package bolt 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() 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) ref := &c.stack[len(c.stack)-1] // If the cursor is pointing to the end of page/node then return nil. if ref.index >= ref.count() { return nil, nil, 0 } // 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) { // 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() 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 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) }