Support resumable image downloads if supported by source (#3167)

Co-authored-by: MajorTanya <39014446+MajorTanya@users.noreply.github.com>
Co-authored-by: AntsyLich <59261191+AntsyLich@users.noreply.github.com>

core/common/src/main/kotlin/eu/kanade/tachiyomi/network/OkHttpExtensions.kt

@@ -118,13 +118,26 @@ suspend fun Call.awaitSuccess(): Response {
     return response
 }
 
-fun OkHttpClient.newCachelessCallWithProgress(request: Request, listener: ProgressListener): Call {
+fun OkHttpClient.newCachelessCallWithProgress(
+    request: Request,
+    listener: ProgressListener,
+    existingSize: Long = 0L,
+): Call {
     val progressClient = newBuilder()
         .cache(null)
         .addNetworkInterceptor { chain ->
-            val originalResponse = chain.proceed(chain.request())
+            val request = chain.request()
+                .newBuilder()
+                .apply {
+                    if (existingSize > 0 && request.header("Range") == null) {
+                        header("Range", "bytes=$existingSize-")
+                    }
+                }
+                .build()
+
+            val originalResponse = chain.proceed(request)
             originalResponse.newBuilder()
-                .body(ProgressResponseBody(originalResponse.body, listener))
+                .body(ProgressResponseBody(originalResponse.body, listener, existingSize))
                 .build()
         }
         .build()

core/common/src/main/kotlin/eu/kanade/tachiyomi/network/ProgressResponseBody.kt

@@ -12,6 +12,7 @@ import java.io.IOException
 class ProgressResponseBody(
     private val responseBody: ResponseBody,
     private val progressListener: ProgressListener,
+    private val existingSize: Long, // bytes already downloaded
 ) : ResponseBody() {
 
     private val bufferedSource: BufferedSource by lazy {
@@ -32,7 +33,7 @@ class ProgressResponseBody(
 
     private fun source(source: Source): Source {
         return object : ForwardingSource(source) {
-            var totalBytesRead = 0L
+            var totalBytesRead = existingSize
 
             @Throws(IOException::class)
             override fun read(sink: Buffer, byteCount: Long): Long {