Content-Length header versus chunked encoding

Question

I\'m trying to weigh the pros and cons of setting the Content-Length HTTP header versus using chunked encoding to return [possibly] large files from my server.

Answer 1

If the content length is known beforehand, then I would certainly prefer it above sending in chunks. If there's means of static files at the local disk file system or in a database, then any self-respected programming language and RDBMS provides ways to get the content length beforehand. You should make use of it.

On the other hand, if the content length is really unpredictable beforehand (e.g. when your intent is to zip several files together and send it as one), then sending it in chunks may be faster than buffering it in server's memory or writing to local disk file system first. But this indeed impacts the user experience negatively because the download progress is unknown. The impatient may then abort the download and move along.

Another benefit of knowing the content length beforehand is the ability to resume downloads. I see in your post history that your main programming language is Java; you can find here an article with more technical background information and a Java Servlet example which does that.