blob: 2f8bc2beda083563af654cbd1e7c06c94bb9766c [file] [log] [blame]
Naveen Sampath04696f72022-06-13 15:19:14 +05301package redis
2
3import (
4 "context"
5 "sync"
6)
7
8// ScanIterator is used to incrementally iterate over a collection of elements.
9// It's safe for concurrent use by multiple goroutines.
10type ScanIterator struct {
11 mu sync.Mutex // protects Scanner and pos
12 cmd *ScanCmd
13 pos int
14}
15
16// Err returns the last iterator error, if any.
17func (it *ScanIterator) Err() error {
18 it.mu.Lock()
19 err := it.cmd.Err()
20 it.mu.Unlock()
21 return err
22}
23
24// Next advances the cursor and returns true if more values can be read.
25func (it *ScanIterator) Next(ctx context.Context) bool {
26 it.mu.Lock()
27 defer it.mu.Unlock()
28
29 // Instantly return on errors.
30 if it.cmd.Err() != nil {
31 return false
32 }
33
34 // Advance cursor, check if we are still within range.
35 if it.pos < len(it.cmd.page) {
36 it.pos++
37 return true
38 }
39
40 for {
41 // Return if there is no more data to fetch.
42 if it.cmd.cursor == 0 {
43 return false
44 }
45
46 // Fetch next page.
47 switch it.cmd.args[0] {
48 case "scan", "qscan":
49 it.cmd.args[1] = it.cmd.cursor
50 default:
51 it.cmd.args[2] = it.cmd.cursor
52 }
53
54 err := it.cmd.process(ctx, it.cmd)
55 if err != nil {
56 return false
57 }
58
59 it.pos = 1
60
61 // Redis can occasionally return empty page.
62 if len(it.cmd.page) > 0 {
63 return true
64 }
65 }
66}
67
68// Val returns the key/field at the current cursor position.
69func (it *ScanIterator) Val() string {
70 var v string
71 it.mu.Lock()
72 if it.cmd.Err() == nil && it.pos > 0 && it.pos <= len(it.cmd.page) {
73 v = it.cmd.page[it.pos-1]
74 }
75 it.mu.Unlock()
76 return v
77}