Added test of partial fetch in Stream Parser

src/test/java/org/jsoup/parser/StreamParserTest.java

@@ -1,7 +1,10 @@
 package org.jsoup.parser;
 
+import org.jsoup.Connection;
+import org.jsoup.Jsoup;
 import org.jsoup.helper.DataUtil;
 import org.jsoup.integration.ParseTest;
+import org.jsoup.integration.servlets.FileServlet;
 import org.jsoup.nodes.Document;
 import org.jsoup.nodes.Element;
 import org.jsoup.nodes.Node;
@@ -17,6 +20,7 @@
 import java.util.Iterator;
 import java.util.List;
 import java.util.NoSuchElementException;
+import java.util.concurrent.atomic.AtomicReference;
 
 import static org.junit.jupiter.api.Assertions.*;
 
@@ -340,6 +344,36 @@ private static CharacterReader getReader(StreamParser streamer) {
         assertTrue(isClosed(streamer));
     }
 
+    @Test void canCleanlyConsumePortionOfUrl() throws IOException {
+        // test that we can get just the head section of large.html, and only read the minimum required from the URL
+        String url = FileServlet.urlTo("/htmltests/large.html"); // 280 K
+
+        AtomicReference<Float> seenPercent = new AtomicReference<>(0.0f);
+        StreamParser parserRef;
+
+        Connection con = Jsoup.connect(url)
+            .onResponseProgress((processed, total, percent, response) -> {
+                System.out.println("Processed: " + processed + " Total: " + total + " Percent: " + percent);
+                seenPercent.set(percent);
+            });
+
+        Connection.Response response = con.execute();
+        try (StreamParser parser = response.streamParser()) {
+            parserRef = parser;
+            // get the head section
+            Element head = parser.selectFirst("head");
+            Element title = head.expectFirst("title");
+            assertEquals("Large HTML", title.text());
+        }
+        // now that we've left the try, the stream parser and the response bodystream should be closed
+        assertTrue(isClosed(parserRef));
+
+        // test that we didn't read all of the stream
+        assertTrue(seenPercent.get() > 0.0f);
+        assertTrue(seenPercent.get() < 100.0f);
+        // not sure of a good way to assert the bufferedInputReader buf (as held by ConstrainableInputStream in Response.BodyStream) is null. But it is via StreamParser.close.
+    }
+
     // Fragments
 
     @Test