a simple url shortener in Go (check it out at qurl.org)
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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)
}
}