I am interested in having a user draw a line on the client side and then passing that to a geoprocessing service to preform further functions. Can you create a Graphics Layer and pass it as a polyline parameter?
Further more, can that graphic also be exported as a Shapefile from the browser? I've found some documentation online involving binaries but it was a little above my head. Didn't know if there was a easier way to do so? Or if there was any resources I could check out.
Or use editing in the API: Edit rivers and waterbodies
To save as a shapefile, you could pass the geometry to a server via AJAX and then write it out. I have an example that uses a single point and returns a shapefile using python.