From 4cc86a1225d97a7e7c17e3f0ab433a2f249b4dff Mon Sep 17 00:00:00 2001
From: Simon Ser <contact@emersion.fr>
Date: Tue, 3 May 2022 17:53:06 +0200
Subject: [PATCH] webdav: add ServePrincipal

---
 elements.go | 32 +++++++++++++++++++++++++++
 server.go   | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 webdav.go   |  6 ++++++
 3 files changed, 100 insertions(+)
 create mode 100644 elements.go

diff --git a/elements.go b/elements.go
new file mode 100644
index 0000000..70f9e9b
--- /dev/null
+++ b/elements.go
@@ -0,0 +1,32 @@
+package webdav
+
+import (
+	"encoding/xml"
+
+	"github.com/emersion/go-webdav/internal"
+)
+
+var (
+	principalName                = xml.Name{"DAV:", "principal"}
+	principalAlternateURISetName = xml.Name{"DAV:", "alternate-URI-set"}
+	principalURLName             = xml.Name{"DAV:", "principal-URL"}
+	groupMembershipName          = xml.Name{"DAV:", "group-membership"}
+)
+
+// https://datatracker.ietf.org/doc/html/rfc3744#section-4.1
+type principalAlternateURISet struct {
+	XMLName xml.Name        `xml:"DAV: alternate-URI-set"`
+	Hrefs   []internal.Href `xml:"href"`
+}
+
+// https://datatracker.ietf.org/doc/html/rfc3744#section-4.2
+type principalURL struct {
+	XMLName xml.Name      `xml:"DAV: principal-URL"`
+	Href    internal.Href `xml:"href"`
+}
+
+// https://datatracker.ietf.org/doc/html/rfc3744#section-4.4
+type groupMembership struct {
+	XMLName xml.Name        `xml:"DAV: group-membership"`
+	Hrefs   []internal.Href `xml:"href"`
+}
diff --git a/server.go b/server.go
index 811ef10..9342863 100644
--- a/server.go
+++ b/server.go
@@ -6,6 +6,7 @@ import (
 	"net/http"
 	"os"
 	"strconv"
+	"strings"
 
 	"github.com/emersion/go-webdav/internal"
 )
@@ -234,3 +235,64 @@ func (b *backend) Move(r *http.Request, dest *internal.Href, overwrite bool) (cr
 	}
 	return created, err
 }
+
+// ServePrincipal replies to a request on a principal URI.
+func ServePrincipal(w http.ResponseWriter, r *http.Request, principal *Principal) {
+	switch r.Method {
+	case http.MethodOptions:
+		caps := append([]string{"1", "3"})
+		allow := []string{http.MethodOptions, "PROPFIND"}
+		w.Header().Add("DAV", strings.Join(caps, ", "))
+		w.Header().Add("Allow", strings.Join(allow, ", "))
+		w.WriteHeader(http.StatusNoContent)
+	case "PROPFIND":
+		if err := servePrincipalPropfind(w, r, principal); err != nil {
+			internal.ServeError(w, err)
+		}
+	default:
+		http.Error(w, "unsupported method", http.StatusMethodNotAllowed)
+	}
+}
+
+func servePrincipalPropfind(w http.ResponseWriter, r *http.Request, principal *Principal) error {
+	var propfind internal.Propfind
+	if err := internal.DecodeXMLRequest(r, &propfind); err != nil {
+		return err
+	}
+
+	// TODO: handle Depth
+
+	props := map[xml.Name]internal.PropfindFunc{
+		internal.ResourceTypeName: func(*internal.RawXMLValue) (interface{}, error) {
+			return internal.NewResourceType(principalName), nil
+		},
+		internal.DisplayNameName: func(*internal.RawXMLValue) (interface{}, error) {
+			return &internal.DisplayName{Name: principal.Name}, nil
+		},
+		internal.CurrentUserPrincipalName: func(*internal.RawXMLValue) (interface{}, error) {
+			// TODO: allow serving a principal different from the current user's
+			return &internal.CurrentUserPrincipal{Href: internal.Href{Path: principal.Path}}, nil
+		},
+		principalAlternateURISetName: func(*internal.RawXMLValue) (interface{}, error) {
+			return &principalAlternateURISet{}, nil // TODO: allow customizing
+		},
+		principalURLName: func(*internal.RawXMLValue) (interface{}, error) {
+			return &principalURL{
+				Href: internal.Href{Path: principal.Path},
+			}, nil
+		},
+		groupMembershipName: func(*internal.RawXMLValue) (interface{}, error) {
+			return &groupMembership{}, nil // TODO: allow customizing
+		},
+	}
+
+	// TODO: allow adding more props such as CardDAV/CalDAV home sets
+
+	resp, err := internal.NewPropfindResponse(r.URL.Path, &propfind, props)
+	if err != nil {
+		return err
+	}
+
+	ms := internal.NewMultistatus(*resp)
+	return internal.ServeMultistatus(w, ms)
+}
diff --git a/webdav.go b/webdav.go
index 4dd369c..baad56e 100644
--- a/webdav.go
+++ b/webdav.go
@@ -7,6 +7,12 @@ import (
 	"time"
 )
 
+// Principal is a DAV principal as defined in RFC 3744 section 2.
+type Principal struct {
+	Path string
+	Name string
+}
+
 type FileInfo struct {
 	Path     string
 	Size     int64