close InputStreams used for attachments

rest/src/main/kotlin/request/Request.kt

@@ -82,17 +82,17 @@ class MultipartRequest<B : Any, R>(
         body?.let {
             append("payload_json", Json.encodeToString(it.strategy, it.body))
         }
-        if (files.size == 1) append("file", filename = files[0].first) {
-            files[0].second.copyTo(outputStream())
-        } else files.forEachIndexed { index, pair ->
-            val name = pair.first
-            val inputStream = pair.second
-            append("file$index", name) { inputStream.copyTo(outputStream()) }
+        try {
+            if (files.size == 1) append("file", filename = files[0].first) {
+                files[0].second.copyTo(outputStream())
+            } else files.forEachIndexed { index, pair ->
+                val name = pair.first
+                val inputStream = pair.second
+                append("file$index", name) { inputStream.copyTo(outputStream()) }
+            }
+        } finally {
+            files.forEach { it.second.close() }
         }
     }
 
 }
-
-
-
-

rest/src/test/kotlin/request/MessageRequests.kt

@@ -0,0 +1,26 @@
+package dev.kord.rest.request
+
+import dev.kord.rest.json.response.GatewayResponse
+import dev.kord.rest.route.Route
+import io.ktor.util.*
+import kotlinx.coroutines.runBlocking
+import org.junit.jupiter.api.*
+import java.io.InputStream
+
+@TestMethodOrder(MethodOrderer.MethodName::class)
+@TestInstance(TestInstance.Lifecycle.PER_CLASS)
+class MessageRequests {
+	@Test
+	fun `attachment stream closed`() = runBlocking {
+		val linusStream = object : InputStream() {
+			val stream = ClassLoader.getSystemResourceAsStream("images/kord.png")!!
+			var closed = false; private set
+			override fun read() = stream.read()
+			override fun close() { stream.close(); closed = true }
+		}
+
+		MultipartRequest<Any, GatewayResponse>(Route.GatewayGet, mapOf(), StringValues.Empty, StringValues.Empty, null, listOf("linus.png" to linusStream))
+
+		assert(linusStream.closed)
+	}
+}