creating tar archives using gulp - gulp

Question

I'm using gulp-tar to create a tar file... how do I add a top level folder so that when the user runs tar -xzf myArchive.tar it extracts into a specific folder.
here's my code:
gulp.task('prod', ['min', 'gittag'], function() {
//copy all files under /server into a zip file
gulp.src('../server/**/*')
.pipe(tar('xoserver' + '-'+ gittag +'.tar'))
.pipe(gzip())
.pipe(gulp.dest('../prod'));
});
The above creates a tar.zip file all right, but I have to be careful to add a -C <folder> while extracting, else the files get extracted to the current folder.
[edited]
What I'm trying to do here is generate a tarball of the format xoserver-alpha-d414ddf.tar.gz which, when extracted with a tar xvf will create a folder xoserver-alpha-d414ddf and unpack all the files under it. Essentially I am trying to add new folder name above my packed files.
If I add a base option, the folder extracted to is just server
[ANSWER]
Thanks to ddprrt for a good answer. I am reproducing the final code in case someone else wants to use a similar strategy of embedding the git tag into the name of the tarball for distribution/testing.
gulp.task('gittag', function(cb) { // generate the git tag
git.exec({args : 'branch -v'}, function (err, stdout) {
var lines = stdout.split('\n');
for (var l in lines) {
if (lines[l][0] == '*') {
var words = lines[l].split(/\s+/);
gittag = words[1]+ '-' + words[2];
console.log('Gittag is %s', gittag);
break;
}
}
cb();
});
});
gulp.task('min', ['runbmin', 'template', 'vendor']); // generate min files
gulp.task('prod', ['min', 'gittag'], function() { // create tarball
//copy all files under /server into a zip file
return gulp.src('../server/**/*')
.pipe(rename(function(path) {
path.dirname = 'server-' + gittag + '/' + path.dirname;
}))
.pipe(tar('xoserver-'+gittag+'.tar'))
.pipe(gzip())
.pipe(gulp.dest('../prod'));
});

Answer 1

This is what the base option is for.
gulp.task('prod', ['min', 'gittag'], function() {
return gulp.src('../server/**/*', { base: '../server/' })
.pipe(tar('xoserver' + '-'+ gittag +'.tar'))
.pipe(gzip())
.pipe(gulp.dest('../prod'));
});
With it you can tell gulp which paths to include when dealing with the globs you receive.
Btw. Don't forget to return streams or call the done callback in your task. Helps gulp orchestrating your build pipeline
As for the second question, you can use gulp-rename task to change the directory where your virtual files are located. Would be something like
.pipe(rename(function(path) {
path.dirname = 'whatever/' + path.dirname
}));