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package redis
import (
"context"
"sync"
)
// ScanIterator is used to incrementally iterate over a collection of elements.
// It's safe for concurrent use by multiple goroutines.
type ScanIterator struct {
mu sync.Mutex // protects Scanner and pos
cmd *ScanCmd
pos int
}
// Err returns the last iterator error, if any.
func (it *ScanIterator) Err() error {
it.mu.Lock()
err := it.cmd.Err()
it.mu.Unlock()
return err
}
// Next advances the cursor and returns true if more values can be read.
func (it *ScanIterator) Next(ctx context.Context) bool {
it.mu.Lock()
defer it.mu.Unlock()
// Instantly return on errors.
if it.cmd.Err() != nil {
return false
}
// Advance cursor, check if we are still within range.
if it.pos < len(it.cmd.page) {
it.pos++
return true
}
for {
// Return if there is no more data to fetch.
if it.cmd.cursor == 0 {
return false
}
// Fetch next page.
switch it.cmd.args[0] {
case "scan", "qscan":
it.cmd.args[1] = it.cmd.cursor
default:
it.cmd.args[2] = it.cmd.cursor
}
err := it.cmd.process(ctx, it.cmd)
if err != nil {
return false
}
it.pos = 1
// Redis can occasionally return empty page.
if len(it.cmd.page) > 0 {
return true
}
}
}
// Val returns the key/field at the current cursor position.
func (it *ScanIterator) Val() string {
var v string
it.mu.Lock()
if it.cmd.Err() == nil && it.pos > 0 && it.pos <= len(it.cmd.page) {
v = it.cmd.page[it.pos-1]
}
it.mu.Unlock()
return v
}
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