mirror of
https://github.com/ncruces/go-sqlite3.git
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122 lines
2.6 KiB
Go
122 lines
2.6 KiB
Go
// Package lines provides a virtual table to read large files line-by-line.
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package lines
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import (
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"bufio"
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"bytes"
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"fmt"
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"io"
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"math"
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"os"
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"github.com/ncruces/go-sqlite3"
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)
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// Register registers the lines and lines_read virtual tables.
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// The lines virtual table reads from a database blob or text.
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// The lines_read virtual table reads from a file or an [io.ReaderAt].
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func Register(db *sqlite3.Conn) {
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sqlite3.CreateModule[lines](db, "lines", nil,
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func(db *sqlite3.Conn, arg ...string) (lines, error) {
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err := db.DeclareVtab(`CREATE TABLE x(line TEXT, data HIDDEN)`)
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db.VtabConfig(sqlite3.VTAB_INNOCUOUS)
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return false, err
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})
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sqlite3.CreateModule[lines](db, "lines_read", nil,
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func(db *sqlite3.Conn, arg ...string) (lines, error) {
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err := db.DeclareVtab(`CREATE TABLE x(line TEXT, data HIDDEN)`)
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db.VtabConfig(sqlite3.VTAB_DIRECTONLY)
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return true, err
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})
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}
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type lines bool
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func (l lines) BestIndex(idx *sqlite3.IndexInfo) error {
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for i, cst := range idx.Constraint {
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if cst.Column == 1 && cst.Op == sqlite3.INDEX_CONSTRAINT_EQ && cst.Usable {
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idx.ConstraintUsage[i] = sqlite3.IndexConstraintUsage{
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Omit: true,
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ArgvIndex: 1,
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}
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idx.EstimatedCost = 1e6
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idx.EstimatedRows = 100
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return nil
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}
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}
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return sqlite3.CONSTRAINT
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}
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func (l lines) Open() (sqlite3.VTabCursor, error) {
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return &cursor{reader: bool(l)}, nil
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}
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type cursor struct {
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reader bool
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scanner *bufio.Scanner
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closer io.Closer
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rowID int64
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eof bool
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}
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func (c *cursor) Close() (err error) {
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if c.closer != nil {
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err = c.closer.Close()
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c.closer = nil
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}
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return err
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}
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func (c *cursor) EOF() bool {
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return c.eof
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}
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func (c *cursor) Next() error {
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c.rowID++
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c.eof = !c.scanner.Scan()
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return c.scanner.Err()
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}
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func (c *cursor) RowID() (int64, error) {
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return c.rowID, nil
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}
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func (c *cursor) Column(ctx *sqlite3.Context, n int) error {
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if n == 0 {
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ctx.ResultRawText(c.scanner.Bytes())
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}
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return nil
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}
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func (c *cursor) Filter(idxNum int, idxStr string, arg ...sqlite3.Value) error {
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if err := c.Close(); err != nil {
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return err
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}
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var r io.Reader
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data := arg[0]
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if c.reader {
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if data.Type() == sqlite3.NULL {
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if p, ok := data.Pointer().(io.ReaderAt); ok {
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r = io.NewSectionReader(p, 0, math.MaxInt64)
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}
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} else {
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f, err := os.Open(data.Text())
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if err != nil {
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return err
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}
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c.closer = f
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r = f
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}
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} else if data.Type() != sqlite3.NULL {
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r = bytes.NewReader(data.RawBlob())
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}
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if r == nil {
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return fmt.Errorf("lines: unsupported argument:%.0w %v", sqlite3.MISMATCH, data.Type())
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}
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c.scanner = bufio.NewScanner(r)
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c.rowID = 0
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return c.Next()
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}
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