Added caching support for headers

logbook-core/src/main/java/org/zalando/logbook/Cache.java

@@ -0,0 +1,19 @@
+package org.zalando.logbook;
+
+import lombok.AllArgsConstructor;
+
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.Supplier;
+
+@AllArgsConstructor
+final class Cache<T> {
+
+    private final AtomicReference<T> cache = new AtomicReference<>();
+    private final Supplier<T> supplier;
+
+    public T get() {
+        return cache.updateAndGet(cached ->
+                cached == null ? supplier.get() : cached);
+    }
+
+}

logbook-core/src/main/java/org/zalando/logbook/CachingHttpRequest.java

@@ -0,0 +1,26 @@
+package org.zalando.logbook;
+
+import java.util.List;
+import java.util.Map;
+
+final class CachingHttpRequest implements ForwardingHttpRequest {
+
+    private final HttpRequest request;
+    private final Cache<Map<String, List<String>>> headers;
+
+    CachingHttpRequest(final HttpRequest request) {
+        this.request = request;
+        this.headers = new Cache<>(request::getHeaders);
+    }
+
+    @Override
+    public HttpRequest delegate() {
+        return request;
+    }
+
+    @Override
+    public Map<String, List<String>> getHeaders() {
+        return headers.get();
+    }
+
+}

logbook-core/src/main/java/org/zalando/logbook/CachingHttpResponse.java

@@ -0,0 +1,26 @@
+package org.zalando.logbook;
+
+import java.util.List;
+import java.util.Map;
+
+final class CachingHttpResponse implements ForwardingHttpResponse {
+
+    private final HttpResponse response;
+    private final Cache<Map<String, List<String>>> headers;
+
+    CachingHttpResponse(final HttpResponse response) {
+        this.response = response;
+        this.headers = new Cache<>(response::getHeaders);
+    }
+
+    @Override
+    public HttpResponse delegate() {
+        return response;
+    }
+
+    @Override
+    public Map<String, List<String>> getHeaders() {
+        return headers.get();
+    }
+
+}

logbook-core/src/main/java/org/zalando/logbook/DefaultLogbook.java

@@ -26,15 +26,18 @@ public RequestWritingStage process(final HttpRequest originalRequest) throws IOE
 
     @Override
     public RequestWritingStage process(final HttpRequest originalRequest, final Strategy strategy) throws IOException {
-        if (sink.isActive() && predicate.test(originalRequest)) {
+        final HttpRequest request = new CachingHttpRequest(originalRequest);
+
+        if (sink.isActive() && predicate.test(request)) {
             final Precorrelation precorrelation = new SimplePrecorrelation(clock);
-            final HttpRequest processedRequest = strategy.process(originalRequest);
+            final HttpRequest processedRequest = strategy.process(request);
 
             return () -> {
                 final HttpRequest filteredRequest = requestFilter.filter(processedRequest);
                 strategy.write(precorrelation, filteredRequest, sink);
                 return originalResponse -> {
-                    final HttpResponse processedResponse = strategy.process(originalRequest, originalResponse);
+                    final HttpResponse response = new CachingHttpResponse(originalResponse);
+                    final HttpResponse processedResponse = strategy.process(request, response);
                     return () -> {
                         final HttpResponse filteredResponse = responseFilter.filter(processedResponse);
                         strategy.write(precorrelation.correlate(), filteredRequest, filteredResponse, sink);

logbook-core/src/test/java/org/zalando/logbook/CachingHttpRequestTest.java

@@ -0,0 +1,35 @@
+package org.zalando.logbook;
+
+import org.junit.jupiter.api.Test;
+
+import static java.util.Collections.emptyMap;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.anEmptyMap;
+import static org.hamcrest.Matchers.is;
+import static org.mockito.Mockito.atMost;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+final class CachingHttpRequestTest {
+
+    @Test
+    void shouldDelegate() {
+        final CachingHttpRequest unit = new CachingHttpRequest(MockHttpRequest.create());
+        assertThat(unit.getHeaders(), is(anEmptyMap()));
+    }
+
+    @Test
+    void shouldCache() {
+        final HttpRequest delegate = mock(HttpRequest.class);
+        when(delegate.getHeaders()).thenReturn(emptyMap());
+
+        final CachingHttpRequest unit = new CachingHttpRequest(delegate);
+
+        unit.getHeaders();
+        unit.getHeaders();
+
+        verify(delegate, atMost(1)).getHeaders();
+    }
+
+}

logbook-core/src/test/java/org/zalando/logbook/CachingHttpResponseTest.java

@@ -0,0 +1,35 @@
+package org.zalando.logbook;
+
+import org.junit.jupiter.api.Test;
+
+import static java.util.Collections.emptyMap;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.anEmptyMap;
+import static org.hamcrest.Matchers.is;
+import static org.mockito.Mockito.atMost;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+final class CachingHttpResponseTest {
+
+    @Test
+    void shouldDelegate() {
+        final CachingHttpResponse unit = new CachingHttpResponse(MockHttpResponse.create());
+        assertThat(unit.getHeaders(), is(anEmptyMap()));
+    }
+
+    @Test
+    void shouldCache() {
+        final HttpResponse delegate = mock(HttpResponse.class);
+        when(delegate.getHeaders()).thenReturn(emptyMap());
+
+        final CachingHttpResponse unit = new CachingHttpResponse(delegate);
+
+        unit.getHeaders();
+        unit.getHeaders();
+
+        verify(delegate, atMost(1)).getHeaders();
+    }
+
+}