htpack/handler.go

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package htpack
import (
"net"
"net/http"
"os"
"path"
"strconv"
"strings"
"time"
2019-04-12 09:07:17 +01:00
"github.com/lwithers/htpack/packed"
"golang.org/x/sys/unix"
)
const (
encodingGzip = "gzip"
encodingBrotli = "br"
)
// TODO: logging
// New returns a new handler. Standard security headers are set.
func New(packfile string) (*Handler, error) {
f, err := os.Open(packfile)
if err != nil {
return nil, err
}
fi, err := f.Stat()
if err != nil {
return nil, err
}
mapped, err := unix.Mmap(int(f.Fd()), 0, int(fi.Size()),
unix.PROT_READ, unix.MAP_SHARED)
if err != nil {
f.Close()
return nil, err
}
_, dir, err := packed.Load(f)
if err != nil {
unix.Munmap(mapped)
f.Close()
return nil, err
}
h := &Handler{
f: f,
mapped: mapped,
dir: dir.Files,
headers: make(map[string]string),
startTime: time.Now(),
}
// https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Frame-Options
h.SetHeader("X-Frame-Options", "sameorigin")
// https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Content-Type-Options
h.SetHeader("X-Content-Type-Options", "nosniff")
return h, nil
}
// Handler implements http.Handler and allows options to be set.
type Handler struct {
f *os.File
mapped []byte
dir map[string]*packed.File
headers map[string]string
startTime time.Time
}
// SetHeader allows a custom header to be set on HTTP responses. These are
// always emitted by ServeHTTP, whether the response status is success or
// otherwise. Note that you can override the standard security headers
// (X-Frame-Options and X-Content-Type-Options) using this function. You can
// remove previously-set headers altogether by passing an empty string for
// value.
func (h *Handler) SetHeader(key, value string) {
if value == "" {
delete(h.headers, key)
} else {
h.headers[key] = value
}
}
// ServeHTTP handles requests for files. It supports GET and HEAD methods, with
// anything else returning a 405. Exact path matches are required, else a 404 is
// returned.
func (h *Handler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
// set custom headers before any processing; ensures these are set even
// on error responses
for hkey, hval := range h.headers {
w.Header().Set(hkey, hval)
}
switch req.Method {
case "HEAD", "GET":
// OK
default:
http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
return
}
info := h.dir[path.Clean(req.URL.Path)]
if info == nil {
http.NotFound(w, req)
return
}
// set standard headers
w.Header().Set("Vary", "Accept-Encoding")
w.Header().Set("Etag", info.Etag)
w.Header().Set("Content-Type", info.ContentType)
// process etag / modtime
if clientHasCachedVersion(info.Etag, h.startTime, req) {
w.WriteHeader(http.StatusNotModified)
return
}
// select compression
data := info.Uncompressed
gzip, brotli := acceptedEncodings(req)
if brotli && info.Brotli != nil {
data = info.Brotli
w.Header().Set("Content-Encoding", encodingBrotli)
} else if gzip && info.Gzip != nil {
data = info.Gzip
w.Header().Set("Content-Encoding", encodingGzip)
}
// TODO: Range
// now we know exactly what we're writing, finalise HTTP header
w.Header().Set("Content-Length", strconv.FormatUint(data.Length, 10))
w.WriteHeader(http.StatusOK)
// send body (though not for HEAD)
if req.Method == "HEAD" {
return
}
h.sendfile(w, data)
}
func (h *Handler) sendfile(w http.ResponseWriter, data *packed.FileData) {
hj, ok := w.(http.Hijacker)
if !ok {
// fallback
h.copyfile(w, data)
return
}
conn, buf, err := hj.Hijack()
if err != nil {
// fallback
h.copyfile(w, data)
return
}
tcp, ok := conn.(*net.TCPConn)
if !ok {
// fallback
h.copyfile(w, data)
return
}
defer tcp.Close()
rawsock, err := tcp.SyscallConn()
if err == nil {
err = buf.Flush()
}
if err != nil {
// error only returned if the underlying connection is broken,
// so there's no point calling sendfile
return
}
off := int64(data.Offset)
remain := data.Length
for remain > 0 {
var amt int
if remain > (1 << 30) {
amt = (1 << 30)
} else {
amt = int(remain)
}
// TODO: outer error handling
rawsock.Control(func(outfd uintptr) {
amt, err = unix.Sendfile(int(outfd), int(h.f.Fd()), &off, amt)
})
remain -= uint64(amt)
if err != nil {
return
}
}
}
func (h *Handler) copyfile(w http.ResponseWriter, data *packed.FileData) {
w.Write(h.mapped[data.Offset : data.Offset+data.Length])
}
func acceptedEncodings(req *http.Request) (gzip, brotli bool) {
encodings := req.Header.Get("Accept-Encoding")
for _, enc := range strings.Split(encodings, ",") {
switch strings.TrimSpace(enc) {
case encodingGzip:
gzip = true
case encodingBrotli:
brotli = true
}
}
return
}
// clientHasCachedVersion returns true if the client has a cached version of
// the resource. We'll check the etags presented by the client, but if etags
// are not present then we'll check the if-modified-since date.
func clientHasCachedVersion(etag string, startTime time.Time, req *http.Request,
) bool {
checkEtags := req.Header.Get("If-None-Match")
for _, check := range strings.Split(checkEtags, ",") {
if etag == strings.TrimSpace(check) {
// client knows the etag, so it has this version of the
// resource cached already
return true
}
}
// if the client presented etags at all, we use that as our definitive
// answer
if _, sawEtags := req.Header["If-None-Match"]; sawEtags {
return false
}
// check the timestamp the client last grabbed the resource
cachedTime, err := http.ParseTime(req.Header.Get("If-Modified-Since"))
if err != nil {
return false
}
return cachedTime.After(startTime)
}