Fix request body re-sent on method-rewritten redirect follows

src/main/java/com/blazemeter/jmeter/http2/core/HTTP2JettyClient.java

@@ -3273,6 +3273,15 @@ private void addProxyIfEmpty(HttpClient target, String host, int port, boolean s
 
   private void setBody(Request request, HTTP2Sampler sampler, HTTPSampleResult result)
       throws IOException {
+    String effectiveMethod = result.getHTTPMethod();
+    if (!effectiveMethod.equals(sampler.getMethod()) && !isMethodWithBody(effectiveMethod)) {
+      // The method being sent only differs from the sampler's configured one when JMeter core
+      // rewrites it while following a redirect (e.g. POST -> GET after a 301/302/303). The
+      // entity belongs to the original request, so the method-rewritten follow-up must not
+      // re-send it (RFC 9110 section 15.4), matching HTTPSamplerProxy behavior.
+      result.setQueryString("");
+      return;
+    }
     String contentEncoding = sampler.getContentEncoding();
     String contentTypeHeader =
         request.getHeaders() != null ? request.getHeaders().get(HTTPConstants.HEADER_CONTENT_TYPE)
@@ -3368,7 +3377,7 @@ private void setBody(Request request, HTTP2Sampler sampler, HTTPSampleResult res
               new StringRequestContent(contentTypeHeader, postBody.toString(),
                   contentCharset);
           request.body(requestContent);
-        } else if (isMethodWithBody(sampler.getMethod())) {
+        } else if (isMethodWithBody(effectiveMethod)) {
           Fields fields = new Fields();
           for (JMeterProperty p : sampler.getArguments()) {
             HTTPArgument arg = (HTTPArgument) p.getObjectValue();

src/test/java/com/blazemeter/jmeter/http2/core/HTTP2JettyClientTest.java

@@ -19,6 +19,7 @@
 import static com.blazemeter.jmeter.http2.core.ServerBuilder.SERVER_PATH_200_ZSTD;
 import static com.blazemeter.jmeter.http2.core.ServerBuilder.SERVER_PATH_200_WITH_BODY;
 import static com.blazemeter.jmeter.http2.core.ServerBuilder.SERVER_PATH_302;
+import static com.blazemeter.jmeter.http2.core.ServerBuilder.SERVER_PATH_302_TO_ECHO;
 import static com.blazemeter.jmeter.http2.core.ServerBuilder.SERVER_PATH_400;
 import static com.blazemeter.jmeter.http2.core.ServerBuilder.SERVER_PATH_BIG_RESPONSE;
 import static com.blazemeter.jmeter.http2.core.ServerBuilder.SERVER_PATH_200_DEFLATE;
@@ -846,6 +847,27 @@ private void validateRedirects(HTTPSampleResult result, HTTPSampleResult expecte
     softly.assertThat(result.getRedirectLocation()).isEqualTo(expected.getRedirectLocation());
   }
 
+  @Test
+  public void shouldNotResendRequestBodyWhenPostRedirectIsFollowedAsGet() throws Exception {
+    buildStartedServer();
+    sampler.setFollowRedirects(true);
+    sampler.setMethod(HTTPConstants.POST);
+    sampler.addArgument("test1", TEST_ARGUMENT_1);
+    sampler.addArgument("test2", TEST_ARGUMENT_2);
+
+    HTTPSampleResult result = sample(SERVER_PATH_302_TO_ECHO, HTTPConstants.POST);
+
+    softly.assertThat(result.getResponseCode()).isEqualTo("200");
+    SampleResult[] subResults = result.getSubResults();
+    softly.assertThat(subResults.length).isGreaterThan(0);
+    HTTPSampleResult followUp = (HTTPSampleResult) subResults[subResults.length - 1];
+    softly.assertThat(followUp.getHTTPMethod()).isEqualTo(HTTPConstants.GET);
+    // The redirect target echoes back any request body it receives. JMeter core rewrites
+    // POST to GET when following a 302, so the follow-up request must not carry the
+    // original POST entity (RFC 9110 section 15.4; matches HTTPSamplerProxy behavior).
+    softly.assertThat(followUp.getResponseDataAsString()).isEmpty();
+  }
+
   @Test
   public void shouldGetOnlyRedirectedResultWhenFollowRedirectDisabledAndRedirected()
       throws Exception {

src/test/java/com/blazemeter/jmeter/http2/core/ServerBuilder.java

@@ -82,6 +82,7 @@ public class ServerBuilder {
   public static final String SERVER_PATH_BIG_RESPONSE = "/test/big-response";
   public static final String SERVER_PATH_400 = "/test/400";
   public static final String SERVER_PATH_302 = "/test/302";
+  public static final String SERVER_PATH_302_TO_ECHO = "/test/302-to-echo";
   public static final String SERVER_PATH_200_WITH_BODY = "/test/body";
   public static final String SERVER_PATH_JSON_ONLY = "/test/json-only";
   public static final String SERVER_PATH_DELETE_DATA = "/test/delete";
@@ -294,6 +295,11 @@ protected void service(HttpServletRequest req, HttpServletResponse resp)
                 "https://localhost:" + req.getLocalPort() + SERVER_PATH_200);
             resp.setStatus(HttpStatus.FOUND_302);
             break;
+          case SERVER_PATH_302_TO_ECHO:
+            resp.addHeader(HTTPConstants.HEADER_LOCATION,
+                "https://localhost:" + req.getLocalPort() + SERVER_PATH_200_WITH_BODY);
+            resp.setStatus(HttpStatus.FOUND_302);
+            break;
           case SERVER_PATH_200_WITH_BODY:
             String bodyRequest = req.getReader().lines().collect(Collectors.joining());
             resp.getWriter().write(bodyRequest);