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
7package readpref // import "go.mongodb.org/mongo-driver/mongo/readpref"
8
9import (
10	"errors"
11	"time"
12
13	"go.mongodb.org/mongo-driver/tag"
14)
15
16var (
17	errInvalidReadPreference = errors.New("can not specify tags or max staleness on primary")
18)
19
20var primary = ReadPref{mode: PrimaryMode}
21
22// Primary constructs a read preference with a PrimaryMode.
23func Primary() *ReadPref {
24	return &primary
25}
26
27// PrimaryPreferred constructs a read preference with a PrimaryPreferredMode.
28func PrimaryPreferred(opts ...Option) *ReadPref {
29	// New only returns an error with a mode of Primary
30	rp, _ := New(PrimaryPreferredMode, opts...)
31	return rp
32}
33
34// SecondaryPreferred constructs a read preference with a SecondaryPreferredMode.
35func SecondaryPreferred(opts ...Option) *ReadPref {
36	// New only returns an error with a mode of Primary
37	rp, _ := New(SecondaryPreferredMode, opts...)
38	return rp
39}
40
41// Secondary constructs a read preference with a SecondaryMode.
42func Secondary(opts ...Option) *ReadPref {
43	// New only returns an error with a mode of Primary
44	rp, _ := New(SecondaryMode, opts...)
45	return rp
46}
47
48// Nearest constructs a read preference with a NearestMode.
49func Nearest(opts ...Option) *ReadPref {
50	// New only returns an error with a mode of Primary
51	rp, _ := New(NearestMode, opts...)
52	return rp
53}
54
55// New creates a new ReadPref.
56func New(mode Mode, opts ...Option) (*ReadPref, error) {
57	rp := &ReadPref{
58		mode: mode,
59	}
60
61	if mode == PrimaryMode && len(opts) != 0 {
62		return nil, errInvalidReadPreference
63	}
64
65	for _, opt := range opts {
66		err := opt(rp)
67		if err != nil {
68			return nil, err
69		}
70	}
71
72	return rp, nil
73}
74
75// ReadPref determines which servers are considered suitable for read operations.
76type ReadPref struct {
77	maxStaleness    time.Duration
78	maxStalenessSet bool
79	mode            Mode
80	tagSets         []tag.Set
81}
82
83// MaxStaleness is the maximum amount of time to allow
84// a server to be considered eligible for selection. The
85// second return value indicates if this value has been set.
86func (r *ReadPref) MaxStaleness() (time.Duration, bool) {
87	return r.maxStaleness, r.maxStalenessSet
88}
89
90// Mode indicates the mode of the read preference.
91func (r *ReadPref) Mode() Mode {
92	return r.mode
93}
94
95// TagSets are multiple tag sets indicating
96// which servers should be considered.
97func (r *ReadPref) TagSets() []tag.Set {
98	return r.tagSets
99}
100