Implement room aliases (#167)

* Add database functions to interact with aliases

* Save room alias

* Check if alias already exists

* Implement local alias lookup

* Implement alias removal

* Move alias API

* Handle case with no alias set for a room

* Apply requested changes

src/github.com/matrix-org/dendrite/clientapi/readers/directory.go

@@ -15,13 +15,13 @@
 package readers
 
 import (
-	"fmt"
 	"net/http"
 
 	"github.com/matrix-org/dendrite/clientapi/auth/authtypes"
 	"github.com/matrix-org/dendrite/clientapi/httputil"
 	"github.com/matrix-org/dendrite/clientapi/jsonerror"
 	"github.com/matrix-org/dendrite/common/config"
+	"github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/gomatrix"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/util"
@@ -34,6 +34,7 @@ func DirectoryRoom(
 	roomAlias string,
 	federation *gomatrixserverlib.FederationClient,
 	cfg *config.Dendrite,
+	aliasAPI api.RoomserverAliasAPI,
 ) util.JSONResponse {
 	_, domain, err := gomatrixserverlib.SplitID('#', roomAlias)
 	if err != nil {
@@ -43,11 +44,30 @@ func DirectoryRoom(
 		}
 	}
 
+	var resp gomatrixserverlib.RespDirectory
+
 	if domain == cfg.Matrix.ServerName {
-		// TODO: Implement lookup up local room aliases.
-		panic(fmt.Errorf("Looking up local room aliases is not implemented"))
+		queryReq := api.GetAliasRoomIDRequest{Alias: roomAlias}
+		var queryRes api.GetAliasRoomIDResponse
+		if err = aliasAPI.GetAliasRoomID(&queryReq, &queryRes); err != nil {
+			return httputil.LogThenError(req, err)
+		}
+
+		if len(queryRes.RoomID) > 0 {
+			// TODO: List servers that are aware of this room alias
+			resp = gomatrixserverlib.RespDirectory{
+				RoomID:  queryRes.RoomID,
+				Servers: []gomatrixserverlib.ServerName{},
+			}
 		} else {
-		resp, err := federation.LookupRoomAlias(domain, roomAlias)
+			// If the response doesn't contain a non-empty string, return an error
+			return util.JSONResponse{
+				Code: 404,
+				JSON: jsonerror.NotFound("Room alias " + roomAlias + " not found."),
+			}
+		}
+	} else {
+		resp, err = federation.LookupRoomAlias(domain, roomAlias)
 		if err != nil {
 			switch x := err.(type) {
 			case gomatrix.HTTPError:
@@ -62,10 +82,88 @@ func DirectoryRoom(
 			// TODO: Return 504 if the remote server timed out.
 			return httputil.LogThenError(req, err)
 		}
+	}
 
 	return util.JSONResponse{
 		Code: 200,
 		JSON: resp,
 	}
+}
+
+// SetLocalAlias implements PUT /directory/room/{roomAlias}
+// TODO: Check if the user has the power level to set an alias
+func SetLocalAlias(
+	req *http.Request,
+	device *authtypes.Device,
+	alias string,
+	cfg *config.Dendrite,
+	aliasAPI api.RoomserverAliasAPI,
+) util.JSONResponse {
+	_, domain, err := gomatrixserverlib.SplitID('#', alias)
+	if err != nil {
+		return util.JSONResponse{
+			Code: 400,
+			JSON: jsonerror.BadJSON("Room alias must be in the form '#localpart:domain'"),
+		}
+	}
+
+	if domain != cfg.Matrix.ServerName {
+		return util.JSONResponse{
+			Code: 403,
+			JSON: jsonerror.Forbidden("Alias must be on local homeserver"),
+		}
+	}
+
+	var r struct {
+		RoomID string `json:"room_id"`
+	}
+	if resErr := httputil.UnmarshalJSONRequest(req, &r); resErr != nil {
+		return *resErr
+	}
+
+	queryReq := api.SetRoomAliasRequest{
+		UserID: device.UserID,
+		RoomID: r.RoomID,
+		Alias:  alias,
+	}
+	var queryRes api.SetRoomAliasResponse
+	if err := aliasAPI.SetRoomAlias(&queryReq, &queryRes); err != nil {
+		return httputil.LogThenError(req, err)
+	}
+
+	if queryRes.AliasExists {
+		return util.JSONResponse{
+			Code: 409,
+			JSON: jsonerror.Unknown("The alias " + alias + " already exists."),
+		}
+	}
+
+	return util.JSONResponse{
+		Code: 200,
+		JSON: struct{}{},
+	}
+}
+
+// RemoveLocalAlias implements DELETE /directory/room/{roomAlias}
+// TODO: Check if the user has the power level to remove an alias
+func RemoveLocalAlias(
+	req *http.Request,
+	device *authtypes.Device,
+	alias string,
+	cfg *config.Dendrite,
+	aliasAPI api.RoomserverAliasAPI,
+) util.JSONResponse {
+	queryReq := api.RemoveRoomAliasRequest{
+		Alias:  alias,
+		UserID: device.UserID,
+	}
+	var queryRes api.RemoveRoomAliasResponse
+	if err := aliasAPI.RemoveRoomAlias(&queryReq, &queryRes); err != nil {
+		return httputil.LogThenError(req, err)
+	}
+
+	return util.JSONResponse{
+		Code: 200,
+		JSON: struct{}{},
 	}
 }

src/github.com/matrix-org/dendrite/clientapi/routing/routing.go

@@ -42,6 +42,7 @@ const pathPrefixUnstable = "/_matrix/client/unstable"
 func Setup(
 	servMux *http.ServeMux, httpClient *http.Client, cfg config.Dendrite,
 	producer *producers.RoomserverProducer, queryAPI api.RoomserverQueryAPI,
+	aliasAPI api.RoomserverAliasAPI,
 	accountDB *accounts.Database,
 	deviceDB *devices.Database,
 	federation *gomatrixserverlib.FederationClient,
@@ -109,9 +110,23 @@ func Setup(
 	r0mux.Handle("/directory/room/{roomAlias}",
 		common.MakeAuthAPI("directory_room", deviceDB, func(req *http.Request, device *authtypes.Device) util.JSONResponse {
 			vars := mux.Vars(req)
-			return readers.DirectoryRoom(req, device, vars["roomAlias"], federation, &cfg)
+			return readers.DirectoryRoom(req, device, vars["roomAlias"], federation, &cfg, aliasAPI)
 		}),
-	)
+	).Methods("GET")
+
+	r0mux.Handle("/directory/room/{roomAlias}",
+		common.MakeAuthAPI("directory_room", deviceDB, func(req *http.Request, device *authtypes.Device) util.JSONResponse {
+			vars := mux.Vars(req)
+			return readers.SetLocalAlias(req, device, vars["roomAlias"], &cfg, aliasAPI)
+		}),
+	).Methods("PUT", "OPTIONS")
+
+	r0mux.Handle("/directory/room/{roomAlias}",
+		common.MakeAuthAPI("directory_room", deviceDB, func(req *http.Request, device *authtypes.Device) util.JSONResponse {
+			vars := mux.Vars(req)
+			return readers.RemoveLocalAlias(req, device, vars["roomAlias"], &cfg, aliasAPI)
+		}),
+	).Methods("DELETE")
 
 	r0mux.Handle("/logout",
 		common.MakeAuthAPI("logout", deviceDB, func(req *http.Request, device *authtypes.Device) util.JSONResponse {

src/github.com/matrix-org/dendrite/cmd/dendrite-client-api-server/main.go

@@ -52,6 +52,7 @@ func main() {
 	log.Info("config: ", cfg)
 
 	queryAPI := api.NewRoomserverQueryAPIHTTP(cfg.RoomServerURL(), nil)
+	aliasAPI := api.NewRoomserverAliasAPIHTTP(cfg.RoomServerURL(), nil)
 
 	roomserverProducer := producers.NewRoomserverProducer(cfg.RoomServerURL())
 	userUpdateProducer, err := producers.NewUserUpdateProducer(
@@ -97,7 +98,8 @@ func main() {
 	log.Info("Starting client API server on ", cfg.Listen.ClientAPI)
 	routing.Setup(
 		http.DefaultServeMux, http.DefaultClient, *cfg, roomserverProducer,
-		queryAPI, accountDB, deviceDB, federation, keyRing, userUpdateProducer,
+		queryAPI, aliasAPI, accountDB, deviceDB, federation, keyRing,
+		userUpdateProducer,
 	)
 	log.Fatal(http.ListenAndServe(string(cfg.Listen.ClientAPI), nil))
 }

src/github.com/matrix-org/dendrite/cmd/dendrite-room-server/main.go

@@ -23,6 +23,7 @@ import (
 	log "github.com/Sirupsen/logrus"
 	"github.com/matrix-org/dendrite/common"
 	"github.com/matrix-org/dendrite/common/config"
+	"github.com/matrix-org/dendrite/roomserver/alias"
 	"github.com/matrix-org/dendrite/roomserver/input"
 	"github.com/matrix-org/dendrite/roomserver/query"
 	"github.com/matrix-org/dendrite/roomserver/storage"
@@ -58,12 +59,6 @@ func main() {
 		panic(err)
 	}
 
-	queryAPI := query.RoomserverQueryAPI{
-		DB: db,
-	}
-
-	queryAPI.SetupHTTP(http.DefaultServeMux)
-
 	inputAPI := input.RoomserverInputAPI{
 		DB:                   db,
 		Producer:             kafkaProducer,
@@ -72,6 +67,19 @@ func main() {
 
 	inputAPI.SetupHTTP(http.DefaultServeMux)
 
+	queryAPI := query.RoomserverQueryAPI{db}
+
+	queryAPI.SetupHTTP(http.DefaultServeMux)
+
+	aliasAPI := alias.RoomserverAliasAPI{
+		DB:       db,
+		Cfg:      cfg,
+		InputAPI: inputAPI,
+		QueryAPI: queryAPI,
+	}
+
+	aliasAPI.SetupHTTP(http.DefaultServeMux)
+
 	http.DefaultServeMux.Handle("/metrics", prometheus.Handler())
 
 	log.Info("Started room server on ", cfg.Listen.RoomServer)

src/github.com/matrix-org/dendrite/roomserver/alias/alias.go

@@ -0,0 +1,256 @@
+// Copyright 2017 Vector Creations Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package alias
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/matrix-org/dendrite/common"
+	"github.com/matrix-org/dendrite/common/config"
+	"github.com/matrix-org/dendrite/roomserver/api"
+	"github.com/matrix-org/dendrite/roomserver/input"
+	"github.com/matrix-org/dendrite/roomserver/query"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/matrix-org/util"
+)
+
+// RoomserverAliasAPIDatabase has the storage APIs needed to implement the alias API.
+type RoomserverAliasAPIDatabase interface {
+	// Save a given room alias with the room ID it refers to.
+	// Returns an error if there was a problem talking to the database.
+	SetRoomAlias(alias string, roomID string) error
+	// Lookup the room ID a given alias refers to.
+	// Returns an error if there was a problem talking to the database.
+	GetRoomIDFromAlias(alias string) (string, error)
+	// Lookup all aliases referring to a given room ID.
+	// Returns an error if there was a problem talking to the database.
+	GetAliasesFromRoomID(roomID string) ([]string, error)
+	// Remove a given room alias.
+	// Returns an error if there was a problem talking to the database.
+	RemoveRoomAlias(alias string) error
+}
+
+// RoomserverAliasAPI is an implementation of api.RoomserverAliasAPI
+type RoomserverAliasAPI struct {
+	DB       RoomserverAliasAPIDatabase
+	Cfg      *config.Dendrite
+	InputAPI input.RoomserverInputAPI
+	QueryAPI query.RoomserverQueryAPI
+}
+
+// SetRoomAlias implements api.RoomserverAliasAPI
+func (r *RoomserverAliasAPI) SetRoomAlias(
+	request *api.SetRoomAliasRequest,
+	response *api.SetRoomAliasResponse,
+) error {
+	// Check if the alias isn't already referring to a room
+	roomID, err := r.DB.GetRoomIDFromAlias(request.Alias)
+	if err != nil {
+		return err
+	}
+	if len(roomID) > 0 {
+		// If the alias already exists, stop the process
+		response.AliasExists = true
+		return nil
+	}
+	response.AliasExists = false
+
+	// Save the new alias
+	if err := r.DB.SetRoomAlias(request.Alias, request.RoomID); err != nil {
+		return err
+	}
+
+	// Send a m.room.aliases event with the updated list of aliases for this room
+	if err := r.sendUpdatedAliasesEvent(request.UserID, request.RoomID); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// GetAliasRoomID implements api.RoomserverAliasAPI
+func (r *RoomserverAliasAPI) GetAliasRoomID(
+	request *api.GetAliasRoomIDRequest,
+	response *api.GetAliasRoomIDResponse,
+) error {
+	// Lookup the room ID in the database
+	roomID, err := r.DB.GetRoomIDFromAlias(request.Alias)
+	if err != nil {
+		return err
+	}
+
+	response.RoomID = roomID
+	return nil
+}
+
+// RemoveRoomAlias implements api.RoomserverAliasAPI
+func (r *RoomserverAliasAPI) RemoveRoomAlias(
+	request *api.RemoveRoomAliasRequest,
+	response *api.RemoveRoomAliasResponse,
+) error {
+	// Lookup the room ID in the database
+	roomID, err := r.DB.GetRoomIDFromAlias(request.Alias)
+	if err != nil {
+		return err
+	}
+
+	// Remove the dalias from the database
+	if err := r.DB.RemoveRoomAlias(request.Alias); err != nil {
+		return err
+	}
+
+	// Send an updated m.room.aliases event
+	if err := r.sendUpdatedAliasesEvent(request.UserID, roomID); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+type roomAliasesContent struct {
+	Aliases []string `json:"aliases"`
+}
+
+// Build the updated m.room.aliases event to send to the room after addition or
+// removal of an alias
+func (r *RoomserverAliasAPI) sendUpdatedAliasesEvent(userID string, roomID string) error {
+	serverName := string(r.Cfg.Matrix.ServerName)
+
+	builder := gomatrixserverlib.EventBuilder{
+		Sender:   userID,
+		RoomID:   roomID,
+		Type:     "m.room.aliases",
+		StateKey: &serverName,
+	}
+
+	// Retrieve the updated list of aliases, marhal it and set it as the
+	// event's content
+	aliases, err := r.DB.GetAliasesFromRoomID(roomID)
+	if err != nil {
+		return err
+	}
+	content := roomAliasesContent{Aliases: aliases}
+	rawContent, err := json.Marshal(content)
+	if err != nil {
+		return err
+	}
+	err = builder.SetContent(json.RawMessage(rawContent))
+	if err != nil {
+		return err
+	}
+
+	// Get needed state events and depth
+	eventsNeeded, err := gomatrixserverlib.StateNeededForEventBuilder(&builder)
+	if err != nil {
+		return err
+	}
+	req := api.QueryLatestEventsAndStateRequest{
+		RoomID:       roomID,
+		StateToFetch: eventsNeeded.Tuples(),
+	}
+	var res api.QueryLatestEventsAndStateResponse
+	if err = r.QueryAPI.QueryLatestEventsAndState(&req, &res); err != nil {
+		return err
+	}
+	builder.Depth = res.Depth
+	builder.PrevEvents = res.LatestEvents
+
+	// Add auth events
+	authEvents := gomatrixserverlib.NewAuthEvents(nil)
+	for i := range res.StateEvents {
+		authEvents.AddEvent(&res.StateEvents[i])
+	}
+	refs, err := eventsNeeded.AuthEventReferences(&authEvents)
+	if err != nil {
+		return err
+	}
+	builder.AuthEvents = refs
+
+	// Build the event
+	eventID := fmt.Sprintf("$%s:%s", util.RandomString(16), r.Cfg.Matrix.ServerName)
+	now := time.Now()
+	event, err := builder.Build(eventID, now, r.Cfg.Matrix.ServerName, r.Cfg.Matrix.KeyID, r.Cfg.Matrix.PrivateKey)
+	if err != nil {
+		return err
+	}
+
+	// Create the request
+	ire := api.InputRoomEvent{
+		Kind:         api.KindNew,
+		Event:        event,
+		AuthEventIDs: event.AuthEventIDs(),
+		SendAsServer: serverName,
+	}
+	inputReq := api.InputRoomEventsRequest{
+		InputRoomEvents: []api.InputRoomEvent{ire},
+	}
+	var inputRes api.InputRoomEventsResponse
+
+	// Send the request
+	if err := r.InputAPI.InputRoomEvents(&inputReq, &inputRes); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// SetupHTTP adds the RoomserverAliasAPI handlers to the http.ServeMux.
+func (r *RoomserverAliasAPI) SetupHTTP(servMux *http.ServeMux) {
+	servMux.Handle(
+		api.RoomserverSetRoomAliasPath,
+		common.MakeAPI("setRoomAlias", func(req *http.Request) util.JSONResponse {
+			var request api.SetRoomAliasRequest
+			var response api.SetRoomAliasResponse
+			if err := json.NewDecoder(req.Body).Decode(&request); err != nil {
+				return util.ErrorResponse(err)
+			}
+			if err := r.SetRoomAlias(&request, &response); err != nil {
+				return util.ErrorResponse(err)
+			}
+			return util.JSONResponse{Code: 200, JSON: &response}
+		}),
+	)
+	servMux.Handle(
+		api.RoomserverGetAliasRoomIDPath,
+		common.MakeAPI("getAliasRoomID", func(req *http.Request) util.JSONResponse {
+			var request api.GetAliasRoomIDRequest
+			var response api.GetAliasRoomIDResponse
+			if err := json.NewDecoder(req.Body).Decode(&request); err != nil {
+				return util.ErrorResponse(err)
+			}
+			if err := r.GetAliasRoomID(&request, &response); err != nil {
+				return util.ErrorResponse(err)
+			}
+			return util.JSONResponse{Code: 200, JSON: &response}
+		}),
+	)
+	servMux.Handle(
+		api.RoomserverRemoveRoomAliasPath,
+		common.MakeAPI("removeRoomAlias", func(req *http.Request) util.JSONResponse {
+			var request api.RemoveRoomAliasRequest
+			var response api.RemoveRoomAliasResponse
+			if err := json.NewDecoder(req.Body).Decode(&request); err != nil {
+				return util.ErrorResponse(err)
+			}
+			if err := r.RemoveRoomAlias(&request, &response); err != nil {
+				return util.ErrorResponse(err)
+			}
+			return util.JSONResponse{Code: 200, JSON: &response}
+		}),
+	)
+}

src/github.com/matrix-org/dendrite/roomserver/api/alias.go

@@ -0,0 +1,129 @@
+// Copyright 2017 Vector Creations Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package api
+
+import (
+	"net/http"
+)
+
+// SetRoomAliasRequest is a request to SetRoomAlias
+type SetRoomAliasRequest struct {
+	// ID of the user setting the alias
+	UserID string `json:"user_id"`
+	// New alias for the room
+	Alias string `json:"alias"`
+	// The room ID the alias is referring to
+	RoomID string `json:"room_id"`
+}
+
+// SetRoomAliasResponse is a response to SetRoomAlias
+type SetRoomAliasResponse struct {
+	// Does the alias already refer to a room?
+	AliasExists bool `json:"alias_exists"`
+}
+
+// GetAliasRoomIDRequest is a request to GetAliasRoomID
+type GetAliasRoomIDRequest struct {
+	// Alias we want to lookup
+	Alias string `json:"alias"`
+}
+
+// GetAliasRoomIDResponse is a response to GetAliasRoomID
+type GetAliasRoomIDResponse struct {
+	// The room ID the alias refers to
+	RoomID string `json:"room_id"`
+}
+
+// RemoveRoomAliasRequest is a request to RemoveRoomAlias
+type RemoveRoomAliasRequest struct {
+	// ID of the user removing the alias
+	UserID string `json:"user_id"`
+	// The room alias to remove
+	Alias string `json:"alias"`
+}
+
+// RemoveRoomAliasResponse is a response to RemoveRoomAlias
+type RemoveRoomAliasResponse struct{}
+
+// RoomserverAliasAPI is used to save, lookup or remove a room alias
+type RoomserverAliasAPI interface {
+	// Set a room alias
+	SetRoomAlias(
+		req *SetRoomAliasRequest,
+		response *SetRoomAliasResponse,
+	) error
+
+	// Get the room ID for an alias
+	GetAliasRoomID(
+		req *GetAliasRoomIDRequest,
+		response *GetAliasRoomIDResponse,
+	) error
+
+	// Remove a room alias
+	RemoveRoomAlias(
+		req *RemoveRoomAliasRequest,
+		response *RemoveRoomAliasResponse,
+	) error
+}
+
+// RoomserverSetRoomAliasPath is the HTTP path for the SetRoomAlias API.
+const RoomserverSetRoomAliasPath = "/api/roomserver/setRoomAlias"
+
+// RoomserverGetAliasRoomIDPath is the HTTP path for the GetAliasRoomID API.
+const RoomserverGetAliasRoomIDPath = "/api/roomserver/getAliasRoomID"
+
+// RoomserverRemoveRoomAliasPath is the HTTP path for the RemoveRoomAlias API.
+const RoomserverRemoveRoomAliasPath = "/api/roomserver/removeRoomAlias"
+
+// NewRoomserverAliasAPIHTTP creates a RoomserverAliasAPI implemented by talking to a HTTP POST API.
+// If httpClient is nil then it uses the http.DefaultClient
+func NewRoomserverAliasAPIHTTP(roomserverURL string, httpClient *http.Client) RoomserverAliasAPI {
+	if httpClient == nil {
+		httpClient = http.DefaultClient
+	}
+	return &httpRoomserverAliasAPI{roomserverURL, httpClient}
+}
+
+type httpRoomserverAliasAPI struct {
+	roomserverURL string
+	httpClient    *http.Client
+}
+
+// SetRoomAlias implements RoomserverAliasAPI
+func (h *httpRoomserverAliasAPI) SetRoomAlias(
+	request *SetRoomAliasRequest,
+	response *SetRoomAliasResponse,
+) error {
+	apiURL := h.roomserverURL + RoomserverSetRoomAliasPath
+	return postJSON(h.httpClient, apiURL, request, response)
+}
+
+// GetAliasRoomID implements RoomserverAliasAPI
+func (h *httpRoomserverAliasAPI) GetAliasRoomID(
+	request *GetAliasRoomIDRequest,
+	response *GetAliasRoomIDResponse,
+) error {
+	// RemoveRoomAlias implements RoomserverAliasAPI
+	apiURL := h.roomserverURL + RoomserverGetAliasRoomIDPath
+	return postJSON(h.httpClient, apiURL, request, response)
+}
+
+func (h *httpRoomserverAliasAPI) RemoveRoomAlias(
+	request *RemoveRoomAliasRequest,
+	response *RemoveRoomAliasResponse,
+) error {
+	apiURL := h.roomserverURL + RoomserverRemoveRoomAliasPath
+	return postJSON(h.httpClient, apiURL, request, response)
+}

src/github.com/matrix-org/dendrite/roomserver/query/query.go

@@ -40,9 +40,21 @@ type RoomserverQueryAPIDatabase interface {
 	// Lookup the numeric IDs for a list of events.
 	// Returns an error if there was a problem talking to the database.
 	EventNIDs(eventIDs []string) (map[string]types.EventNID, error)
+	// Save a given room alias with the room ID it refers to.
+	// Returns an error if there was a problem talking to the database.
+	SetRoomAlias(alias string, roomID string) error
+	// Lookup the room ID a given alias refers to.
+	// Returns an error if there was a problem talking to the database.
+	GetRoomIDFromAlias(alias string) (string, error)
+	// Lookup all aliases referring to a given room ID.
+	// Returns an error if there was a problem talking to the database.
+	GetAliasesFromRoomID(roomID string) ([]string, error)
+	// Remove a given room alias.
+	// Returns an error if there was a problem talking to the database.
+	RemoveRoomAlias(alias string) error
 }
 
-// RoomserverQueryAPI is an implementation of RoomserverQueryAPI
+// RoomserverQueryAPI is an implementation of api.RoomserverQueryAPI
 type RoomserverQueryAPI struct {
 	DB RoomserverQueryAPIDatabase
 }

src/github.com/matrix-org/dendrite/roomserver/storage/room_aliases_table.go

@@ -0,0 +1,100 @@
+// Copyright 2017 Vector Creations Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package storage
+
+import (
+	"database/sql"
+)
+
+const roomAliasesSchema = `
+-- Stores room aliases and room IDs they refer to
+CREATE TABLE IF NOT EXISTS room_aliases (
+    -- Alias of the room
+    alias TEXT NOT NULL PRIMARY KEY,
+    -- Room ID the alias refers to
+    room_id TEXT NOT NULL
+);
+
+CREATE UNIQUE INDEX IF NOT EXISTS room_id_idx ON room_aliases(room_id);
+`
+
+const insertRoomAliasSQL = "" +
+	"INSERT INTO room_aliases (alias, room_id) VALUES ($1, $2)"
+
+const selectRoomIDFromAliasSQL = "" +
+	"SELECT room_id FROM room_aliases WHERE alias = $1"
+
+const selectAliasesFromRoomIDSQL = "" +
+	"SELECT alias FROM room_aliases WHERE room_id = $1"
+
+const deleteRoomAliasSQL = "" +
+	"DELETE FROM room_aliases WHERE alias = $1"
+
+type roomAliasesStatements struct {
+	insertRoomAliasStmt         *sql.Stmt
+	selectRoomIDFromAliasStmt   *sql.Stmt
+	selectAliasesFromRoomIDStmt *sql.Stmt
+	deleteRoomAliasStmt         *sql.Stmt
+}
+
+func (s *roomAliasesStatements) prepare(db *sql.DB) (err error) {
+	_, err = db.Exec(roomAliasesSchema)
+	if err != nil {
+		return
+	}
+	return statementList{
+		{&s.insertRoomAliasStmt, insertRoomAliasSQL},
+		{&s.selectRoomIDFromAliasStmt, selectRoomIDFromAliasSQL},
+		{&s.selectAliasesFromRoomIDStmt, selectAliasesFromRoomIDSQL},
+		{&s.deleteRoomAliasStmt, deleteRoomAliasSQL},
+	}.prepare(db)
+}
+
+func (s *roomAliasesStatements) insertRoomAlias(alias string, roomID string) (err error) {
+	_, err = s.insertRoomAliasStmt.Exec(alias, roomID)
+	return
+}
+
+func (s *roomAliasesStatements) selectRoomIDFromAlias(alias string) (roomID string, err error) {
+	err = s.selectRoomIDFromAliasStmt.QueryRow(alias).Scan(&roomID)
+	if err == sql.ErrNoRows {
+		return "", nil
+	}
+	return
+}
+
+func (s *roomAliasesStatements) selectAliasesFromRoomID(roomID string) (aliases []string, err error) {
+	aliases = []string{}
+	rows, err := s.selectAliasesFromRoomIDStmt.Query(roomID)
+	if err != nil {
+		return
+	}
+
+	for rows.Next() {
+		var alias string
+		if err = rows.Scan(&alias); err != nil {
+			return
+		}
+
+		aliases = append(aliases, alias)
+	}
+
+	return
+}
+
+func (s *roomAliasesStatements) deleteRoomAlias(alias string) (err error) {
+	_, err = s.deleteRoomAliasStmt.Exec(alias)
+	return
+}

src/github.com/matrix-org/dendrite/roomserver/storage/sql.go

@@ -27,6 +27,7 @@ type statements struct {
 	stateSnapshotStatements
 	stateBlockStatements
 	previousEventStatements
+	roomAliasesStatements
 }
 
 func (s *statements) prepare(db *sql.DB) error {
@@ -64,5 +65,9 @@ func (s *statements) prepare(db *sql.DB) error {
 		return err
 	}
 
+	if err = s.roomAliasesStatements.prepare(db); err != nil {
+		return err
+	}
+
 	return nil
 }

src/github.com/matrix-org/dendrite/roomserver/storage/storage.go

@@ -355,6 +355,26 @@ func (d *Database) LatestEventIDs(roomNID types.RoomNID) ([]gomatrixserverlib.Ev
 	return references, currentStateSnapshotNID, depth, nil
 }
 
+// SetRoomAlias implements alias.RoomserverAliasAPIDB
+func (d *Database) SetRoomAlias(alias string, roomID string) error {
+	return d.statements.insertRoomAlias(alias, roomID)
+}
+
+// GetRoomIDFromAlias implements alias.RoomserverAliasAPIDB
+func (d *Database) GetRoomIDFromAlias(alias string) (string, error) {
+	return d.statements.selectRoomIDFromAlias(alias)
+}
+
+// GetAliasesFromRoomID implements alias.RoomserverAliasAPIDB
+func (d *Database) GetAliasesFromRoomID(roomID string) ([]string, error) {
+	return d.statements.selectAliasesFromRoomID(roomID)
+}
+
+// RemoveRoomAlias implements alias.RoomserverAliasAPIDB
+func (d *Database) RemoveRoomAlias(alias string) error {
+	return d.statements.deleteRoomAlias(alias)
+}
+
 // StateEntriesForTuples implements state.RoomStateDatabase
 func (d *Database) StateEntriesForTuples(
 	stateBlockNIDs []types.StateBlockNID, stateKeyTuples []types.StateKeyTuple,