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// 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 readpref defines read preferences for MongoDB queries.
package readpref // import "go.mongodb.org/mongo-driver/mongo/readpref"
import (
"bytes"
"errors"
"fmt"
"time"
"go.mongodb.org/mongo-driver/tag"
)
var (
errInvalidReadPreference = errors.New("can not specify tags, max staleness, or hedge with mode primary")
)
// Primary constructs a read preference with a PrimaryMode.
func Primary() *ReadPref {
return &ReadPref{mode: PrimaryMode}
}
// PrimaryPreferred constructs a read preference with a PrimaryPreferredMode.
func PrimaryPreferred(opts ...Option) *ReadPref {
// New only returns an error with a mode of Primary
rp, _ := New(PrimaryPreferredMode, opts...)
return rp
}
// SecondaryPreferred constructs a read preference with a SecondaryPreferredMode.
func SecondaryPreferred(opts ...Option) *ReadPref {
// New only returns an error with a mode of Primary
rp, _ := New(SecondaryPreferredMode, opts...)
return rp
}
// Secondary constructs a read preference with a SecondaryMode.
func Secondary(opts ...Option) *ReadPref {
// New only returns an error with a mode of Primary
rp, _ := New(SecondaryMode, opts...)
return rp
}
// Nearest constructs a read preference with a NearestMode.
func Nearest(opts ...Option) *ReadPref {
// New only returns an error with a mode of Primary
rp, _ := New(NearestMode, opts...)
return rp
}
// New creates a new ReadPref.
func New(mode Mode, opts ...Option) (*ReadPref, error) {
rp := &ReadPref{
mode: mode,
}
if mode == PrimaryMode && len(opts) != 0 {
return nil, errInvalidReadPreference
}
for _, opt := range opts {
if opt == nil {
continue
}
err := opt(rp)
if err != nil {
return nil, err
}
}
return rp, nil
}
// ReadPref determines which servers are considered suitable for read operations.
type ReadPref struct {
maxStaleness time.Duration
maxStalenessSet bool
mode Mode
tagSets []tag.Set
hedgeEnabled *bool
}
// MaxStaleness is the maximum amount of time to allow
// a server to be considered eligible for selection. The
// second return value indicates if this value has been set.
func (r *ReadPref) MaxStaleness() (time.Duration, bool) {
return r.maxStaleness, r.maxStalenessSet
}
// Mode indicates the mode of the read preference.
func (r *ReadPref) Mode() Mode {
return r.mode
}
// TagSets are multiple tag sets indicating
// which servers should be considered.
func (r *ReadPref) TagSets() []tag.Set {
return r.tagSets
}
// HedgeEnabled returns whether or not hedged reads are enabled for this read preference. If this option was not
// specified during read preference construction, nil is returned.
func (r *ReadPref) HedgeEnabled() *bool {
return r.hedgeEnabled
}
// String returns a human-readable description of the read preference.
func (r *ReadPref) String() string {
var b bytes.Buffer
b.WriteString(r.mode.String())
delim := "("
if r.maxStalenessSet {
fmt.Fprintf(&b, "%smaxStaleness=%v", delim, r.maxStaleness)
delim = " "
}
for _, tagSet := range r.tagSets {
fmt.Fprintf(&b, "%stagSet=%s", delim, tagSet.String())
delim = " "
}
if r.hedgeEnabled != nil {
fmt.Fprintf(&b, "%shedgeEnabled=%v", delim, *r.hedgeEnabled)
delim = " "
}
if delim != "(" {
b.WriteString(")")
}
return b.String()
}