go-unixfs: github.com/ipfs/go-unixfs/hamt Index | Files

package hamt

import "github.com/ipfs/go-unixfs/hamt"

Package hamt implements a Hash Array Mapped Trie over ipfs merkledag nodes. It is implemented mostly as described in the wikipedia article on HAMTs, however the table size is variable (usually 256 in our usages) as opposed to 32 as suggested in the article. The hash function used is currently Murmur3, but this value is configurable (the datastructure reports which hash function its using).

The one algorithmic change we implement that is not mentioned in the wikipedia article is the collapsing of empty shards. Given the following tree: ( '[' = shards, '{' = values ) [ 'A' ] -> [ 'B' ] -> { "ABC" }

|       L-> { "ABD" }
L-> { "ASDF" }

If we simply removed "ABC", we would end up with a tree where shard 'B' only has a single child. This causes two issues, the first, is that now we have an extra lookup required to get to "ABD". The second issue is that now we have a tree that contains only "ABD", but is not the same tree that we would get by simply inserting "ABD" into a new tree. To address this, we always check for empty shard nodes upon deletion and prune them to maintain a consistent tree, independent of insertion order.

Index

Package Files

hamt.go util.go

Constants

const (
    // HashMurmur3 is the multiformats identifier for Murmur3
    HashMurmur3 uint64 = 0x22
)

type Shard Uses

type Shard struct {
    // contains filtered or unexported fields
}

A Shard represents the HAMT. It should be initialized with NewShard().

func NewHamtFromDag Uses

func NewHamtFromDag(dserv ipld.DAGService, nd ipld.Node) (*Shard, error)

NewHamtFromDag creates new a HAMT shard from the given DAG.

func NewShard Uses

func NewShard(dserv ipld.DAGService, size int) (*Shard, error)

NewShard creates a new, empty HAMT shard with the given size.

func (*Shard) CidBuilder Uses

func (ds *Shard) CidBuilder() cid.Builder

CidBuilder gets the CID Builder, may be nil if unset

func (ds *Shard) EnumLinks(ctx context.Context) ([]*ipld.Link, error)

EnumLinks collects all links in the Shard.

func (*Shard) EnumLinksAsync Uses

func (ds *Shard) EnumLinksAsync(ctx context.Context) <-chan format.LinkResult

EnumLinksAsync returns a channel which will receive Links in the directory as they are enumerated, where order is not guaranteed

func (*Shard) Find Uses

func (ds *Shard) Find(ctx context.Context, name string) (*ipld.Link, error)

Find searches for a child node by 'name' within this hamt

func (ds *Shard) ForEachLink(ctx context.Context, f func(*ipld.Link) error) error

ForEachLink walks the Shard and calls the given function.

func (ds *Shard) Link() (*ipld.Link, error)

Link returns a merklelink to this shard node

func (*Shard) Node Uses

func (ds *Shard) Node() (ipld.Node, error)

Node serializes the HAMT structure into a merkledag node with unixfs formatting

func (*Shard) Remove Uses

func (ds *Shard) Remove(ctx context.Context, name string) error

Remove deletes the named entry if it exists. Otherwise, it returns os.ErrNotExist.

func (*Shard) Set Uses

func (ds *Shard) Set(ctx context.Context, name string, nd ipld.Node) error

Set sets 'name' = nd in the HAMT

func (*Shard) SetCidBuilder Uses

func (ds *Shard) SetCidBuilder(builder cid.Builder)

SetCidBuilder sets the CID Builder

Package hamt imports 10 packages (graph) and is imported by 1 packages. Updated 2020-02-22. Refresh now. Tools for package owners.