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