CSV type affinity (#102)

Use sqlite-createtable-parser compiled to Wasm to parse the CREATE TABLE statement.

util/vtabutil/parse.go

@@ -0,0 +1,145 @@
+package vtabutil
+
+import (
+	"context"
+	"sync"
+
+	_ "embed"
+
+	"github.com/ncruces/go-sqlite3/internal/util"
+	"github.com/tetratelabs/wazero"
+	"github.com/tetratelabs/wazero/api"
+)
+
+const (
+	code = 4
+	base = 8
+)
+
+var (
+	//go:embed parse/sql3parse_table.wasm
+	binary  []byte
+	ctx     context.Context
+	once    sync.Once
+	runtime wazero.Runtime
+)
+
+// Table holds metadata about a table.
+type Table struct {
+	mod api.Module
+	ptr uint32
+	sql string
+}
+
+// Parse parses a [CREATE] or [ALTER TABLE] command.
+//
+// [CREATE]: https://sqlite.org/lang_createtable.html
+// [ALTER TABLE]: https://sqlite.org/lang_altertable.html
+func Parse(sql string) (*Table, error) {
+	once.Do(func() {
+		ctx = context.Background()
+		cfg := wazero.NewRuntimeConfigInterpreter().WithDebugInfoEnabled(false)
+		runtime = wazero.NewRuntimeWithConfig(ctx, cfg)
+	})
+
+	mod, err := runtime.InstantiateWithConfig(ctx, binary, wazero.NewModuleConfig().WithName(""))
+	if err != nil {
+		return nil, err
+	}
+
+	if buf, ok := mod.Memory().Read(base, uint32(len(sql))); ok {
+		copy(buf, sql)
+	}
+	r, err := mod.ExportedFunction("sql3parse_table").Call(ctx, base, uint64(len(sql)), code)
+	if err != nil {
+		return nil, err
+	}
+
+	c, _ := mod.Memory().ReadUint32Le(code)
+	if c == uint32(_MEMORY) {
+		panic(util.OOMErr)
+	}
+	if c != uint32(_NONE) {
+		return nil, ecode(c)
+	}
+	if r[0] == 0 {
+		return nil, nil
+	}
+	return &Table{
+		sql: sql,
+		mod: mod,
+		ptr: uint32(r[0]),
+	}, nil
+}
+
+// Close closes a table handle.
+func (t *Table) Close() error {
+	mod := t.mod
+	t.mod = nil
+	return mod.Close(ctx)
+}
+
+// NumColumns returns the number of columns of the table.
+func (t *Table) NumColumns() int {
+	r, err := t.mod.ExportedFunction("sql3table_num_columns").Call(ctx, uint64(t.ptr))
+	if err != nil {
+		panic(err)
+	}
+	return int(int32(r[0]))
+}
+
+// Column returns data for the ith column of the table.
+//
+// https://sqlite.org/lang_createtable.html#column_definitions
+func (t *Table) Column(i int) Column {
+	r, err := t.mod.ExportedFunction("sql3table_get_column").Call(ctx, uint64(t.ptr), uint64(i))
+	if err != nil {
+		panic(err)
+	}
+	return Column{
+		tab: t,
+		ptr: uint32(r[0]),
+	}
+}
+
+// Column holds metadata about a column.
+type Column struct {
+	tab *Table
+	ptr uint32
+}
+
+// Type returns the declared type of a column.
+//
+// https://sqlite.org/lang_createtable.html#column_data_types
+func (c Column) Type() string {
+	r, err := c.tab.mod.ExportedFunction("sql3column_type").Call(ctx, uint64(c.ptr))
+	if err != nil {
+		panic(err)
+	}
+	if r[0] == 0 {
+		return ""
+	}
+	off, _ := c.tab.mod.Memory().ReadUint32Le(uint32(r[0]) + 0)
+	len, _ := c.tab.mod.Memory().ReadUint32Le(uint32(r[0]) + 4)
+	return c.tab.sql[off-base : off+len-base]
+}
+
+type ecode uint32
+
+const (
+	_NONE ecode = iota
+	_MEMORY
+	_SYNTAX
+	_UNSUPPORTEDSQL
+)
+
+func (e ecode) Error() string {
+	switch e {
+	case _SYNTAX:
+		return "sql3parse: invalid syntax"
+	case _UNSUPPORTEDSQL:
+		return "sql3parse: unsupported SQL"
+	default:
+		panic(util.AssertErr())
+	}
+}