qurl/static/static.go

package static

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

type StaticContent struct {
	ContentType string
	Content     string
	ETag        string
	GZIPContent []byte
	GZIPETag    string
	DisableGZIP bool
}

func (ctx *StaticContent) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	// By default, don't use gzip
	useGZIP := false

	// If gzip isn't explicitly disabled, test for it
	if !ctx.DisableGZIP {
		useGZIP = strings.Contains(r.Header.Get("Accept-Encoding"), "gzip")
	}

	// If gzip is enabled, and there's no gzip etag,
	// generate the gzip'd content plus the etag
	if useGZIP && len(ctx.GZIPETag) == 0 {
		var buf bytes.Buffer

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

		if _, err := gz.Write(Assets[ctx.Content]); err != nil {
			http.Error(w, fmt.Sprintf("GZIP write error: %s", err.Error()),
				http.StatusInternalServerError)
			return
		}

		if err := gz.Flush(); err != nil {
			http.Error(w, fmt.Sprintf("GZIP flush error: %s", err.Error()),
				http.StatusInternalServerError)
			return
		}

		// Check if GZIP actually resulted in a smaller file
		if buf.Len() < len(Assets[ctx.Content]) {
			ctx.GZIPContent = buf.Bytes()
			ctx.GZIPETag = fmt.Sprintf("%x", md5.Sum(Assets[ctx.Content]))
		} else {
			// If gzip turns out to be ineffective, disable it
			ctx.DisableGZIP = true
			useGZIP = false
		}
	}

	var localETag string
	if useGZIP {
		localETag = ctx.GZIPETag
	} else {
		// Generate an ETag for content if necessary
		if ctx.ETag == "" {
			ctx.ETag = fmt.Sprintf("%x", md5.Sum(Assets[ctx.Content]))
		}
		localETag = ctx.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)

	// Check the content type, if we don't already
	// have one, make one
	if ctx.ContentType == "" {
		ext := path.Ext(ctx.Content)
		ctx.ContentType = mime.TypeByExtension(ext)
		// Fallback to default mime type
		if ctx.ContentType == "" {
			ctx.ContentType = "application/octet-stream"
		}
	}

	w.Header().Set("Content-Type", ctx.ContentType)

	// Finally, write our content
	if useGZIP {
		w.Header().Set("Content-Encoding", "gzip")
		w.Header().Set("Content-Length", fmt.Sprintf("%d", len(ctx.GZIPContent)))
		w.Write(ctx.GZIPContent)
	} else {
		w.Header().Set("Content-Length", fmt.Sprintf("%d", len(Assets[ctx.Content])))
		w.Write(Assets[ctx.Content])
	}
}