Add support for custom CSS files

Specify the ```styles``` config option for a host and point to a
valid CSS file to use this instead of the default one. This fixes #9.

CONFIGURATION.md

@@ -81,6 +81,11 @@ Set this option to `true` to disable this feature.
 
 Pages are converted automatically by [gmitohtml](https://code.rocketnine.space/tslocum/gmitohtml).
 
+## Styles
+
+Specify a custom CSS styles file if you want to override the default. This only
+affects the `HTTPS` protocol (obviously).
+
 ### DisableSize
 
 The size of the response body is included in the media type header by default.
@@ -223,6 +228,7 @@ hosts:
   gemini.rocks:
     cert: /srv/gemini.rocks/data/cert.crt
     key: /srv/gemini.rocks/data/cert.key
+    styles: /srv/gemini.rocks/styles.css # Custom CSS styles
     paths:
       -
         path: ^/.*\.php$

config.go

@@ -66,6 +66,9 @@ type hostConfig struct {
 	Key   string
 	Paths []*pathConfig
 
+	// Custom CSS styles. If specified, it will be used for all paths in that host/domain.
+	Styles string
+
 	cert *tls.Certificate
 }
 

serve_https.go

@@ -31,6 +31,22 @@ func serveHTTPS(w http.ResponseWriter, r *http.Request) (int, int64, string) {
 		http.Redirect(w, r, u.String(), status)
 		return status, -1, ""
 	} else if r.URL.Path == "/assets/style.css" {
+		// Do we have a custom CSS file? If so, we use this instead.
+		styleFilepath := config.Hosts[r.URL.Hostname()].Styles
+		if styleFilepath != "" {
+			_, err := os.Stat(styleFilepath)
+			if os.IsNotExist(err) {
+				http.Error(w, "Custom styles not found", http.StatusNotFound)
+				return http.StatusNotFound, -1, ""
+			}
+
+			cssBytes, err = ioutil.ReadFile(styleFilepath)
+			if err != nil {
+				http.Error(w, "Cannot process custom styles", http.StatusInternalServerError)
+				return http.StatusInternalServerError, -1, ""
+			}
+		}
+
 		status := http.StatusOK
 		w.Header().Set("Content-Type", cssType)
 		w.WriteHeader(status)
@@ -38,6 +54,7 @@ func serveHTTPS(w http.ResponseWriter, r *http.Request) (int, int64, string) {
 		if r.Method == "HEAD" {
 			return status, 0, ""
 		}
+
 		w.Write(cssBytes)
 		return status, int64(len(cssBytes)), ""
 	}