fix: resolve SonarCloud java:S3077 rule in UploadIdFactory

src/main/java/me/desair/tus/server/upload/UploadIdFactory.java

@@ -1,6 +1,8 @@
 package me.desair.tus.server.upload;
 
 import java.io.Serializable;
+import java.util.concurrent.locks.ReadWriteLock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 import me.desair.tus.server.util.Utils;
@@ -14,10 +16,13 @@
  */
 public abstract class UploadIdFactory {
 
+  private final ReadWriteLock lock = new ReentrantReadWriteLock();
   private String uploadUri = "/";
-  // volatile ensures changes made via setUploadUri(..) are immediately visible across
-  // multiple concurrent request threads without stale caching.
-  private volatile Pattern uploadUriPattern = null;
+  // Read and write operations on uploadUri and uploadUriPattern are guarded by a
+  // ReentrantReadWriteLock.
+  // This enables concurrent lock-free reads for high performance while ensuring thread-safe lazy
+  // pattern compilation and state mutation without triggering Sonar S3077 warnings.
+  private Pattern uploadUriPattern = null;
 
   /**
    * Set the URI or absolute URL under which the main tus upload endpoint is hosted. Optionally,
@@ -35,8 +40,14 @@ public void setUploadUri(String uploadUri) {
             || Strings.CS.startsWith(uploadUri, "https://"),
         "The upload URI should start with /, http://, or https://");
     Validate.isTrue(!Strings.CS.endsWith(uploadUri, "$"), "The upload URI should not end with $");
-    this.uploadUri = uploadUri;
-    this.uploadUriPattern = null;
+
+    lock.writeLock().lock();
+    try {
+      this.uploadUri = uploadUri;
+      this.uploadUriPattern = null;
+    } finally {
+      lock.writeLock().unlock();
+    }
   }
 
   /**
@@ -46,7 +57,12 @@ public void setUploadUri(String uploadUri) {
    * @return The URI of the main tus upload endpoint.
    */
   public String getUploadUri() {
-    return uploadUri;
+    lock.readLock().lock();
+    try {
+      return uploadUri;
+    } finally {
+      lock.readLock().unlock();
+    }
   }
 
   /**
@@ -91,13 +107,27 @@ public UploadId readUploadId(String url) {
    * @return A (cached) Pattern to match upload URI's
    */
   protected Pattern getUploadUriPattern() {
-    if (uploadUriPattern == null) {
-      // We will extract the upload ID's by removing the upload URI from the start of the
-      // request URI
-      String path = Utils.extractUriPath(uploadUri);
-      uploadUriPattern =
-          Pattern.compile("^.*" + path + (Strings.CS.endsWith(path, "/") ? "" : "/?"));
+    lock.readLock().lock();
+    try {
+      if (uploadUriPattern != null) {
+        return uploadUriPattern;
+      }
+    } finally {
+      lock.readLock().unlock();
+    }
+
+    lock.writeLock().lock();
+    try {
+      if (uploadUriPattern == null) {
+        // Extract upload IDs by removing upload URI from start of request URI.
+        // Write lock ensures single pattern compilation across concurrent threads.
+        String path = Utils.extractUriPath(uploadUri);
+        uploadUriPattern =
+            Pattern.compile("^.*" + path + (Strings.CS.endsWith(path, "/") ? "" : "/?"));
+      }
+      return uploadUriPattern;
+    } finally {
+      lock.writeLock().unlock();
     }
-    return uploadUriPattern;
   }
 }

src/test/java/me/desair/tus/server/upload/UuidUploadIdFactoryTest.java

@@ -6,6 +6,11 @@
 import static org.hamcrest.Matchers.not;
 import static org.hamcrest.Matchers.nullValue;
 
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
 import org.junit.Before;
 import org.junit.Test;
 
@@ -159,4 +164,53 @@ public void readUploadIdRegexAbsoluteUrl() throws Exception {
   public void createId() throws Exception {
     assertThat(idFactory.createId(), not(nullValue()));
   }
+
+  @Test
+  public void testConcurrentUploadUriAccessAndUpdates() throws Exception {
+    int threadCount = 12;
+    int iterations = 100;
+    ExecutorService executor = Executors.newFixedThreadPool(threadCount);
+    CountDownLatch startLatch = new CountDownLatch(1);
+    CountDownLatch doneLatch = new CountDownLatch(threadCount);
+    AtomicBoolean errorOccurred = new AtomicBoolean(false);
+
+    idFactory.setUploadUri("/test/upload");
+
+    for (int i = 0; i < threadCount; i++) {
+      final int threadId = i;
+      executor.submit(
+          () -> {
+            try {
+              startLatch.await();
+              for (int j = 0; j < iterations; j++) {
+                if (threadId % 3 == 0) {
+                  idFactory.setUploadUri("/test/upload" + (j % 5));
+                } else if (threadId % 3 == 1) {
+                  String uri = idFactory.getUploadUri();
+                  if (uri == null || !uri.startsWith("/test/upload")) {
+                    errorOccurred.set(true);
+                  }
+                } else {
+                  UploadId id =
+                      idFactory.readUploadId(
+                          "/test/upload" + (j % 5) + "/1911e8a4-6939-490c-b58b-a5d70f8d91fb");
+                  if (id != null && !id.toString().equals("1911e8a4-6939-490c-b58b-a5d70f8d91fb")) {
+                    errorOccurred.set(true);
+                  }
+                }
+              }
+            } catch (Exception e) {
+              errorOccurred.set(true);
+            } finally {
+              doneLatch.countDown();
+            }
+          });
+    }
+
+    startLatch.countDown();
+    assertThat(doneLatch.await(5, TimeUnit.SECONDS), is(true));
+    executor.shutdown();
+
+    assertThat(errorOccurred.get(), is(false));
+  }
 }