Introduce and relax restriction

Author: e5l

TODO.md

@@ -3,18 +3,10 @@
     - Input: bypass source exceptions in `Input.fill`
     - Input: `eof` vs `exhausted`
     - Output: Appendable
-    - `Input.discard()`, discardExact
     - Idempotent close
     - Make `fill` public (and then rename it) to enable zero-copy delegates
 - Implementation
-    -  Input
-    -  Output
-    -  Index preconditions
-    - `bytesInput = buildInput { BytesOutput -> }`
-        - `Bytes.createInput()` copy on consume
-    - Introduce `BytesInput` and `BytesOutput` `(Input/Output + size, remaining)`
-    - Introduce `readByteArray(), copyTo(output)`
-    - Introduce `Input.copyAvailableTo(Output | Buffer)`: consume single buffer(wait if no buffer available)
+    - Index preconditions
     - Prototype `PipedOutput`
 - Test
     - Verify pool has no leaks

core/commonMain/src/kotlinx/io/Exceptions.kt

@@ -31,3 +31,5 @@ internal fun checkSize(size: Int) {
 internal fun checkCount(count: Int) {
     require(count >= 0) { "Count ($count) should be positive." }
 }
+
+internal fun unexpectedEOF(text: String): Nothing = throw EOFException(text)

core/commonMain/src/kotlinx/io/Input.kt

@@ -267,8 +267,10 @@ public abstract class Input : Closeable {
 
     /**
      * Skips [count] bytes from input.
+     *
+     * @return skipped bytes count. It could be less than [count] if no more bytes available.
      */
-    public fun discard(count: Int) {
+    public fun discard(count: Int): Int {
         checkCount(count)
 
         var remaining = count
@@ -279,11 +281,13 @@ public abstract class Input : Closeable {
             }
 
             if (skipCount == 0) {
-                throw EOFException("Fail to skip $count bytes, remaining $remaining.")
+                break
             }
 
             remaining -= skipCount
         }
+
+        return count - remaining
     }
 
     /**

core/commonMain/src/kotlinx/io/InputOperations.kt

@@ -130,6 +130,24 @@ public fun Input.readByteArray(array: UByteArray, startIndex: Int = 0, length: I
     readByteArray(array.asByteArray(), startIndex, length)
 }
 
+/**
+ * Discards exact [count] of bytes.
+ *
+ * @throws [EOFException] if this input ends before discard finished.
+ * @return discarded bytes count
+ */
+public fun Input.discardExact(count: Int): Int {
+    checkCount(count)
+
+    val skipped = discard(count)
+    if (skipped < count) {
+        unexpectedEOF("Fail to skip $count bytes, remaining ${count - skipped}.")
+    }
+
+    return count
+}
+
+
 /**
  * Reads a [Byte] from this Input.
  *

core/commonTest/src/kotlinx/io/InputOutputTest.common.kt

@@ -69,12 +69,17 @@ class InputOutputTest {
     }
 
     @Test
-    fun testDiscardOnEmpty() {
+    fun testDiscardExactOnEmpty() {
         assertFails {
-            EmptyInput.discard(1)
+            EmptyInput.discardExact(1)
         }
     }
 
+    @Test
+    fun testDiscardOnEmpty() {
+        assertEquals(0, EmptyInput.discard(1))
+    }
+
     @Test
     fun testPrefetchOnEmpty() {
         assertFalse { EmptyInput.prefetch(1) }
@@ -90,7 +95,7 @@ class InputOutputTest {
         checkException { ErrorInput.readByte() }
         checkException { ErrorInput.preview { } }
         checkException { ErrorInput.prefetch(1) }
-        checkException { ErrorInput.discard(1) }
+        checkException { ErrorInput.discardExact(1) }
         checkException { ErrorInput.eof() }
         checkException {
             ErrorInput.readAvailableTo(

core/commonTest/src/kotlinx/io/bytes/BytesTest.kt

@@ -128,7 +128,7 @@ class BytesTest {
         buildBytes {
             writeByteArray(ByteArray(99999))
         }.useInput {
-            discard(99999)
+            discardExact(99999)
             assertTrue { eof() }
         }