diff --git a/webdav/prop.go b/webdav/prop.go
index ba595d7ac..4d7be3492 100644
--- a/webdav/prop.go
+++ b/webdav/prop.go
@@ -7,6 +7,7 @@ package webdav
 import (
 	"bytes"
 	"encoding/xml"
+	"errors"
 	"fmt"
 	"io"
 	"mime"
@@ -379,7 +380,34 @@ func findLastModified(ctx context.Context, fs FileSystem, ls LockSystem, name st
 	return fi.ModTime().UTC().Format(http.TimeFormat), nil
 }
 
+// ErrNotImplemented should be returned by optional interfaces if they
+// want the original implementation to be used.
+var ErrNotImplemented = errors.New("not implemented")
+
+// ContentTyper is an optional interface for the os.FileInfo
+// objects returned by the FileSystem.
+//
+// If this interface is defined then it will be used to read the
+// content type from the object.
+//
+// If this interface is not defined the file will be opened and the
+// content type will be guessed from the initial contents of the file.
+type ContentTyper interface {
+	// ContentType returns the content type for the file.
+	//
+	// If this returns error ErrNotImplemented then the error will
+	// be ignored and the base implementation will be used
+	// instead.
+	ContentType(ctx context.Context) (string, error)
+}
+
 func findContentType(ctx context.Context, fs FileSystem, ls LockSystem, name string, fi os.FileInfo) (string, error) {
+	if do, ok := fi.(ContentTyper); ok {
+		ctype, err := do.ContentType(ctx)
+		if err != ErrNotImplemented {
+			return ctype, err
+		}
+	}
 	f, err := fs.OpenFile(ctx, name, os.O_RDONLY, 0)
 	if err != nil {
 		return "", err
@@ -402,7 +430,31 @@ func findContentType(ctx context.Context, fs FileSystem, ls LockSystem, name str
 	return ctype, err
 }
 
+// ETager is an optional interface for the os.FileInfo objects
+// returned by the FileSystem.
+//
+// If this interface is defined then it will be used to read the ETag
+// for the object.
+//
+// If this interface is not defined an ETag will be computed using the
+// ModTime() and the Size() methods of the os.FileInfo object.
+type ETager interface {
+	// ETag returns an ETag for the file.  This should be of the
+	// form "value" or W/"value"
+	//
+	// If this returns error ErrNotImplemented then the error will
+	// be ignored and the base implementation will be used
+	// instead.
+	ETag(ctx context.Context) (string, error)
+}
+
 func findETag(ctx context.Context, fs FileSystem, ls LockSystem, name string, fi os.FileInfo) (string, error) {
+	if do, ok := fi.(ETager); ok {
+		etag, err := do.ETag(ctx)
+		if err != ErrNotImplemented {
+			return etag, err
+		}
+	}
 	// The Apache http 2.4 web server by default concatenates the
 	// modification time and size of a file. We replicate the heuristic
 	// with nanosecond granularity.
diff --git a/webdav/prop_test.go b/webdav/prop_test.go
index 914f9504d..bc42b9132 100644
--- a/webdav/prop_test.go
+++ b/webdav/prop_test.go
@@ -10,6 +10,7 @@ import (
 	"net/http"
 	"os"
 	"reflect"
+	"regexp"
 	"sort"
 	"testing"
 
@@ -611,3 +612,106 @@ func (f noDeadPropsFile) Readdir(count int) ([]os.FileInfo, error)  { return f.f
 func (f noDeadPropsFile) Seek(off int64, whence int) (int64, error) { return f.f.Seek(off, whence) }
 func (f noDeadPropsFile) Stat() (os.FileInfo, error)                { return f.f.Stat() }
 func (f noDeadPropsFile) Write(p []byte) (int, error)               { return f.f.Write(p) }
+
+type overrideContentType struct {
+	os.FileInfo
+	contentType string
+	err         error
+}
+
+func (o *overrideContentType) ContentType(ctx context.Context) (string, error) {
+	return o.contentType, o.err
+}
+
+func TestFindContentTypeOverride(t *testing.T) {
+	fs, err := buildTestFS([]string{"touch /file"})
+	if err != nil {
+		t.Fatalf("cannot create test filesystem: %v", err)
+	}
+	ctx := context.Background()
+	fi, err := fs.Stat(ctx, "/file")
+	if err != nil {
+		t.Fatalf("cannot Stat /file: %v", err)
+	}
+
+	// Check non overridden case
+	originalContentType, err := findContentType(ctx, fs, nil, "/file", fi)
+	if err != nil {
+		t.Fatalf("findContentType /file failed: %v", err)
+	}
+	if originalContentType != "text/plain; charset=utf-8" {
+		t.Fatalf("ContentType wrong want %q got %q", "text/plain; charset=utf-8", originalContentType)
+	}
+
+	// Now try overriding the ContentType
+	o := &overrideContentType{fi, "OverriddenContentType", nil}
+	ContentType, err := findContentType(ctx, fs, nil, "/file", o)
+	if err != nil {
+		t.Fatalf("findContentType /file failed: %v", err)
+	}
+	if ContentType != o.contentType {
+		t.Fatalf("ContentType wrong want %q got %q", o.contentType, ContentType)
+	}
+
+	// Now return ErrNotImplemented and check we get the original content type
+	o = &overrideContentType{fi, "OverriddenContentType", ErrNotImplemented}
+	ContentType, err = findContentType(ctx, fs, nil, "/file", o)
+	if err != nil {
+		t.Fatalf("findContentType /file failed: %v", err)
+	}
+	if ContentType != originalContentType {
+		t.Fatalf("ContentType wrong want %q got %q", originalContentType, ContentType)
+	}
+}
+
+type overrideETag struct {
+	os.FileInfo
+	eTag string
+	err  error
+}
+
+func (o *overrideETag) ETag(ctx context.Context) (string, error) {
+	return o.eTag, o.err
+}
+
+func TestFindETagOverride(t *testing.T) {
+	fs, err := buildTestFS([]string{"touch /file"})
+	if err != nil {
+		t.Fatalf("cannot create test filesystem: %v", err)
+	}
+	ctx := context.Background()
+	fi, err := fs.Stat(ctx, "/file")
+	if err != nil {
+		t.Fatalf("cannot Stat /file: %v", err)
+	}
+
+	// Check non overridden case
+	originalETag, err := findETag(ctx, fs, nil, "/file", fi)
+	if err != nil {
+		t.Fatalf("findETag /file failed: %v", err)
+	}
+	matchETag := regexp.MustCompile(`^"-?[0-9a-f]{6,}"$`)
+	if !matchETag.MatchString(originalETag) {
+		t.Fatalf("ETag wrong, wanted something matching %v got %q", matchETag, originalETag)
+	}
+
+	// Now try overriding the ETag
+	o := &overrideETag{fi, `"OverriddenETag"`, nil}
+	ETag, err := findETag(ctx, fs, nil, "/file", o)
+	if err != nil {
+		t.Fatalf("findETag /file failed: %v", err)
+	}
+	if ETag != o.eTag {
+		t.Fatalf("ETag wrong want %q got %q", o.eTag, ETag)
+	}
+
+	// Now return ErrNotImplemented and check we get the original Etag
+	o = &overrideETag{fi, `"OverriddenETag"`, ErrNotImplemented}
+	ETag, err = findETag(ctx, fs, nil, "/file", o)
+	if err != nil {
+		t.Fatalf("findETag /file failed: %v", err)
+	}
+	if ETag != originalETag {
+		t.Fatalf("ETag wrong want %q got %q", originalETag, ETag)
+	}
+}