qurl/assets/assets.go

package assets

import (
	"bytes"
	"compress/gzip"
	"crypto/md5"
	"embed"
	"fmt"
	"net/http"
	"strings"
)

//go:embed *.ico *.html *.css
var assets embed.FS

func ReadFile(name string) ([]byte, error) {
	return assets.ReadFile(name)
}

type StaticContent struct {
	Type        string
	Content     []byte
	ETag        string
	GZIPContent []byte
	GZIPETag    string
}

func NewStaticContent(name string, mime string) (*StaticContent, error) {
	// Load data
	data, err := assets.ReadFile(name)
	if err != nil {
		return nil, err
	}
	sc := &StaticContent{Type: mime, Content: data}

	// Set a default Content-Type, if needed
	if sc.Type == "" {
		sc.Type = "application/octet-stream"
	}

	// Populate ETag
	sc.ETag = fmt.Sprintf("%x", md5.Sum(sc.Content))

	var buf bytes.Buffer
	gz, _ := gzip.NewWriterLevel(&buf, gzip.BestCompression)
	defer gz.Close()

	if _, err := gz.Write(sc.Content); err != nil {
		return nil, err
	}

	if err := gz.Flush(); err != nil {
		return nil, err
	}

	// Using gzip encoding adds a minimum of 24 characters to the HTTP
	// header, so only accept gzip encoding if we save that much or more
	if (buf.Len() + 24) < len(sc.Content) {
		sc.GZIPContent = buf.Bytes()
		sc.GZIPETag = fmt.Sprintf("%x", md5.Sum(sc.GZIPContent))
	}
	return sc, nil
}

func (sc *StaticContent) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	gzok := strings.Contains(r.Header.Get("Accept-Encoding"), "gzip")
	gzlen := len(sc.GZIPContent)

	// Use the correct etag
	var localETag string
	if gzok && gzlen > 0 {
		localETag = sc.GZIPETag
	} else {
		localETag = sc.ETag
	}

	// Check the etag, maybe we don't need to send content
	remoteETag := r.Header.Get("If-None-Match")
	if localETag == remoteETag {
		w.WriteHeader(http.StatusNotModified)
		return
	}
	w.Header().Set("ETag", localETag)
	w.Header().Set("Content-Type", sc.Type)

	// Finally, write our content
	if gzok && gzlen > 0 {
		w.Header().Set("Content-Encoding", "gzip")
		w.Header().Set("Content-Length", fmt.Sprintf("%d", gzlen))
		w.Write(sc.GZIPContent)
	} else {
		w.Header().Set("Content-Length", fmt.Sprintf("%d", len(sc.Content)))
		w.Write(sc.Content)
	}
}