Do not run npm install if generated package json content has not changed

flow-server/src/main/java/com/vaadin/flow/server/frontend/NodeUpdater.java

@@ -259,16 +259,18 @@ void writeMainPackageFile(JsonObject packageJson) throws IOException {
         writePackageFile(packageJson, new File(npmFolder, PACKAGE_JSON));
     }
 
-    void writeAppPackageFile(JsonObject packageJson) throws IOException {
-        writePackageFile(packageJson, new File(generatedFolder, PACKAGE_JSON));
+    String writeAppPackageFile(JsonObject packageJson) throws IOException {
+        return writePackageFile(packageJson,
+                new File(generatedFolder, PACKAGE_JSON));
     }
 
-    void writePackageFile(JsonObject json, File packageFile)
+    String writePackageFile(JsonObject json, File packageFile)
             throws IOException {
         log().info("Updated npm {}.", packageFile.getAbsolutePath());
         FileUtils.forceMkdirParent(packageFile);
-        FileUtils.writeStringToFile(packageFile, stringify(json, 2) + "\n",
-                UTF_8.name());
+        String content = stringify(json, 2) + "\n";
+        FileUtils.writeStringToFile(packageFile, content, UTF_8.name());
+        return content;
     }
 
     Logger log() {

flow-server/src/main/java/com/vaadin/flow/server/frontend/TaskUpdatePackages.java

@@ -19,11 +19,14 @@
 import java.io.IOException;
 import java.io.Serializable;
 import java.io.UncheckedIOException;
+import java.nio.charset.StandardCharsets;
 import java.nio.file.FileVisitResult;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.SimpleFileVisitor;
 import java.nio.file.attribute.BasicFileAttributes;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Objects;
@@ -44,6 +47,7 @@
  */
 public class TaskUpdatePackages extends NodeUpdater {
 
+    static final String APP_PACKAGE_HASH = "vaadinAppPackageHash";
     private static final String VALUE = "value";
     private static final String SHRINK_WRAP = "@vaadin/vaadin-shrinkwrap";
     private boolean forceCleanUp;
@@ -78,9 +82,8 @@ public FileVisitResult postVisitDirectory(Path dir, IOException exc)
      * @param generatedPath
      *            folder where flow generated files will be placed.
      * @param forceCleanUp
-     *            forces the clean up process to be run. If {@code false},
-     *            clean up will be performed when platform version update is
-     *            detected.
+     *            forces the clean up process to be run. If {@code false}, clean
+     *            up will be performed when platform version update is detected.
      */
     TaskUpdatePackages(ClassFinder finder,
             FrontendDependencies frontendDependencies, File npmFolder,
@@ -97,9 +100,11 @@ public void execute() {
             if (packageJson == null) {
                 packageJson = Json.createObject();
             }
-            modified = updatePackageJsonDependencies(packageJson, deps);
-            if (modified) {
-                writeAppPackageFile(packageJson);
+            boolean isModified = updatePackageJsonDependencies(packageJson,
+                    deps);
+            if (isModified) {
+                String content = writeAppPackageFile(packageJson);
+                modified = updateAppPackageHash(getHash(content));
             }
         } catch (IOException e) {
             throw new UncheckedIOException(e);
@@ -153,8 +158,7 @@ private boolean ensureReleaseVersion(JsonObject dependencies)
             shrinkWrapVersion = dependencies.getString(SHRINK_WRAP);
         }
 
-        return Objects.equals(shrinkWrapVersion,
-                getCurrentShrinkWrapVersion());
+        return Objects.equals(shrinkWrapVersion, getCurrentShrinkWrapVersion());
     }
 
     private void cleanUp() throws IOException {
@@ -245,4 +249,42 @@ private String getShrinkWrapVersion(JsonObject packageJson)
         }
         return null;
     }
+
+    private String getHash(String content) {
+        try {
+            MessageDigest digest = MessageDigest.getInstance("SHA-256");
+            return bytesToHex(
+                    digest.digest(content.getBytes(StandardCharsets.UTF_8)));
+        } catch (NoSuchAlgorithmException e) {
+            // Unrecoverable runime exception, it may not happen
+            throw new RuntimeException(
+                    "Unable to find a provider for SHA-256 algorithm", e);
+        }
+    }
+
+    private boolean updateAppPackageHash(String hash) throws IOException {
+        JsonObject mainContent = getMainPackageJson();
+        if (mainContent == null) {
+            mainContent = Json.createObject();
+        }
+        boolean modified = !mainContent.hasKey(APP_PACKAGE_HASH)
+                || !hash.equals(mainContent.getString(APP_PACKAGE_HASH));
+        if (modified) {
+            mainContent.put(APP_PACKAGE_HASH, hash);
+            writeMainPackageFile(mainContent);
+        }
+        return modified;
+    }
+
+    private String bytesToHex(byte[] hash) {
+        StringBuilder result = new StringBuilder();
+        for (byte bit : hash) {
+            String hex = Integer.toHexString(0xff & bit);
+            if (hex.length() == 1) {
+                result.append('0');
+            }
+            result.append(hex);
+        }
+        return result.toString();
+    }
 }

flow-server/src/test/java/com/vaadin/flow/server/frontend/NodeUpdatePackagesTest.java

@@ -22,6 +22,7 @@
 import java.nio.file.Files;
 import java.util.Collections;
 
+import org.apache.commons.io.FileUtils;
 import org.junit.Assert;
 import org.junit.Before;
 import org.junit.Rule;
@@ -35,6 +36,7 @@
 import static com.vaadin.flow.server.Constants.PACKAGE_JSON;
 import static com.vaadin.flow.server.frontend.FrontendUtils.DEFAULT_GENERATED_DIR;
 import static elemental.json.impl.JsonUtil.stringify;
+import static java.nio.charset.StandardCharsets.UTF_8;
 
 public class NodeUpdatePackagesTest extends NodeUpdateTestUtil {
 
@@ -242,6 +244,58 @@ public void versionsMatch_forceCleanUp_cleanUp() throws IOException {
         assertCleanUp();
     }
 
+    @Test
+    public void generateAppPackageJsonFromScratch_updaterIsModified()
+            throws IOException {
+        packageCreator.execute();
+        packageUpdater.execute();
+
+        JsonObject mainJson = getPackageJson(mainPackageJson);
+        Assert.assertTrue(mainJson.hasKey(TaskUpdatePackages.APP_PACKAGE_HASH));
+
+        Assert.assertTrue(packageUpdater.modified);
+    }
+
+    @Test
+    public void regenerateAppPackageJson_sameContent_updaterIsNotModified()
+            throws IOException {
+        packageCreator.execute();
+        packageUpdater.execute();
+
+        System.out.println("xx " + getPackageJson(appPackageJson));
+
+        // delete generated file
+        appPackageJson.delete();
+
+        // regenerate it (with the same content)
+        packageCreator.execute();
+        packageUpdater.execute();
+
+        // the modified flag should be false (because the hash written in the
+        // main package json matches the content of the generated file) and "npm
+        // install" won't be executed
+        // as a result of this flag value
+        Assert.assertFalse(packageUpdater.modified);
+    }
+
+    @Test
+    public void generateAppPackageJson_changedContent_updaterIsModified()
+            throws IOException {
+        packageCreator.execute();
+        packageUpdater.execute();
+
+        System.out.println("xx " + getPackageJson(appPackageJson));
+
+        // delete generated file
+        appPackageJson.delete();
+
+        // generate it one more time, the content will be different since
+        // packageCreator has not added its content
+        packageUpdater.execute();
+
+        Assert.assertTrue(packageUpdater.modified);
+    }
+
     private void makeNodeModulesAndPackageLock() throws IOException {
         // Make two node_modules folders and package lock
         mainNodeModules.mkdirs();
@@ -320,4 +374,14 @@ private JsonObject makePackageLock(String version) {
         return object;
     }
 
+    JsonObject getPackageJson(File packageFile) throws IOException {
+        JsonObject packageJson = null;
+        if (packageFile.exists()) {
+            String fileContent = FileUtils.readFileToString(packageFile,
+                    UTF_8.name());
+            packageJson = Json.parse(fileContent);
+        }
+        return packageJson;
+    }
+
 }