server: use real content length, use system MIME info instead of handrolling it

main.go

@@ -5,8 +5,9 @@ import (
 	"fmt"
 	"io/ioutil"
 	"log"
+	"mime"
 	"net/http"
-	"strings"
+	"path/filepath"
 
 	"code.ivysaur.me/libnmdc"
 	"github.com/googollee/go-socket.io"
@@ -204,27 +205,8 @@ func (this *App) StaticRequestHandler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	knownContentTypes := map[string]string{
+	w.Header().Set("Content-Type", mime.TypeByExtension(filepath.Ext(fileName)))
-		".htm": "text/html",
+	w.Header().Set("Content-Length", fmt.Sprintf("%d", len(data)))
-		".png": "image/png",
-		".ico": "image/x-icon",
-		// No CSS/JS since they're embedded in the HTML
-	}
-
-	foundMime := false
-	for ext, mimeType := range knownContentTypes {
-		if strings.HasSuffix(fileName, ext) {
-			w.Header().Set("Content-Type", mimeType)
-			foundMime = true
-			break
-		}
-	}
-	if !foundMime {
-		w.Header().Set("Content-Type", "application/x-octet-stream")
-	}
-	dataInfo, _ := AssetInfo(fileName)
-	w.Header().Set("Content-Length", fmt.Sprintf("%d", dataInfo.Size()))
-
 	w.Write(data)
 }