KTOR-5372 Fix EOF in ByteBufferChannel when min is 0 (#3327)

Author: rsinukov1

ktor-io/jvm/src/io/ktor/utils/io/ByteBufferChannel.kt

@@ -1655,7 +1655,7 @@ internal open class ByteBufferChannel(
         }
 
         if (!read) {
-            if (isClosedForRead) {
+            if (isClosedForRead && min > 0) {
                 throw EOFException("Got EOF but at least $min bytes were expected")
             }
 

ktor-io/jvm/src/io/ktor/utils/io/jvm/nio/Writing.kt

@@ -5,8 +5,9 @@ import java.nio.*
 import java.nio.channels.*
 
 /**
- * Copy up to [limit] bytes to blocking NIO [channel]. Copying to non-blocking channel requires selection and
- * not supported. It does suspend if no data available in byte channel but may block if destination NIO channel blocks.
+ * Copy up to [limit] bytes to blocking NIO [channel].
+ * Copying to a non-blocking channel requires selection and not supported.
+ * It is suspended if no data are available in a byte channel but may block if destination NIO channel blocks.
  *
  * @return number of bytes copied
  */

ktor-io/jvm/test/io/ktor/utils/io/ByteBufferChannelTest.kt

@@ -253,4 +253,19 @@ class ByteBufferChannelTest {
         reader.await()
         writer.join()
     }
+
+    @Test
+    fun testReadWithNoMinDoesntThrow() = runBlocking {
+        val channel = ByteChannel(true)
+
+        channel.writeByte(1)
+        channel.read(0) {
+            assertEquals(1, it.remaining())
+            it.get()
+        }
+        channel.close()
+        channel.read(0) {
+            assertEquals(0, it.remaining())
+        }
+    }
 }