htpack/handler.go

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package htpack
import (
"fmt"
"net/http"
"os"
"path"
"path/filepath"
"strconv"
"strings"
"time"
"golang.org/x/sys/unix"
2020-01-15 18:28:43 +00:00
"src.lwithers.me.uk/go/htpack/packed"
)
const (
encodingGzip = "gzip"
encodingBrotli = "br"
)
// 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
}
defer f.Close()
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 {
return nil, err
}
_, dir, err := packed.Load(f)
if err != nil {
unix.Munmap(mapped)
return nil, err
}
h := &Handler{
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 {
mapped []byte
dir map[string]*packed.File
headers map[string]string
startTime time.Time
notFound *packed.File
}
// 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
}
}
// SetIndex allows setting an index.html (or equivalent) that can be used to
// serve requests landing at a directory. For instance, if a file named
// "/foo/index.html" exists, and this function is called with "index.html",
// then a route will be registered to serve the contents of this file at
// "/foo". Noting that the ServeHTTP handler discards a trailing "/" on non
// root URLs, this means that it will serve equivalent content for requests
// to "/foo/index.html", "/foo/" and "/foo".
//
// Existing routes are not overwritten, and this function could be called
// multiple times with different filenames (noting later calls would not
// overwrite files matching earlier calls).
func (h *Handler) SetIndex(filename string) {
for k, v := range h.dir {
if filepath.Base(k) == filename {
routeToAdd := filepath.Dir(k)
if _, exists := h.dir[routeToAdd]; !exists {
h.dir[routeToAdd] = v
}
}
}
}
// SetNotFound allows overriding the returned resource when a request is made
// for a resource that does not exist. The default behaviour would be to return
// a standard HTTP 404 Not Found response; calling this function with an empty
// string will restore that behaviour.
//
// This function will return an error if the named resource is not present in
// the packfile.
func (h *Handler) SetNotFound(notFound string) error {
if notFound == "" {
h.notFound = nil
return nil
}
notFound = path.Clean(notFound)
dir := h.dir[path.Clean(notFound)]
if dir == nil {
return fmt.Errorf("no such resource %q", notFound)
}
h.notFound = dir
return nil
}
// 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 {
if h.notFound == nil {
http.NotFound(w, req)
return
}
info = h.notFound
}
// set standard headers
w.Header().Set("Vary", "Accept-Encoding")
w.Header().Set("Etag", info.Etag)
w.Header().Set("Content-Type", info.ContentType)
w.Header().Set("Accept-Ranges", "bytes")
// 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)
}
// range support (single-part ranges only)
// https://developer.mozilla.org/en-US/docs/Web/HTTP/Range_requests#Single_part_ranges
offset, length, isPartial := getFileRange(data, req)
if isPartial {
w.Header().Set("Content-Range", fmt.Sprintf("bytes %d-%d/%d",
offset, offset+length-1, data.Length))
}
// now we know exactly what we're writing, finalise HTTP header
w.Header().Set("Content-Length", strconv.FormatUint(length, 10))
if isPartial {
w.WriteHeader(http.StatusPartialContent)
} else {
w.WriteHeader(http.StatusOK)
}
// send body (though not for HEAD)
if req.Method == "HEAD" {
return
}
offset += data.Offset
w.Write(h.mapped[offset : offset+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)
}
// getFileRange returns the byte offset and length of the file to serve, along
// with whether or not it's partial content.
func getFileRange(data *packed.FileData, req *http.Request) (offset, length uint64, isPartial bool) {
length = data.Length
// only accept "Range: bytes=…"
r := req.Header.Get("Range")
if !strings.HasPrefix(r, "bytes=") {
return
}
r = strings.TrimPrefix(r, "bytes=")
// only accept a single range, "from-to", mapping to interval [from,to]
pos := strings.IndexByte(r, '-')
if pos == -1 {
return
}
sfrom, sto := r[:pos], r[pos+1:]
from, err := strconv.ParseUint(sfrom, 10, 64)
if err != nil {
return
}
to, err := strconv.ParseUint(sto, 10, 64)
if err != nil {
return
}
// validate the interval lies within the file
switch {
case from > to,
from >= data.Length,
to >= data.Length:
return
}
// all good
offset = from
length = to - from + 1
isPartial = true
return
}