Optimize DialogueFeignClient small response reader

Avoid InputStreamReader / HeapByteBuffer overhead for small (less than 8KiB) inputs,
see FasterXML/jackson-core#1081

Author: schlosna

conjure-java-jaxrs-client/src/main/java/com/palantir/conjure/java/client/jaxrs/DialogueFeignClient.java

@@ -43,13 +43,15 @@
 import com.palantir.logsafe.UnsafeArg;
 import com.palantir.logsafe.exceptions.SafeIllegalStateException;
 import com.palantir.logsafe.exceptions.SafeRuntimeException;
+import com.palantir.logsafe.exceptions.SafeUncheckedIoException;
 import feign.Request;
 import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.InputStreamReader;
 import java.io.OutputStream;
 import java.io.Reader;
+import java.io.StringReader;
 import java.io.UnsupportedEncodingException;
 import java.net.URLDecoder;
 import java.nio.charset.StandardCharsets;
@@ -239,6 +241,18 @@ public InputStream asInputStream() {
 
         @Override
         public Reader asReader() {
+            Integer maybeLength = length();
+            if (maybeLength != null && maybeLength.intValue() < 8192) {
+                // Avoid InputStreamReader / HeapByteBuffer overhead for small (less than 8KiB) inputs,
+                // see https://github.com/FasterXML/jackson-core/pull/1081
+                try (InputStream inputStream = asInputStream()) {
+                    String content = new String(inputStream.readAllBytes(), StandardCharsets.UTF_8);
+                    return new StringReader(content);
+                } catch (IOException e) {
+                    throw new SafeUncheckedIoException(
+                            "Failed to read response body", e, SafeArg.of("length", maybeLength));
+                }
+            }
             return new InputStreamReader(asInputStream(), StandardCharsets.UTF_8);
         }