Reimplement Buffer.snapshot to use bulk append

Author: fzhinkin

core/common/src/Buffers.kt

@@ -7,26 +7,28 @@ package kotlinx.io
 
 import kotlinx.io.bytestring.ByteString
 import kotlinx.io.bytestring.buildByteString
+import kotlinx.io.unsafe.UnsafeBufferOperations
+import kotlinx.io.unsafe.withData
 
 /**
  * Creates a byte string containing a copy of all the data from this buffer.
  *
  * This call doesn't consume data from the buffer, but instead copies it.
  */
+@OptIn(UnsafeIoApi::class)
 public fun Buffer.snapshot(): ByteString {
     if (size == 0L) return ByteString()
 
     check(size <= Int.MAX_VALUE) { "Buffer is too long ($size) to be converted into a byte string." }
 
     return buildByteString(size.toInt()) {
-        var curr = head
-        do {
-            check(curr != null) { "Current segment is null" }
-            for (idx in 0 until curr.size) {
-                append(curr.getUnchecked(idx))
+        UnsafeBufferOperations.iterate(this@snapshot) { ctx, head ->
+            var curr = head
+            while (curr != null) {
+                ctx.withData(curr, this::append)
+                curr = ctx.next(curr)
             }
-            curr = curr.next
-        } while (curr != null)
+        }
     }
 }
 

core/common/src/unsafe/UnsafeBufferOperations.kt

@@ -254,12 +254,11 @@ public object UnsafeBufferOperations {
     public inline fun writeToTail(
         buffer: Buffer,
         minimumCapacity: Int,
-        writeAction: (SegmentWriteContext, Segment) -> Int
+        writeAction: (context: SegmentWriteContext, tail: Segment) -> Int
     ): Int {
         contract {
             callsInPlace(writeAction, EXACTLY_ONCE)
         }
-
         val tail = buffer.writableSegment(minimumCapacity)
         val bytesWritten = writeAction(SegmentWriteContextImpl, tail)
 
@@ -304,7 +303,10 @@ public object UnsafeBufferOperations {
      * @sample kotlinx.io.samples.unsafe.UnsafeReadWriteSamplesJvm.messageDigest
      * @sample kotlinx.io.samples.unsafe.UnsafeBufferOperationsSamples.crc32Unsafe
      */
-    public inline fun iterate(buffer: Buffer, iterationAction: (BufferIterationContext, Segment?) -> Unit) {
+    public inline fun iterate(
+        buffer: Buffer,
+        iterationAction: (context: BufferIterationContext, head: Segment?) -> Unit
+    ) {
         contract {
             callsInPlace(iterationAction, EXACTLY_ONCE)
         }
@@ -335,7 +337,7 @@ public object UnsafeBufferOperations {
      */
     public inline fun iterate(
         buffer: Buffer, offset: Long,
-        iterationAction: (BufferIterationContext, Segment?, Long) -> Unit
+        iterationAction: (context: BufferIterationContext, segment: Segment?, startOfTheSegmentOffset: Long) -> Unit
     ) {
         contract {
             callsInPlace(iterationAction, EXACTLY_ONCE)
@@ -393,7 +395,10 @@ public interface SegmentReadContext {
 @UnsafeIoApi
 @JvmSynthetic
 @OptIn(ExperimentalContracts::class)
-public inline fun SegmentReadContext.withData(segment: Segment, readAction: (ByteArray, Int, Int) -> Unit) {
+public inline fun SegmentReadContext.withData(
+    segment: Segment,
+    readAction: (bytes: ByteArray, startIndexInclusive: Int, endIndexExclusive: Int) -> Unit
+) {
     contract {
         callsInPlace(readAction, EXACTLY_ONCE)
     }