Setting the 'charset' property on the Content-Type header in the golang HTTP FileServer

Question

I've got an issue when testing a golang web app. In the deployed version, nginx fronts the application and explicitly sets charset utf8; so that all textual content types are appended with a charset declaration.

In testing, I'm hitting the golang application directly, and here the content type does not have a charset set. This is causing problems when trying to serve libraries like d3 which has lines like:

var ε = 1e-6, ε2 = ε * ε, π = Math.PI, τ = 2 * π, τε = τ - ε, halfπ = π / 2, d3_radians = π / 180, d3_degrees = 180 / π;

Because golang doesn't specify the charset, these are rendered in chrome as:

var ε = 1e-6, ε2 = ε * ε....

What's the best way of getting the golang http server to output the charset=utf8 declaration on the HTTP headers?

Answer 1

FileServer calls mime.TypeByExtension to get the content type. If no type is registered for the extension, then FileServer calls http.DetectContentType to guess the type from the contents of the file.

If a text/ content type does not specify a charset parameter, then the mime package automatically adds the 'charset=utf-8' parameter to the content type.

To debug this problem, check to see if the system mime.types file specifies a content type for the file extension and that the charset parameter is'charset=utf-8' or the charset parameter is not set.

If the system mime.types entry is missing or incorrect, then call mime.AddExtensionType to override the system setting. This can be called once before any content is served.