| // Copyright (C) MongoDB, Inc. 2017-present. |
| // |
| // 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 |
| |
| package mongo |
| |
| import ( |
| "context" |
| "errors" |
| |
| "github.com/mongodb/mongo-go-driver/bson" |
| "github.com/mongodb/mongo-go-driver/bson/bsoncodec" |
| "github.com/mongodb/mongo-go-driver/x/mongo/driver" |
| ) |
| |
| // Cursor is used to iterate a stream of documents. Each document is decoded into the result |
| // according to the rules of the bson package. |
| // |
| // A typical usage of the Cursor type would be: |
| // |
| // var cur *Cursor |
| // ctx := context.Background() |
| // defer cur.Close(ctx) |
| // |
| // for cur.Next(ctx) { |
| // elem := &bson.D{} |
| // if err := cur.Decode(elem); err != nil { |
| // log.Fatal(err) |
| // } |
| // |
| // // do something with elem.... |
| // } |
| // |
| // if err := cur.Err(); err != nil { |
| // log.Fatal(err) |
| // } |
| // |
| type Cursor struct { |
| // Current is the BSON bytes of the current document. This property is only valid until the next |
| // call to Next or Close. If continued access is required to the bson.Raw, you must make a copy |
| // of it. |
| Current bson.Raw |
| |
| bc batchCursor |
| pos int |
| batch []byte |
| registry *bsoncodec.Registry |
| |
| err error |
| } |
| |
| func newCursor(bc batchCursor, registry *bsoncodec.Registry) (*Cursor, error) { |
| if registry == nil { |
| registry = bson.DefaultRegistry |
| } |
| if bc == nil { |
| return nil, errors.New("batch cursor must not be nil") |
| } |
| return &Cursor{bc: bc, pos: 0, batch: make([]byte, 0, 256), registry: registry}, nil |
| } |
| |
| func newEmptyCursor() *Cursor { |
| return &Cursor{bc: driver.NewEmptyBatchCursor()} |
| } |
| |
| // ID returns the ID of this cursor. |
| func (c *Cursor) ID() int64 { return c.bc.ID() } |
| |
| func (c *Cursor) advanceCurrentDocument() bool { |
| if len(c.batch[c.pos:]) < 4 { |
| c.err = errors.New("could not read next document: insufficient bytes") |
| return false |
| } |
| length := (int(c.batch[c.pos]) | int(c.batch[c.pos+1])<<8 | int(c.batch[c.pos+2])<<16 | int(c.batch[c.pos+3])<<24) |
| if len(c.batch[c.pos:]) < length { |
| c.err = errors.New("could not read next document: insufficient bytes") |
| return false |
| } |
| if len(c.Current) > 4 { |
| c.Current[0], c.Current[1], c.Current[2], c.Current[3] = 0x00, 0x00, 0x00, 0x00 // Invalidate the current document |
| } |
| c.Current = c.batch[c.pos : c.pos+length] |
| c.pos += length |
| return true |
| } |
| |
| // Next gets the next result from this cursor. Returns true if there were no errors and the next |
| // result is available for decoding. |
| func (c *Cursor) Next(ctx context.Context) bool { |
| if ctx == nil { |
| ctx = context.Background() |
| } |
| if c.pos < len(c.batch) { |
| return c.advanceCurrentDocument() |
| } |
| |
| // clear the batch |
| c.batch = c.batch[:0] |
| c.pos = 0 |
| c.Current = c.Current[:0] |
| |
| // call the Next method in a loop until at least one document is returned in the next batch or |
| // the context times out. |
| for len(c.batch) == 0 { |
| // If we don't have a next batch |
| if !c.bc.Next(ctx) { |
| // Do we have an error? If so we return false. |
| c.err = c.bc.Err() |
| if c.err != nil { |
| return false |
| } |
| // Is the cursor ID zero? |
| if c.bc.ID() == 0 { |
| return false |
| } |
| // empty batch, but cursor is still valid, so continue. |
| continue |
| } |
| |
| c.batch = c.bc.Batch(c.batch[:0]) |
| } |
| |
| return c.advanceCurrentDocument() |
| } |
| |
| // Decode will decode the current document into val. |
| func (c *Cursor) Decode(val interface{}) error { |
| return bson.UnmarshalWithRegistry(c.registry, c.Current, val) |
| } |
| |
| // Err returns the current error. |
| func (c *Cursor) Err() error { return c.err } |
| |
| // Close closes this cursor. |
| func (c *Cursor) Close(ctx context.Context) error { return c.bc.Close(ctx) } |