admin: Implement sychronization backends

We are now able, depending on configuration, to retrieve files from either WebDAV or local file system.

admin/sync/file.go

@@ -0,0 +1,98 @@
+package sync
+
+import (
+	"bufio"
+	"encoding/base32"
+	"errors"
+	"fmt"
+	"os"
+	"path"
+	"strings"
+
+	"srs.epita.fr/fic-server/libfic"
+
+	"github.com/dchest/blake2b"
+)
+
+type Importer interface {
+	Kind() string
+	exists(filename string) bool
+	toURL(filename string) string
+	getFile(filename string, writer *bufio.Writer) error
+	listDir(filename string) ([]string, error)
+}
+
+var GlobalImporter Importer
+
+func getFile(i Importer, URI string, writer *bufio.Writer) error {
+	// Import file if it exists
+	if i.exists(URI) {
+		return i.getFile(URI, writer)
+	}
+
+	// Try to find file parts
+	dirname := path.Dir(URI)
+	if i.exists(dirname) {
+		filename := path.Base(URI)
+		if files, err := i.listDir(dirname); err != nil {
+			return err
+		} else {
+			for _, fname := range []string{filename, filename + "."} {
+				found := false
+				for _, file := range files {
+					if matched, _ := path.Match(fname + "[0-9][0-9]", file); matched {
+						found = true
+						if err := i.getFile(path.Join(dirname, file), writer); err != nil {
+							return err
+						}
+					}
+				}
+
+				if found {
+					return nil
+				}
+			}
+		}
+	}
+
+	return errors.New(fmt.Sprintf("%q: no such file or directory", i.toURL(URI)))
+}
+
+func ImportFile(URI string, next func(string, string) (interface{}, error)) (interface{}, error) {
+	hash := blake2b.Sum512([]byte(URI))
+	dest := path.Join(fic.FilesDir, strings.ToLower(base32.StdEncoding.WithPadding(base32.NoPadding).EncodeToString(hash[:])), path.Base(URI))
+
+	// If the present file is still valide, don't erase it
+	if _, err := os.Stat(dest); !os.IsNotExist(err) {
+		if r, err := next(dest, URI); err == nil {
+			return r, err
+		}
+
+		if err := os.Remove(dest); err != nil {
+			return nil, err
+		}
+	}
+
+	// Ensure no more file is registered with this path
+	if f, err := fic.GetFileByPath(dest); err == nil {
+		f.Delete()
+	}
+
+	if err := os.MkdirAll(path.Dir(dest), 0755); err != nil {
+		return nil, err
+	}
+
+	// Write file
+	if fdto, err := os.Create(dest); err != nil {
+		return nil, err
+	} else {
+		defer fdto.Close()
+		writer := bufio.NewWriter(fdto)
+		if err := getFile(GlobalImporter, URI, writer); err != nil {
+			os.Remove(dest)
+			return nil, err
+		}
+	}
+
+	return next(dest, URI)
+}