add QueryBinary, an alloc-free way to read all rows into a buffer

WIP; goal is alloc-free reads of a query into a Go-provided buffer.
Go code can then parse the simple binary format and alloc if needed
(doing its own cache lookups, including alloc-free m[string([]byte)]
lookups, and returning existing Views if data is unmodified)

Signed-off-by: Brad Fitzpatrick <[email protected]>

Author: bradfitz

binary.go

@@ -0,0 +1,170 @@
+// Copyright (c) 2023 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package sqlite
+
+import (
+	"context"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"math"
+	"sync"
+
+	"github.com/tailscale/sqlite/sqliteh"
+	"golang.org/x/sys/cpu"
+)
+
+type driverConnRawCall struct {
+	f func(driverConn any) error
+
+	// results
+	dc *conn
+	ok bool
+}
+
+var driverConnRawCallPool = &sync.Pool{
+	New: func() any {
+		c := new(driverConnRawCall)
+		c.f = func(driverConn any) error {
+			c.dc, c.ok = driverConn.(*conn)
+			return nil
+		}
+		return c
+	},
+}
+
+func getDriverConn(sc SQLConn) (dc *conn, ok bool) {
+	c := driverConnRawCallPool.Get().(*driverConnRawCall)
+	defer driverConnRawCallPool.Put(c)
+	err := sc.Raw(c.f)
+	if err != nil {
+		return nil, false
+	}
+	return c.dc, c.ok
+}
+
+func QueryBinary(ctx context.Context, sqlconn SQLConn, optScratch []byte, query string, args ...any) (BinaryResults, error) {
+	c, ok := getDriverConn(sqlconn)
+	if !ok {
+		return nil, errors.New("sqlconn is not of expected type")
+	}
+	st, err := c.prepare(ctx, query, IsPersist(ctx))
+	if err != nil {
+		return nil, err
+	}
+	buf := optScratch
+	if len(buf) == 0 {
+		buf = make([]byte, 128)
+	}
+	for {
+		st.stmt.ResetAndClear()
+		// TODO(bradfitz): bind args
+		n, err := st.stmt.StepAllBinary(buf)
+		if err == nil {
+			return BinaryResults(buf[:n]), nil
+		}
+		if e, ok := err.(sqliteh.BufferSizeTooSmallError); ok {
+			buf = make([]byte, e.EncodedSize)
+			continue
+		}
+		return nil, err
+	}
+}
+
+// BinaryResults is the result of QueryBinary.
+//
+// You should not depend on its specific format and parse it via its methods
+// instead.
+type BinaryResults []byte
+
+type BinaryToken struct {
+	StartRow bool
+	EndRow   bool
+	EndRows  bool
+	IsInt    bool // if so, use Int() method
+	IsFloat  bool // if so, use Float() method
+	IsNull   bool
+	IsBytes  bool
+	Error    bool
+
+	x     uint64
+	Bytes []byte
+}
+
+func (t *BinaryToken) String() string {
+	switch {
+	case t.StartRow:
+		return "start-row"
+	case t.EndRow:
+		return "end-row"
+	case t.EndRows:
+		return "end-rows"
+	case t.IsNull:
+		return "null"
+	case t.IsInt:
+		return fmt.Sprintf("int: %v", t.Int())
+	case t.IsFloat:
+		return fmt.Sprintf("float: %g", t.Float())
+	case t.IsBytes:
+		return fmt.Sprintf("bytes: %q", t.Bytes)
+	case t.Error:
+		return "error"
+	default:
+		return "unknown"
+	}
+}
+
+func (t *BinaryToken) Int() int64     { return int64(t.x) }
+func (t *BinaryToken) Float() float64 { return math.Float64frombits(t.x) }
+
+func (r *BinaryResults) Next() BinaryToken {
+	if len(*r) == 0 {
+		return BinaryToken{Error: true}
+	}
+	first := (*r)[0]
+	*r = (*r)[1:]
+	switch first {
+	default:
+		return BinaryToken{Error: true}
+	case '(':
+		return BinaryToken{StartRow: true}
+	case ')':
+		return BinaryToken{EndRow: true}
+	case 'E':
+		return BinaryToken{EndRows: true}
+	case 'n':
+		return BinaryToken{IsNull: true}
+	case 'i', 'f':
+		if len(*r) < 8 {
+			return BinaryToken{Error: true}
+		}
+		t := BinaryToken{IsInt: first == 'i', IsFloat: first == 'f'}
+		if cpu.IsBigEndian {
+			t.x = binary.BigEndian.Uint64((*r)[:8])
+		} else {
+			t.x = binary.LittleEndian.Uint64((*r)[:8])
+		}
+		*r = (*r)[8:]
+		return t
+	case 'b':
+		if len(*r) < 8 {
+			return BinaryToken{Error: true}
+		}
+		t := BinaryToken{IsBytes: true}
+		var n int64
+		if cpu.IsBigEndian {
+			n = int64(binary.BigEndian.Uint64((*r)[:8]))
+		} else {
+			n = int64(binary.LittleEndian.Uint64((*r)[:8]))
+		}
+		*r = (*r)[8:]
+		if int64(len(*r)) < n {
+			return BinaryToken{Error: true}
+		}
+		t.Bytes = (*r)[:n]
+		*r = (*r)[n:]
+		return t
+	}
+}

binary_test.go

@@ -0,0 +1,110 @@
+// Copyright (c) 2023 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package sqlite
+
+import (
+	"context"
+	"math"
+	"reflect"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+func TestQueryBinary(t *testing.T) {
+	ctx := WithPersist(context.Background())
+	db := openTestDB(t)
+	exec(t, db, "CREATE TABLE t (id INTEGER PRIMARY KEY, f REAL, txt TEXT, blb BLOB)")
+	exec(t, db, "INSERT INTO t VALUES (?, ?, ?, ?)", math.MinInt64, 1.0, "text-a", "blob-a")
+	exec(t, db, "INSERT INTO t VALUES (?, ?, ?, ?)", -1, -1.0, "text-b", "blob-b")
+	exec(t, db, "INSERT INTO t VALUES (?, ?, ?, ?)", 0, 0, "text-c", "blob-c")
+	exec(t, db, "INSERT INTO t VALUES (?, ?, ?, ?)", 20, 2, "text-d", "blob-d")
+	exec(t, db, "INSERT INTO t VALUES (?, ?, ?, ?)", math.MaxInt64, nil, "text-e", "blob-e")
+	exec(t, db, "INSERT INTO t VALUES (?, ?, ?, ?)", 42, 0.25, "text-f", nil)
+	exec(t, db, "INSERT INTO t VALUES (?, ?, ?, ?)", 43, 1.75, "text-g", nil)
+
+	conn, err := db.Conn(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	buf, err := QueryBinary(ctx, conn, make([]byte, 100), "SELECT * FROM t ORDER BY id")
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Logf("Got %d bytes: %q", len(buf), buf)
+
+	var got []string
+	iter := buf
+	for len(iter) > 0 {
+		t := iter.Next()
+		got = append(got, t.String())
+		if t.Error {
+			break
+		}
+	}
+	want := []string{
+		"start-row", "int: -9223372036854775808", "float: 1", "bytes: \"text-a\"", "bytes: \"blob-a\"", "end-row",
+		"start-row", "int: -1", "float: -1", "bytes: \"text-b\"", "bytes: \"blob-b\"", "end-row",
+		"start-row", "int: 0", "float: 0", "bytes: \"text-c\"", "bytes: \"blob-c\"", "end-row",
+		"start-row", "int: 20", "float: 2", "bytes: \"text-d\"", "bytes: \"blob-d\"", "end-row",
+		"start-row", "int: 42", "float: 0.25", "bytes: \"text-f\"", "null", "end-row",
+		"start-row", "int: 43", "float: 1.75", "bytes: \"text-g\"", "null", "end-row",
+		"start-row", "int: 9223372036854775807", "null", "bytes: \"text-e\"", "bytes: \"blob-e\"", "end-row",
+		"end-rows",
+	}
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("wrong results\n got: %q\nwant: %q\n\ndiff:\n%s", got, want, cmp.Diff(want, got))
+	}
+
+	allocs := int(testing.AllocsPerRun(10000, func() {
+		_, err := QueryBinary(ctx, conn, buf, "SELECT * FROM t")
+		if err != nil {
+			t.Fatal(err)
+		}
+	}))
+	const maxAllocs = 5 // as of Go 1.20
+	if allocs > maxAllocs {
+		t.Errorf("allocs = %v; want max %v", allocs, maxAllocs)
+	}
+}
+
+func BenchmarkQueryBinaryParallel(b *testing.B) {
+	ctx := WithPersist(context.Background())
+	db := openTestDB(b)
+	exec(b, db, "CREATE TABLE t (id INTEGER PRIMARY KEY, f REAL, txt TEXT, blb BLOB)")
+	exec(b, db, "INSERT INTO t VALUES (?, ?, ?, ?)", 42, 0.25, "text-f", "some big big big big blob so big like so many bytes even")
+
+	b.ResetTimer()
+	b.ReportAllocs()
+	b.RunParallel(func(pb *testing.PB) {
+		conn, err := db.Conn(ctx)
+		if err != nil {
+			b.Error(err)
+			return
+		}
+
+		var buf = make([]byte, 250)
+
+		for pb.Next() {
+			res, err := QueryBinary(ctx, conn, buf, "SELECT id, f, txt, blb FROM t WHERE id=42")
+			if err != nil {
+				b.Error(err)
+				return
+			}
+			t := res.Next()
+			if !t.StartRow {
+				b.Errorf("didn't get start row; got %v", t)
+				return
+			}
+			t = res.Next()
+			if t.Int() != 42 {
+				b.Errorf("got %v; want 42", t)
+				return
+			}
+		}
+	})
+
+}

cgosqlite/cgosqlite.go

@@ -54,6 +54,7 @@ package cgosqlite
 // #include "cgosqlite.h"
 import "C"
 import (
+	"errors"
 	"sync"
 	"time"
 	"unsafe"
@@ -120,6 +121,7 @@ type Stmt struct {
 	// used as scratch space when calling into cgo
 	rowid, changes C.sqlite3_int64
 	duration       C.int64_t
+	encodedSize    C.int
 }
 
 // Open implements sqliteh.OpenFunc.
@@ -416,6 +418,23 @@ func (stmt *Stmt) ColumnDeclType(col int) string {
 	return res
 }
 
+func (stmt *Stmt) StepAllBinary(dstBuf []byte) (n int, err error) {
+	if len(dstBuf) == 0 {
+		return 0, errors.New("zero-length buffer to StepAllBinary")
+	}
+	ret := C.ts_sqlite_step_all(stmt.stmt.int(), (*C.char)(unsafe.Pointer(&dstBuf[0])), C.int(len(dstBuf)), &stmt.encodedSize)
+
+	if int(stmt.encodedSize) > len(dstBuf) {
+		return 0, sqliteh.BufferSizeTooSmallError{
+			EncodedSize: int(stmt.encodedSize),
+		}
+	}
+	if err := errCode(ret); err != nil {
+		return 0, err
+	}
+	return int(stmt.encodedSize), nil
+}
+
 var emptyCStr = C.CString("")
 
 func errCode(code C.int) error { return sqliteh.CodeAsError(sqliteh.Code(code)) }