Don Newton | 379ae25 | 2019-04-01 12:17:06 -0400 | [diff] [blame^] | 1 | // Copyright (C) MongoDB, Inc. 2017-present. |
| 2 | // |
| 3 | // Licensed under the Apache License, Version 2.0 (the "License"); you may |
| 4 | // not use this file except in compliance with the License. You may obtain |
| 5 | // a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 |
| 6 | |
| 7 | package mongo |
| 8 | |
| 9 | import ( |
| 10 | "context" |
| 11 | "errors" |
| 12 | |
| 13 | "github.com/mongodb/mongo-go-driver/bson" |
| 14 | "github.com/mongodb/mongo-go-driver/bson/bsoncodec" |
| 15 | "github.com/mongodb/mongo-go-driver/x/mongo/driver" |
| 16 | ) |
| 17 | |
| 18 | // Cursor is used to iterate a stream of documents. Each document is decoded into the result |
| 19 | // according to the rules of the bson package. |
| 20 | // |
| 21 | // A typical usage of the Cursor type would be: |
| 22 | // |
| 23 | // var cur *Cursor |
| 24 | // ctx := context.Background() |
| 25 | // defer cur.Close(ctx) |
| 26 | // |
| 27 | // for cur.Next(ctx) { |
| 28 | // elem := &bson.D{} |
| 29 | // if err := cur.Decode(elem); err != nil { |
| 30 | // log.Fatal(err) |
| 31 | // } |
| 32 | // |
| 33 | // // do something with elem.... |
| 34 | // } |
| 35 | // |
| 36 | // if err := cur.Err(); err != nil { |
| 37 | // log.Fatal(err) |
| 38 | // } |
| 39 | // |
| 40 | type Cursor struct { |
| 41 | // Current is the BSON bytes of the current document. This property is only valid until the next |
| 42 | // call to Next or Close. If continued access is required to the bson.Raw, you must make a copy |
| 43 | // of it. |
| 44 | Current bson.Raw |
| 45 | |
| 46 | bc batchCursor |
| 47 | pos int |
| 48 | batch []byte |
| 49 | registry *bsoncodec.Registry |
| 50 | |
| 51 | err error |
| 52 | } |
| 53 | |
| 54 | func newCursor(bc batchCursor, registry *bsoncodec.Registry) (*Cursor, error) { |
| 55 | if registry == nil { |
| 56 | registry = bson.DefaultRegistry |
| 57 | } |
| 58 | if bc == nil { |
| 59 | return nil, errors.New("batch cursor must not be nil") |
| 60 | } |
| 61 | return &Cursor{bc: bc, pos: 0, batch: make([]byte, 0, 256), registry: registry}, nil |
| 62 | } |
| 63 | |
| 64 | func newEmptyCursor() *Cursor { |
| 65 | return &Cursor{bc: driver.NewEmptyBatchCursor()} |
| 66 | } |
| 67 | |
| 68 | // ID returns the ID of this cursor. |
| 69 | func (c *Cursor) ID() int64 { return c.bc.ID() } |
| 70 | |
| 71 | func (c *Cursor) advanceCurrentDocument() bool { |
| 72 | if len(c.batch[c.pos:]) < 4 { |
| 73 | c.err = errors.New("could not read next document: insufficient bytes") |
| 74 | return false |
| 75 | } |
| 76 | 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) |
| 77 | if len(c.batch[c.pos:]) < length { |
| 78 | c.err = errors.New("could not read next document: insufficient bytes") |
| 79 | return false |
| 80 | } |
| 81 | if len(c.Current) > 4 { |
| 82 | c.Current[0], c.Current[1], c.Current[2], c.Current[3] = 0x00, 0x00, 0x00, 0x00 // Invalidate the current document |
| 83 | } |
| 84 | c.Current = c.batch[c.pos : c.pos+length] |
| 85 | c.pos += length |
| 86 | return true |
| 87 | } |
| 88 | |
| 89 | // Next gets the next result from this cursor. Returns true if there were no errors and the next |
| 90 | // result is available for decoding. |
| 91 | func (c *Cursor) Next(ctx context.Context) bool { |
| 92 | if ctx == nil { |
| 93 | ctx = context.Background() |
| 94 | } |
| 95 | if c.pos < len(c.batch) { |
| 96 | return c.advanceCurrentDocument() |
| 97 | } |
| 98 | |
| 99 | // clear the batch |
| 100 | c.batch = c.batch[:0] |
| 101 | c.pos = 0 |
| 102 | c.Current = c.Current[:0] |
| 103 | |
| 104 | // call the Next method in a loop until at least one document is returned in the next batch or |
| 105 | // the context times out. |
| 106 | for len(c.batch) == 0 { |
| 107 | // If we don't have a next batch |
| 108 | if !c.bc.Next(ctx) { |
| 109 | // Do we have an error? If so we return false. |
| 110 | c.err = c.bc.Err() |
| 111 | if c.err != nil { |
| 112 | return false |
| 113 | } |
| 114 | // Is the cursor ID zero? |
| 115 | if c.bc.ID() == 0 { |
| 116 | return false |
| 117 | } |
| 118 | // empty batch, but cursor is still valid, so continue. |
| 119 | continue |
| 120 | } |
| 121 | |
| 122 | c.batch = c.bc.Batch(c.batch[:0]) |
| 123 | } |
| 124 | |
| 125 | return c.advanceCurrentDocument() |
| 126 | } |
| 127 | |
| 128 | // Decode will decode the current document into val. |
| 129 | func (c *Cursor) Decode(val interface{}) error { |
| 130 | return bson.UnmarshalWithRegistry(c.registry, c.Current, val) |
| 131 | } |
| 132 | |
| 133 | // Err returns the current error. |
| 134 | func (c *Cursor) Err() error { return c.err } |
| 135 | |
| 136 | // Close closes this cursor. |
| 137 | func (c *Cursor) Close(ctx context.Context) error { return c.bc.Close(ctx) } |