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package bbolt
import (
"bytes"
"fmt"
"sort"
)
// Cursor represents an iterator that can traverse over all key/value pairs in a bucket in sorted order.
// Cursors see nested buckets with value == nil.
// Cursors can be obtained from a transaction and are valid as long as the transaction is open.
//
// Keys and values returned from the cursor are only valid for the life of the transaction.
//
// Changing data while traversing with a cursor may cause it to be invalidated
// and return unexpected keys and/or values. You must reposition your cursor
// after mutating data.
type Cursor struct {
bucket *Bucket
stack []elemRef
}
// Bucket returns the bucket that this cursor was created from.
func (c *Cursor) Bucket() *Bucket {
return c.bucket
}
// First moves the cursor to the first item in the bucket and returns its key and value.
// If the bucket is empty then a nil key and value are returned.
// The returned key and value are only valid for the life of the transaction.
func (c *Cursor) First() (key []byte, value []byte) {
_assert(c.bucket.tx.db != nil, "tx closed")
c.stack = c.stack[:0]
p, n := c.bucket.pageNode(c.bucket.root)
c.stack = append(c.stack, elemRef{page: p, node: n, index: 0})
c.first()
// If we land on an empty page then move to the next value.
// https://github.com/boltdb/bolt/issues/450
if c.stack[len(c.stack)-1].count() == 0 {
c.next()
}
k, v, flags := c.keyValue()
if (flags & uint32(bucketLeafFlag)) != 0 {
return k, nil
}
return k, v
}
// Last moves the cursor to the last item in the bucket and returns its key and value.
// If the bucket is empty then a nil key and value are returned.
// The returned key and value are only valid for the life of the transaction.
func (c *Cursor) Last() (key []byte, value []byte) {
_assert(c.bucket.tx.db != nil, "tx closed")
c.stack = c.stack[:0]
p, n := c.bucket.pageNode(c.bucket.root)
ref := elemRef{page: p, node: n}
ref.index = ref.count() - 1
c.stack = append(c.stack, ref)
c.last()
k, v, flags := c.keyValue()
if (flags & uint32(bucketLeafFlag)) != 0 {
return k, nil
}
return k, v
}
// Next moves the cursor to the next item in the bucket and returns its key and value.
// If the cursor is at the end of the bucket then a nil key and value are returned.
// The returned key and value are only valid for the life of the transaction.
func (c *Cursor) Next() (key []byte, value []byte) {
_assert(c.bucket.tx.db != nil, "tx closed")
k, v, flags := c.next()
if (flags & uint32(bucketLeafFlag)) != 0 {
return k, nil
}
return k, v
}
// Prev moves the cursor to the previous item in the bucket and returns its key and value.
// If the cursor is at the beginning of the bucket then a nil key and value are returned.
// The returned key and value are only valid for the life of the transaction.
func (c *Cursor) Prev() (key []byte, value []byte) {
_assert(c.bucket.tx.db != nil, "tx closed")
// Attempt to move back one element until we're successful.
// Move up the stack as we hit the beginning of each page in our stack.
for i := len(c.stack) - 1; i >= 0; i-- {
elem := &c.stack[i]
if elem.index > 0 {
elem.index--
break
}
c.stack = c.stack[:i]
}
// If we've hit the end then return nil.
if len(c.stack) == 0 {
return nil, nil
}
// Move down the stack to find the last element of the last leaf under this branch.
c.last()
k, v, flags := c.keyValue()
if (flags & uint32(bucketLeafFlag)) != 0 {
return k, nil
}
return k, v
}
// Seek moves the cursor to a given key and returns it.
// If the key does not exist then the next key is used. If no keys
// follow, a nil key is returned.
// The returned key and value are only valid for the life of the transaction.
func (c *Cursor) Seek(seek []byte) (key []byte, value []byte) {
k, v, flags := c.seek(seek)
// If we ended up after the last element of a page then move to the next one.
if ref := &c.stack[len(c.stack)-1]; ref.index >= ref.count() {
k, v, flags = c.next()
}
if k == nil {
return nil, nil
} else if (flags & uint32(bucketLeafFlag)) != 0 {
return k, nil
}
return k, v
}
// Delete removes the current key/value under the cursor from the bucket.
// Delete fails if current key/value is a bucket or if the transaction is not writable.
func (c *Cursor) Delete() error {
if c.bucket.tx.db == nil {
return ErrTxClosed
} else if !c.bucket.Writable() {
return ErrTxNotWritable
}
key, _, flags := c.keyValue()
// Return an error if current value is a bucket.
if (flags & bucketLeafFlag) != 0 {
return ErrIncompatibleValue
}
c.node().del(key)
return nil
}
// seek moves the cursor to a given key and returns it.
// If the key does not exist then the next key is used.
func (c *Cursor) seek(seek []byte) (key []byte, value []byte, flags uint32) {
_assert(c.bucket.tx.db != nil, "tx closed")
// Start from root page/node and traverse to correct page.
c.stack = c.stack[:0]
c.search(seek, c.bucket.root)
// If this is a bucket then return a nil value.
return c.keyValue()
}
// first moves the cursor to the first leaf element under the last page in the stack.
func (c *Cursor) first() {
for {
// Exit when we hit a leaf page.
var ref = &c.stack[len(c.stack)-1]
if ref.isLeaf() {
break
}
// Keep adding pages pointing to the first element to the stack.
var pgid pgid
if ref.node != nil {
pgid = ref.node.inodes[ref.index].pgid
} else {
pgid = ref.page.branchPageElement(uint16(ref.index)).pgid
}
p, n := c.bucket.pageNode(pgid)
c.stack = append(c.stack, elemRef{page: p, node: n, index: 0})
}
}
// last moves the cursor to the last leaf element under the last page in the stack.
func (c *Cursor) last() {
for {
// Exit when we hit a leaf page.
ref := &c.stack[len(c.stack)-1]
if ref.isLeaf() {
break
}
// Keep adding pages pointing to the last element in the stack.
var pgid pgid
if ref.node != nil {
pgid = ref.node.inodes[ref.index].pgid
} else {
pgid = ref.page.branchPageElement(uint16(ref.index)).pgid
}
p, n := c.bucket.pageNode(pgid)
var nextRef = elemRef{page: p, node: n}
nextRef.index = nextRef.count() - 1
c.stack = append(c.stack, nextRef)
}
}
// next moves to the next leaf element and returns the key and value.
// If the cursor is at the last leaf element then it stays there and returns nil.
func (c *Cursor) next() (key []byte, value []byte, flags uint32) {
for {
// Attempt to move over one element until we're successful.
// Move up the stack as we hit the end of each page in our stack.
var i int
for i = len(c.stack) - 1; i >= 0; i-- {
elem := &c.stack[i]
if elem.index < elem.count()-1 {
elem.index++
break
}
}
// If we've hit the root page then stop and return. This will leave the
// cursor on the last element of the last page.
if i == -1 {
return nil, nil, 0
}
// Otherwise start from where we left off in the stack and find the
// first element of the first leaf page.
c.stack = c.stack[:i+1]
c.first()
// If this is an empty page then restart and move back up the stack.
// https://github.com/boltdb/bolt/issues/450
if c.stack[len(c.stack)-1].count() == 0 {
continue
}
return c.keyValue()
}
}
// search recursively performs a binary search against a given page/node until it finds a given key.
func (c *Cursor) search(key []byte, pgid pgid) {
p, n := c.bucket.pageNode(pgid)
if p != nil && (p.flags&(branchPageFlag|leafPageFlag)) == 0 {
panic(fmt.Sprintf("invalid page type: %d: %x", p.id, p.flags))
}
e := elemRef{page: p, node: n}
c.stack = append(c.stack, e)
// If we're on a leaf page/node then find the specific node.
if e.isLeaf() {
c.nsearch(key)
return
}
if n != nil {
c.searchNode(key, n)
return
}
c.searchPage(key, p)
}
func (c *Cursor) searchNode(key []byte, n *node) {
var exact bool
index := sort.Search(len(n.inodes), func(i int) bool {
// TODO(benbjohnson): Optimize this range search. It's a bit hacky right now.
// sort.Search() finds the lowest index where f() != -1 but we need the highest index.
ret := bytes.Compare(n.inodes[i].key, key)
if ret == 0 {
exact = true
}
return ret != -1
})
if !exact && index > 0 {
index--
}
c.stack[len(c.stack)-1].index = index
// Recursively search to the next page.
c.search(key, n.inodes[index].pgid)
}
func (c *Cursor) searchPage(key []byte, p *page) {
// Binary search for the correct range.
inodes := p.branchPageElements()
var exact bool
index := sort.Search(int(p.count), func(i int) bool {
// TODO(benbjohnson): Optimize this range search. It's a bit hacky right now.
// sort.Search() finds the lowest index where f() != -1 but we need the highest index.
ret := bytes.Compare(inodes[i].key(), key)
if ret == 0 {
exact = true
}
return ret != -1
})
if !exact && index > 0 {
index--
}
c.stack[len(c.stack)-1].index = index
// Recursively search to the next page.
c.search(key, inodes[index].pgid)
}
// nsearch searches the leaf node on the top of the stack for a key.
func (c *Cursor) nsearch(key []byte) {
e := &c.stack[len(c.stack)-1]
p, n := e.page, e.node
// If we have a node then search its inodes.
if n != nil {
index := sort.Search(len(n.inodes), func(i int) bool {
return bytes.Compare(n.inodes[i].key, key) != -1
})
e.index = index
return
}
// If we have a page then search its leaf elements.
inodes := p.leafPageElements()
index := sort.Search(int(p.count), func(i int) bool {
return bytes.Compare(inodes[i].key(), key) != -1
})
e.index = index
}
// keyValue returns the key and value of the current leaf element.
func (c *Cursor) keyValue() ([]byte, []byte, uint32) {
ref := &c.stack[len(c.stack)-1]
// If the cursor is pointing to the end of page/node then return nil.
if ref.count() == 0 || ref.index >= ref.count() {
return nil, nil, 0
}
// Retrieve value from node.
if ref.node != nil {
inode := &ref.node.inodes[ref.index]
return inode.key, inode.value, inode.flags
}
// Or retrieve value from page.
elem := ref.page.leafPageElement(uint16(ref.index))
return elem.key(), elem.value(), elem.flags
}
// node returns the node that the cursor is currently positioned on.
func (c *Cursor) node() *node {
_assert(len(c.stack) > 0, "accessing a node with a zero-length cursor stack")
// If the top of the stack is a leaf node then just return it.
if ref := &c.stack[len(c.stack)-1]; ref.node != nil && ref.isLeaf() {
return ref.node
}
// Start from root and traverse down the hierarchy.
var n = c.stack[0].node
if n == nil {
n = c.bucket.node(c.stack[0].page.id, nil)
}
for _, ref := range c.stack[:len(c.stack)-1] {
_assert(!n.isLeaf, "expected branch node")
n = n.childAt(int(ref.index))
}
_assert(n.isLeaf, "expected leaf node")
return n
}
// elemRef represents a reference to an element on a given page/node.
type elemRef struct {
page *page
node *node
index int
}
// isLeaf returns whether the ref is pointing at a leaf page/node.
func (r *elemRef) isLeaf() bool {
if r.node != nil {
return r.node.isLeaf
}
return (r.page.flags & leafPageFlag) != 0
}
// count returns the number of inodes or page elements.
func (r *elemRef) count() int {
if r.node != nil {
return len(r.node.inodes)
}
return int(r.page.count)
}