server.go

package spaserver

import (
	"bytes"
	"errors"
	"fmt"
	"io"
	"mime"
	"mime/multipart"
	"net/http"
	"net/textproto"
	"net/url"
	"os"
	"path"
	"path/filepath"
	"regexp"
	"sort"
	"strconv"
	"strings"
	"time"
)

// toHTTPError returns a non-specific HTTP error message and status code
// for a given non-nil error value. It's important that toHTTPError does not
// actually return err.Error(), since msg and httpStatus are returned to users,
// and historically Go's ServeContent always returned just "404 Not Found" for
// all errors. We don't want to start leaking information in error messages.
func toHTTPError(err error) (msg string, httpStatus int) {
	if os.IsNotExist(err) {
		return "404 page not found", http.StatusNotFound
	}
	if os.IsPermission(err) {
		return "403 Forbidden", http.StatusForbidden
	}
	// Default:
	return "500 Internal Server Error", http.StatusInternalServerError
}

// localRedirect gives a Moved Permanently response.
// It does not convert relative paths to absolute paths like Redirect does.
func localRedirect(w http.ResponseWriter, r *http.Request, newPath string) {
	if q := r.URL.RawQuery; q != "" {
		newPath += "?" + q
	}
	w.Header().Set("Location", newPath)
	w.WriteHeader(http.StatusMovedPermanently)
}

var unixEpochTime = time.Unix(0, 0)

// modtime is the modification time of the resource to be served, or IsZero().
// return value is whether this request is now complete.
func checkLastModified(w http.ResponseWriter, r *http.Request, modtime time.Time) bool {
	if modtime.IsZero() || modtime.Equal(unixEpochTime) {
		// If the file doesn't have a modtime (IsZero), or the modtime
		// is obviously garbage (Unix time == 0), then ignore modtimes
		// and don't process the If-Modified-Since header.
		return false
	}

	// The Date-Modified header truncates sub-second precision, so
	// use mtime < t+1s instead of mtime <= t to check for unmodified.
	if t, err := time.Parse(http.TimeFormat, r.Header.Get("If-Modified-Since")); err == nil && modtime.Before(t.Add(1*time.Second)) {
		h := w.Header()
		delete(h, "Content-Type")
		delete(h, "Content-Length")
		w.WriteHeader(http.StatusNotModified)
		return true
	}
	w.Header().Set("Last-Modified", modtime.UTC().Format(http.TimeFormat))
	return false
}

// checkETag implements If-None-Match and If-Range checks.
//
// The ETag or modtime must have been previously set in the
// ResponseWriter's headers.  The modtime is only compared at second
// granularity and may be the zero value to mean unknown.
//
// The return value is the effective request "Range" header to use and
// whether this request is now considered done.
func checkETag(w http.ResponseWriter, r *http.Request, modtime time.Time) (rangeReq string, done bool) {
	etag := w.Header().Get("Etag")
	rangeReq = r.Header.Get("Range")

	// Invalidate the range request if the entity doesn't match the one
	// the client was expecting.
	// "If-Range: version" means "ignore the Range: header unless version matches the
	// current file."
	// We only support ETag versions.
	// The caller must have set the ETag on the response already.
	if ir := r.Header.Get("If-Range"); ir != "" && ir != etag {
		// The If-Range value is typically the ETag value, but it may also be
		// the modtime date. See golang.org/issue/8367.
		timeMatches := false
		if !modtime.IsZero() {
			if t, err := http.ParseTime(ir); err == nil && t.Unix() == modtime.Unix() {
				timeMatches = true
			}
		}
		if !timeMatches {
			rangeReq = ""
		}
	}

	if inm := r.Header.Get("If-None-Match"); inm != "" {
		// Must know ETag.
		if etag == "" {
			return rangeReq, false
		}

		// TODO(bradfitz): non-GET/HEAD requests require more work:
		// sending a different status code on matches, and
		// also can't use weak cache validators (those with a "W/
		// prefix).  But most users of ServeContent will be using
		// it on GET or HEAD, so only support those for now.
		if r.Method != "GET" && r.Method != "HEAD" {
			return rangeReq, false
		}

		// TODO(bradfitz): deal with comma-separated or multiple-valued
		// list of If-None-match values.  For now just handle the common
		// case of a single item.
		if inm == etag || inm == "*" {
			h := w.Header()
			delete(h, "Content-Type")
			delete(h, "Content-Length")
			w.WriteHeader(http.StatusNotModified)
			return "", true
		}
	}
	return rangeReq, false
}

func sumRangesSize(ranges []httpRange) (size int64) {
	for _, ra := range ranges {
		size += ra.length
	}
	return
}

// make a sortable type
type byName []os.FileInfo

func (s byName) Len() int           { return len(s) }
func (s byName) Less(i, j int) bool { return s[i].Name() < s[j].Name() }
func (s byName) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }

var htmlReplacer = strings.NewReplacer(
	"&", "&amp;",
	"<", "&lt;",
	">", "&gt;",
	// "&#34;" is shorter than "&quot;".
	// "&#39;" is shorter than "&apos;" and apos was not in HTML until HTML5.
	"'", "&#39;",
)

func dirList(w http.ResponseWriter, f http.File) {
	dirs, err := f.Readdir(-1)
	if err != nil {
		// TODO: log err.Error() to the Server.ErrorLog, once it's possible
		// for a handler to get at its Server via the ResponseWriter. See
		// Issue 12438.
		http.Error(w, "Error reading directory", http.StatusInternalServerError)
		return
	}
	sort.Sort(byName(dirs))

	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	fmt.Fprintf(w, "<pre>\n")
	for _, d := range dirs {
		name := d.Name()
		if d.IsDir() {
			name += "/"
		}
		// name may contain '?' or '#', which must be escaped to remain
		// part of the URL path, and not indicate the start of a query
		// string or fragment.
		url := url.URL{Path: name}
		fmt.Fprintf(w, "<a href=\"%s\">%s</a>\n", url.String(), htmlReplacer.Replace(name))
	}
	fmt.Fprintf(w, "</pre>\n")
}

type fileHandler struct {
	root      http.FileSystem
	rootDir   string
	baseHref  string
	hasPrefix bool
}

// FileServer returns a handler that serves HTTP requests
// with the contents of the file system rooted at root.
//
// To use the operating system's file system implementation,
// use http.Dir:
//
//     http.Handle("/", spaserver.New(http.Dir("/tmp"), "mount/point"))
//
// As a special case, the returned file server redirects any request
// ending in "/index.html" to the same path, without the final
// "index.html".
func New(root, baseHref string) http.Handler {
	return &fileHandler{http.Dir(root), root, baseHref, baseHref != ""}
}

func (f *fileHandler) getBaseHref() string {
	if !f.hasPrefix {
		return ""
	}
	if f.baseHref[0] == '/' {
		return f.baseHref
	}
	return "/" + f.baseHref
}

func (f *fileHandler) getBaseHrefTag() string {
	return fmt.Sprintf(`<base href="%s/">`, f.getBaseHref())
}

var looper = 0

func (f *fileHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	upath := r.URL.Path
	debug("%s requested", upath)
	if !strings.HasPrefix(upath, "/") {
		upath = "/" + upath
	}
	if f.hasPrefix {
		debug(`replacing %s in %s with ""`, f.getBaseHref(), upath)
		upath = strings.Replace(upath, f.getBaseHref(), "", 1)
	}
	r.URL.Path = upath
	debug("%s being served", path.Clean(upath))
	looper = 0
	f.serveFile(w, r, f.root, path.Clean(upath), true)
}

var testIfFile = regexp.MustCompile(`\.[a-z0-9A-Z]+$`)

// name is '/'-separated, not filepath.Separator.
func (f *fileHandler) serveFile(w http.ResponseWriter, r *http.Request, fs http.FileSystem, name string, redirect bool) {
	looper += 1
	if looper > 10 {
		panic("TILT")
	}
	const indexPage = "/index.html"

	debug("opening %s from fs", name)
	file, err := fs.Open(name)
	if err != nil {
		if os.IsNotExist(err) {
			if !testIfFile.MatchString(name) {
				f.serveFile(w, r, fs, ".", redirect)
				return
			}
		}
		msg, code := toHTTPError(err)
		http.Error(w, msg, code)
		return
	}
	defer file.Close()

	debug("getting stat")
	d, err1 := file.Stat()
	if err1 != nil {
		if os.IsNotExist(err1) {
			if !testIfFile.MatchString(name) {
				f.serveFile(w, r, fs, f.rootDir, redirect)
				return
			}
		}
		msg, code := toHTTPError(err1)
		http.Error(w, msg, code)
		return
	}

	// use contents of index.html for directory, if present
	if d.IsDir() {
		index := strings.TrimSuffix(name, "/") + indexPage
		ff, err := fs.Open(index)
		if err == nil {
			defer ff.Close()
			dd, err := ff.Stat()
			if err == nil {
				name = index
				d = dd
				file = ff
			}
		}
	}

	// Still a directory? (we didn't find an index.html file)
	if d.IsDir() {
		f.serveFile(w, r, fs, ".", redirect)
	}

	// serveContent will check modification time
	sizeFunc := func() (int64, error) { return d.Size(), nil }
	f.serveContent(w, r, d.Name(), d.ModTime(), sizeFunc, file)
}

// errSeeker is returned by ServeContent's sizeFunc when the content
// doesn't seek properly. The underlying Seeker's error text isn't
// included in the sizeFunc reply so it's not sent over HTTP to end
// users.
var errSeeker = errors.New("seeker can't seek")

// The algorithm uses at most sniffLen bytes to make its decision
const sniffLen = 512

// countingWriter counts how many bytes have been written to it.
type countingWriter int64

func (w *countingWriter) Write(p []byte) (n int, err error) {
	*w += countingWriter(len(p))
	return len(p), nil
}

// rangesMIMESize returns the number of bytes it takes to encode the
// provided ranges as a multipart response.
func rangesMIMESize(ranges []httpRange, contentType string, contentSize int64) (encSize int64) {
	var w countingWriter
	mw := multipart.NewWriter(&w)
	for _, ra := range ranges {
		mw.CreatePart(ra.mimeHeader(contentType, contentSize))
		encSize += ra.length
	}
	mw.Close()
	encSize += int64(w)
	return
}

// if name is empty, filename is unknown. (used for mime type, before sniffing)
// if modtime.IsZero(), modtime is unknown.
// content must be seeked to the beginning of the file.
// The sizeFunc is called at most once. Its error, if any, is sent in the HTTP response.
func (f *fileHandler) serveContent(w http.ResponseWriter, r *http.Request, name string, modtime time.Time, sizeFunc func() (int64, error), content io.ReadSeeker) {
	if checkLastModified(w, r, modtime) {
		return
	}
	rangeReq, done := checkETag(w, r, modtime)
	if done {
		return
	}

	code := http.StatusOK

	// If Content-Type isn't set, use the file's extension to find it, but
	// if the Content-Type is unset explicitly, do not sniff the type.
	ctypes, haveType := w.Header()["Content-Type"]
	var ctype string
	if !haveType {
		ctype = mime.TypeByExtension(filepath.Ext(name))
		if ctype == "" {
			// read a chunk to decide between utf-8 text and binary
			var buf [sniffLen]byte
			n, _ := io.ReadFull(content, buf[:])
			ctype = http.DetectContentType(buf[:n])
			_, err := content.Seek(0, os.SEEK_SET) // rewind to output whole file
			if err != nil {
				http.Error(w, "seeker can't seek", http.StatusInternalServerError)
				return
			}
		}
		w.Header().Set("Content-Type", ctype)
	} else if len(ctypes) > 0 {
		ctype = ctypes[0]
	}

	size, err := sizeFunc()
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	var sendContent io.Reader
	const indexPage = "index.html"
	debug("testing if %s is an index page", name)
	debug("size %d", size)
	// add the correct base href
	if strings.HasSuffix(name, indexPage) {
		debug("replacing base href tag with %s", f.getBaseHrefTag())
		original := make([]byte, size)
		_, err := content.Read(original)
		if err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
		newContent := bytes.Replace(original, []byte(`<base href="">`), []byte(f.getBaseHrefTag()), 1)
		size = int64(len(newContent))
		sendContent = bytes.NewBuffer(newContent)
	} else {
		sendContent = content
	}
	debug("new size %d", size)
	// handle Content-Range header.
	sendSize := size
	if size >= 0 {
		ranges, err := parseRange(rangeReq, size)
		if err != nil {
			http.Error(w, err.Error(), http.StatusRequestedRangeNotSatisfiable)
			return
		}
		if sumRangesSize(ranges) > size {
			// The total number of bytes in all the ranges
			// is larger than the size of the file by
			// itself, so this is probably an attack, or a
			// dumb client.  Ignore the range request.
			ranges = nil
		}
		switch {
		case len(ranges) == 1:
			// RFC 2616, Section 14.16:
			// "When an HTTP message includes the content of a single
			// range (for example, a response to a request for a
			// single range, or to a request for a set of ranges
			// that overlap without any holes), this content is
			// transmitted with a Content-Range header, and a
			// Content-Length header showing the number of bytes
			// actually transferred.
			// ...
			// A response to a request for a single range MUST NOT
			// be sent using the multipart/byteranges media type."
			ra := ranges[0]
			if _, err := content.Seek(ra.start, os.SEEK_SET); err != nil {
				http.Error(w, err.Error(), http.StatusRequestedRangeNotSatisfiable)
				return
			}
			sendSize = ra.length
			code = http.StatusPartialContent
			w.Header().Set("Content-Range", ra.contentRange(size))
		case len(ranges) > 1:
			sendSize = rangesMIMESize(ranges, ctype, size)
			code = http.StatusPartialContent

			pr, pw := io.Pipe()
			mw := multipart.NewWriter(pw)
			w.Header().Set("Content-Type", "multipart/byteranges; boundary="+mw.Boundary())
			sendContent = pr
			defer pr.Close() // cause writing goroutine to fail and exit if CopyN doesn't finish.
			go func() {
				for _, ra := range ranges {
					part, err := mw.CreatePart(ra.mimeHeader(ctype, size))
					if err != nil {
						pw.CloseWithError(err)
						return
					}
					if _, err := content.Seek(ra.start, os.SEEK_SET); err != nil {
						pw.CloseWithError(err)
						return
					}
					if _, err := io.CopyN(part, content, ra.length); err != nil {
						pw.CloseWithError(err)
						return
					}
				}
				mw.Close()
				pw.Close()
			}()
		}

		w.Header().Set("Accept-Ranges", "bytes")
		if w.Header().Get("Content-Encoding") == "" {
			w.Header().Set("Content-Length", strconv.FormatInt(sendSize, 10))
		}
	}

	w.WriteHeader(code)

	if r.Method != "HEAD" {
		io.CopyN(w, sendContent, sendSize)
	}
}

// httpRange specifies the byte range to be sent to the client.
type httpRange struct {
	start, length int64
}

func (r httpRange) contentRange(size int64) string {
	return fmt.Sprintf("bytes %d-%d/%d", r.start, r.start+r.length-1, size)
}

func (r httpRange) mimeHeader(contentType string, size int64) textproto.MIMEHeader {
	return textproto.MIMEHeader{
		"Content-Range": {r.contentRange(size)},
		"Content-Type":  {contentType},
	}
}

// parseRange parses a Range header string as per RFC 2616.
func parseRange(s string, size int64) ([]httpRange, error) {
	if s == "" {
		return nil, nil // header not present
	}
	const b = "bytes="
	if !strings.HasPrefix(s, b) {
		return nil, errors.New("invalid range")
	}
	var ranges []httpRange
	for _, ra := range strings.Split(s[len(b):], ",") {
		ra = strings.TrimSpace(ra)
		if ra == "" {
			continue
		}
		i := strings.Index(ra, "-")
		if i < 0 {
			return nil, errors.New("invalid range")
		}
		start, end := strings.TrimSpace(ra[:i]), strings.TrimSpace(ra[i+1:])
		var r httpRange
		if start == "" {
			// If no start is specified, end specifies the
			// range start relative to the end of the file.
			i, err := strconv.ParseInt(end, 10, 64)
			if err != nil {
				return nil, errors.New("invalid range")
			}
			if i > size {
				i = size
			}
			r.start = size - i
			r.length = size - r.start
		} else {
			i, err := strconv.ParseInt(start, 10, 64)
			if err != nil || i >= size || i < 0 {
				return nil, errors.New("invalid range")
			}
			r.start = i
			if end == "" {
				// If no end is specified, range extends to end of the file.
				r.length = size - r.start
			} else {
				i, err := strconv.ParseInt(end, 10, 64)
				if err != nil || r.start > i {
					return nil, errors.New("invalid range")
				}
				if i >= size {
					i = size - 1
				}
				r.length = i - r.start + 1
			}
		}
		ranges = append(ranges, r)
	}
	return ranges, nil
}

func debug(message string, fmtArgs ...interface{}) {
	if message[:len(message)-1] != "\n" {
		message += "\n"
	}
	// fmt.Fprintf(os.Stderr, message, fmtArgs...)
}