Add Tee response wrappers for capturing response body

Introduces TeeHttpServletResponseWrapper and TeeServletOutputStream to capture HTTP response bodies while streaming to the client. Updates CachedBodyHttpServletResponse to extend the new wrapper and removes redundant body copying logic from HttpResponseEventPublisher.

Author: david-randoll

spring-web-captor/src/main/java/com/davidrandoll/spring_web_captor/publisher/response/CachedBodyHttpServletResponse.java

@@ -19,7 +19,7 @@
 import static java.util.Objects.nonNull;
 
 @Slf4j
-public class CachedBodyHttpServletResponse extends ContentCachingResponseWrapper {
+public class CachedBodyHttpServletResponse extends TeeHttpServletResponseWrapper {
     @Getter
     private final CachedBodyHttpServletRequest request;
 
@@ -67,8 +67,7 @@ public void onStartAsync(AsyncEvent asyncEvent) {
     }
 
     private void getBody(CompletableFuture<byte[]> future) throws IOException {
-        future.complete(this.getContentAsByteArray());
-        this.copyBodyToResponse(); // IMPORTANT: copy response back into original response
+        future.complete(this.getCapturedResponseBody());
     }
 
     public HttpStatus getResponseStatus() {

spring-web-captor/src/main/java/com/davidrandoll/spring_web_captor/publisher/response/HttpResponseEventPublisher.java

@@ -49,8 +49,6 @@ protected void doFilterInternal(@NonNull HttpServletRequest request, @NonNull Ht
             responseWrapper.getResponseBody()
                     .completeExceptionally(ex);
             throw ex;
-        } finally {
-            responseWrapper.copyBodyToResponse(); // IMPORTANT: copy response back into original response
         }
     }
 }

spring-web-captor/src/main/java/com/davidrandoll/spring_web_captor/publisher/response/TeeHttpServletResponseWrapper.java

@@ -0,0 +1,30 @@
+package com.davidrandoll.spring_web_captor.publisher.response;
+
+import jakarta.servlet.ServletOutputStream;
+import jakarta.servlet.http.HttpServletResponse;
+import jakarta.servlet.http.HttpServletResponseWrapper;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+
+public class TeeHttpServletResponseWrapper extends HttpServletResponseWrapper {
+    private final ByteArrayOutputStream copy = new ByteArrayOutputStream();
+    private ServletOutputStream teeStream;
+
+    public TeeHttpServletResponseWrapper(HttpServletResponse response) {
+        super(response);
+    }
+
+    @Override
+    public ServletOutputStream getOutputStream() throws IOException {
+        if (teeStream == null) {
+            teeStream = new TeeServletOutputStream(super.getOutputStream(), copy);
+        }
+        return teeStream;
+    }
+
+    public byte[] getCapturedResponseBody() {
+        return copy.toByteArray();
+    }
+}
+

spring-web-captor/src/main/java/com/davidrandoll/spring_web_captor/publisher/response/TeeServletOutputStream.java

@@ -0,0 +1,51 @@
+package com.davidrandoll.spring_web_captor.publisher.response;
+
+import jakarta.servlet.ServletOutputStream;
+import jakarta.servlet.WriteListener;
+
+import java.io.IOException;
+import java.io.OutputStream;
+
+public class TeeServletOutputStream extends ServletOutputStream {
+    private final ServletOutputStream original;
+    private final OutputStream copy;
+
+    public TeeServletOutputStream(ServletOutputStream original, OutputStream copy) {
+        this.original = original;
+        this.copy = copy;
+    }
+
+    @Override
+    public void write(int b) throws IOException {
+        original.write(b);
+        copy.write(b);
+    }
+
+    @Override
+    public void write(byte[] b, int off, int len) throws IOException {
+        original.write(b, off, len);
+        copy.write(b, off, len);
+    }
+
+    @Override
+    public void flush() throws IOException {
+        original.flush();
+        copy.flush();
+    }
+
+    @Override
+    public void close() throws IOException {
+        original.close();
+        copy.close();
+    }
+
+    @Override
+    public boolean isReady() {
+        return original.isReady();
+    }
+
+    @Override
+    public void setWriteListener(WriteListener writeListener) {
+        original.setWriteListener(writeListener);
+    }
+}