add some comments about path sanitisation

If the client accepts gzip, just serve the file as a gzip-encoded plain text.

If it doesn't, gunzip it first.

README.md

@@ -5,14 +5,13 @@ Web service which collects and serves bug reports.
 To run it, do:
 
 ```
-BUGS_USER=<user> BUGS_PASS=<password> go run src/github.com/matrix-org/rageshake/main.go PORT
+go get github.com/constabulary/gb/...
+gb build
+BUGS_USER=<user> BUGS_PASS=<password> ./bin/rageshake PORT
+# example:
+# BUGS_USER=alice BUGS_PASS=secret ./bin/rageshake 8080
 ```
 
-Example:
-
-```
-BUGS_USER=alice BUGS_PASS=secret go run src/github.com/matrix-org/rageshake/main.go 8080
-```
 
 ## HTTP endpoints
 

src/github.com/matrix-org/rageshake/logserver.go

@@ -0,0 +1,167 @@
+/*
+Copyright 2017 Vector Creations Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package main
+
+import (
+	"compress/gzip"
+	"io"
+	"log"
+	"net/http"
+	"os"
+	"path"
+	"path/filepath"
+	"strconv"
+	"strings"
+)
+
+// logServer is an http.handler which will serve up bugreports
+type logServer struct {
+	root string
+}
+
+func (f *logServer) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	upath := r.URL.Path
+
+	if !strings.HasPrefix(upath, "/") {
+		upath = "/" + upath
+		r.URL.Path = upath
+	}
+
+	log.Println("Serving", upath)
+
+	// eliminate ., .., //, etc
+	upath = path.Clean(upath)
+
+	// reject some dodgy paths. This is based on the code for http.Dir.Open (see https://golang.org/src/net/http/fs.go#L37).
+	//
+	// the check for '..' is a sanity-check because my understanding of `path.Clean` is that it should never return
+	// a value including '..' for input starting with '/'. It's taken from the code for http.ServeFile
+	// (https://golang.org/src/net/http/fs.go#L637).
+	if containsDotDot(upath) || strings.Contains(upath, "\x00") || (filepath.Separator != '/' && strings.IndexRune(upath, filepath.Separator) >= 0) {
+		http.Error(w, "invalid URL path", http.StatusBadRequest)
+		return
+	}
+
+	// convert to abs path
+	upath, err := filepath.Abs(filepath.Join(f.root, filepath.FromSlash(upath)))
+
+	if err != nil {
+		msg, code := toHTTPError(err)
+		http.Error(w, msg, code)
+		return
+	}
+
+	serveFile(w, r, upath)
+}
+
+func serveFile(w http.ResponseWriter, r *http.Request, path string) {
+	d, err := os.Stat(path)
+	if err != nil {
+		msg, code := toHTTPError(err)
+		http.Error(w, msg, code)
+		return
+	}
+
+	// if it's a directory, or doesn't look like a gzip, serve as normal
+	if d.IsDir() || !strings.HasSuffix(path, ".gz") {
+		log.Println("Serving", path)
+		http.ServeFile(w, r, path)
+		return
+	}
+
+	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
+
+	acceptsGzip := false
+	splitRune := func(s rune) bool { return s == ' ' || s == '\t' || s == '\n' || s == ',' }
+	for _, hdr := range r.Header["Accept-Encoding"] {
+		for _, enc := range strings.FieldsFunc(hdr, splitRune) {
+			if enc == "gzip" {
+				acceptsGzip = true
+				break
+			}
+		}
+	}
+
+	if acceptsGzip {
+		serveGzip(w, r, path, d.Size())
+	} else {
+		serveUngzipped(w, r, path)
+	}
+}
+
+// serveGzip serves a gzipped file with gzip content-encoding
+func serveGzip(w http.ResponseWriter, r *http.Request, path string, size int64) {
+	f, err := os.Open(path)
+	if err != nil {
+		msg, code := toHTTPError(err)
+		http.Error(w, msg, code)
+		return
+	}
+	defer f.Close()
+
+	w.Header().Set("Content-Encoding", "gzip")
+	w.Header().Set("Content-Length", strconv.FormatInt(size, 10))
+
+	w.WriteHeader(http.StatusOK)
+	io.Copy(w, f)
+}
+
+// serveUngzipped ungzips a gzipped file and serves it
+func serveUngzipped(w http.ResponseWriter, r *http.Request, path string) {
+	f, err := os.Open(path)
+	if err != nil {
+		msg, code := toHTTPError(err)
+		http.Error(w, msg, code)
+		return
+	}
+	defer f.Close()
+
+	gz, err := gzip.NewReader(f)
+	if err != nil {
+		msg, code := toHTTPError(err)
+		http.Error(w, msg, code)
+		return
+	}
+	defer gz.Close()
+
+	w.WriteHeader(http.StatusOK)
+	io.Copy(w, gz)
+}
+
+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
+}
+
+func containsDotDot(v string) bool {
+	if !strings.Contains(v, "..") {
+		return false
+	}
+	for _, ent := range strings.FieldsFunc(v, isSlashRune) {
+		if ent == ".." {
+			return true
+		}
+	}
+	return false
+}
+func isSlashRune(r rune) bool { return r == '/' || r == '\\' }

src/github.com/matrix-org/rageshake/main.go

@@ -140,8 +140,8 @@ func main() {
 	_ = os.Mkdir("bugs", os.ModePerm)
 
 	// serve files under "bugs"
-	fs := http.FileServer(http.Dir("bugs"))
+	ls := &logServer{"bugs"}
-	fs = http.StripPrefix("/api/listing/", fs)
+	fs := http.StripPrefix("/api/listing/", ls)
 
 	// set auth if env vars exist
 	usr := os.Getenv("BUGS_USER")
@@ -154,5 +154,7 @@ func main() {
 	http.Handle("/api/listing/", fs)
 
 	port := os.Args[1]
+	log.Println("Listening on port", port)
+
 	log.Fatal(http.ListenAndServe(":"+port, nil))
 }