First working version

[nsscash/nsscash.git] / file.go

diff --git a/file.go b/file.go
new file mode 100644 (file)
index 0000000..b48d075
--- /dev/null
+++ b/file.go
@@ -0,0 +1,152 @@
+// Download and write files atomically to the file system
+
+// Copyright (C) 2019  Simon Ruderich
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package main
+
+import (
+       "bytes"
+       "fmt"
+       "io/ioutil"
+       "log"
+       "net/http"
+       "os"
+       "path/filepath"
+       "syscall"
+
+       "github.com/pkg/errors"
+)
+
+func handleFiles(cfg *Config, state *State) error {
+       for i, f := range cfg.Files {
+               err := fetchFile(&cfg.Files[i], state)
+               if err != nil {
+                       return errors.Wrapf(err, "%q (%s)", f.Url, f.Type)
+               }
+       }
+
+       for i, f := range cfg.Files {
+               // No update required
+               if f.body == nil {
+                       continue
+               }
+
+               err := deployFile(&cfg.Files[i])
+               if err != nil {
+                       return errors.Wrapf(err, "%q (%s)", f.Url, f.Type)
+               }
+       }
+
+       return nil
+}
+
+func fetchFile(file *File, state *State) error {
+       t := state.LastModified[file.Url]
+       status, body, err := fetchIfModified(file.Url, &t)
+       if err != nil {
+               return err
+       }
+       if status == http.StatusNotModified {
+               log.Printf("%q -> %q: not modified", file.Url, file.Path)
+               return nil
+       }
+       if status != http.StatusOK {
+               return fmt.Errorf("status code %v", status)
+       }
+       state.LastModified[file.Url] = t
+
+       if file.Type == FileTypePlain {
+               if len(body) == 0 {
+                       return fmt.Errorf("refusing to use empty response")
+               }
+               file.body = body
+
+       } else if file.Type == FileTypePasswd {
+               pws, err := ParsePasswds(bytes.NewReader(body))
+               if err != nil {
+                       return err
+               }
+               // Safety check: having no users can be very dangerous, don't
+               // permit it
+               if len(pws) == 0 {
+                       return fmt.Errorf("refusing to use empty passwd file")
+               }
+
+               var x bytes.Buffer
+               err = SerializePasswds(&x, pws)
+               if err != nil {
+                       return err
+               }
+               file.body = x.Bytes()
+
+       } else {
+               return fmt.Errorf("unsupported file type %v", file.Type)
+       }
+       return nil
+}
+
+func deployFile(file *File) error {
+       log.Printf("%q -> %q: updating file", file.Url, file.Path)
+
+       // Safety check
+       if len(file.body) == 0 {
+               return fmt.Errorf("refusing to write empty file")
+       }
+
+       // Write the file in an atomic fashion by creating a temporary file
+       // and renaming it over the target file
+
+       dir := filepath.Dir(file.Path)
+       name := filepath.Base(file.Path)
+
+       f, err := ioutil.TempFile(dir, "tmp-"+name+"-")
+       if err != nil {
+               return err
+       }
+       defer os.Remove(f.Name())
+       defer f.Close()
+
+       // Apply permissions/user/group from the target file
+       stat, err := os.Stat(file.Path)
+       if err != nil {
+               // We do not create the path if it doesn't exist, because we
+               // do not know the proper permissions
+               return errors.Wrapf(err, "file.path %q must exist", file.Path)
+       }
+       err = f.Chmod(stat.Mode())
+       if err != nil {
+               return err
+       }
+       // TODO: support more systems
+       sys, ok := stat.Sys().(*syscall.Stat_t)
+       if !ok {
+               return fmt.Errorf("unsupported FileInfo.Sys()")
+       }
+       err = f.Chown(int(sys.Uid), int(sys.Gid))
+       if err != nil {
+               return err
+       }
+
+       _, err = f.Write(file.body)
+       if err != nil {
+               return err
+       }
+       err = f.Sync()
+       if err != nil {
+               return err
+       }
+       return os.Rename(f.Name(), file.Path)
+}