forked from crawshaw/sqlite
/
buffer.go
318 lines (275 loc) · 6.94 KB
/
buffer.go
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// Copyright (c) 2018 David Crawshaw <david@zentus.com>
//
// Permission to use, copy, modify, and distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
package sqlitex
import (
"errors"
"io"
"github.com/moleculer-go/sqlite"
)
// A Buffer is a variable-sized bytes buffer backed by SQLite blobs.
//
// The bytes are broken into pages, with the first and last pages
// stored in memory, and intermediate pages loaded into blobs.
// Unlike a single SQLite blob, a Buffer can grow beyond its initial size.
// The blobs are allocated in a temporary table.
//
// A Buffer is very similar to a bytes.Buffer.
type Buffer struct {
io.Reader
io.Writer
io.ByteScanner
err error
conn *sqlite.Conn
// cap(rbuf) == cap(wbuf) == blobs[N].Size()
rbuf []byte // read buffer
roff int // read head position in roff
blobs []tblob // blobs storing data between rbuf and wbuf
wbuf []byte // write buffer
freelist []tblob
}
type tblob struct {
blob *sqlite.Blob
rowid int64
}
// NewBuffer creates a Buffer with 16KB pages.
func NewBuffer(conn *sqlite.Conn) (*Buffer, error) {
return NewBufferSize(conn, 16*1024)
}
// NewBufferSize creates a Buffer with a specified page size.
func NewBufferSize(conn *sqlite.Conn, pageSize int) (*Buffer, error) {
bb := &Buffer{
conn: conn,
rbuf: make([]byte, 0, pageSize),
wbuf: make([]byte, 0, pageSize),
}
stmt := conn.Prep("CREATE TEMP TABLE IF NOT EXISTS BlobBuffer (blob BLOB);")
if _, err := stmt.Step(); err != nil {
return nil, err
}
return bb, nil
}
func (bb *Buffer) alloc() (tblob, error) {
if len(bb.freelist) > 0 {
b := bb.freelist[len(bb.freelist)-1]
bb.freelist = bb.freelist[:len(bb.freelist)-1]
return b, nil
}
stmt := bb.conn.Prep("INSERT INTO BlobBuffer (blob) VALUES ($blob);")
stmt.SetZeroBlob("$blob", int64(len(bb.rbuf)))
if _, err := stmt.Step(); err != nil {
return tblob{}, err
}
rowid := bb.conn.LastInsertRowID()
blob, err := bb.conn.OpenBlob("temp", "BlobBuffer", "blob", rowid, true)
if err != nil {
return tblob{}, err
}
return tblob{
blob: blob,
rowid: rowid,
}, nil
}
func (bb *Buffer) free(b tblob) {
bb.freelist = append(bb.freelist, b)
}
func (bb *Buffer) wbufEnsureSpace() error {
if len(bb.wbuf) < cap(bb.wbuf) {
return nil
}
// Flush the write buffer.
if len(bb.blobs) == 0 && bb.roff == len(bb.rbuf) {
// Short cut. The write buffer is full, but
// there are no on-disk blobs and the read
// buffer is empty. So push these bytes
// directly to the front of the Buffer.
bb.rbuf, bb.wbuf = bb.wbuf, bb.rbuf[:0]
bb.roff = 0
} else {
tblob, err := bb.alloc()
if err != nil {
bb.err = err
return err
}
if _, err := tblob.blob.WriteAt(bb.wbuf, 0); err != nil {
bb.err = err
return err
}
bb.blobs = append(bb.blobs, tblob)
bb.wbuf = bb.wbuf[:0]
}
return nil
}
// WriteByte appends a byte to the buffer, growing it as needed.
func (bb *Buffer) WriteByte(c byte) error {
if bb.err != nil {
return bb.err
}
if err := bb.wbufEnsureSpace(); err != nil {
return err
}
bb.wbuf = append(bb.wbuf, c)
return nil
}
func (bb *Buffer) UnreadByte() error {
if bb.err != nil {
return bb.err
}
if bb.roff == 0 {
return errors.New("sqlitex.Buffer: UnreadByte: no byte to unread")
}
bb.roff--
return nil
}
func (bb *Buffer) Write(p []byte) (n int, err error) {
if bb.err != nil {
return 0, bb.err
}
for len(p) > 0 {
if err := bb.wbufEnsureSpace(); err != nil {
return n, err
}
// TODO: shortcut for writing large p directly into a new blob
nn := len(p)
if rem := cap(bb.wbuf) - len(bb.wbuf); nn > rem {
nn = rem
}
bb.wbuf = append(bb.wbuf, p[:nn]...) // never grows wbuf
n += nn
p = p[nn:]
}
return n, nil
}
func (bb *Buffer) WriteString(p string) (n int, err error) {
if bb.err != nil {
return 0, bb.err
}
for len(p) > 0 {
if err := bb.wbufEnsureSpace(); err != nil {
return n, err
}
// TODO: shortcut for writing large p directly into a new blob
nn := len(p)
if rem := cap(bb.wbuf) - len(bb.wbuf); nn > rem {
nn = rem
}
bb.wbuf = append(bb.wbuf, p[:nn]...) // never grows wbuf
n += nn
p = p[nn:]
}
return n, nil
}
func (bb *Buffer) rbufFill() error {
if bb.roff < len(bb.rbuf) {
return nil
}
// Read buffer is empty. Fill it.
if len(bb.blobs) > 0 {
// Read the first blob entirely into the read buffer.
// TODO: shortcut for if len(p) >= blob.Size()
bb.roff = 0
bb.rbuf = bb.rbuf[:cap(bb.rbuf)]
tblob := bb.blobs[0]
bb.blobs = bb.blobs[1:]
if nn, err := tblob.blob.ReadAt(bb.rbuf, 0); err != nil {
bb.err = err
return err
} else if nn != len(bb.rbuf) {
panic("sqlitex.Buffer: short read from blob")
}
bb.free(tblob)
return nil
}
if len(bb.wbuf) > 0 {
// No blobs. Swap the write buffer bytes here directly.
bb.rbuf, bb.wbuf = bb.wbuf, bb.rbuf[:0]
bb.roff = 0
}
if bb.roff == len(bb.rbuf) {
return io.EOF
}
return nil
}
func (bb *Buffer) ReadByte() (byte, error) {
if bb.err != nil {
return 0, bb.err
}
if err := bb.rbufFill(); err != nil {
return 0, err
}
c := bb.rbuf[bb.roff]
bb.roff++
return c, nil
}
func (bb *Buffer) Read(p []byte) (n int, err error) {
if bb.err != nil {
return 0, bb.err
}
if err := bb.rbufFill(); err != nil {
return 0, err
}
if bb.roff == len(bb.rbuf) {
return 0, io.EOF
}
n = copy(p, bb.rbuf[bb.roff:])
bb.roff += n
return n, nil
}
func (bb *Buffer) Len() (n int64) {
n = int64(len(bb.rbuf) - bb.roff)
n += int64(cap(bb.rbuf) * len(bb.blobs))
n += int64(len(bb.wbuf))
return n
}
func (bb *Buffer) Cap() (n int64) {
pageSize := int64(cap(bb.rbuf))
return (2 + int64(len(bb.blobs)+len(bb.freelist))) * pageSize
}
func (bb *Buffer) Reset() {
bb.rbuf = bb.rbuf[:0]
bb.wbuf = bb.wbuf[:0]
bb.roff = 0
bb.freelist = append(bb.freelist, bb.blobs...)
bb.blobs = nil
}
func (bb *Buffer) Close() error {
close := func(tblob tblob) {
err := tblob.blob.Close()
if bb.err == nil {
bb.err = err
}
}
for _, tblob := range bb.blobs {
close(tblob)
}
for _, tblob := range bb.freelist {
close(tblob)
}
stmt := bb.conn.Prep("DELETE FROM BlobBuffer WHERE rowid = $rowid;")
del := func(tblob tblob) {
stmt.Reset()
stmt.SetInt64("$rowid", tblob.rowid)
if _, err := stmt.Step(); err != nil && bb.err == nil {
bb.err = err
}
}
for _, tblob := range bb.blobs {
del(tblob)
}
for _, tblob := range bb.freelist {
del(tblob)
}
bb.blobs = nil
bb.freelist = nil
return bb.err
}