Use Content-Length for optimal read to byte[]

If content-length is available, pass it to readNBytes in
ByteArrayHttpMessageConverter. When the content length is less than
the internal buffer size in InputStream (8192), this avoids a copy,
as readNBytes will return the buffer directly. When the content length
is greater than the buffer size used in InputStream, passing the
content-length at least avoids over-allocating the final buffer (e.g.,
if the content length were 8193 bytes, 1 byte more than the default
buffer size).

If the content length isn't present or is too large to represent as
an integer, fall back to the default behavior of readAllBytes by
passing in Integer.MAX_VALUE.

See gh-30010

spring-web/src/main/java/org/springframework/http/converter/ByteArrayHttpMessageConverter.java

@@ -52,7 +52,15 @@ public boolean supports(Class<?> clazz) {
 
 	@Override
 	public byte[] readInternal(Class<? extends byte[]> clazz, HttpInputMessage inputMessage) throws IOException {
-		return inputMessage.getBody().readAllBytes();
+		long contentLength = inputMessage.getHeaders().getContentLength();
+		final int len;
+		if (contentLength >= 0 && contentLength <= Integer.MAX_VALUE) {
+			len = (int) contentLength;
+		}
+		else {
+			len = Integer.MAX_VALUE;
+		}
+		return inputMessage.getBody().readNBytes(len);
 	}
 
 	@Override

spring-web/src/test/java/org/springframework/http/converter/ByteArrayHttpMessageConverterTests.java

@@ -57,6 +57,16 @@ public void read() throws IOException {
 		assertThat(result).as("Invalid result").isEqualTo(body);
 	}
 
+	@Test
+	public void readWithContentLengthHeaderSet() throws IOException {
+		byte[] body = new byte[]{0x1, 0x2, 0x3, 0x4, 0x5};
+		MockHttpInputMessage inputMessage = new MockHttpInputMessage(body);
+		inputMessage.getHeaders().setContentType(new MediaType("application", "octet-stream"));
+		inputMessage.getHeaders().setContentLength(body.length);
+		byte[] result = converter.read(byte[].class, inputMessage);
+		assertThat(result).as("Invalid result").isEqualTo(body);
+	}
+
 	@Test
 	public void write() throws IOException {
 		MockHttpOutputMessage outputMessage = new MockHttpOutputMessage();