Add parameter to check current revision to prevent conflicts

scm-core/src/main/java/sonia/scm/repository/api/ModifyCommandBuilder.java

@@ -57,15 +57,6 @@ public class ModifyCommandBuilder {
     this.workdir = workdirProvider.createNewWorkdir();
   }
 
-  /**
-   * Set the branch that should be modified. The new commit will be made for this branch.
-   * @param branchToModify The branch to modify.
-   * @return This builder instance.
-   */
-  public ModifyCommandBuilder setBranchToModify(String branchToModify) {
-    return this;
-  }
-
   /**
    * Create a new file. The content of the file will be specified in a subsequent call to
    * {@link ContentLoader#withData(ByteSource)} or {@link ContentLoader#withData(InputStream)}.
@@ -158,6 +149,17 @@ public class ModifyCommandBuilder {
     return this;
   }
 
+  /**
+   * Set the expected revision of the branch, before the changes are applied. If the branch does not have the
+   * expected revision, a concurrent modification exception will be thrown when the command is executed and no
+   * changes will be applied.
+   * @return This builder instance.
+   */
+  public ModifyCommandBuilder setExpectedRevision(String expectedRevision) {
+    request.setExpectedRevision(expectedRevision);
+    return this;
+  }
+
   public interface ContentLoader {
     /**
      * Specify the data of the file using a {@link ByteSource}.

scm-core/src/main/java/sonia/scm/repository/spi/ModifyCommandRequest.java

@@ -22,6 +22,7 @@ public class ModifyCommandRequest implements Resetable, Validateable {
   private Person author;
   private String commitMessage;
   private String branch;
+  private String expectedRevision;
 
   @Override
   public void reset() {
@@ -63,11 +64,19 @@ public class ModifyCommandRequest implements Resetable, Validateable {
     return branch;
   }
 
+  public String getExpectedRevision() {
+    return expectedRevision;
+  }
+
   @Override
   public boolean isValid() {
     return StringUtils.isNotEmpty(commitMessage) && !requests.isEmpty();
   }
 
+  public void setExpectedRevision(String expectedRevision) {
+    this.expectedRevision = expectedRevision;
+  }
+
   public interface PartialRequest {
     void execute(ModifyCommand.Worker worker) throws IOException;
   }

scm-plugins/scm-git-plugin/src/main/java/sonia/scm/repository/spi/AbstractGitCommand.java

@@ -240,6 +240,10 @@ class AbstractGitCommand
       logger.debug("pushed changes");
     }
 
+    Ref getCurrentRevision() throws IOException {
+      return getClone().getRepository().getRefDatabase().findRef("HEAD");
+    }
+
     private Person determineAuthor(Person author) {
       if (author == null) {
         Subject subject = SecurityUtils.getSubject();

scm-plugins/scm-git-plugin/src/main/java/sonia/scm/repository/spi/GitModifyCommand.java

@@ -5,6 +5,7 @@ import org.eclipse.jgit.api.Git;
 import org.eclipse.jgit.api.errors.GitAPIException;
 import org.eclipse.jgit.revwalk.RevCommit;
 import sonia.scm.BadRequestException;
+import sonia.scm.ConcurrentModificationException;
 import sonia.scm.ContextEntry;
 import sonia.scm.repository.GitWorkdirFactory;
 import sonia.scm.repository.InternalRepositoryException;
@@ -51,6 +52,11 @@ public class GitModifyCommand extends AbstractGitCommand implements ModifyComman
       if (!StringUtils.isEmpty(request.getBranch())) {
         checkOutBranch(request.getBranch());
       }
+      if (!StringUtils.isEmpty(request.getExpectedRevision())) {
+        if (!request.getExpectedRevision().equals(getCurrentRevision().getName())) {
+          throw new ConcurrentModificationException("branch", request.getBranch() == null? "default": request.getBranch());
+        }
+      }
       for (ModifyCommandRequest.PartialRequest r : request.getRequests()) {
         r.execute(this);
       }

scm-plugins/scm-git-plugin/src/test/java/sonia/scm/repository/spi/GitModifyCommandTest.java

@@ -15,6 +15,7 @@ import org.junit.Test;
 import org.junit.rules.TemporaryFolder;
 import sonia.scm.AlreadyExistsException;
 import sonia.scm.BadRequestException;
+import sonia.scm.ConcurrentModificationException;
 import sonia.scm.repository.Person;
 import sonia.scm.repository.util.WorkdirProvider;
 
@@ -56,7 +57,7 @@ public class GitModifyCommandTest extends AbstractGitCommandTestBase {
   }
 
   @Test
-  public void shouldCreateCommitOnSelectedBranch() throws IOException, GitAPIException {
+  public void shouldCreateCommitOnSelectedBranch() throws IOException {
     File newFile = Files.write(temporaryFolder.newFile().toPath(), "new content".getBytes()).toFile();
 
     GitModifyCommand command = createCommand();
@@ -95,7 +96,7 @@ public class GitModifyCommandTest extends AbstractGitCommandTestBase {
   }
 
   @Test(expected = AlreadyExistsException.class)
-  public void shouldFailIfOverwritingExistingFileWithoutOverwriteFlag() throws IOException, GitAPIException {
+  public void shouldFailIfOverwritingExistingFileWithoutOverwriteFlag() throws IOException {
     File newFile = Files.write(temporaryFolder.newFile().toPath(), "new content".getBytes()).toFile();
 
     GitModifyCommand command = createCommand();
@@ -140,6 +141,21 @@ public class GitModifyCommandTest extends AbstractGitCommandTestBase {
     command.execute(request);
   }
 
+  @Test(expected = ConcurrentModificationException.class)
+  public void shouldFailBranchDoesNotHaveExpectedRevision() throws IOException {
+    File newFile = Files.write(temporaryFolder.newFile().toPath(), "irrelevant\n".getBytes()).toFile();
+
+    GitModifyCommand command = createCommand();
+
+    ModifyCommandRequest request = new ModifyCommandRequest();
+    request.setCommitMessage("test commit");
+    request.addRequest(new ModifyCommandRequest.CreateFileRequest("irrelevant", newFile, true));
+    request.setAuthor(new Person("Dirk Gently", "dirk@holistic.det"));
+    request.setExpectedRevision("abc");
+
+    command.execute(request);
+  }
+
   private void assertInTree(TreeAssertions assertions) throws IOException, GitAPIException {
     try (Git git = new Git(createContext().open())) {
       RevCommit lastCommit = getLastCommit(git);