github.com/endocode/docker@v1.4.2-0.20160113120958-46eb4700391e/pkg/truncindex/truncindex.go (about)

     1  // Package truncindex provides a general 'index tree', used by Docker
     2  // in order to be able to reference containers by only a few unambiguous
     3  // characters of their id.
     4  package truncindex
     5  
     6  import (
     7  	"errors"
     8  	"fmt"
     9  	"strings"
    10  	"sync"
    11  
    12  	"github.com/tchap/go-patricia/patricia"
    13  )
    14  
    15  var (
    16  	// ErrEmptyPrefix is an error returned if the prefix was empty.
    17  	ErrEmptyPrefix = errors.New("Prefix can't be empty")
    18  
    19  	// ErrAmbiguousPrefix is returned if the prefix was ambiguous
    20  	// (multiple ids for the prefix).
    21  	ErrAmbiguousPrefix = errors.New("Multiple IDs found with provided prefix")
    22  
    23  	// ErrIllegalChar is returned when a space is in the ID
    24  	ErrIllegalChar = errors.New("illegal character: ' '")
    25  
    26  	// ErrNotExist is returned when ID or its prefix not found in index.
    27  	ErrNotExist = errors.New("ID does not exist")
    28  )
    29  
    30  // TruncIndex allows the retrieval of string identifiers by any of their unique prefixes.
    31  // This is used to retrieve image and container IDs by more convenient shorthand prefixes.
    32  type TruncIndex struct {
    33  	sync.RWMutex
    34  	trie *patricia.Trie
    35  	ids  map[string]struct{}
    36  }
    37  
    38  // NewTruncIndex creates a new TruncIndex and initializes with a list of IDs.
    39  func NewTruncIndex(ids []string) (idx *TruncIndex) {
    40  	idx = &TruncIndex{
    41  		ids: make(map[string]struct{}),
    42  
    43  		// Change patricia max prefix per node length,
    44  		// because our len(ID) always 64
    45  		trie: patricia.NewTrie(patricia.MaxPrefixPerNode(64)),
    46  	}
    47  	for _, id := range ids {
    48  		idx.addID(id)
    49  	}
    50  	return
    51  }
    52  
    53  func (idx *TruncIndex) addID(id string) error {
    54  	if strings.Contains(id, " ") {
    55  		return ErrIllegalChar
    56  	}
    57  	if id == "" {
    58  		return ErrEmptyPrefix
    59  	}
    60  	if _, exists := idx.ids[id]; exists {
    61  		return fmt.Errorf("id already exists: '%s'", id)
    62  	}
    63  	idx.ids[id] = struct{}{}
    64  	if inserted := idx.trie.Insert(patricia.Prefix(id), struct{}{}); !inserted {
    65  		return fmt.Errorf("failed to insert id: %s", id)
    66  	}
    67  	return nil
    68  }
    69  
    70  // Add adds a new ID to the TruncIndex.
    71  func (idx *TruncIndex) Add(id string) error {
    72  	idx.Lock()
    73  	defer idx.Unlock()
    74  	if err := idx.addID(id); err != nil {
    75  		return err
    76  	}
    77  	return nil
    78  }
    79  
    80  // Delete removes an ID from the TruncIndex. If there are multiple IDs
    81  // with the given prefix, an error is thrown.
    82  func (idx *TruncIndex) Delete(id string) error {
    83  	idx.Lock()
    84  	defer idx.Unlock()
    85  	if _, exists := idx.ids[id]; !exists || id == "" {
    86  		return fmt.Errorf("no such id: '%s'", id)
    87  	}
    88  	delete(idx.ids, id)
    89  	if deleted := idx.trie.Delete(patricia.Prefix(id)); !deleted {
    90  		return fmt.Errorf("no such id: '%s'", id)
    91  	}
    92  	return nil
    93  }
    94  
    95  // Get retrieves an ID from the TruncIndex. If there are multiple IDs
    96  // with the given prefix, an error is thrown.
    97  func (idx *TruncIndex) Get(s string) (string, error) {
    98  	if s == "" {
    99  		return "", ErrEmptyPrefix
   100  	}
   101  	var (
   102  		id string
   103  	)
   104  	subTreeVisitFunc := func(prefix patricia.Prefix, item patricia.Item) error {
   105  		if id != "" {
   106  			// we haven't found the ID if there are two or more IDs
   107  			id = ""
   108  			return ErrAmbiguousPrefix
   109  		}
   110  		id = string(prefix)
   111  		return nil
   112  	}
   113  
   114  	idx.RLock()
   115  	defer idx.RUnlock()
   116  	if err := idx.trie.VisitSubtree(patricia.Prefix(s), subTreeVisitFunc); err != nil {
   117  		return "", err
   118  	}
   119  	if id != "" {
   120  		return id, nil
   121  	}
   122  	return "", ErrNotExist
   123  }
   124  
   125  // Iterate iterates over all stored IDs, and passes each of them to the given handler.
   126  func (idx *TruncIndex) Iterate(handler func(id string)) {
   127  	idx.trie.Visit(func(prefix patricia.Prefix, item patricia.Item) error {
   128  		handler(string(prefix))
   129  		return nil
   130  	})
   131  }