Don't block on 0-byte reads (#1479)

* Don't block on 0-byte reads

Closes: #1476

* Fixup another test

Author: squarejesse

okio/src/commonMain/kotlin/okio/internal/RealBufferedSource.kt

@@ -39,6 +39,7 @@ internal inline fun RealBufferedSource.commonRead(sink: Buffer, byteCount: Long)
   check(!closed) { "closed" }
 
   if (buffer.size == 0L) {
+    if (byteCount == 0L) return 0L
     val read = source.read(buffer, Segment.SIZE.toLong())
     if (read == -1L) return -1L
   }
@@ -134,6 +135,7 @@ internal inline fun RealBufferedSource.commonRead(sink: ByteArray, offset: Int,
   checkOffsetAndCount(sink.size.toLong(), offset.toLong(), byteCount.toLong())
 
   if (buffer.size == 0L) {
+    if (byteCount == 0) return 0
     val read = source.read(buffer, Segment.SIZE.toLong())
     if (read == -1L) return -1
   }

okio/src/commonTest/kotlin/okio/AbstractBufferedSourceTest.kt

@@ -289,7 +289,8 @@ abstract class AbstractBufferedSourceTest internal constructor(
 
     // Either 0 or -1 is reasonable here. For consistency with Android's
     // ByteArrayInputStream we return 0.
-    assertEquals(-1, source.read(sink, 0))
+    val readResult = source.read(sink, 0)
+    assertTrue(readResult == 0L || readResult == -1L)
     assertEquals(10, sink.size)
     assertTrue(source.exhausted())
   }

okio/src/commonTest/kotlin/okio/CommonRealBufferedSourceTest.kt

@@ -153,4 +153,31 @@ class CommonRealBufferedSourceTest {
       "write($write3, ${write3.size})",
     )
   }
+
+  @Test fun readZeroBytesIntoBufferDoesNotRefillBuffer() {
+    val source = Buffer()
+    source.writeUtf8("abc")
+
+    val sink = Buffer()
+
+    val bufferedSource = (source as Source).buffer()
+    assertEquals(0L, bufferedSource.read(sink, 0L))
+
+    assertEquals(0, sink.size)
+    assertEquals(0, bufferedSource.buffer.size)
+    assertEquals(3, source.size)
+  }
+
+  @Test fun readZeroBytesIntoByteArrayDoesNotRefillBuffer() {
+    val source = Buffer()
+    source.writeUtf8("abc")
+
+    val sink = ByteArray(1024)
+
+    val bufferedSource = (source as Source).buffer()
+    assertEquals(0, bufferedSource.read(sink, 0, 0))
+
+    assertEquals(0, bufferedSource.buffer.size)
+    assertEquals(3, source.size)
+  }
 }

okio/src/jvmTest/kotlin/okio/BufferedSourceTest.kt

@@ -371,9 +371,9 @@ class BufferedSourceTest(
     val sink = Buffer()
     sink.writeUtf8("a".repeat(10))
 
-    // Either 0 or -1 is reasonable here. For consistency with Android's
-    // ByteArrayInputStream we return 0.
-    assertEquals(-1, source.read(sink, 0))
+    // Either 0 or -1 is reasonable here.
+    val readResult = source.read(sink, 0)
+    assertTrue(readResult == 0L || readResult == -1L)
     assertEquals(10, sink.size)
     assertTrue(source.exhausted())
   }