System in can use less home-made code

README.md

@@ -220,7 +220,7 @@ void Scanner_reads_text_from_System_in(
   withTextFromSystemIn("first line", "second line")
     .execute(() -> {
       Scanner scanner = new Scanner(System.in);
-      scanner.nextLine();
+      assertEquals("first line", scanner.nextLine());
       assertEquals("second line", scanner.nextLine());
     });
 }

src/main/java/com/github/stefanbirkner/systemlambda/SystemLambda.java

@@ -1,8 +1,10 @@
 package com.github.stefanbirkner.systemlambda;
 
+import javax.print.DocFlavor;
 import java.io.*;
 import java.lang.reflect.Field;
 import java.net.InetAddress;
+import java.nio.charset.StandardCharsets;
 import java.security.Permission;
 import java.util.*;
 import java.util.concurrent.Callable;
@@ -913,96 +915,45 @@ public void execute(
 
 
 		private static class ReplacementInputStream extends InputStream {
-			private final StringReader reader;
 			private final IOException ioException;
 			private final RuntimeException runtimeException;
+			private final ByteArrayInputStream byteArrayInputStream;
 
 			ReplacementInputStream(
 				String text,
 				IOException ioException,
 				RuntimeException runtimeException
 			) {
-				this.reader = new StringReader(text);
+				this.byteArrayInputStream = new ByteArrayInputStream(text.getBytes(defaultCharset()));
 				this.ioException = ioException;
 				this.runtimeException = runtimeException;
 			}
 
 			@Override
 			public int read(
 			) throws IOException {
-				int character = reader.read();
+				int character = byteArrayInputStream.read();
 				if (character == -1)
 					handleEmptyReader();
 				return character;
 			}
 
+			@Override
+			public int read(byte[] b, int off, int len) throws IOException {
+				int bytesRead = byteArrayInputStream.read(b, off, len);
+				if (len > 0 && bytesRead < 0)
+					handleEmptyReader();
+
+				return bytesRead;
+			}
+
 			private void handleEmptyReader(
 			) throws IOException {
 				if (ioException != null)
 					throw ioException;
 				else if (runtimeException != null)
 					throw runtimeException;
 			}
-
-			@Override
-			public int read(
-				byte[] buffer,
-				int offset,
-				int len
-			) throws IOException {
-				if (buffer == null)
-					throw new NullPointerException();
-				else if (offset < 0 || len < 0 || len > buffer.length - offset)
-					throw new IndexOutOfBoundsException();
-				else if (len == 0)
-					return 0;
-				else
-					return readNextLine(buffer, offset, len);
-			}
-
-			private int readNextLine(
-				byte[] buffer,
-				int offset,
-				int len
-			) throws IOException {
-				int c = read();
-				if (c == -1)
-					return -1;
-				buffer[offset] = (byte) c;
-
-				int i = 1;
-				for (; (i < len) && !isCompleteLineWritten(buffer, i - 1); ++i) {
-					byte read = (byte) read();
-					if (read == -1)
-						break;
-					else
-						buffer[offset + i] = read;
-				}
-				return i;
-			}
-
-			private boolean isCompleteLineWritten(
-				byte[] buffer,
-				int indexLastByteWritten
-			) {
-				byte[] separator = getProperty("line.separator")
-					.getBytes(defaultCharset());
-				int indexFirstByteOfSeparator = indexLastByteWritten
-					- separator.length + 1;
-				return indexFirstByteOfSeparator >= 0
-					&& contains(buffer, separator, indexFirstByteOfSeparator);
-			}
-
-			private boolean contains(
-				byte[] array,
-				byte[] pattern,
-				int indexStart
-			) {
-				for (int i = 0; i < pattern.length; ++i)
-					if (array[indexStart + i] != pattern[i])
-						return false;
-				return true;
-			}
 		}
 	}
 

src/test/java/com/github/stefanbirkner/systemlambda/WithTextFromSystemInTest.java

@@ -37,18 +37,19 @@ static void checkArrayConstants() {
 	@Test
 	void provided_text_is_available_from_system_in(
 	) throws Exception {
+		AtomicReference<String> firstLineCapture = new AtomicReference<>();
 		AtomicReference<String> secondLineCapture = new AtomicReference<>();
 
 		withTextFromSystemIn(
 			"first line",
 			"second line"
 		).execute(() -> {
-			Scanner firstScanner = new Scanner(in);
-			firstScanner.nextLine();
-			Scanner secondScanner = new Scanner(in);
-			secondLineCapture.set(secondScanner.nextLine());
+			Scanner scanner = new Scanner(in);
+			firstLineCapture.set(scanner.nextLine());
+			secondLineCapture.set(scanner.nextLine());
 		});
 
+		assertThat(firstLineCapture).hasValue("first line");
 		assertThat(secondLineCapture).hasValue("second line");
 	}
 
@@ -201,24 +202,24 @@ void system_in_throws_IndexOutOfBoundsException_when_read_is_called_with_oversiz
 	}
 
 	@Test
-	void system_in_reads_zero_bytes_even_if_mock_should_throw_IOException_on_input_end(
+	void system_in_reads_no_bytes_even_if_mock_should_throw_IOException_on_input_end(
 	) throws Exception {
 		withTextFromSystemIn()
 			.andExceptionThrownOnInputEnd(DUMMY_IO_EXCEPTION)
 			.execute(() -> {
 				int numBytesRead = System.in.read(DUMMY_ARRAY, VALID_OFFSET, 0);
-				assertThat(numBytesRead).isZero();
+				assertThat(numBytesRead).isEqualTo(-1);
 			});
 	}
 
 	@Test
-	void system_in_reads_zero_bytes_even_if_mock_should_throw_RuntimeException_on_input_end(
+	void system_in_reads_no_bytes_even_if_mock_should_throw_RuntimeException_on_input_end(
 	) throws Exception {
 		withTextFromSystemIn()
 			.andExceptionThrownOnInputEnd(DUMMY_RUNTIME_EXCEPTION)
 			.execute(() -> {
 				int numBytesRead = System.in.read(DUMMY_ARRAY, VALID_OFFSET, 0);
-				assertThat(numBytesRead).isZero();
+				assertThat(numBytesRead).isEqualTo(-1);
 			});
 	}