How to send compressed (deflated) SVG via Apache2?

Question

I have specified the following attributes in my site's .htaccess file:

AddOutputFilterByType DEFLATE image/svg+xml DeflateCompressionLevel 9 Header append Vary Accept-Encoding 

However, my SVG asset is not being sent in compressed form:

$ curl https://example.org/assets/svg/asset.svg --silent -H "Accept-Encoding: gzip,deflate" --write-out "${size_download}\n" --output /dev/null                  152655                                                                                                                                                                                                                                   $ curl https://example.org/assets/svg/asset.svg --silent --write-out "%{size_download}\n" --output /dev/null 152655 

I verified that this asset (asset.svg) is being sent with MIME type image/svg+xml using Chrome, but using the Web Developer tools, this specific file is not being compressed when sent to the client.

Adding other MIME types to the .htaccess file is successful (e.g., adding text/html compresses the HTML assets).

This seems specific to how SVG data are handled. What else can I try or troubleshoot to get SVG compression working?

Answer 1

If Apache doesn't know the mime type of the file (here image/svg+xml), you need to tell it specifically (not needed in most Apaches):

AddType image/svg+xml svg svgz 

Now when Apache knows about the filetype, just add this to deflate it:

AddOutputFilterByType DEFLATE image/svg+xml 

For more information see https://httpd.apache.org/docs/2.4/mod/mod_deflate.html

Answer 2

I suspect this is due to the plus sign in the MIME type, which may need escaping in the AddOutputFilterByType directive. You can also try using the AddOutputFilter directive instead, to process all files with a certain extension:

AddOutputFilter DEFLATE svg