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// Copyright 2017 Google LLC
//
// 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 firestore
import (
"context"
"errors"
"fmt"
"io"
"reflect"
"sort"
vkit "cloud.google.com/go/firestore/apiv1"
"cloud.google.com/go/internal/trace"
"google.golang.org/api/iterator"
pb "google.golang.org/genproto/googleapis/firestore/v1"
"google.golang.org/grpc/codes"
"google.golang.org/grpc/status"
)
var errNilDocRef = errors.New("firestore: nil DocumentRef")
// A DocumentRef is a reference to a Firestore document.
type DocumentRef struct {
// The CollectionRef that this document is a part of. Never nil.
Parent *CollectionRef
// The full resource path of the document. A document "doc-1" in collection
// "coll-1" would be: "projects/P/databases/D/documents/coll-1/doc-1".
Path string
// The shorter resource path of the document. A document "doc-1" in
// collection "coll-1" would be: "coll-1/doc-1".
shortPath string
// The ID of the document: the last component of the resource path.
ID string
}
func newDocRef(parent *CollectionRef, id string) *DocumentRef {
return &DocumentRef{
Parent: parent,
ID: id,
Path: parent.Path + "/" + id,
shortPath: parent.selfPath + "/" + id,
}
}
// Collection returns a reference to sub-collection of this document.
func (d *DocumentRef) Collection(id string) *CollectionRef {
return newCollRefWithParent(d.Parent.c, d, id)
}
// Get retrieves the document. If the document does not exist, Get return a NotFound error, which
// can be checked with
// status.Code(err) == codes.NotFound
// In that case, Get returns a non-nil DocumentSnapshot whose Exists method return false and whose
// ReadTime is the time of the failed read operation.
func (d *DocumentRef) Get(ctx context.Context) (_ *DocumentSnapshot, err error) {
ctx = trace.StartSpan(ctx, "cloud.google.com/go/firestore.DocumentRef.Get")
defer func() { trace.EndSpan(ctx, err) }()
if d == nil {
return nil, errNilDocRef
}
docsnaps, err := d.Parent.c.getAll(ctx, []*DocumentRef{d}, nil)
if err != nil {
return nil, err
}
ds := docsnaps[0]
if !ds.Exists() {
return ds, status.Errorf(codes.NotFound, "%q not found", d.Path)
}
return ds, nil
}
// Create creates the document with the given data.
// It returns an error if a document with the same ID already exists.
//
// The data argument can be a map with string keys, a struct, or a pointer to a
// struct. The map keys or exported struct fields become the fields of the firestore
// document.
// The values of data are converted to Firestore values as follows:
//
// - bool converts to Bool.
// - string converts to String.
// - int, int8, int16, int32 and int64 convert to Integer.
// - uint8, uint16 and uint32 convert to Integer. uint, uint64 and uintptr are disallowed,
// because they may be able to represent values that cannot be represented in an int64,
// which is the underlying type of a Integer.
// - float32 and float64 convert to Double.
// - []byte converts to Bytes.
// - time.Time and *ts.Timestamp convert to Timestamp. ts is the package
// "github.com/golang/protobuf/ptypes/timestamp".
// - *latlng.LatLng converts to GeoPoint. latlng is the package
// "google.golang.org/genproto/googleapis/type/latlng". You should always use
// a pointer to a LatLng.
// - Slices convert to Array.
// - *firestore.DocumentRef converts to Reference.
// - Maps and structs convert to Map.
// - nils of any type convert to Null.
//
// Pointers and interface{} are also permitted, and their elements processed
// recursively.
//
// Struct fields can have tags like those used by the encoding/json package. Tags
// begin with "firestore:" and are followed by "-", meaning "ignore this field," or
// an alternative name for the field. Following the name, these comma-separated
// options may be provided:
//
// - omitempty: Do not encode this field if it is empty. A value is empty
// if it is a zero value, or an array, slice or map of length zero.
// - serverTimestamp: The field must be of type time.Time. serverTimestamp
// is a sentinel token that tells Firestore to substitute the server time
// into that field. When writing, if the field has the zero value, the
// server will populate the stored document with the time that the request
// is processed. However, if the field value is non-zero it won't be saved.
func (d *DocumentRef) Create(ctx context.Context, data interface{}) (_ *WriteResult, err error) {
ctx = trace.StartSpan(ctx, "cloud.google.com/go/firestore.DocumentRef.Create")
defer func() { trace.EndSpan(ctx, err) }()
ws, err := d.newCreateWrites(data)
if err != nil {
return nil, err
}
return d.Parent.c.commit1(ctx, ws)
}
func (d *DocumentRef) newCreateWrites(data interface{}) ([]*pb.Write, error) {
if d == nil {
return nil, errNilDocRef
}
doc, transforms, err := toProtoDocument(data)
if err != nil {
return nil, err
}
doc.Name = d.Path
pc, err := exists(false).preconditionProto()
if err != nil {
return nil, err
}
return d.newUpdateWithTransform(doc, nil, pc, transforms, false), nil
}
// Set creates or overwrites the document with the given data. See DocumentRef.Create
// for the acceptable values of data. Without options, Set overwrites the document
// completely. Specify one of the Merge options to preserve an existing document's
// fields. To delete some fields, use a Merge option with firestore.Delete as the
// field value.
func (d *DocumentRef) Set(ctx context.Context, data interface{}, opts ...SetOption) (_ *WriteResult, err error) {
ctx = trace.StartSpan(ctx, "cloud.google.com/go/firestore.DocumentRef.Set")
defer func() { trace.EndSpan(ctx, err) }()
ws, err := d.newSetWrites(data, opts)
if err != nil {
return nil, err
}
return d.Parent.c.commit1(ctx, ws)
}
func (d *DocumentRef) newSetWrites(data interface{}, opts []SetOption) ([]*pb.Write, error) {
if d == nil {
return nil, errNilDocRef
}
if data == nil {
return nil, errors.New("firestore: nil document contents")
}
if len(opts) == 0 { // Set without merge
doc, serverTimestampPaths, err := toProtoDocument(data)
if err != nil {
return nil, err
}
doc.Name = d.Path
return d.newUpdateWithTransform(doc, nil, nil, serverTimestampPaths, true), nil
}
// Set with merge.
// This is just like Update, except for the existence precondition.
// So we turn data into a list of (FieldPath, interface{}) pairs (fpv's), as we do
// for Update.
fieldPaths, allPaths, err := processSetOptions(opts)
if err != nil {
return nil, err
}
var fpvs []fpv
v := reflect.ValueOf(data)
if allPaths {
// Set with MergeAll. Collect all the leaves of the map.
if v.Kind() != reflect.Map {
return nil, errors.New("firestore: MergeAll can only be specified with map data")
}
if v.Len() == 0 {
// Special case: MergeAll with an empty map.
return d.newUpdateWithTransform(&pb.Document{Name: d.Path}, []FieldPath{}, nil, nil, true), nil
}
fpvsFromData(v, nil, &fpvs)
} else {
// Set with merge paths. Collect only the values at the given paths.
for _, fp := range fieldPaths {
val, err := getAtPath(v, fp)
if err != nil {
return nil, err
}
fpvs = append(fpvs, fpv{fp, val})
}
}
return d.fpvsToWrites(fpvs, nil)
}
// fpvsFromData converts v into a list of (FieldPath, value) pairs.
func fpvsFromData(v reflect.Value, prefix FieldPath, fpvs *[]fpv) {
switch v.Kind() {
case reflect.Map:
for _, k := range v.MapKeys() {
fpvsFromData(v.MapIndex(k), prefix.with(k.String()), fpvs)
}
case reflect.Interface:
fpvsFromData(v.Elem(), prefix, fpvs)
default:
var val interface{}
if v.IsValid() {
val = v.Interface()
}
*fpvs = append(*fpvs, fpv{prefix, val})
}
}
// Delete deletes the document. If the document doesn't exist, it does nothing
// and returns no error.
func (d *DocumentRef) Delete(ctx context.Context, preconds ...Precondition) (_ *WriteResult, err error) {
ctx = trace.StartSpan(ctx, "cloud.google.com/go/firestore.DocumentRef.Delete")
defer func() { trace.EndSpan(ctx, err) }()
ws, err := d.newDeleteWrites(preconds)
if err != nil {
return nil, err
}
return d.Parent.c.commit1(ctx, ws)
}
func (d *DocumentRef) newDeleteWrites(preconds []Precondition) ([]*pb.Write, error) {
if d == nil {
return nil, errNilDocRef
}
pc, err := processPreconditionsForDelete(preconds)
if err != nil {
return nil, err
}
return []*pb.Write{{
Operation: &pb.Write_Delete{d.Path},
CurrentDocument: pc,
}}, nil
}
func (d *DocumentRef) newUpdatePathWrites(updates []Update, preconds []Precondition) ([]*pb.Write, error) {
if len(updates) == 0 {
return nil, errors.New("firestore: no paths to update")
}
var fpvs []fpv
for _, u := range updates {
v, err := u.process()
if err != nil {
return nil, err
}
fpvs = append(fpvs, v)
}
pc, err := processPreconditionsForUpdate(preconds)
if err != nil {
return nil, err
}
return d.fpvsToWrites(fpvs, pc)
}
func (d *DocumentRef) fpvsToWrites(fpvs []fpv, pc *pb.Precondition) ([]*pb.Write, error) {
// Make sure there are no duplications or prefixes among the field paths.
var fps []FieldPath
for _, fpv := range fpvs {
fps = append(fps, fpv.fieldPath)
}
if err := checkNoDupOrPrefix(fps); err != nil {
return nil, err
}
// Process each fpv.
var updatePaths []FieldPath
var transforms []*pb.DocumentTransform_FieldTransform
doc := &pb.Document{
Name: d.Path,
Fields: map[string]*pb.Value{},
}
for _, fpv := range fpvs {
switch fpv.value.(type) {
case arrayUnion:
au := fpv.value.(arrayUnion)
t, err := arrayUnionTransform(au, fpv.fieldPath)
if err != nil {
return nil, err
}
transforms = append(transforms, t)
case arrayRemove:
ar := fpv.value.(arrayRemove)
t, err := arrayRemoveTransform(ar, fpv.fieldPath)
if err != nil {
return nil, err
}
transforms = append(transforms, t)
case transform:
t, err := fieldTransform(fpv.value.(transform), fpv.fieldPath)
if err != nil {
return nil, err
}
transforms = append(transforms, t)
default:
switch fpv.value {
case Delete:
// Send the field path without a corresponding value.
updatePaths = append(updatePaths, fpv.fieldPath)
case ServerTimestamp:
// Use the path in a transform operation.
transforms = append(transforms, serverTimestamp(fpv.fieldPath.toServiceFieldPath()))
default:
updatePaths = append(updatePaths, fpv.fieldPath)
// Convert the value to a proto and put it into the document.
v := reflect.ValueOf(fpv.value)
pv, _, err := toProtoValue(v)
if err != nil {
return nil, err
}
setAtPath(doc.Fields, fpv.fieldPath, pv)
// Also accumulate any transforms within the value.
ts, err := extractTransforms(v, fpv.fieldPath)
if err != nil {
return nil, err
}
transforms = append(transforms, ts...)
}
}
}
return d.newUpdateWithTransform(doc, updatePaths, pc, transforms, false), nil
}
// newUpdateWithTransform constructs operations for a commit. Most generally, it
// returns an update operation followed by a transform.
//
// If there are no serverTimestampPaths, the transform is omitted.
//
// If doc.Fields is empty, there are no updatePaths, and there is no precondition,
// the update is omitted, unless updateOnEmpty is true.
func (d *DocumentRef) newUpdateWithTransform(doc *pb.Document, updatePaths []FieldPath, pc *pb.Precondition, transforms []*pb.DocumentTransform_FieldTransform, updateOnEmpty bool) []*pb.Write {
var ws []*pb.Write
if updateOnEmpty || len(doc.Fields) > 0 ||
len(updatePaths) > 0 || (pc != nil && len(transforms) == 0) {
var mask *pb.DocumentMask
if updatePaths != nil {
sfps := toServiceFieldPaths(updatePaths)
sort.Strings(sfps) // TODO(jba): make tests pass without this
mask = &pb.DocumentMask{FieldPaths: sfps}
}
w := &pb.Write{
Operation: &pb.Write_Update{doc},
UpdateMask: mask,
CurrentDocument: pc,
}
ws = append(ws, w)
pc = nil // If the precondition is in the write, we don't need it in the transform.
}
if len(transforms) > 0 || pc != nil {
ws = append(ws, &pb.Write{
Operation: &pb.Write_Transform{
Transform: &pb.DocumentTransform{
Document: d.Path,
FieldTransforms: transforms,
},
},
CurrentDocument: pc,
})
}
return ws
}
// arrayUnion is a special type in firestore. It instructs the server to add its
// elements to whatever array already exists, or to create an array if no value
// exists.
type arrayUnion struct {
elems []interface{}
}
// ArrayUnion specifies elements to be added to whatever array already exists in
// the server, or to create an array if no value exists.
//
// If a value exists and it's an array, values are appended to it. Any duplicate
// value is ignored.
// If a value exists and it's not an array, the value is replaced by an array of
// the values in the ArrayUnion.
// If a value does not exist, an array of the values in the ArrayUnion is created.
//
// ArrayUnion must be the value of a field directly; it cannot appear in
// array or struct values, or in any value that is itself inside an array or
// struct.
func ArrayUnion(elems ...interface{}) arrayUnion {
return arrayUnion{elems: elems}
}
// This helper converts an arrayUnion into a proto object.
func arrayUnionTransform(au arrayUnion, fp FieldPath) (*pb.DocumentTransform_FieldTransform, error) {
var elems []*pb.Value
for _, v := range au.elems {
pv, _, err := toProtoValue(reflect.ValueOf(v))
if err != nil {
return nil, err
}
elems = append(elems, pv)
}
return &pb.DocumentTransform_FieldTransform{
FieldPath: fp.toServiceFieldPath(),
TransformType: &pb.DocumentTransform_FieldTransform_AppendMissingElements{
AppendMissingElements: &pb.ArrayValue{Values: elems},
},
}, nil
}
// arrayRemove is a special type in firestore. It instructs the server to remove
// the specified values.
type arrayRemove struct {
elems []interface{}
}
// ArrayRemove specifies elements to be removed from whatever array already
// exists in the server.
//
// If a value exists and it's an array, values are removed from it. All
// duplicate values are removed.
// If a value exists and it's not an array, the value is replaced by an empty
// array.
// If a value does not exist, an empty array is created.
//
// ArrayRemove must be the value of a field directly; it cannot appear in
// array or struct values, or in any value that is itself inside an array or
// struct.
func ArrayRemove(elems ...interface{}) arrayRemove {
return arrayRemove{elems: elems}
}
// This helper converts an arrayRemove into a proto object.
func arrayRemoveTransform(ar arrayRemove, fp FieldPath) (*pb.DocumentTransform_FieldTransform, error) {
var elems []*pb.Value
for _, v := range ar.elems {
// ServerTimestamp cannot occur in an array, so we ignore transformations here.
pv, _, err := toProtoValue(reflect.ValueOf(v))
if err != nil {
return nil, err
}
elems = append(elems, pv)
}
return &pb.DocumentTransform_FieldTransform{
FieldPath: fp.toServiceFieldPath(),
TransformType: &pb.DocumentTransform_FieldTransform_RemoveAllFromArray{
RemoveAllFromArray: &pb.ArrayValue{Values: elems},
},
}, nil
}
type transform struct {
t *pb.DocumentTransform_FieldTransform
// For v2 of this package, we may want to remove this field and
// return an error directly from the FieldTransformX functions.
err error
}
// FieldTransformIncrement returns a special value that can be used with Set, Create, or
// Update that tells the server to transform the field's current value
// by the given value.
//
// The supported values are:
//
// int, int8, int16, int32, int64
// uint8, uint16, uint32
// float32, float64
//
// If the field does not yet exist, the transformation will set the field to
// the given value.
func FieldTransformIncrement(n interface{}) transform {
v, err := numericTransformValue(n)
return transform{
t: &pb.DocumentTransform_FieldTransform{
TransformType: &pb.DocumentTransform_FieldTransform_Increment{
Increment: v,
},
},
err: err,
}
}
// Increment is an alias for FieldTransformIncrement.
func Increment(n interface{}) transform {
return FieldTransformIncrement(n)
}
// FieldTransformMaximum returns a special value that can be used with Set, Create, or
// Update that tells the server to set the field to the maximum of the
// field's current value and the given value.
//
// The supported values are:
//
// int, int8, int16, int32, int64
// uint8, uint16, uint32
// float32, float64
//
// If the field is not an integer or double, or if the field does not yet
// exist, the transformation will set the field to the given value. If a
// maximum operation is applied where the field and the input value are of
// mixed types (that is - one is an integer and one is a double) the field
// takes on the type of the larger operand. If the operands are equivalent
// (e.g. 3 and 3.0), the field does not change. 0, 0.0, and -0.0 are all zero.
// The maximum of a zero stored value and zero input value is always the
// stored value. The maximum of any numeric value x and NaN is NaN.
func FieldTransformMaximum(n interface{}) transform {
v, err := numericTransformValue(n)
return transform{
t: &pb.DocumentTransform_FieldTransform{
TransformType: &pb.DocumentTransform_FieldTransform_Maximum{
Maximum: v,
},
},
err: err,
}
}
// FieldTransformMinimum returns a special value that can be used with Set, Create, or
// Update that tells the server to set the field to the minimum of the
// field's current value and the given value.
//
// The supported values are:
//
// int, int8, int16, int32, int64
// uint8, uint16, uint32
// float32, float64
//
// If the field is not an integer or double, or if the field does not yet
// exist, the transformation will set the field to the given value. If a
// minimum operation is applied where the field and the input value are of
// mixed types (that is - one is an integer and one is a double) the field
// takes on the type of the smaller operand. If the operands are equivalent
// (e.g. 3 and 3.0), the field does not change. 0, 0.0, and -0.0 are all zero.
// The minimum of a zero stored value and zero input value is always the
// stored value. The minimum of any numeric value x and NaN is NaN.
func FieldTransformMinimum(n interface{}) transform {
v, err := numericTransformValue(n)
return transform{
t: &pb.DocumentTransform_FieldTransform{
TransformType: &pb.DocumentTransform_FieldTransform_Minimum{
Minimum: v,
},
},
err: err,
}
}
func numericTransformValue(n interface{}) (*pb.Value, error) {
switch n.(type) {
case int, int8, int16, int32, int64,
uint8, uint16, uint32,
float32, float64:
default:
return nil, fmt.Errorf("unsupported type %T for Increment; supported values include int, int8, int16, int32, int64, uint8, uint16, uint32, float32, float64", n)
}
v, _, err := toProtoValue(reflect.ValueOf(n))
if err != nil {
return nil, err
}
return v, nil
}
func fieldTransform(ar transform, fp FieldPath) (*pb.DocumentTransform_FieldTransform, error) {
if ar.err != nil {
return nil, ar.err
}
ft := *ar.t
ft.FieldPath = fp.toServiceFieldPath()
return &ft, nil
}
type sentinel int
const (
// Delete is used as a value in a call to Update or Set with merge to indicate
// that the corresponding key should be deleted.
Delete sentinel = iota
// ServerTimestamp is used as a value in a call to Update to indicate that the
// key's value should be set to the time at which the server processed
// the request.
//
// ServerTimestamp must be the value of a field directly; it cannot appear in
// array or struct values, or in any value that is itself inside an array or
// struct.
ServerTimestamp
)
func (s sentinel) String() string {
switch s {
case Delete:
return "Delete"
case ServerTimestamp:
return "ServerTimestamp"
default:
return "<?sentinel?>"
}
}
// An Update describes an update to a value referred to by a path.
// An Update should have either a non-empty Path or a non-empty FieldPath,
// but not both.
//
// See DocumentRef.Create for acceptable values.
// To delete a field, specify firestore.Delete as the value.
type Update struct {
Path string // Will be split on dots, and must not contain any of "˜*/[]".
FieldPath FieldPath
Value interface{}
}
// An fpv is a pair of validated FieldPath and value.
type fpv struct {
fieldPath FieldPath
value interface{}
}
func (u *Update) process() (fpv, error) {
if (u.Path != "") == (u.FieldPath != nil) {
return fpv{}, fmt.Errorf("firestore: update %+v should have exactly one of Path or FieldPath", u)
}
fp := u.FieldPath
var err error
if fp == nil {
fp, err = parseDotSeparatedString(u.Path)
if err != nil {
return fpv{}, err
}
}
if err := fp.validate(); err != nil {
return fpv{}, err
}
return fpv{fp, u.Value}, nil
}
// Update updates the document. The values at the given
// field paths are replaced, but other fields of the stored document are untouched.
func (d *DocumentRef) Update(ctx context.Context, updates []Update, preconds ...Precondition) (_ *WriteResult, err error) {
ctx = trace.StartSpan(ctx, "cloud.google.com/go/firestore.DocumentRef.Update")
defer func() { trace.EndSpan(ctx, err) }()
ws, err := d.newUpdatePathWrites(updates, preconds)
if err != nil {
return nil, err
}
return d.Parent.c.commit1(ctx, ws)
}
// Collections returns an iterator over the immediate sub-collections of the document.
func (d *DocumentRef) Collections(ctx context.Context) *CollectionIterator {
client := d.Parent.c
it := &CollectionIterator{
client: client,
parent: d,
it: client.c.ListCollectionIds(
withResourceHeader(ctx, client.path()),
&pb.ListCollectionIdsRequest{Parent: d.Path}),
}
it.pageInfo, it.nextFunc = iterator.NewPageInfo(
it.fetch,
func() int { return len(it.items) },
func() interface{} { b := it.items; it.items = nil; return b })
return it
}
// CollectionIterator is an iterator over sub-collections of a document.
type CollectionIterator struct {
client *Client
parent *DocumentRef
it *vkit.StringIterator
pageInfo *iterator.PageInfo
nextFunc func() error
items []*CollectionRef
err error
}
// PageInfo supports pagination. See the google.golang.org/api/iterator package for details.
func (it *CollectionIterator) PageInfo() *iterator.PageInfo { return it.pageInfo }
// Next returns the next result. Its second return value is iterator.Done if there
// are no more results. Once Next returns Done, all subsequent calls will return
// Done.
func (it *CollectionIterator) Next() (*CollectionRef, error) {
if err := it.nextFunc(); err != nil {
return nil, err
}
item := it.items[0]
it.items = it.items[1:]
return item, nil
}
func (it *CollectionIterator) fetch(pageSize int, pageToken string) (string, error) {
if it.err != nil {
return "", it.err
}
return iterFetch(pageSize, pageToken, it.it.PageInfo(), func() error {
id, err := it.it.Next()
if err != nil {
return err
}
var cr *CollectionRef
if it.parent == nil {
cr = newTopLevelCollRef(it.client, it.client.path(), id)
} else {
cr = newCollRefWithParent(it.client, it.parent, id)
}
it.items = append(it.items, cr)
return nil
})
}
// GetAll returns all the collections remaining from the iterator.
func (it *CollectionIterator) GetAll() ([]*CollectionRef, error) {
var crs []*CollectionRef
for {
cr, err := it.Next()
if err == iterator.Done {
break
}
if err != nil {
return nil, err
}
crs = append(crs, cr)
}
return crs, nil
}
// Common fetch code for iterators that are backed by vkit iterators.
// TODO(jba): dedup with same function in logging/logadmin.
func iterFetch(pageSize int, pageToken string, pi *iterator.PageInfo, next func() error) (string, error) {
pi.MaxSize = pageSize
pi.Token = pageToken
// Get one item, which will fill the buffer.
if err := next(); err != nil {
return "", err
}
// Collect the rest of the buffer.
for pi.Remaining() > 0 {
if err := next(); err != nil {
return "", err
}
}
return pi.Token, nil
}
// Snapshots returns an iterator over snapshots of the document. Each time the document
// changes or is added or deleted, a new snapshot will be generated.
func (d *DocumentRef) Snapshots(ctx context.Context) *DocumentSnapshotIterator {
return &DocumentSnapshotIterator{
docref: d,
ws: newWatchStreamForDocument(ctx, d),
}
}
// DocumentSnapshotIterator is an iterator over snapshots of a document.
// Call Next on the iterator to get a snapshot of the document each time it changes.
// Call Stop on the iterator when done.
//
// For an example, see DocumentRef.Snapshots.
type DocumentSnapshotIterator struct {
docref *DocumentRef
ws *watchStream
}
// Next blocks until the document changes, then returns the DocumentSnapshot for
// the current state of the document. If the document has been deleted, Next
// returns a DocumentSnapshot whose Exists method returns false.
//
// Next never returns iterator.Done unless it is called after Stop.
func (it *DocumentSnapshotIterator) Next() (*DocumentSnapshot, error) {
btree, _, readTime, err := it.ws.nextSnapshot()
if err != nil {
if err == io.EOF {
err = iterator.Done
}
// watchStream's error is sticky, so SnapshotIterator does not need to remember it.
return nil, err
}
if btree.Len() == 0 { // document deleted
return &DocumentSnapshot{Ref: it.docref, ReadTime: readTime}, nil
}
snap, _ := btree.At(0)
return snap.(*DocumentSnapshot), nil
}
// Stop stops receiving snapshots. You should always call Stop when you are done with
// a DocumentSnapshotIterator, to free up resources. It is not safe to call Stop
// concurrently with Next.
func (it *DocumentSnapshotIterator) Stop() {
it.ws.stop()
}