SOLR-8669: Non binary responses use chunked encoding because we flush the outputstream early.

solr/CHANGES.txt

@@ -188,6 +188,9 @@ Optimizations
 * SOLR-8532: Optimize GraphQuery when maxDepth is set by not collecting edges at the maxDepth level.
   (Kevin Watters via yonik)
 
+* SOLR-8669: Non binary responses use chunked encoding because we flush the outputstream early.
+  (Mark Miller)
+
 Other Changes
 ----------------------
 
@@ -544,6 +547,9 @@ Optimizations
 
 * SOLR-7281: Add an overseer action to publish an entire node as 'down'. (Mark Miller, shalin)
 
+* SOLR-8669: Non binary responses use chunked encoding because we flush the outputstream early.
+  (Mark Miller)
+
 Other Changes
 ----------------------
 

solr/core/src/java/org/apache/solr/response/QueryResponseWriterUtil.java

@@ -48,7 +48,20 @@ public final class QueryResponseWriterUtil {
       BinaryQueryResponseWriter binWriter = (BinaryQueryResponseWriter) responseWriter;
       binWriter.write(outputStream, solrRequest, solrResponse);
     } else {
-      Writer writer = buildWriter(outputStream, ContentStreamBase.getCharsetFromContentType(contentType));
+      OutputStream out = new OutputStream() {
+        @Override
+        public void write(int b) throws IOException {
+          outputStream.write(b);
+        }
+        @Override
+        public void flush() throws IOException {
+          // We don't flush here, which allows us to flush below
+          // and only flush internal buffers, not the response.
+          // If we flush the response early, we trigger chunked encoding.
+          // See SOLR-8669.
+        }
+      };
+      Writer writer = buildWriter(out, ContentStreamBase.getCharsetFromContentType(contentType));
       responseWriter.write(writer, solrRequest, solrResponse);
       writer.flush();
     }

solr/core/src/java/org/apache/solr/servlet/HttpSolrCall.java

@@ -580,7 +580,6 @@ public class HttpSolrCall {
         OutputStream os = resp.getOutputStream();
 
         IOUtils.copyLarge(is, os);
-        os.flush();
       }
 
     } catch (IOException e) {