Git fetch failing using jgit: Remote does not have <branchname> available for fetch

Question

I have a bare repo located at main.git and am trying to fetch a branch (foo, let's say) in another repo, test, which has only just been git init'd:

fetchtest/
  |- main.git/
  |- test/
       |- .git/

Using regular git commands, I can do a git fetch ../main.git foo:foo and this will make a new branch foo in test/ and fetch the objects required for the branch. I then want to do the same thing but programmatically using JGit, ie not using the git CLI but using only Java code. There is no way I can use the git CLI:

Git git = Git.init().setDirectory(new File("fetchtest/test/")).call();

git.fetch().setRemote(new File("../main.git"))
           .setRefSpecs(new RefSpec("foo:foo"))
           .call();

but it just errors with:

org.eclipse.jgit.api.errors.TransportException: Remote does not have foo available for fetch.
    at org.eclipse.jgit.api.FetchCommand.call(FetchCommand.java:137)
    // ......
Caused by: org.eclipse.jgit.errors.TransportException: Remote does not have foo available for fetch.
    at org.eclipse.jgit.transport.FetchProcess.expandSingle(FetchProcess.java:349)
    at org.eclipse.jgit.transport.FetchProcess.executeImp(FetchProcess.java:139)
    at org.eclipse.jgit.transport.FetchProcess.execute(FetchProcess.java:113)
    at org.eclipse.jgit.transport.Transport.fetch(Transport.java:1069)
    at org.eclipse.jgit.api.FetchCommand.call(FetchCommand.java:128)

How do I get this to work?

Answer 1

What should work:

Git git = Git.init().setDirectory(new File("fetchtest/test/")).call();

git.fetch().setRemote(new File("../main.git"))
           .setRefSpecs(new RefSpec("refs/heads/foo:refs/heads/foo"))
           .call();

Note the RefSpec definition.
At least, try in your example:

new RefSpec("refs/heads/foo:refs/heads/foo")

The RefSpec class mentions:

/**
 * Parse a ref specification for use during transport operations.
 * <p>
 * Specifications are typically one of the following forms:
 * <ul>
 * <li><code>refs/head/master</code></li>
 * <li><code>refs/head/master:refs/remotes/origin/master</code></li>
 * <li><code>refs/head/*:refs/remotes/origin/*</code></li>
 * <li><code>+refs/head/master</code></li>
 * <li><code>+refs/head/master:refs/remotes/origin/master</code></li>
 * <li><code>+refs/head/*:refs/remotes/origin/*</code></li>
 * <li><code>:refs/head/master</code></li>
 * </ul>
 *
 * @param spec
 * string describing the specification.
 * @throws IllegalArgumentException
 * the specification is invalid.
*/

So "refs/head/" seems mandatory.

---

Original answer:

The setRemote() function on api.FetchCommand takes a name or an URI.

And looking at the FetchCommandTest URI definition, I prefer making the remote more visible:
I would rather define a named remote (here below: "test") for your second repo (referring your first repo), and then fetch.

// setup the first repository to fetch from the second repository
final StoredConfig config = db.getConfig();
RemoteConfig remoteConfig = new RemoteConfig(config, "test");
URIish uri = new URIish(db2.getDirectory().toURI().toURL());
remoteConfig.addURI(uri);
remoteConfig.update(config);
config.save();

// create some refs via commits and tag
RevCommit commit = git2.commit().setMessage("initial commit").call();
Ref tagRef = git2.tag().setName("tag").call();

Git git1 = new Git(db);

RefSpec spec = new RefSpec("refs/heads/master:refs/heads/x");
git1.fetch().setRemote("test").setRefSpecs(spec)
.call();