Esempio n. 1
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func TestRebuildRoleChannels(t *testing.T) {
	computer := mockComputer{channels: ch.AtSequence(ch.SetOf("derived1", "derived2"), 1)}
	auth := NewAuthenticator(gTestBucket, &computer)
	role, _ := auth.NewRole("testRole", ch.SetOf("explicit1"))
	err := auth.InvalidateChannels(role)
	assert.Equals(t, err, nil)

	role2, err := auth.GetRole("testRole")
	assert.Equals(t, err, nil)
	assert.DeepEquals(t, role2.Channels(), ch.AtSequence(ch.SetOf("explicit1", "derived1", "derived2", "!"), 1))
}
Esempio n. 2
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func TestRebuildUserChannels(t *testing.T) {
	computer := mockComputer{channels: ch.AtSequence(ch.SetOf("derived1", "derived2"), 1)}
	auth := NewAuthenticator(gTestBucket, &computer)
	user, _ := auth.NewUser("testUser", "password", ch.SetOf("explicit1"))
	user.setChannels(nil)
	err := auth.Save(user)
	assert.Equals(t, err, nil)

	user2, err := auth.GetUser("testUser")
	assert.Equals(t, err, nil)
	assert.DeepEquals(t, user2.Channels(), ch.AtSequence(ch.SetOf("explicit1", "derived1", "derived2", "!"), 1))
}
Esempio n. 3
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func TestRebuildUserRoles(t *testing.T) {
	computer := mockComputer{roles: ch.AtSequence(base.SetOf("role1", "role2"), 3)}
	auth := NewAuthenticator(gTestBucket, &computer)
	user, _ := auth.NewUser("testUser", "letmein", nil)
	user.SetExplicitRoles(ch.TimedSet{"role3": ch.NewVbSimpleSequence(1), "role1": ch.NewVbSimpleSequence(1)})
	err := auth.InvalidateRoles(user)
	assert.Equals(t, err, nil)

	user2, err := auth.GetUser("testUser")
	assert.Equals(t, err, nil)
	expected := ch.AtSequence(base.SetOf("role1", "role3"), 1)
	expected.AddChannel("role2", 3)
	assert.DeepEquals(t, user2.RoleNames(), expected)
}
Esempio n. 4
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// Updates a document's channel/role UserAccessMap with new access settings from an AccessMap.
// Returns an array of the user/role names whose access has changed as a result.
func (accessMap *UserAccessMap) updateAccess(doc *document, newAccess channels.AccessMap) (changedUsers []string) {
	// Update users already appearing in doc.Access:
	for name, access := range *accessMap {
		if access.UpdateAtSequence(newAccess[name], doc.Sequence) {
			if len(access) == 0 {
				delete(*accessMap, name)
			}
			changedUsers = append(changedUsers, name)
		}
	}
	// Add new users who are in newAccess but not accessMap:
	for name, access := range newAccess {
		if _, existed := (*accessMap)[name]; !existed {
			if *accessMap == nil {
				*accessMap = UserAccessMap{}
			}
			(*accessMap)[name] = channels.AtSequence(access, doc.Sequence)
			changedUsers = append(changedUsers, name)
		}
	}
	if changedUsers != nil {
		what := "channel"
		if accessMap == &doc.RoleAccess {
			what = "role"
		}
		base.LogTo("Access", "Doc %q grants %s access: %v", doc.ID, what, *accessMap)
	}
	return changedUsers
}
Esempio n. 5
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func (auth *Authenticator) defaultGuestUser() User {
	user := &userImpl{
		roleImpl: roleImpl{
			ExplicitChannels_: ch.AtSequence(ch.SetOf(), 1),
		},
		userImplBody: userImplBody{
			Disabled_: true,
		},
		auth: auth,
	}
	user.Channels_ = user.ExplicitChannels_.Copy()
	return user
}
Esempio n. 6
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func (user *userImpl) UnmarshalJSON(data []byte) error {
	if err := json.Unmarshal(data, &user.userImplBody); err != nil {
		return err
	} else if err := json.Unmarshal(data, &user.roleImpl); err != nil {
		return err
	}

	// Migrate "admin_roles" field:
	if user.OldExplicitRoles_ != nil {
		user.ExplicitRoles_ = ch.AtSequence(base.SetFromArray(user.OldExplicitRoles_), 1)
		user.OldExplicitRoles_ = nil
	}

	return nil
}
Esempio n. 7
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func TestAccessFunction(t *testing.T) {

	/*
		var logKeys = map[string]bool {
			"CRUD": true,
			"Access": true,
		}

		base.UpdateLogKeys(logKeys, true)
	*/

	db := setupTestDB(t)
	defer tearDownTestDB(t, db)

	authenticator := auth.NewAuthenticator(db.Bucket, db)

	var err error
	db.ChannelMapper = channels.NewChannelMapper(`function(doc){access(doc.users,doc.userChannels);}`)

	user, _ := authenticator.NewUser("naomi", "letmein", channels.SetOf("Netflix"))
	user.SetExplicitRoles(channels.TimedSet{"animefan": channels.NewVbSimpleSequence(1), "tumblr": channels.NewVbSimpleSequence(1)})
	assertNoError(t, authenticator.Save(user), "Save")

	body := Body{"users": []string{"naomi"}, "userChannels": []string{"Hulu"}}
	_, err = db.Put("doc1", body)
	assertNoError(t, err, "")

	body = Body{"users": []string{"role:animefan"}, "userChannels": []string{"CrunchyRoll"}}
	_, err = db.Put("doc2", body)
	assertNoError(t, err, "")

	// Create the role _after_ creating the documents, to make sure the previously-indexed access
	// privileges are applied.
	role, _ := authenticator.NewRole("animefan", nil)
	authenticator.Save(role)

	user, err = authenticator.GetUser("naomi")
	assertNoError(t, err, "GetUser")
	expected := channels.AtSequence(channels.SetOf("Hulu", "Netflix", "!"), 1)
	assert.DeepEquals(t, user.Channels(), expected)

	expected.AddChannel("CrunchyRoll", 2)
	assert.DeepEquals(t, user.InheritedChannels(), expected)
}
Esempio n. 8
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func WriteDirectWithChannelGrant(db *Database, channelArray []string, sequence uint64, username string, channelGrantArray []string) {

	docId := fmt.Sprintf("doc-%v", sequence)
	rev := "1-a"
	chanMap := make(map[string]*channels.ChannelRemoval, 10)

	for _, channel := range channelArray {
		chanMap[channel] = nil
	}

	accessMap := make(map[string]channels.TimedSet)
	channelTimedSet := channels.AtSequence(base.SetFromArray(channelGrantArray), sequence)
	accessMap[username] = channelTimedSet

	syncData := &syncData{
		CurrentRev: rev,
		Sequence:   sequence,
		Channels:   chanMap,
		Access:     accessMap,
	}
	db.Bucket.Add(docId, 0, Body{"_sync": syncData, "key": docId})
}
Esempio n. 9
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func TestRoleInheritance(t *testing.T) {
	// Create some roles:
	auth := NewAuthenticator(gTestBucket, nil)
	role, _ := auth.NewRole("square", ch.SetOf("dull", "duller", "dullest"))
	assert.Equals(t, auth.Save(role), nil)
	role, _ = auth.NewRole("frood", ch.SetOf("hoopy", "hoopier", "hoopiest"))
	assert.Equals(t, auth.Save(role), nil)

	user, _ := auth.NewUser("arthur", "password", ch.SetOf("britain"))
	user.(*userImpl).setRolesSince(ch.TimedSet{"square": ch.NewVbSimpleSequence(0x3), "nonexistent": ch.NewVbSimpleSequence(0x42), "frood": ch.NewVbSimpleSequence(0x4)})
	assert.DeepEquals(t, user.RoleNames(), ch.TimedSet{"square": ch.NewVbSimpleSequence(0x3), "nonexistent": ch.NewVbSimpleSequence(0x42), "frood": ch.NewVbSimpleSequence(0x4)})
	auth.Save(user)

	user2, err := auth.GetUser("arthur")
	assert.Equals(t, err, nil)
	log.Printf("Channels = %s", user2.Channels())
	assert.DeepEquals(t, user2.Channels(), ch.AtSequence(ch.SetOf("!", "britain"), 1))
	assert.DeepEquals(t, user2.InheritedChannels(),
		ch.TimedSet{"!": ch.NewVbSimpleSequence(0x1), "britain": ch.NewVbSimpleSequence(0x1), "dull": ch.NewVbSimpleSequence(0x3), "duller": ch.NewVbSimpleSequence(0x3), "dullest": ch.NewVbSimpleSequence(0x3), "hoopy": ch.NewVbSimpleSequence(0x4), "hoopier": ch.NewVbSimpleSequence(0x4), "hoopiest": ch.NewVbSimpleSequence(0x4)})
	assert.True(t, user2.CanSeeChannel("britain"))
	assert.True(t, user2.CanSeeChannel("duller"))
	assert.True(t, user2.CanSeeChannel("hoopy"))
	assert.Equals(t, user2.AuthorizeAllChannels(ch.SetOf("britain", "dull", "hoopiest")), nil)
}
Esempio n. 10
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// Returns the (ordered) union of all of the changes made to multiple channels.
func (db *Database) VectorMultiChangesFeed(chans base.Set, options ChangesOptions) (<-chan *ChangeEntry, error) {
	to := ""
	var userVbNo uint16
	if db.user != nil && db.user.Name() != "" {
		to = fmt.Sprintf("  (to %s)", db.user.Name())
		userVbNo = uint16(db.Bucket.VBHash(db.user.DocID()))
	}

	base.LogTo("Changes+", "Vector MultiChangesFeed(%s, %+v) ... %s", chans, options, to)
	output := make(chan *ChangeEntry, 50)

	go func() {
		var cumulativeClock *base.SyncSequenceClock
		var lastHashedValue string
		hashedEntryCount := 0
		defer func() {
			base.LogTo("Changes+", "MultiChangesFeed done %s", to)
			close(output)
		}()

		var changeWaiter *changeWaiter
		var userChangeCount uint64
		var addedChannels base.Set // Tracks channels added to the user during changes processing.

		if options.Wait {
			// Note (Adam): I don't think there's a reason to set this to false here.  We're outside the
			// main iteration loop (so the if check above should only happen once), and I don't believe
			// options.Wait is referenced elsewhere once MultiChangesFeed is called.  Leaving it as-is
			// makes it possible for channels to identify whether a getChanges call has options.Wait set to true,
			// which is useful to identify active change listeners.  However, it's possible there's a subtlety of
			// longpoll or continuous processing I'm missing here - leaving this note instead of just deleting for now.
			//options.Wait = false
			changeWaiter = db.startChangeWaiter(chans)
			userChangeCount = changeWaiter.CurrentUserCount()
		}

		cumulativeClock = base.NewSyncSequenceClock()
		cumulativeClock.SetTo(getChangesClock(options.Since))

		// This loop is used to re-run the fetch after every database change, in Wait mode
	outer:
		for {
			// Get the last polled stable sequence.  We don't return anything later than stable sequence in each iteration
			stableClock, err := db.changeCache.GetStableClock(true)
			if err != nil {
				base.Warn("MultiChangesFeed got error reading stable sequence: %v", err)
				return
			}

			// Restrict to available channels, expand wild-card, and find since when these channels
			// have been available to the user:
			var channelsSince channels.TimedSet
			if db.user != nil {
				channelsSince = db.user.FilterToAvailableChannels(chans)
			} else {
				channelsSince = channels.AtSequence(chans, 0)
			}

			// Updates the changeWaiter to the current set of available channels.
			if changeWaiter != nil {
				changeWaiter.UpdateChannels(channelsSince)
			}
			base.LogTo("Changes+", "MultiChangesFeed: channels expand to %#v ... %s", channelsSince, to)

			// Build the channel feeds.
			feeds, err := db.initializeChannelFeeds(channelsSince, options, addedChannels, userVbNo)
			if err != nil {
				return
			}

			// This loop reads the available entries from all the feeds in parallel, merges them,
			// and writes them to the output channel:
			current := make([]*ChangeEntry, len(feeds))
			var sentSomething bool
			nextEntry := getNextSequenceFromFeeds(current, feeds)
			for {
				minEntry := nextEntry

				if minEntry == nil {
					break // Exit the loop when there are no more entries
				}

				// Calculate next entry here, to help identify whether minEntry is the last entry we're sending,
				// to guarantee hashing
				nextEntry = getNextSequenceFromFeeds(current, feeds)

				// Don't send any entries later than the stable sequence
				if stableClock.GetSequence(minEntry.Seq.vbNo) < minEntry.Seq.Seq {
					continue
				}

				// Add the doc body or the conflicting rev IDs, if those options are set:
				if options.IncludeDocs || options.Conflicts {
					db.addDocToChangeEntry(minEntry, options)
				}

				// Clock handling
				if minEntry.Seq.TriggeredBy == 0 {
					// Update the cumulative clock, and stick it on the entry.
					cumulativeClock.SetMaxSequence(minEntry.Seq.vbNo, minEntry.Seq.Seq)
					// Force new hash generation for non-continuous changes feeds if this is the last entry to be sent - either
					// because there are no more entries in the channel feeds, or we're going to hit the limit.
					forceHash := false
					if options.Continuous == false && (nextEntry == nil || options.Limit == 1) {
						forceHash = true
					}
					lastHashedValue = db.calculateHashWhenNeeded(
						options,
						minEntry,
						cumulativeClock,
						&hashedEntryCount,
						lastHashedValue,
						forceHash,
					)

				} else {
					// For backfill (triggered by), we don't want to update the cumulative clock.  All entries triggered by the
					// same sequence reference the same triggered by clock, so it should only need to get hashed once.
					// If this is the first entry for this triggered by, initialize the triggered by clock's
					// hash value.
					if minEntry.Seq.TriggeredByClock.GetHashedValue() == "" {
						cumulativeClock.SetMaxSequence(minEntry.Seq.TriggeredByVbNo, minEntry.Seq.TriggeredBy)
						clockHash, err := db.SequenceHasher.GetHash(cumulativeClock)
						if err != nil {
							base.Warn("Error calculating hash for triggered by clock:%v", base.PrintClock(cumulativeClock))
						} else {
							minEntry.Seq.TriggeredByClock.SetHashedValue(clockHash)
						}
					}
				}

				// Send the entry, and repeat the loop:
				select {
				case <-options.Terminator:
					return
				case output <- minEntry:
				}
				sentSomething = true

				// Stop when we hit the limit (if any):
				if options.Limit > 0 {
					options.Limit--
					if options.Limit == 0 {
						break outer
					}
				}
			}

			if !options.Continuous && (sentSomething || changeWaiter == nil) {
				break
			}

			// Update options.Since for use in the next outer loop iteration.
			options.Since.Clock = cumulativeClock

			// If nothing found, and in wait mode: wait for the db to change, then run again.
			// First notify the reader that we're waiting by sending a nil.
			base.LogTo("Changes+", "MultiChangesFeed waiting... %s", to)
			output <- nil

		waitForChanges:
			for {
				waitResponse := changeWaiter.Wait()
				if waitResponse == WaiterClosed {
					break outer
				} else if waitResponse == WaiterHasChanges {
					select {
					case <-options.Terminator:
						return
					default:
						break waitForChanges
					}
				} else if waitResponse == WaiterCheckTerminated {
					// Check whether I was terminated while waiting for a change.  If not, resume wait.
					select {
					case <-options.Terminator:
						return
					default:
					}
				}
			}

			// Before checking again, update the User object in case its channel access has
			// changed while waiting:
			userChangeCount, addedChannels, err = db.checkForUserUpdates(userChangeCount, changeWaiter)
			if err != nil {
				change := makeErrorEntry("User not found during reload - terminating changes feed")
				base.LogTo("Changes+", "User not found during reload - terminating changes feed with entry %+v", change)
				output <- &change
				return
			}
		}
	}()

	return output, nil
}
Esempio n. 11
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func TestUserAccess(t *testing.T) {
	// User with no access:
	auth := NewAuthenticator(gTestBucket, nil)
	user, _ := auth.NewUser("foo", "password", nil)
	assert.DeepEquals(t, user.ExpandWildCardChannel(ch.SetOf("*")), ch.SetOf("!"))
	assert.False(t, user.CanSeeChannel("x"))
	assert.True(t, canSeeAllChannels(user, ch.SetOf()))
	assert.False(t, canSeeAllChannels(user, ch.SetOf("x")))
	assert.False(t, canSeeAllChannels(user, ch.SetOf("x", "y")))
	assert.False(t, canSeeAllChannels(user, ch.SetOf("*")))
	assert.False(t, user.AuthorizeAllChannels(ch.SetOf("*")) == nil)
	assert.False(t, user.AuthorizeAnyChannel(ch.SetOf("x", "y")) == nil)
	assert.False(t, user.AuthorizeAnyChannel(ch.SetOf()) == nil)

	// User with access to one channel:
	user.setChannels(ch.AtSequence(ch.SetOf("x"), 1))
	assert.DeepEquals(t, user.ExpandWildCardChannel(ch.SetOf("*")), ch.SetOf("x"))
	assert.True(t, canSeeAllChannels(user, ch.SetOf()))
	assert.True(t, canSeeAllChannels(user, ch.SetOf("x")))
	assert.False(t, canSeeAllChannels(user, ch.SetOf("x", "y")))
	assert.False(t, user.AuthorizeAllChannels(ch.SetOf("x", "y")) == nil)
	assert.False(t, user.AuthorizeAllChannels(ch.SetOf("*")) == nil)
	assert.True(t, user.AuthorizeAnyChannel(ch.SetOf("x", "y")) == nil)
	assert.False(t, user.AuthorizeAnyChannel(ch.SetOf("y")) == nil)
	assert.False(t, user.AuthorizeAnyChannel(ch.SetOf()) == nil)

	// User with access to one channel and one derived channel:
	user.setChannels(ch.AtSequence(ch.SetOf("x", "z"), 1))
	assert.DeepEquals(t, user.ExpandWildCardChannel(ch.SetOf("*")), ch.SetOf("x", "z"))
	assert.DeepEquals(t, user.ExpandWildCardChannel(ch.SetOf("x")), ch.SetOf("x"))
	assert.True(t, canSeeAllChannels(user, ch.SetOf()))
	assert.True(t, canSeeAllChannels(user, ch.SetOf("x")))
	assert.False(t, canSeeAllChannels(user, ch.SetOf("x", "y")))
	assert.False(t, user.AuthorizeAllChannels(ch.SetOf("x", "y")) == nil)
	assert.False(t, user.AuthorizeAllChannels(ch.SetOf("*")) == nil)

	// User with access to two channels:
	user.setChannels(ch.AtSequence(ch.SetOf("x", "z"), 1))
	assert.DeepEquals(t, user.ExpandWildCardChannel(ch.SetOf("*")), ch.SetOf("x", "z"))
	assert.DeepEquals(t, user.ExpandWildCardChannel(ch.SetOf("x")), ch.SetOf("x"))
	assert.True(t, canSeeAllChannels(user, ch.SetOf()))
	assert.True(t, canSeeAllChannels(user, ch.SetOf("x")))
	assert.False(t, canSeeAllChannels(user, ch.SetOf("x", "y")))
	assert.False(t, user.AuthorizeAllChannels(ch.SetOf("x", "y")) == nil)
	assert.False(t, user.AuthorizeAllChannels(ch.SetOf("*")) == nil)

	user.setChannels(ch.AtSequence(ch.SetOf("x", "y"), 1))
	assert.DeepEquals(t, user.ExpandWildCardChannel(ch.SetOf("*")), ch.SetOf("x", "y"))
	assert.True(t, canSeeAllChannels(user, ch.SetOf()))
	assert.True(t, canSeeAllChannels(user, ch.SetOf("x")))
	assert.True(t, canSeeAllChannels(user, ch.SetOf("x", "y")))
	assert.False(t, canSeeAllChannels(user, ch.SetOf("x", "y", "z")))
	assert.True(t, user.AuthorizeAllChannels(ch.SetOf("x", "y")) == nil)
	assert.False(t, user.AuthorizeAllChannels(ch.SetOf("*")) == nil)

	// User with wildcard access:
	user.setChannels(ch.AtSequence(ch.SetOf("*", "q"), 1))
	assert.DeepEquals(t, user.ExpandWildCardChannel(ch.SetOf("*")), ch.SetOf("*", "q"))
	assert.True(t, user.CanSeeChannel("*"))
	assert.True(t, canSeeAllChannels(user, ch.SetOf()))
	assert.True(t, canSeeAllChannels(user, ch.SetOf("x")))
	assert.True(t, canSeeAllChannels(user, ch.SetOf("x", "y")))
	assert.True(t, user.AuthorizeAllChannels(ch.SetOf("x", "y")) == nil)
	assert.True(t, user.AuthorizeAllChannels(ch.SetOf("*")) == nil)
	assert.True(t, user.AuthorizeAnyChannel(ch.SetOf("x")) == nil)
	assert.True(t, user.AuthorizeAnyChannel(ch.SetOf("*")) == nil)
	assert.True(t, user.AuthorizeAnyChannel(ch.SetOf()) == nil)
}
Esempio n. 12
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func (role *roleImpl) initRole(name string, channels base.Set) error {
	channels = ch.ExpandingStar(channels)
	role.Name_ = name
	role.ExplicitChannels_ = ch.AtSequence(channels, 1)
	return role.validate()
}
Esempio n. 13
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// Returns the (ordered) union of all of the changes made to multiple channels.
func (db *Database) SimpleMultiChangesFeed(chans base.Set, options ChangesOptions) (<-chan *ChangeEntry, error) {
	to := ""
	if db.user != nil && db.user.Name() != "" {
		to = fmt.Sprintf("  (to %s)", db.user.Name())
	}

	base.LogTo("Changes", "MultiChangesFeed(%s, %+v) ... %s", chans, options, to)
	output := make(chan *ChangeEntry, 50)

	go func() {
		defer func() {
			base.LogTo("Changes", "MultiChangesFeed done %s", to)
			close(output)
		}()

		var changeWaiter *changeWaiter
		var userChangeCount uint64
		var lowSequence uint64
		var lateSequenceFeeds map[string]*lateSequenceFeed
		var addedChannels base.Set // Tracks channels added to the user during changes processing.

		// lowSequence is used to send composite keys to clients, so that they can obtain any currently
		// skipped sequences in a future iteration or request.
		oldestSkipped := db.changeCache.getOldestSkippedSequence()
		if oldestSkipped > 0 {
			lowSequence = oldestSkipped - 1
		} else {
			lowSequence = 0
		}

		if options.Wait {
			options.Wait = false
			changeWaiter = db.startChangeWaiter(chans)
			userChangeCount = changeWaiter.CurrentUserCount()

		}

		// If a request has a low sequence that matches the current lowSequence,
		// ignore the low sequence.  This avoids infinite looping of the records between
		// low::high.  It also means any additional skipped sequences between low::high won't
		// be sent until low arrives or is abandoned.
		if options.Since.LowSeq != 0 && options.Since.LowSeq == lowSequence {
			options.Since.LowSeq = 0
		}

		// For a continuous feed, initialise the lateSequenceFeeds that track late-arriving sequences
		// to the channel caches.
		if options.Continuous {
			lateSequenceFeeds = make(map[string]*lateSequenceFeed)
		}

		// This loop is used to re-run the fetch after every database change, in Wait mode
	outer:
		for {
			// Restrict to available channels, expand wild-card, and find since when these channels
			// have been available to the user:
			var channelsSince channels.TimedSet
			if db.user != nil {
				channelsSince = db.user.FilterToAvailableChannels(chans)
			} else {
				channelsSince = channels.AtSequence(chans, 0)
			}

			// Updates the changeWaiter to the current set of available channels
			if changeWaiter != nil {
				changeWaiter.UpdateChannels(channelsSince)
			}
			base.LogTo("Changes+", "MultiChangesFeed: channels expand to %#v ... %s", channelsSince, to)

			// lowSequence is used to send composite keys to clients, so that they can obtain any currently
			// skipped sequences in a future iteration or request.
			oldestSkipped = db.changeCache.getOldestSkippedSequence()
			if oldestSkipped > 0 {
				lowSequence = oldestSkipped - 1
			} else {
				lowSequence = 0
			}

			// Populate the parallel arrays of channels and names:
			feeds := make([]<-chan *ChangeEntry, 0, len(channelsSince))
			names := make([]string, 0, len(channelsSince))

			// Get read lock for late-arriving sequences, to avoid sending the same late arrival in
			// two different changes iterations.  e.g. without the RLock, a late-arriving sequence
			// could be written to channel X during one iteration, and channel Y during another.  Users
			// with access to both channels would see two versions on the feed.
			for name, vbSeqAddedAt := range channelsSince {
				chanOpts := options
				seqAddedAt := vbSeqAddedAt.Sequence

				// Check whether requires backfill based on addedChannels in this _changes feed
				isNewChannel := false
				if addedChannels != nil {
					_, isNewChannel = addedChannels[name]
				}

				// Check whether requires backfill based on current sequence, seqAddedAt
				// Triggered by handling:
				//   1. options.Since.TriggeredBy == seqAddedAt : We're in the middle of backfill for this channel, based
				//    on the access grant in sequence options.Since.TriggeredBy.  Normally the entire backfill would be done in one
				//    changes feed iteration, but this can be split over multiple iterations when 'limit' is used.
				//   2. options.Since.TriggeredBy == 0 : Not currently doing a backfill
				//   3. options.Since.TriggeredBy != 0 and <= seqAddedAt: We're in the middle of a backfill for another channel, but the backfill for
				//     this channel is still pending.  Initiate the backfill for this channel - will be ordered below in the usual way (iterating over all channels)

				// Backfill required when seqAddedAt is before current sequence
				backfillRequired := seqAddedAt > 1 && options.Since.Before(SequenceID{Seq: seqAddedAt})

				// Ensure backfill isn't already in progress for this seqAddedAt
				backfillPending := options.Since.TriggeredBy == 0 || options.Since.TriggeredBy < seqAddedAt

				if isNewChannel || (backfillRequired && backfillPending) {
					// Newly added channel so initiate backfill:
					chanOpts.Since = SequenceID{Seq: 0, TriggeredBy: seqAddedAt}
				}
				feed, err := db.changesFeed(name, chanOpts)
				if err != nil {
					base.Warn("MultiChangesFeed got error reading changes feed %q: %v", name, err)
					return
				}
				feeds = append(feeds, feed)
				names = append(names, name)

				// Late sequence handling - for out-of-order sequences prior to options.Since that
				// have arrived in the channel cache since this changes request started.  Only need for
				// continuous feeds - one-off changes requests only need the standard channel cache.
				if options.Continuous {
					lateSequenceFeedHandler := lateSequenceFeeds[name]
					if lateSequenceFeedHandler != nil {
						latefeed, err := db.getLateFeed(lateSequenceFeedHandler)
						if err != nil {
							base.Warn("MultiChangesFeed got error reading late sequence feed %q: %v", name, err)
						} else {
							// Mark feed as actively used in this iteration.  Used to remove lateSequenceFeeds
							// when the user loses channel access
							lateSequenceFeedHandler.active = true
							feeds = append(feeds, latefeed)
							names = append(names, fmt.Sprintf("late_%s", name))
						}

					} else {
						// Initialize lateSequenceFeeds[name] for next iteration
						lateSequenceFeeds[name] = db.newLateSequenceFeed(name)
					}
				}
			}
			// If the user object has changed, create a special pseudo-feed for it:
			if db.user != nil {
				feeds, names = db.appendUserFeed(feeds, names, options)
			}

			current := make([]*ChangeEntry, len(feeds))

			// This loop reads the available entries from all the feeds in parallel, merges them,
			// and writes them to the output channel:
			var sentSomething bool
			for {
				// Read more entries to fill up the current[] array:
				for i, cur := range current {
					if cur == nil && feeds[i] != nil {
						var ok bool
						current[i], ok = <-feeds[i]
						if !ok {
							feeds[i] = nil
						}
					}
				}

				// Find the current entry with the minimum sequence:
				minSeq := MaxSequenceID
				var minEntry *ChangeEntry
				for _, cur := range current {
					if cur != nil && cur.Seq.Before(minSeq) {
						minSeq = cur.Seq
						minEntry = cur
					}
				}

				if minEntry == nil {
					break // Exit the loop when there are no more entries
				}

				// Clear the current entries for the sequence just sent:
				if minEntry.Removed != nil {
					minEntry.allRemoved = true
				}
				for i, cur := range current {
					if cur != nil && cur.Seq == minSeq {
						current[i] = nil
						// Track whether this is a removal from all user's channels
						if cur.Removed == nil && minEntry.allRemoved == true {
							minEntry.allRemoved = false
						}
						// Also concatenate the matching entries' Removed arrays:
						if cur != minEntry && cur.Removed != nil {
							if minEntry.Removed == nil {
								minEntry.Removed = cur.Removed
							} else {
								minEntry.Removed = minEntry.Removed.Union(cur.Removed)
							}
						}
					}
				}

				if options.ActiveOnly {
					if minEntry.Deleted || minEntry.allRemoved {
						continue
					}
				}

				// Update options.Since for use in the next outer loop iteration.  Only update
				// when minSeq is greater than the previous options.Since value - we don't want to
				// roll back the Since value when we get an late sequence is processed.
				if options.Since.Before(minSeq) {
					options.Since = minSeq
				}

				// Add the doc body or the conflicting rev IDs, if those options are set:
				if options.IncludeDocs || options.Conflicts {
					db.addDocToChangeEntry(minEntry, options)
				}

				// Update the low sequence on the entry we're going to send
				minEntry.Seq.LowSeq = lowSequence

				// Send the entry, and repeat the loop:
				base.LogTo("Changes+", "MultiChangesFeed sending %+v %s", minEntry, to)
				select {
				case <-options.Terminator:
					return
				case output <- minEntry:
				}
				sentSomething = true

				// Stop when we hit the limit (if any):
				if options.Limit > 0 {
					options.Limit--
					if options.Limit == 0 {
						break outer
					}
				}
			}

			if !options.Continuous && (sentSomething || changeWaiter == nil) {
				break
			}

			// If nothing found, and in wait mode: wait for the db to change, then run again.
			// First notify the reader that we're waiting by sending a nil.
			base.LogTo("Changes+", "MultiChangesFeed waiting... %s", to)
			output <- nil
		waitForChanges:
			for {
				waitResponse := changeWaiter.Wait()
				if waitResponse == WaiterClosed {
					break outer
				} else if waitResponse == WaiterHasChanges {
					select {
					case <-options.Terminator:
						return
					default:
						break waitForChanges
					}
				} else if waitResponse == WaiterCheckTerminated {
					// Check whether I was terminated while waiting for a change.  If not, resume wait.
					select {
					case <-options.Terminator:
						return
					default:
					}
				}
			}

			// Check whether user channel access has changed while waiting:
			var err error
			userChangeCount, addedChannels, err = db.checkForUserUpdates(userChangeCount, changeWaiter)
			if err != nil {
				change := makeErrorEntry("User not found during reload - terminating changes feed")
				base.LogTo("Changes+", "User not found during reload - terminating changes feed with entry %+v", change)
				output <- &change
				return
			}

			// Clean up inactive lateSequenceFeeds (because user has lost access to the channel)
			for channel, lateFeed := range lateSequenceFeeds {
				if !lateFeed.active {
					db.closeLateFeed(lateFeed)
					delete(lateSequenceFeeds, channel)
				} else {
					lateFeed.active = false
				}
			}
		}
	}()

	return output, nil
}