GET("getStarred2.view")
     fun getStarred2(@Query("musicFolderId") musicFolderId: Long? = null): Call<GetStarredTwoResponse>
+
+    @Streaming
+    @GET("getCoverArt.view")
+    fun getCoverArt(@Query("id") id: String,
+                    @Query("size") size: Long? = null): Call<ResponseBody>
 }

subsonic-api/src/main/kotlin/org/moire/ultrasonic/api/subsonic/response/StreamResponse.kt

@@ -0,0 +1,19 @@
+package org.moire.ultrasonic.api.subsonic.response
+
+import org.moire.ultrasonic.api.subsonic.SubsonicError
+import java.io.InputStream
+
+/**
+ * Special response that contains either [stream] of data from api, or [apiError],
+ * or [requestErrorCode].
+ *
+ * [requestErrorCode] will be only if there problem on http level.
+ */
+class StreamResponse(val stream: InputStream? = null,
+                     val apiError: SubsonicError? = null,
+                     val requestErrorCode: Int? = null) {
+    /**
+     * Check if this response has error.
+     */
+    fun hasError(): Boolean = apiError != null || requestErrorCode != null
+}

subsonic-api/src/test/kotlin/org/moire/ultrasonic/api/subsonic/response/StreamResponseTest.kt

@@ -0,0 +1,25 @@
+package org.moire.ultrasonic.api.subsonic.response
+
+import org.amshove.kluent.`should equal to`
+import org.junit.Test
+import org.moire.ultrasonic.api.subsonic.SubsonicError.GENERIC
+
+/**
+ * Unit test for [StreamResponse].
+ */
+class StreamResponseTest {
+    @Test
+    fun `Should have error if subsonic error is not null`() {
+        StreamResponse(apiError = GENERIC).hasError() `should equal to` true
+    }
+
+    @Test
+    fun `Should have error if http error is not null`() {
+        StreamResponse(requestErrorCode = 500).hasError() `should equal to` true
+    }
+
+    @Test
+    fun `Should not have error if subsonic error and http error is null`() {
+        StreamResponse().hasError() `should equal to` false
+    }
+}