syncthing/cmd/stcrashreceiver/stcrashreceiver.go

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// Copyright (C) 2019 The Syncthing Authors.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at https://mozilla.org/MPL/2.0/.
// Command stcrashreceiver is a trivial HTTP server that allows two things:
//
// - uploading files (crash reports) named like a SHA256 hash using a PUT request
// - checking whether such file exists using a HEAD request
//
// Typically this should be deployed behind something that manages HTTPS.
package main
import (
"bytes"
"compress/gzip"
"flag"
"io"
"io/ioutil"
"log"
"net/http"
"os"
"path"
"path/filepath"
"strings"
)
const maxRequestSize = 1 << 20 // 1 MiB
func main() {
dir := flag.String("dir", ".", "Directory to store reports in")
dsn := flag.String("dsn", "", "Sentry DSN")
listen := flag.String("listen", ":22039", "HTTP listen address")
flag.Parse()
cr := &crashReceiver{
dir: *dir,
dsn: *dsn,
}
log.SetOutput(os.Stdout)
if err := http.ListenAndServe(*listen, cr); err != nil {
log.Fatalln("HTTP serve:", err)
}
}
type crashReceiver struct {
dir string
dsn string
}
func (r *crashReceiver) ServeHTTP(w http.ResponseWriter, req *http.Request) {
// The final path component should be a SHA256 hash in hex, so 64 hex
// characters. We don't care about case on the request but use lower
// case internally.
reportID := strings.ToLower(path.Base(req.URL.Path))
if len(reportID) != 64 {
http.Error(w, "Bad request", http.StatusBadRequest)
return
}
for _, c := range reportID {
if c >= 'a' && c <= 'f' {
continue
}
if c >= '0' && c <= '9' {
continue
}
http.Error(w, "Bad request", http.StatusBadRequest)
return
}
// The location of the report on disk, compressed
fullPath := filepath.Join(r.dir, r.dirFor(reportID), reportID) + ".gz"
switch req.Method {
case http.MethodGet:
r.serveGet(fullPath, w, req)
case http.MethodHead:
r.serveHead(fullPath, w, req)
case http.MethodPut:
r.servePut(reportID, fullPath, w, req)
default:
http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
}
}
// serveGet responds to GET requests by serving the uncompressed report.
func (r *crashReceiver) serveGet(fullPath string, w http.ResponseWriter, _ *http.Request) {
fd, err := os.Open(fullPath)
if err != nil {
http.Error(w, "Not found", http.StatusNotFound)
return
}
defer fd.Close()
gr, err := gzip.NewReader(fd)
if err != nil {
http.Error(w, "Internal server error", http.StatusInternalServerError)
return
}
_, _ = io.Copy(w, gr) // best effort
}
// serveHead responds to HEAD requests by checking if the named report
// already exists in the system.
func (r *crashReceiver) serveHead(fullPath string, w http.ResponseWriter, _ *http.Request) {
if _, err := os.Lstat(fullPath); err != nil {
http.Error(w, "Not found", http.StatusNotFound)
}
}
// servePut accepts and stores the given report.
func (r *crashReceiver) servePut(reportID, fullPath string, w http.ResponseWriter, req *http.Request) {
// Ensure the destination directory exists
if err := os.MkdirAll(filepath.Dir(fullPath), 0755); err != nil {
log.Println("Creating directory:", err)
http.Error(w, "Internal server error", http.StatusInternalServerError)
return
}
// Read at most maxRequestSize of report data.
log.Println("Receiving report", reportID)
lr := io.LimitReader(req.Body, maxRequestSize)
bs, err := ioutil.ReadAll(lr)
if err != nil {
log.Println("Reading report:", err)
http.Error(w, "Internal server error", http.StatusInternalServerError)
return
}
// Compress the report for storage
buf := new(bytes.Buffer)
gw := gzip.NewWriter(buf)
_, _ = gw.Write(bs) // can't fail
gw.Close()
// Create an output file with the compressed report
err = ioutil.WriteFile(fullPath, buf.Bytes(), 0644)
if err != nil {
log.Println("Saving report:", err)
http.Error(w, "Internal server error", http.StatusInternalServerError)
return
}
// Send the report to Sentry
if r.dsn != "" {
go func() {
// There's no need for the client to have to wait for this part.
if err := sendReport(r.dsn, reportID, bs); err != nil {
log.Println("Failed to send report:", err)
}
}()
}
}
// 01234567890abcdef... => 01/23
func (r *crashReceiver) dirFor(base string) string {
return filepath.Join(base[0:2], base[2:4])
}