Add CalDAV support, refactor

The filesystem storage backend now implements the required functions to
act as a basic CalDAV server. Some refactoring was done based on the
go-webdav development: introduce a UserPrincipalBackend, a new function
to serve the user principal URL, and more. See this PR for lots of
details: https://github.com/emersion/go-webdav/pull/62

Also adds a simple facility for debug output.

cmd/tokidoki/main.go

@@ -1,19 +1,83 @@
 package main
 
 import (
+	"context"
+	"encoding/base64"
 	"flag"
+	"fmt"
 	"log"
 	"net/http"
 	"os"
 
+	"github.com/emersion/go-webdav"
+	"github.com/emersion/go-webdav/caldav"
 	"github.com/emersion/go-webdav/carddav"
 	"github.com/go-chi/chi/v5"
 	"github.com/go-chi/chi/v5/middleware"
 
 	"git.sr.ht/~sircmpwn/tokidoki/auth"
+	"git.sr.ht/~sircmpwn/tokidoki/debug"
 	"git.sr.ht/~sircmpwn/tokidoki/storage"
 )
 
+type userPrincipalBackend struct{}
+
+func (u *userPrincipalBackend) CurrentUserPrincipal(ctx context.Context) (string, error) {
+	authCtx, ok := auth.FromContext(ctx)
+	if !ok {
+		panic("Invalid data in auth context!")
+	}
+	if authCtx == nil {
+		return "", fmt.Errorf("unauthenticated requests are not supported")
+	}
+
+	userDir := base64.RawStdEncoding.EncodeToString([]byte(authCtx.UserName))
+	return "/" + userDir + "/", nil
+}
+
+type tokidokiHandler struct {
+	upBackend      webdav.UserPrincipalBackend
+	authBackend    auth.AuthProvider
+	caldavBackend  caldav.Backend
+	carddavBackend carddav.Backend
+}
+
+func (u *tokidokiHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	userPrincipalPath, err := u.upBackend.CurrentUserPrincipal(r.Context())
+	if err != nil {
+		http.Error(w, http.StatusText(http.StatusBadRequest), http.StatusBadRequest)
+	}
+
+	var homeSets []webdav.BackendSuppliedHomeSet
+	if u.caldavBackend != nil {
+		path, err := u.caldavBackend.CalendarHomeSetPath(r.Context())
+		if err != nil {
+			http.Error(w, http.StatusText(http.StatusBadRequest), http.StatusBadRequest)
+		} else {
+			homeSets = append(homeSets, caldav.NewCalendarHomeSet(path))
+		}
+	}
+	if u.carddavBackend != nil {
+		path, err := u.carddavBackend.AddressbookHomeSetPath(r.Context())
+		if err != nil {
+			http.Error(w, http.StatusText(http.StatusBadRequest), http.StatusBadRequest)
+		} else {
+			homeSets = append(homeSets, carddav.NewAddressBookHomeSet(path))
+		}
+	}
+
+	opts := webdav.ServeUserPrincipalOptions{
+		UserPrincipalPath: userPrincipalPath,
+		HomeSets:          homeSets,
+	}
+
+	if webdav.ServeUserPrincipal(w, r, opts) {
+		return
+	}
+
+	http.Error(w, http.StatusText(http.StatusBadRequest), http.StatusBadRequest)
+}
+
 func main() {
 	var (
 		addr       string
@@ -23,6 +87,7 @@ func main() {
 	flag.StringVar(&addr, "addr", ":8080", "listening address")
 	flag.StringVar(&authURL, "auth.url", "", "auth backend URL (required)")
 	flag.StringVar(&storageURL, "storage.url", "", "storage backend URL (required)")
+	flag.BoolVar(&debug.Enable, "debug", false, "enable debug output")
 	flag.Parse()
 
 	if len(flag.Args()) != 0 || authURL == "" || storageURL == "" {
@@ -48,17 +113,36 @@ func main() {
 	}
 	mux.Use(authProvider.Middleware())
 
-	backend, err := storage.NewFromURL(storageURL)
+	upBackend := &userPrincipalBackend{}
+
+	caldavBackend, carddavBackend, err := storage.NewFromURL(storageURL, "/calendar/", "/contacts/", upBackend)
 	if err != nil {
 		log.Fatalf("failed to load storage backend: %s", err.Error())
 	}
-	mux.Mount("/", &carddav.Handler{Backend: backend})
+
+	carddavHandler := carddav.Handler{Backend: carddavBackend}
+	caldavHandler := caldav.Handler{Backend: caldavBackend}
+	handler := tokidokiHandler{
+		upBackend:      upBackend,
+		authBackend:    authProvider,
+		caldavBackend:  caldavBackend,
+		carddavBackend: carddavBackend,
+	}
+
+	mux.Mount("/", &handler)
+	mux.Mount("/.well-known/caldav", &caldavHandler)
+	mux.Mount("/.well-known/carddav", &carddavHandler)
+	mux.Mount("/{user}/contacts", &carddavHandler)
+	mux.Mount("/{user}/calendar", &caldavHandler)
 
 	server := http.Server{
 		Addr:    addr,
 		Handler: mux,
 	}
+
 	log.Printf("Server running on %s", addr)
+	debug.Printf("Debug output enabled")
+
 	err = server.ListenAndServe()
 	if err != http.ErrServerClosed {
 		log.Fatalf("ListenAndServe: %s", err.Error())

debug/debug.go

@@ -0,0 +1,15 @@
+package debug
+
+import (
+	"log"
+)
+
+var (
+	Enable = false
+)
+
+func Printf(format string, v ...any) {
+	if Enable {
+		log.Printf("[debug] "+format, v...)
+	}
+}

go.mod

@@ -1,8 +1,9 @@
 module git.sr.ht/~sircmpwn/tokidoki
 
-go 1.17
+go 1.18
 
 require (
+	github.com/emersion/go-ical v0.0.0-20200224201310-cd514449c39e
 	github.com/emersion/go-imap v1.2.0
 	github.com/emersion/go-sasl v0.0.0-20211008083017-0b9dcfb154ac
 	github.com/emersion/go-vcard v0.0.0-20210521075357-3445b9171995
@@ -11,3 +12,5 @@ require (
 )
 
 require golang.org/x/text v0.3.7 // indirect
+
+replace github.com/emersion/go-webdav v0.3.2-0.20220310154811-85d2b222bbcd => github.com/bitfehler/go-webdav v0.3.2-0.20220503133151-e5312775c02f

go.sum

@@ -1,3 +1,6 @@
+github.com/bitfehler/go-webdav v0.3.2-0.20220503133151-e5312775c02f h1:gRchuZEVTYh+ymMqejZKbD67ZLLm59Q9lTG49e0Qu20=
+github.com/bitfehler/go-webdav v0.3.2-0.20220503133151-e5312775c02f/go.mod h1:uSM1VveeKtogBVWaYccTksToczooJ0rrVGNsgnDsr4Q=
+github.com/emersion/go-ical v0.0.0-20200224201310-cd514449c39e h1:YGM1sI7edZOt8KAfX9Miq/X99d2QXdgjkJ7vN4HjxAA=
 github.com/emersion/go-ical v0.0.0-20200224201310-cd514449c39e/go.mod h1:4xVTBPcT43a1pp3vdaa+FuRdX5XhKCZPpWv7m0z9ByM=
 github.com/emersion/go-imap v1.2.0 h1:lyUQ3+EVM21/qbWE/4Ya5UG9r5+usDxlg4yfp3TgHFA=
 github.com/emersion/go-imap v1.2.0/go.mod h1:Qlx1FSx2FTxjnjWpIlVNEuX+ylerZQNFE5NsmKFSejY=

storage/filesystem.go

@@ -5,74 +5,129 @@ import (
 	"crypto/sha1"
 	"encoding/base64"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
+	"io/fs"
 	"io/ioutil"
 	"os"
+	"path"
 	"path/filepath"
 	"regexp"
 
+	"github.com/emersion/go-ical"
 	"github.com/emersion/go-vcard"
+	"github.com/emersion/go-webdav"
+	"github.com/emersion/go-webdav/caldav"
 	"github.com/emersion/go-webdav/carddav"
 
-	"git.sr.ht/~sircmpwn/tokidoki/auth"
+	"git.sr.ht/~sircmpwn/tokidoki/debug"
 )
 
 type filesystemBackend struct {
-	path string
+	path                 string
+	caldavPrefix         string
+	carddavPrefix        string
+	userPrincipalBackend webdav.UserPrincipalBackend
 }
 
 var (
-	nilBackend         carddav.Backend = (*filesystemBackend)(nil)
+	validFilenameRegex = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9_-]+(.[a-zA-Z]+)?$`)
-	validFilenameRegex                 = regexp.MustCompile(`^/[A-Za-z0-9][A-Za-z0-9_-]+(.[a-zA-Z]+)?$`)
 )
 
-func NewFilesystem(path string) (carddav.Backend, error) {
+func NewFilesystem(fsPath, caldavPrefix, carddavPrefix string, userPrincipalBackend webdav.UserPrincipalBackend) (caldav.Backend, carddav.Backend, error) {
-	info, err := os.Stat(path)
+	info, err := os.Stat(fsPath)
 	if err != nil {
-		return nilBackend, fmt.Errorf("failed to create filesystem backend: %s", err.Error())
+		return nil, nil, fmt.Errorf("failed to create filesystem backend: %s", err.Error())
 	}
 	if !info.IsDir() {
-		return nilBackend, fmt.Errorf("base path for filesystem backend must be a directory")
+		return nil, nil, fmt.Errorf("base path for filesystem backend must be a directory")
 	}
-	return &filesystemBackend{
+	backend := &filesystemBackend{
-		path: path,
+		path:                 fsPath,
-	}, nil
+		caldavPrefix:         caldavPrefix,
+		carddavPrefix:        carddavPrefix,
+		userPrincipalBackend: userPrincipalBackend,
+	}
+	return backend, backend, nil
 }
 
-func (b *filesystemBackend) pathForContext(ctx context.Context) (string, error) {
+func (b *filesystemBackend) CurrentUserPrincipal(ctx context.Context) (string, error) {
-	authCtx, ok := auth.FromContext(ctx)
+	return b.userPrincipalBackend.CurrentUserPrincipal(ctx)
-	if !ok {
-		panic("Invalid data in auth context!")
-	}
-	if authCtx == nil {
-		return "", fmt.Errorf("unauthenticated requests are not supported")
-	}
-
-	userDir := base64.RawStdEncoding.EncodeToString([]byte(authCtx.UserName))
-	path := filepath.Join(b.path, userDir)
-
-	_, err := os.Stat(path)
-	if os.IsNotExist(err) {
-		err = os.Mkdir(path, 0755)
-		if err != nil {
-			return "", fmt.Errorf("error creating '%s': %s", path, err.Error())
-		}
-	}
-	return path, nil
 }
 
-func (b *filesystemBackend) safePath(ctx context.Context, path string) (string, error) {
+func (b *filesystemBackend) AddressbookHomeSetPath(ctx context.Context) (string, error) {
-	basePath, err := b.pathForContext(ctx)
+	upPath, err := b.userPrincipalBackend.CurrentUserPrincipal(ctx)
 	if err != nil {
 		return "", err
 	}
+
+	return path.Join(upPath, b.carddavPrefix) + "/", nil
+}
+
+func (b *filesystemBackend) CalendarHomeSetPath(ctx context.Context) (string, error) {
+	upPath, err := b.userPrincipalBackend.CurrentUserPrincipal(ctx)
+	if err != nil {
+		return "", err
+	}
+
+	return path.Join(upPath, b.caldavPrefix) + "/", nil
+}
+
+func ensureLocalDir(path string) error {
+	if _, err := os.Stat(path); os.IsNotExist(err) {
+		err = os.MkdirAll(path, 0755)
+		if err != nil {
+			return fmt.Errorf("error creating '%s': %s", path, err.Error())
+		}
+	}
+	return nil
+}
+
+// don't use this directly, use localCalDAVPath or localCardDAVPath instead.
+func (b *filesystemBackend) safeLocalPath(homeSetPath string, urlPath string) (string, error) {
+	localPath := filepath.Join(b.path, homeSetPath)
+	if err := ensureLocalDir(localPath); err != nil {
+		return "", err
+	}
+
+	if urlPath == "" {
+		return localPath, nil
+	}
+
 	// We are mapping to local filesystem path, so be conservative about what to accept
 	// TODO this changes once multiple addess books are supported
-	if !validFilenameRegex.MatchString(path) {
+	dir, file := path.Split(urlPath)
-		return "", fmt.Errorf("invalid request path")
+	// only accept resources in prefix, no subdirs for now
+	if dir != homeSetPath {
+		return "", fmt.Errorf("invalid request path %s", urlPath)
 	}
-	return filepath.Join(basePath, path), nil
+	// only accept simple file names for now
+	if !validFilenameRegex.MatchString(file) {
+		fmt.Printf("%s does not match regex!\n", file)
+		return "", fmt.Errorf("invalid file name")
+	}
+
+	// dir (= homeSetPath) is already included in path, so only file here
+	return filepath.Join(localPath, file), nil
+}
+
+func (b *filesystemBackend) localCalDAVPath(ctx context.Context, urlPath string) (string, error) {
+	homeSetPath, err := b.CalendarHomeSetPath(ctx)
+	if err != nil {
+		return "", err
+	}
+
+	return b.safeLocalPath(homeSetPath, urlPath)
+}
+
+func (b *filesystemBackend) localCardDAVPath(ctx context.Context, urlPath string) (string, error) {
+	homeSetPath, err := b.AddressbookHomeSetPath(ctx)
+	if err != nil {
+		return "", err
+	}
+
+	return b.safeLocalPath(homeSetPath, urlPath)
 }
 
 func etagForFile(path string) (string, error) {
@@ -128,10 +183,27 @@ func vcardFromFile(path string, propFilter []string) (vcard.Card, error) {
 	return vcardPropFilter(card, propFilter), nil
 }
 
-func createDefaultAddressBook(path string) error {
+func calendarFromFile(path string, propFilter []string) (*ical.Calendar, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	dec := ical.NewDecoder(f)
+	cal, err := dec.Decode()
+	if err != nil {
+		return nil, err
+	}
+
+	return cal, nil
+	//	return vcardPropFilter(card, propFilter), nil
+}
+
+func createDefaultAddressBook(path, localPath string) error {
 	// TODO what should the default address book look like?
 	defaultAB := carddav.AddressBook{
-		Path:                 "/default",
+		Path:                 path,
 		Name:                 "My contacts",
 		Description:          "Default address book",
 		MaxResourceSize:      1024,
@@ -141,7 +213,7 @@ func createDefaultAddressBook(path string) error {
 	if err != nil {
 		return fmt.Errorf("error creating default address book: %s", err.Error())
 	}
-	err = os.WriteFile(path, blob, 0644)
+	err = os.WriteFile(localPath, blob, 0644)
 	if err != nil {
 		return fmt.Errorf("error writing default address book: %s", err.Error())
 	}
@@ -149,15 +221,23 @@ func createDefaultAddressBook(path string) error {
 }
 
 func (b *filesystemBackend) AddressBook(ctx context.Context) (*carddav.AddressBook, error) {
-	path, err := b.pathForContext(ctx)
+	debug.Printf("filesystem.AddressBook()")
+	path, err := b.localCardDAVPath(ctx, "")
 	if err != nil {
 		return nil, err
 	}
-	path = filepath.Join(path, "_default_ab.json")
+	path = filepath.Join(path, "addressbook.json")
+
+	debug.Printf("loading addressbook from %s", path)
 
 	data, err := ioutil.ReadFile(path)
 	if os.IsNotExist(err) {
-		err = createDefaultAddressBook(path)
+		urlPath, err := b.AddressbookHomeSetPath(ctx)
+		if err != nil {
+			return nil, err
+		}
+		debug.Printf("creating default addressbook (URL:path): %s:%s", urlPath, path)
+		err = createDefaultAddressBook(urlPath, path)
 		if err != nil {
 			return nil, err
 		}
@@ -175,8 +255,9 @@ func (b *filesystemBackend) AddressBook(ctx context.Context) (*carddav.AddressBo
 	return &addressBook, nil
 }
 
-func (b *filesystemBackend) GetAddressObject(ctx context.Context, path string, req *carddav.AddressDataRequest) (*carddav.AddressObject, error) {
+func (b *filesystemBackend) GetAddressObject(ctx context.Context, objPath string, req *carddav.AddressDataRequest) (*carddav.AddressObject, error) {
-	localPath, err := b.safePath(ctx, path)
+	debug.Printf("filesystem.GetAddressObject(%s, %v)", objPath, req)
+	localPath, err := b.localCardDAVPath(ctx, objPath)
 	if err != nil {
 		return nil, err
 	}
@@ -202,7 +283,7 @@ func (b *filesystemBackend) GetAddressObject(ctx context.Context, path string, r
 	}
 
 	obj := carddav.AddressObject{
-		Path:    path,
+		Path:    objPath,
 		ModTime: info.ModTime(),
 		ETag:    etag,
 		Card:    card,
@@ -210,17 +291,21 @@ func (b *filesystemBackend) GetAddressObject(ctx context.Context, path string, r
 	return &obj, nil
 }
 
-func (b *filesystemBackend) loadAll(ctx context.Context, propFilter []string) ([]carddav.AddressObject, error) {
+func (b *filesystemBackend) loadAllContacts(ctx context.Context, propFilter []string) ([]carddav.AddressObject, error) {
 	var result []carddav.AddressObject
 
-	path, err := b.pathForContext(ctx)
+	localPath, err := b.localCardDAVPath(ctx, "")
 	if err != nil {
 		return result, err
 	}
 
-	err = filepath.Walk(path, func(filename string, info os.FileInfo, err error) error {
+	homeSetPath, err := b.AddressbookHomeSetPath(ctx)
-		// Skip address book meta data files
+	if err != nil {
-		if !info.Mode().IsRegular() || filepath.Ext(filename) == ".json" {
+		return result, err
+	}
+
+	err = filepath.Walk(localPath, func(filename string, info os.FileInfo, err error) error {
+		if !info.Mode().IsRegular() || filepath.Ext(filename) != ".vcf" {
 			return nil
 		}
 
@@ -235,7 +320,7 @@ func (b *filesystemBackend) loadAll(ctx context.Context, propFilter []string) ([
 		}
 
 		obj := carddav.AddressObject{
-			Path:    "/" + filepath.Base(filename),
+			Path:    path.Join(homeSetPath, filepath.Base(filename)),
 			ModTime: info.ModTime(),
 			ETag:    etag,
 			Card:    card,
@@ -244,25 +329,72 @@ func (b *filesystemBackend) loadAll(ctx context.Context, propFilter []string) ([
 		return nil
 	})
 
+	debug.Printf("filesystem.loadAllContacts() returning %d results from %s", len(result), localPath)
+	return result, err
+}
+
+func (b *filesystemBackend) loadAllCalendars(ctx context.Context, propFilter []string) ([]caldav.CalendarObject, error) {
+	var result []caldav.CalendarObject
+
+	localPath, err := b.localCalDAVPath(ctx, "")
+	if err != nil {
+		return result, err
+	}
+
+	homeSetPath, err := b.CalendarHomeSetPath(ctx)
+	if err != nil {
+		return result, err
+	}
+
+	err = filepath.Walk(localPath, func(filename string, info os.FileInfo, err error) error {
+		// Skip address book meta data files
+		if !info.Mode().IsRegular() || filepath.Ext(filename) != ".ics" {
+			return nil
+		}
+
+		cal, err := calendarFromFile(filename, propFilter)
+		if err != nil {
+			fmt.Printf("load calendar error for %s: %v\n", filename, err)
+			return err
+		}
+
+		etag, err := etagForFile(filename)
+		if err != nil {
+			return err
+		}
+
+		obj := caldav.CalendarObject{
+			Path:    path.Join(homeSetPath, filepath.Base(filename)),
+			ModTime: info.ModTime(),
+			ETag:    etag,
+			Data:    cal,
+		}
+		result = append(result, obj)
+		return nil
+	})
+
+	debug.Printf("filesystem.loadAllCalendars() returning %d results from %s", len(result), localPath)
 	return result, err
 }
 
 func (b *filesystemBackend) ListAddressObjects(ctx context.Context, req *carddav.AddressDataRequest) ([]carddav.AddressObject, error) {
+	debug.Printf("filesystem.ListAddressObjects(%v)", req)
 	var propFilter []string
 	if req != nil && !req.AllProp {
 		propFilter = req.Props
 	}
 
-	return b.loadAll(ctx, propFilter)
+	return b.loadAllContacts(ctx, propFilter)
 }
 
 func (b *filesystemBackend) QueryAddressObjects(ctx context.Context, query *carddav.AddressBookQuery) ([]carddav.AddressObject, error) {
+	debug.Printf("filesystem.QueryAddressObjects(%v)", query)
 	var propFilter []string
 	if query != nil && !query.DataRequest.AllProp {
 		propFilter = query.DataRequest.Props
 	}
 
-	result, err := b.loadAll(ctx, propFilter)
+	result, err := b.loadAllContacts(ctx, propFilter)
 	if err != nil {
 		return result, err
 	}
@@ -270,31 +402,19 @@ func (b *filesystemBackend) QueryAddressObjects(ctx context.Context, query *card
 	return carddav.Filter(query, result)
 }
 
-func (b *filesystemBackend) hasUIDConflict(ctx context.Context, uid, path string) (bool, error) {
+func (b *filesystemBackend) PutAddressObject(ctx context.Context, objPath string, card vcard.Card, opts *carddav.PutAddressObjectOptions) (loc string, err error) {
-	all, err := b.loadAll(ctx, nil)
+	debug.Printf("filesystem.PutAddressObject(%v, %v, %v)", objPath, card, opts)
-	if err != nil {
-		return false, err
-	}
-	for _, contact := range all {
-		if contact.Path != path && contact.Card.Value(vcard.FieldUID) == uid {
-			return true, nil
-		}
-	}
 
-	return false, nil
+	// Object always get saved as <UID>.vcf
-}
+	dirname, _ := path.Split(objPath)
+	objPath = path.Join(dirname, card.Value(vcard.FieldUID)+".vcf")
 
-func (b *filesystemBackend) PutAddressObject(ctx context.Context, path string, card vcard.Card) (loc string, err error) {
+	localPath, err := b.localCardDAVPath(ctx, objPath)
-	localPath, err := b.safePath(ctx, path)
 	if err != nil {
 		return "", err
 	}
 
-	conflict, err := b.hasUIDConflict(ctx, card.Value(vcard.FieldUID), path)
+	if _, err := os.Stat(localPath); !os.IsNotExist(err) {
-	if err != nil {
-		return "", err
-	}
-	if conflict {
 		return "", carddav.NewPreconditionError(carddav.PreconditionNoUIDConflict)
 	}
 
@@ -310,11 +430,13 @@ func (b *filesystemBackend) PutAddressObject(ctx context.Context, path string, c
 		return "", err
 	}
 
-	return path, nil
+	return objPath, nil
 }
 
 func (b *filesystemBackend) DeleteAddressObject(ctx context.Context, path string) error {
-	localPath, err := b.safePath(ctx, path)
+	debug.Printf("filesystem.DeleteAddressObject(%s)", path)
+
+	localPath, err := b.localCardDAVPath(ctx, path)
 	if err != nil {
 		return err
 	}
@@ -324,3 +446,167 @@ func (b *filesystemBackend) DeleteAddressObject(ctx context.Context, path string
 	}
 	return nil
 }
+
+func createDefaultCalendar(path, localPath string) error {
+	// TODO what should the default calendar look like?
+	defaultC := caldav.Calendar{
+		Path:            path,
+		Name:            "My calendar",
+		Description:     "Default calendar",
+		MaxResourceSize: 4096,
+	}
+	blob, err := json.MarshalIndent(defaultC, "", "  ")
+	if err != nil {
+		return fmt.Errorf("error creating default calendar: %s", err.Error())
+	}
+	err = os.WriteFile(localPath, blob, 0644)
+	if err != nil {
+		return fmt.Errorf("error writing default calendar: %s", err.Error())
+	}
+	return nil
+}
+
+func (b *filesystemBackend) Calendar(ctx context.Context) (*caldav.Calendar, error) {
+	debug.Printf("filesystem.Calendar()")
+
+	path, err := b.localCalDAVPath(ctx, "")
+	if err != nil {
+		return nil, err
+	}
+	path = filepath.Join(path, "calendar.json")
+
+	debug.Printf("loading calendar from %s", path)
+
+	data, err := ioutil.ReadFile(path)
+	if os.IsNotExist(err) {
+		homeSetPath, err := b.CalendarHomeSetPath(ctx)
+		if err != nil {
+			return nil, err
+		}
+		debug.Printf("creating default calendar (URL:path): %s:%s", homeSetPath, path)
+		err = createDefaultCalendar(homeSetPath, path)
+		if err != nil {
+			return nil, err
+		}
+		data, err = ioutil.ReadFile(path)
+	}
+	if err != nil {
+		return nil, fmt.Errorf("error opening calendar: %s", err.Error())
+	}
+	var calendar caldav.Calendar
+	err = json.Unmarshal(data, &calendar)
+	if err != nil {
+		return nil, fmt.Errorf("error reading calendar: %s", err.Error())
+	}
+
+	return &calendar, nil
+}
+
+func (b *filesystemBackend) GetCalendarObject(ctx context.Context, objPath string, req *caldav.CalendarCompRequest) (*caldav.CalendarObject, error) {
+	debug.Printf("filesystem.GetCalendarObject(%s, %v)", objPath, req)
+
+	localPath, err := b.localCalDAVPath(ctx, objPath)
+	if err != nil {
+		return nil, err
+	}
+
+	info, err := os.Stat(localPath)
+	if err != nil {
+		if errors.Is(err, fs.ErrNotExist) {
+			debug.Printf("not found: %s", localPath)
+			return nil, nil
+		}
+		return nil, err
+	}
+
+	var propFilter []string
+	if req != nil && !req.AllProps {
+		propFilter = req.Props
+	}
+
+	calendar, err := calendarFromFile(localPath, propFilter)
+	if err != nil {
+		debug.Printf("error reading calendar: %v", err)
+		return nil, err
+	}
+
+	etag, err := etagForFile(localPath)
+	if err != nil {
+		return nil, err
+	}
+
+	obj := caldav.CalendarObject{
+		Path:    objPath,
+		ModTime: info.ModTime(),
+		ETag:    etag,
+		Data:    calendar,
+	}
+	return &obj, nil
+	return nil, fmt.Errorf("not implemented")
+}
+
+func (b *filesystemBackend) ListCalendarObjects(ctx context.Context, req *caldav.CalendarCompRequest) ([]caldav.CalendarObject, error) {
+	debug.Printf("filesystem.ListCalendarObjects(%v)", req)
+
+	var propFilter []string
+	if req != nil && !req.AllProps {
+		propFilter = req.Props
+	}
+
+	return b.loadAllCalendars(ctx, propFilter)
+}
+
+func (b *filesystemBackend) QueryCalendarObjects(ctx context.Context, query *caldav.CalendarQuery) ([]caldav.CalendarObject, error) {
+	debug.Printf("filesystem.QueryCalendarObjects(%v)", query)
+
+	var propFilter []string
+	if query != nil && !query.CompRequest.AllProps {
+		propFilter = query.CompRequest.Props
+	}
+
+	result, err := b.loadAllCalendars(ctx, propFilter)
+	if err != nil {
+		return result, err
+	}
+
+	return result, nil
+	// TODO implement:
+	//return caldav.Filter(query, result)
+}
+
+func (b *filesystemBackend) PutCalendarObject(ctx context.Context, objPath string, calendar *ical.Calendar, opts *caldav.PutCalendarObjectOptions) (loc string, err error) {
+	debug.Printf("filesystem.PutCalendarObject(%s, %v, %v)", objPath, calendar, opts)
+
+	_, uid, err := caldav.ValidateCalendarObject(calendar)
+	if err != nil {
+		return "", caldav.NewPreconditionError(caldav.PreconditionValidCalendarObjectResource)
+	}
+
+	// Object always get saved as <UID>.ics
+	dirname, _ := path.Split(objPath)
+	objPath = path.Join(dirname, uid+".ics")
+
+	localPath, err := b.localCalDAVPath(ctx, objPath)
+	if err != nil {
+		return "", err
+	}
+
+	if _, err := os.Stat(localPath); !os.IsNotExist(err) {
+		return "", caldav.NewPreconditionError(caldav.PreconditionNoUIDConflict)
+	}
+
+	f, err := os.Create(localPath)
+	if err != nil {
+		return "", err
+	}
+	defer f.Close()
+
+	enc := ical.NewEncoder(f)
+	err = enc.Encode(calendar)
+	if err != nil {
+		return "", err
+	}
+
+	return objPath, nil
+	return "", nil
+}

storage/postgresql.go

@@ -4,6 +4,7 @@ import (
 	"context"
 
 	"github.com/emersion/go-vcard"
+	"github.com/emersion/go-webdav/caldav"
 	"github.com/emersion/go-webdav/carddav"
 )
 
@@ -11,8 +12,16 @@ type psqlBackend struct{}
 
 var _ carddav.Backend = (*psqlBackend)(nil)
 
-func NewPostgreSQL() carddav.Backend {
+func NewPostgreSQL() (caldav.Backend, carddav.Backend, error) {
-	return &psqlBackend{}
+	return nil, &psqlBackend{}, nil
+}
+
+func (*psqlBackend) CurrentUserPrincipal(ctx context.Context) (string, error) {
+	panic("TODO")
+}
+
+func (*psqlBackend) AddressbookHomeSetPath(ctx context.Context) (string, error) {
+	panic("TODO")
 }
 
 func (*psqlBackend) AddressBook(ctx context.Context) (*carddav.AddressBook, error) {
@@ -31,7 +40,7 @@ func (*psqlBackend) QueryAddressObjects(ctx context.Context, query *carddav.Addr
 	panic("TODO")
 }
 
-func (*psqlBackend) PutAddressObject(ctx context.Context, path string, card vcard.Card) (loc string, err error) {
+func (*psqlBackend) PutAddressObject(ctx context.Context, path string, card vcard.Card, opts *carddav.PutAddressObjectOptions) (loc string, err error) {
 	panic("TODO")
 }
 

storage/url.go

@@ -4,21 +4,23 @@ import (
 	"fmt"
 	"net/url"
 
+	"github.com/emersion/go-webdav"
+	"github.com/emersion/go-webdav/caldav"
 	"github.com/emersion/go-webdav/carddav"
 )
 
-func NewFromURL(storageURL string) (carddav.Backend, error) {
+func NewFromURL(storageURL, caldavPrefix, carddavPrefix string, userPrincipalBackend webdav.UserPrincipalBackend) (caldav.Backend, carddav.Backend, error) {
 	u, err := url.Parse(storageURL)
 	if err != nil {
-		return nil, fmt.Errorf("error parsing storage URL: %s", err.Error())
+		return nil, nil, fmt.Errorf("error parsing storage URL: %s", err.Error())
 	}
 
 	switch u.Scheme {
 	case "file":
-		return NewFilesystem(u.Path)
+		return NewFilesystem(u.Path, caldavPrefix, carddavPrefix, userPrincipalBackend)
 	case "postgresql":
-		return NewPostgreSQL(), nil
+		return NewPostgreSQL()
 	default:
-		return nil, fmt.Errorf("no storage provider found for %s:// URL", u.Scheme)
+		return nil, nil, fmt.Errorf("no storage provider found for %s:// URL", u.Scheme)
 	}
 }