mirror of https://github.com/hak5/bolt.git
115 lines
2.8 KiB
Go
115 lines
2.8 KiB
Go
package bolt
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import (
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"bytes"
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"sort"
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)
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type Cursor struct {
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transaction *Transaction
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root pgid
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stack []elem
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}
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// elem represents a node on a page that's on the cursor's stack.
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type elem struct {
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page *page
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index uint16
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}
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// First moves the cursor to the first item in the bucket and returns its key and data.
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func (c *Cursor) First() ([]byte, []byte) {
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// TODO: Traverse to the first key.
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return nil, nil
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}
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// Move the cursor to the next key/value.
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func (c *Cursor) Next() ([]byte, []byte) {
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return nil, nil
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}
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// Get positions the cursor at a specific key and returns the its value.
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func (c *Cursor) Get(key []byte) []byte {
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// Start from root page and traverse to correct page.
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c.stack = c.stack[:0]
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c.search(key, c.transaction.page(c.root))
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p, index := c.top()
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// If the cursor is pointing to the end of page then return nil.
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if index == p.count {
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return nil
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}
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// If our target node isn't the same key as what's passed in then return nil.
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// c.page().hexdump(512)
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if !bytes.Equal(key, c.node().key()) {
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return nil
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}
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return c.node().value()
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}
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func (c *Cursor) search(key []byte, p *page) {
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if (p.flags & (p_branch | p_leaf)) == 0 {
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panic("invalid page type: " + p.typ())
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}
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e := elem{page: p}
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c.stack = append(c.stack, e)
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// If we're on a leaf page then find the specific node.
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if (p.flags & p_leaf) != 0 {
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c.nsearch(key, p)
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return
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}
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// Binary search for the correct range.
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inodes := p.branchPageElements()
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var exact bool
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index := sort.Search(int(p.count), func(i int) bool {
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// TODO(benbjohnson): Optimize this range search. It's a bit hacky right now.
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// sort.Search() finds the lowest index where f() != -1 but we need the highest index.
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ret := bytes.Compare(inodes[i].key(), key)
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if ret == 0 {
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exact = true
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}
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return ret != -1
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})
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if !exact && index > 0 {
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index--
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}
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e.index = uint16(index)
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// Recursively search to the next page.
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c.search(key, c.transaction.page(inodes[e.index].pgid))
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}
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// nsearch searches a leaf node for the index of the node that matches key.
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func (c *Cursor) nsearch(key []byte, p *page) {
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e := &c.stack[len(c.stack)-1]
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// Binary search for the correct leaf node index.
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inodes := p.leafPageElements()
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index := sort.Search(int(p.count), func(i int) bool {
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return bytes.Compare(inodes[i].key(), key) != -1
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})
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e.index = uint16(index)
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}
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// top returns the page and leaf node that the cursor is currently pointing at.
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func (c *Cursor) top() (*page, uint16) {
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elem := c.stack[len(c.stack)-1]
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return elem.page, elem.index
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}
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// page returns the page that the cursor is currently pointing at.
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func (c *Cursor) page() *page {
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return c.stack[len(c.stack)-1].page
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}
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// node returns the leaf node that the cursor is currently positioned on.
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func (c *Cursor) node() *leafPageElement {
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elem := c.stack[len(c.stack)-1]
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return elem.page.leafPageElement(elem.index)
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}
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