Improve handling of response larger than content-length

Author: schlosna

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

@@ -50,6 +50,7 @@
 import java.io.InputStreamReader;
 import java.io.OutputStream;
 import java.io.Reader;
+import java.io.SequenceInputStream;
 import java.io.StringReader;
 import java.net.URLDecoder;
 import java.nio.charset.StandardCharsets;
@@ -235,18 +236,32 @@ public InputStream asInputStream() {
 
         @Override
         public Reader asReader() {
+            InputStream inputStream = asInputStream();
             Integer maybeLength = length();
-            if (maybeLength != null && maybeLength < 8192) {
-                // Avoid InputStreamReader / HeapByteBuffer overhead for small (less than 8KiB) inputs,
-                // see https://github.com/FasterXML/jackson-core/pull/1081
-                try (InputStream inputStream = asInputStream()) {
-                    return new StringReader(new String(inputStream.readAllBytes(), StandardCharsets.UTF_8));
-                } catch (IOException e) {
-                    throw new SafeUncheckedIoException(
-                            "Failed to read response body", e, SafeArg.of("length", maybeLength));
+            if (maybeLength != null) {
+                int length = maybeLength;
+                if (length < 8192) {
+                    // Avoid InputStreamReader / HeapByteBuffer overhead for small (less than 8KiB) inputs,
+                    // see https://github.com/FasterXML/jackson-core/pull/1081
+                    // try to read an extra byte to determine if more bytes were provided than actual content-length
+                    int toRead = length + 1;
+                    byte[] bytes = new byte[toRead];
+                    try {
+                        int read = inputStream.readNBytes(bytes, 0, toRead);
+                        if (read == length) {
+                            // fully read input
+                            inputStream.close();
+                            return new StringReader(new String(bytes, 0, read, StandardCharsets.UTF_8));
+                        }
+                        // input was larger than provided content length, fallback to stream path
+                        inputStream = new SequenceInputStream(new ByteArrayInputStream(bytes), inputStream);
+                    } catch (IOException e) {
+                        throw new SafeUncheckedIoException(
+                                "Failed to read response body", e, SafeArg.of("length", maybeLength));
+                    }
                 }
             }
-            return new InputStreamReader(asInputStream(), StandardCharsets.UTF_8);
+            return new InputStreamReader(inputStream, StandardCharsets.UTF_8);
         }
 
         @Override