iterator.go

Documentation: github.com/go-redis/redis

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