X on generating own sqlite query wrappers

b66bd11f · Kirill Smelkov · 18be70c7 · b66bd11f
Commit b66bd11f authored Mar 18, 2018 by Kirill Smelkov
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go/neo/storage/sqlite/goquery.patch go/neo/storage/sqlite/goquery.patch +1755 -0

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--- a/go/neo/storage/sqlite/goquery.patch
+++ b/go/neo/storage/sqlite/goquery.patch
+diff --git a/go/neo/storage/sqlite/goquery.go b/go/neo/storage/sqlite/goquery.go
+new file mode 100644
+index 00000000..ce72a4d7
+--- /dev/null
+++ b/go/neo/storage/sqlite/goquery.go
+@@ -0,0 +1,1277 @@
+// Copyright (C) 2017-2018  Nexedi SA and Contributors.
+//                          Kirill Smelkov <kirr@nexedi.com>
+//
+// This program is free software: you can Use, Study, Modify and Redistribute
+// it under the terms of the GNU General Public License version 3, or (at your
+// option) any later version, as published by the Free Software Foundation.
+//
+// You can also Link and Combine this program with other software covered by
+// the terms of any of the Free Software licenses or any of the Open Source
+// Initiative approved licenses and Convey the resulting work. Corresponding
+// source of such a combination shall include the source code for all other
+// software used.
+//
+// This program is distributed WITHOUT ANY WARRANTY; without even the implied
+// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+//
+// See COPYING file for full licensing terms.
+// See https://www.nexedi.com/licensing for rationale and options.
+
+// +build ignore
+
+/*
+Goquery XXX
+
+Goquery was inspired by lab.nexedi.com/kirr/go123/tracing/cmd/gotrace.
+(https://lab.nexedi.com/kirr/go123/blob/master/tracing/cmd/gotrace/gotrace.go)
+
+FIXME FIXME FIXME factor-out special-comments parsing + writeout functionality
+into package common to gotrace & goquery to avoid duplicating code. FIXME FIXME FIXME !!!
+*/
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"flag"
+	"fmt"
+	"go/ast"
+	"go/build"
+	"go/parser"
+	"go/token"
+	"go/types"
+	"io"
+	"io/ioutil"
+	"log"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+	"text/template"
+
+	"golang.org/x/tools/go/loader"
+
+	"lab.nexedi.com/kirr/go123/prog"
+	"lab.nexedi.com/kirr/go123/xerr"
+)
+
+
+// Query represent one sql:query1 declaration
+//
+// XXX + sql:exec & sql:query - all residing in one type
+type Query struct {
+	Pos  token.Position
+	Pkgq *Package // package this query is part of
+
+	// declaration of function to make the query.
+	// the declaration is constructe on the fly via converting e.g.
+	//
+	//	//sql:query1 sql_load(oid zodb.Oid, at zodb.Tid) (serial zodb.Tid, ...)
+	//
+	// into
+	//
+	//	func sql_load(oid zodb.Oid, at zodb.Tid) (serial zodb.Tid, ..., error)
+	//
+	// when sql:query1 is parsed the func declaration is not added anywhere
+	// in the sources - just its AST + package (XXX) is virtually
+	// constructed.
+	//
+	// See parseQuery for details.
+	*ast.FuncDecl
+
+	// query SQL text itself.
+	Sql string
+}
+
+
+// Package represents query-related information about a package.
+type Package struct {
+	Pkgi *loader.PackageInfo // original non-augmented package
+
+	Queryv []*Query // queries this package defines
+
+	// original package is augmented with query code
+	// information about query code is below:
+
+	queryFilev []*ast.File    // files for added sql:query1 + friends funcs
+	queryFset  *token.FileSet // fset for ^^^
+
+	queryChecker  *types.Checker // to typecheck ^^^
+	queryPkg      *types.Package // original package augmented with ^^^
+	queryTypeInfo *types.Info    // typeinfo for ^^^
+
+}
+
+// parseQuery parses query definition into Query.
+//
+// text is text argument after "//sql:query1 ".
+// XXX need prefix to decide whether it is exec or query or query1
+// XXX + sql text itself.
+func (p *Package) parseQuery(tag string, srcfile *ast.File, pos token.Position, text string) (*Query, error) {
+	posErr := func(format string, argv ...interface{}) error {
+		return fmt.Errorf("%v: "+format, append([]interface{}{pos}, argv...)...)
+	}
+
+	// prepare artificial package with query definition as func declaration
+	buf := &Buffer{}
+	buf.emit("package %s", p.Pkgi.Pkg.Name())
+
+	// add all imports from original source file
+	// so that inside it all looks like as if it was in original source context
+	buf.emit("\nimport (")
+
+	for _, imp := range srcfile.Imports {
+		impline := ""
+		if imp.Name != nil {
+			impline += imp.Name.Name + " "
+		}
+		impline += imp.Path.Value
+		buf.emit("\t%s", impline)
+	}
+
+	buf.emit(")")
+
+	// func itself
+	buf.emit("\nfunc " + text)
+
+	// now parse/typecheck
+	filename := fmt.Sprintf("%v:%v+%s %v", pos.Filename, pos.Line, tag, text)
+	//println("---- 8< ----", filename)
+	//println(buf.String())
+	//println("---- 8< ----")
+	tf, err := parser.ParseFile(p.queryFset, filename, buf.String(), 0)
+	if err != nil {
+		return nil, err // already has pos' as prefix
+	}
+
+	p.queryFilev = append(p.queryFilev, tf)
+
+	// must be:
+	// GenDecl{IMPORT}
+	// FuncDecl
+	if len(tf.Decls) != 2 {
+		return nil, posErr("%s must be func-like", tag)
+	}
+
+	declf, ok := tf.Decls[1].(*ast.FuncDecl)
+	if !ok {
+		return nil, posErr("%s must be func-like, not %v", tag, tf.Decls[0])
+	}
+	// XXX ok to allow methods (declf.Recv != nil) ?
+
+	// typecheck prepared file to get query func argument types
+	// (type information lands into p.queryTypeInfo)
+	err = p.queryChecker.Files([]*ast.File{tf})
+	if err != nil {
+		return nil, err // already has pos' as prefix
+	}
+
+	return &Query{Pos: pos, Pkgq: p, FuncDecl: declf}, nil
+}
+
+
+// progImporter is types.Importer that imports packages from loaded loader.Program
+type progImporter struct {
+	prog *loader.Program
+}
+
+func (pi *progImporter) Import(path string) (*types.Package, error) {
+	pkgi := pi.prog.Package(path)
+	if pkgi == nil {
+		return nil, fmt.Errorf("package %q not found", path)
+	}
+
+	return pkgi.Pkg, nil
+}
+
+// packageSQL returns information about SQL-queries defined by a package.
+func packageSQL(prog *loader.Program, pkgi *loader.PackageInfo) (*Package, error) {
+	// prepare Package with typechecker ready to typecheck query files
+	// (to get query func argument types)
+	qconf := &types.Config{
+		Importer: &progImporter{prog},
+
+		// to ignore query calls from original package code
+		IgnoreFuncBodies: true,
+
+		// we take imports from original source file verbatim,	XXX needed?
+		// but most of them probably won't be used.
+		DisableUnusedImportCheck: true,
+	}
+
+	qfset := prog.Fset
+	qpkg := types.NewPackage(pkgi.Pkg.Path(), pkgi.Pkg.Name())
+	qinfo := &types.Info{Types: make(map[ast.Expr]types.TypeAndValue)}
+
+	p := &Package{
+		Pkgi: pkgi,
+
+		// XXX vvv do we need separate field for queryFset if it is = prog.Fset?
+		queryFset:     qfset,
+		queryChecker:  types.NewChecker(qconf, qfset, qpkg, qinfo),
+		queryPkg:      qpkg,
+		queryTypeInfo: qinfo,
+	}
+
+	// preload original package files into query package
+	err := p.queryChecker.Files(p.Pkgi.Files)
+	if err != nil {
+		// must not happen
+		panic(fmt.Errorf("%v: error rechecking original package: %v", pkgi.Pkg.Path(), err))
+	}
+
+	// go through files of the original package and process //trace: directives
+	//
+	// FIXME we currently don't process cgo files as go/loader passes to us	XXX might be fixed already
+	// already preprocessed results with comments stripped, not original source.	XXX -> recheck
+	// Maybe in some time it will be possible to have AST of original source:
+	// https://golang.org/issues/16623
+	for _, file := range pkgi.Files { // ast.File
+		for _, commgroup := range file.Comments { // ast.CommentGroup
+			for i, comment := range commgroup.List { // ast.Comment
+				pos := prog.Fset.Position(comment.Slash)
+				//fmt.Printf("%v %q\n", pos, comment.Text)
+
+				// only directives starting from beginning of line
+				if pos.Column != 1 {
+					continue
+				}
+
+				if !strings.HasPrefix(comment.Text, "//sql:") {
+					continue
+				}
+
+				textv := strings.SplitN(comment.Text, " ", 2)
+				if len(textv) != 2 {
+					return nil, fmt.Errorf("%v: invalid directive format", pos)
+				}
+
+				directive, arg := textv[0], textv[1]
+				directive = directive[2:] // strip '^//'
+				switch directive {
+				case "sql:query1":
+					//fmt.Println("*", textv)
+					query, err := p.parseQuery(directive, file, pos, arg)
+					if err != nil {
+						return nil, err
+					}
+
+					// the rest of comment group becomes query text
+					for _, tail := range commgroup.List[i+1:] {
+						line := tail.Text
+						line = strings.TrimPrefix(line, "//")
+						line = strings.TrimPrefix(line, "\t")
+						if query.Sql != "" {
+							query.Sql += "\n"
+						}
+						query.Sql += line
+					}
+					// no trailing \n
+					query.Sql = strings.TrimSuffix(query.Sql, "\n")
+
+					// XXX needed here? - better append in parseTraceEvent
+					p.Queryv = append(p.Queryv, query)
+
+				default:
+					return nil, fmt.Errorf("%v: unknown directive %q", pos, directive)
+				}
+			}
+		}
+	}
+
+	// queries go in canonical order
+	sort.Sort(byQueryName(p.Queryv))
+
+	return p, nil
+}
+
+// byQueryName provides []*Query ordering by query name
+type byQueryName []*Query
+
+func (v byQueryName) Less(i, j int) bool { return v[i].Name.Name < v[j].Name.Name }
+func (v byQueryName) Swap(i, j int)      { v[i], v[j] = v[j], v[i] }
+func (v byQueryName) Len() int           { return len(v) }
+
+
+// ----------------------------------------
+
+// govar represents Go variable.
+//
+// It has name and type. A variable can be part of either passed or returned
+// arguments of a query.
+type govar struct {
+	Name	string
+	Type	types.Type
+}
+
+// Xargv returns query arguments as []govar
+func (q *Query) Xargv() (argv []govar) {
+	for _, field := range q.FuncDecl.Type.Params.List {
+		typ := q.Pkgq.queryTypeInfo.Types[field.Type].Type
+		for _, name := range field.Names {
+			argv = append(argv, govar{name.Name, typ})
+		}
+	}
+	return argv
+}
+
+// Xretv returns query results as []govar
+func (q *Query) Xretv() (retv []govar) {
+	for _, field := range q.FuncDecl.Type.Results.List {
+		typ := q.Pkgq.queryTypeInfo.Types[field.Type].Type
+		for _, name := range field.Names {
+			retv = append(retv, govar{name.Name, typ})
+		}
+	}
+	return retv
+}
+
+func fieldvStr(fieldv []*ast.Field) string {
+	argv := []string{}
+
+	for _, field := range fieldv {
+		for _, name := range field.Names {
+			argv = append(argv, name.Name)
+		}
+	}
+
+	return strings.Join(argv, ", ")
+}
+
+// Argv returns comma-separated argument-list		XXX neeed?
+func (q *Query) Argv() string {
+	return fieldvStr(q.FuncDecl.Type.Params.List)
+}
+
+// XXX
+func (q *Query) Retv() string {
+	return fieldvStr(q.FuncDecl.Type.Results.List)
+}
+
+// ArgvTyped returns argument list with types. 		XXX needed?
+//
+// types are qualified relative to original package.
+func (q *Query) ArgvTyped() string {
+	return q.ArgvTypedRelativeTo(q.Pkgq.queryPkg, nil)
+}
+
+// RetvTyped returns return list with types.
+//
+// types are qualified relative to original package.
+func (q *Query) RetvTyped() string {
+	return q.RetvTypedRelativeTo(q.Pkgq.queryPkg, nil)
+}
+
+// pkgQualifier returns qualifier that qualifies names relative to pkg.
+//
+// importedAs specifies under which name a package was imported, if name was explicitly set.
+func pkgQualifier(pkg *types.Package, importedAs map[string]string /*pkgpath -> pkgname*/) func(*types.Package) string {
+	return func(p *types.Package) string {
+		// specified package - unqualified
+		if p == pkg {
+			return ""
+		}
+
+		// qualify as explicitly named
+		pkgname := importedAs[p.Path()]
+		if pkgname != "" {
+			return pkgname
+		}
+
+		// default qualification
+		return p.Name()
+	}
+}
+
+// fieldv should be either params or results
+func (q *Query) fieldvTypedRelativeTo(fieldv []*ast.Field, pkg *types.Package, importedAs map[string]string /*pkgpath -> pkgname*/) string {
+	argv := []string{}
+
+	// default qualifier - relative to original package
+	qf := pkgQualifier(pkg, importedAs)
+
+	for _, field := range fieldv {
+		namev := []string{}
+		for _, name := range field.Names {
+			namev = append(namev, name.Name)
+		}
+
+		arg := strings.Join(namev, ", ")
+		typ := q.Pkgq.queryTypeInfo.Types[field.Type].Type
+		arg += " " + types.TypeString(typ, qf)
+
+		argv = append(argv, arg)
+	}
+
+	return strings.Join(argv, ", ")
+}
+
+// ArgvTypedRelativeTo returns argument list with types qualified relative to specified package.
+//
+// importedAs specifies under which name a package was imported, if name was explicitly set
+func (q *Query) ArgvTypedRelativeTo(pkg *types.Package, importedAs map[string]string /*pkgpath -> pkgname*/) string {
+	return q.fieldvTypedRelativeTo(q.FuncDecl.Type.Params.List, pkg, importedAs)
+}
+
+// XXX
+func (q *Query) RetvTypedRelativeTo(pkg *types.Package, importedAs map[string]string /*pkgpath -> pkgname*/) string {
+	return q.fieldvTypedRelativeTo(q.FuncDecl.Type.Results.List, pkg, importedAs)
+}
+
+// NeedPkgv returns packages that are needed for types used in query.
+func (q *Query) NeedPkgv() []string {
+	pkgset := StrSet{ /*pkgpath*/ }
+	qf := func(pkg *types.Package) string {
+		// if we are called - pkg is used
+		pkgset.Add(pkg.Path())
+		return "" // don't care
+	}
+
+	for _, field := range q.FuncDecl.Type.Params.List {
+		typ := q.Pkgq.queryTypeInfo.Types[field.Type].Type
+		_ = types.TypeString(typ, qf)
+	}
+	for _, field := range q.FuncDecl.Type.Results.List {
+		typ := q.Pkgq.queryTypeInfo.Types[field.Type].Type
+		_ = types.TypeString(typ, qf)
+	}
+
+	return pkgset.Itemv()
+}
+
+
+// xtmpl creates/parses template and panic if the template is invalid.
+func xtmpl(name, text string) *template.Template {
+	return template.Must(template.New(name).Funcs(template.FuncMap{
+		"add":		func(a, b int) int { return a + b },
+		"isarray":	isarray,
+		"asarray":	asarray,
+		"sqliteType":	sqliteType,
+		"sqliteBind":	sqliteBind,
+		"cstrlit":	cstrlit,
+	}).Parse(text))
+}
+
+// cstrlit converts string s to C string literal.
+func cstrlit(s string) string {
+	sv := strings.Split(s, "\n")
+	for i := range sv {
+		sv[i] = "\"" + sv[i] + "\""
+	}
+	return strings.Join(sv, "\n")
+}
+
+// query1GoTmpl is Go code template generated for one query1.
+var query1GoTmpl = xtmpl("query1/go", `
+// query1: {{.Name}}({{.Argv}}) ({{.Retv}})
+func {{.Name}}(_db db, {{.ArgvTyped}}) ({{.RetvTyped}}, err error) {
+	_conn, err := _db.getConn()
+	if err != nil {
+		return
+	}
+
+	_r := C.{{.Name}}(_conn
+		{{- range .Xargv -}}
+			, {{if eq .Type.String "string" -}}	{{/* no need to cast to C */ -}}
+				{{.Name}}
+			{{- else -}}
+				{{- /* cast to C */ -}}
+				C.{{- .Cinput.Ctype}}({{.Name}})
+			{{- end -}}
+		{{- end}})
+
+	_ = _r
+	_cp.putConn(_conn)
+	panic("TODO")
+}
+`)
+
+// query1CTmpl is C code template generated for one query1.
+var query1CTmpl = xtmpl("query1/c", `
+// query1: {{.Name}}({{.Argv}}) ({{.Retv}})
+
+{{/* result type for this query */ -}}
+typedef struct {
+{{- range .Xretv}}
+    {{- range .Coutput }}
+	{{.Ctype}}	{{.Cname}};
+    {{- end }}
+{{- end}}
+
+	int rc;
+} {{.Name}}_ret;
+
+{{/* function to perform the query */ -}}
+{{.Name}}_ret {{.Name}}(Conn *conn {{- range .Xargv -}}
+, {{.Cinput -}}
+{{end}}) {
+	{{.Name}}_ret r;
+	sqlite3_stmt *qstmt;
+	int rc;
+
+	qstmt = conn->_qstmt_{{.Name}};
+	conn->_qstmt_{{.Name}} = NULL;	// XXX just in case
+	if (!qstmt) {
+		rc = sqlite3_prepare_v2(conn->db,
+{{cstrlit .Sql}}, -1, &qstmt, NULL);
+		if (rc != SQLITE_OK) {
+			r.rc = rc;
+			return r;
+		}
+	}
+
+	// bind arguments
+	//
+	// NOTE for strings we pass SQLITE_STATIC which means to SQLite "that
+	// the content pointer is constant and will never change". It is valid
+	// to do so because we'll unbind all arguments when returning.
+{{- range $i, $_ := .Xargv}}
+    {{- $bind := .Type | sqliteBind -}}
+    {{- if eq $bind "text"}}  {{- /* go string */}}
+	rc = sqlite3_bind_text(qstmt, {{add $i 1}}, gostr_ptr({{.Name}}), gostr_len({{.Name}}), SQLITE_STATIC);
+    {{- else}}
+	rc = sqlite3_bind_{{$bind}}(qstmt, {{add $i 1}}, {{.Name}});
+    {{- end}}
+	OK(rc);
+{{- end}}
+
+	// run the query
+	rc = sqlite3_step(qstmt);
+	switch (rc) {
+	case SQLITE_ROW:
+		{{/* ok */ -}}
+		break;	// ok
+
+	case SQLITE_DONE:
+		{{/* nothing */ -}}
+		r.rc = rc;
+		goto out;
+
+	default:
+		{{/* not ok */ -}}
+		r.rc = rc;
+		goto out;
+	}
+
+	// we got data -> read columns
+{{- range $i, $_ := .Xretv}}
+	// ... {{.Name}}
+	switch ( sqlite3_column_type(qstmt, {{add $i 1}}) ) {
+	case {{.Type | sqliteType}}:
+		{{/* ok */ -}}
+		// XXX also NULL?
+		break;
+
+	default:
+		r.rc = SQLITE_MISMATCH;		// XXX details
+		return r;
+	}
+{{$bind := .Type | sqliteBind -}}
+    {{- if eq $bind "text"}}  {{- /* -> will be converted to go string by caller */}}
+	r.{{.Name}}_ptr = sqlite3_column_text (qstmt, {{add $i 1}});
+	r.{{.Name}}_len = sqlite3_column_bytes(qstmt, {{add $i 1}});
+    {{- else if eq $bind "blob"}}
+
+      {{- if .Type | isarray }}	{{- /* fixed size array*/}}
+	{{- $tarr := .Type | asarray}}
+	// array - check lenght matching + read directly here
+	if ({{$tarr.Len}} != sqlite3_column_bytes(qstmt, {{add $i 1}})) {
+		r.rc = SQLITE_MISMATCH;		// XXX detail
+		goto out;
+	}
+	memcpy(r.{{.Name}}, sqlite3_column_blob(qstmt, {{add $i 1}}), {{$tarr.Len}});
+
+      {{- else}}	{{- /* blob */}}
+	// TODO blob
+      {{- end}}
+    {{- else}}
+	r.{{.Name}} = sqlite3_column_{{.Type | sqliteBind}}(qstmt, {{add $i 1}});
+    {{- end}}
+{{end}}
+
+	r.rc = SQLITE_OK;
+
+out:
+	// clear bindings so that we put qstmt back with all arguments cleared.
+	// in particular we HAVE to unbind go strings memory (see bind part for why).
+	//
+	// ignore rc - sqlite3_clear_bindings always returns SQLITE_OK.
+	rc = sqlite3_clear_bindings(qstmt);
+	assert(rc == SQLITE_OK);
+
+	// reset the statement so it can be executed again.
+	// ignore rc as sqlite3_reset returns error of last sqlite3_step.
+	(void)sqlite3_reset(qstmt);
+
+	// put statment back to conn for reuse
+	conn->_qstmt_{{.Name}} = qstmt;
+
+	return r;
+}
+`)
+
+
+var cBasicTypes = map[types.BasicKind]string {
+	types.Int:	"int",
+	types.Int8:	"int8_t",
+	types.Int32:	"int32_t",
+	types.Int64:	"int64_t",
+	types.Uint:	"unsigned",
+	types.Uint8:	"uint8_t",
+	types.Uint32:	"uint32_t",
+	types.Uint64:	"uint64_t",
+
+	//types.String:	"_GoString_",	string is handled specially
+	// XXX more?
+}
+
+var sqliteBasicTypes = map[types.BasicKind]string {
+	types.Int:	"SQLITE_INTEGER",
+	types.Int8:	"SQLITE_INTEGER",
+	types.Int32:	"SQLITE_INTEGER",
+	types.Int64:	"SQLITE_INTEGER",
+	types.Uint:	"SQLITE_INTEGER",
+	types.Uint8:	"SQLITE_INTEGER",
+	types.Uint32:	"SQLITE_INTEGER",
+	types.Uint64:	"SQLITE_INTEGER",
+
+	types.String:	"SQLITE_TEXT",
+	// XXX more?
+}
+
+
+func isarray(typ types.Type) bool {
+	_, err := asarray(typ)
+	return err == nil
+}
+
+func asarray(typ types.Type) (*types.Array, error) {
+	atyp, ok := typ.Underlying().(*types.Array)
+	var err error
+	if !ok {
+		err = fmt.Errorf("type %q is not array", typ)
+	}
+	return atyp, err
+}
+
+// cvar represent C variable.
+//
+// It has C name and C type. A C-variable can be part of either passed or
+// returned arguments in C-part of query implementation.
+//
+// for arrays name, not type, contains trailing [n].	XXX ok?
+type cvar struct {
+	Cname	string
+	Ctype	string
+}
+
+func (v cvar) String() string {
+	return v.Ctype + " " + v.Cname
+}
+
+// Cinput converts Go variable to C variable as how it should be used for
+// implementing input parameters.
+func (v *govar) Cinput() (*cvar, error) {
+	cv, err := v.asC(false)
+	if err != nil {
+		return nil, err
+	} else {
+		return &cv[0], nil	// always only 1 element for input
+	}
+}
+
+// Coutput converts Go variable to list of C variables as how it should be used
+// for implementing return arguments.
+//
+// ( we need to potentially map 1 go varible to several C variables e.g. for
+//   returning string / slice: we cannot construct go string from in C code, so
+//   we return raw pointer and length, let corresponding go wrapper construct the
+//   go object, and call C part again to free the resources. )
+func (v *govar) Coutput() ([]cvar, error) {
+	return v.asC(true)
+}
+
+// asC is the worker for Cinput/Coutput
+func (v *govar) asC(output bool) (retv []cvar, _ error) {
+	ret := func(name, typ string) {
+		retv = append(retv, cvar{name, typ})
+	}
+
+	switch u := v.Type.Underlying().(type) {
+	case *types.Basic:
+		switch u.Kind() {
+		case types.String:
+			if output {
+				ret(v.Name + "_ptr", "const char *")
+				ret(v.Name + "_len", "size_t")
+			} else {
+				ret(v.Name, "_GoString_")
+			}
+
+		default:
+			cbasic, ok := cBasicTypes[u.Kind()]
+			if ok {
+				ret(v.Name, cbasic)
+			}
+		}
+
+	case *types.Array:
+		velem := govar{v.Name, u.Elem()}
+		celem, err := velem.Cinput()
+		if err == nil {
+			ret(fmt.Sprintf("%s[%d]", v.Name, u.Len()), celem.Ctype)
+		}
+
+	case *types.Slice:
+		elem, ok := u.Elem().(*types.Basic)
+		if ok && elem.Kind() == types.Byte {
+			if output {
+				ret(v.Name + "_ptr", "const char *")
+				ret(v.Name + "_len", "size_t")
+			} else {
+				// we are passing []byte as string via unsafe to C.
+				// reason: cgo allows to pass strings to C without copying.
+				ret(v.Name, "_GoString_")
+			}
+		}
+	}
+
+	var err error
+	if retv == nil {
+		err = fmt.Errorf("cannot map type %q to C", v.Type)
+	}
+	return retv, err
+}
+
+
+// sqliteType return SQLite type corresponding to typ.
+func sqliteType(typ types.Type) (string, error) {
+	switch u := typ.Underlying().(type) {
+	case *types.Basic:
+		sqliteBasic, ok := sqliteBasicTypes[u.Kind()]
+		if ok {
+			return sqliteBasic, nil
+		}
+
+	case *types.Array:
+		elem, ok := u.Elem().(*types.Basic)
+		if ok && elem.Kind() == types.Byte {
+			return "SQLITE_BLOB", nil
+		}
+
+	case *types.Slice:
+		elem, ok := u.Elem().(*types.Basic)
+		if ok && elem.Kind() == types.Byte {
+			return "SQLITE_BLOB", nil
+		}
+	}
+
+	return "", fmt.Errorf("cannot map type %q to SQLite", typ)
+}
+
+// {} sqliteType -> bind suffix
+var sqliteBindTab = map[string]string {
+	"SQLITE_INTEGER":	"int64",
+	"SQLITE_BLOB":		"blob",
+	"SQLITE_TEXT":		"text",
+
+	// XXX more?
+}
+
+// sqliteBind returns SQLite suffix that should be used in sqlite3_bind_* and
+// sqlite3_column_* for typ.
+func sqliteBind(typ types.Type) (string, error) {
+	styp, err := sqliteType(typ)
+	if err != nil {
+		return "", err
+	}
+
+	sbind, ok := sqliteBindTab[styp]
+	if ok {
+		return sbind, nil
+	}
+
+	return "", fmt.Errorf("cannot map type %q to SQLite bind", typ)
+}
+
+
+
+// ----------------------------------------
+
+// magic begins all files generated by goquery
+const magic = "// Code generated by lab.nexedi.com/kirr/neo/.../goquery; DO NOT EDIT.\n" // XXX
+
+// checkCanWrite checks whether it is safe to write to file at path.
+//
+// it is safe to write when either
+// - the file does not exist, or
+// - it exits but was previously generated by us
+func checkCanWrite(path string) error {
+	f, err := os.Open(path)
+	if e, ok := err.(*os.PathError); ok && os.IsNotExist(e.Err) {
+		return nil
+	}
+
+	defer f.Close()
+	bf := bufio.NewReader(f)
+
+	headline, err := bf.ReadString('\n')
+	if err != nil || headline != magic {
+		return fmt.Errorf("refusing to make output: %v exists but was not generated by goquery", path)
+	}
+
+	return nil
+}
+
+// writeFile writes data to a file at path after checking it is safe to write there
+func writeFile(path string, data []byte) error {
+	err := checkCanWrite(path)
+	if err != nil {
+		return err
+	}
+
+	return ioutil.WriteFile(path, data, 0666)
+}
+
+// removeFile make sure there is no file at path after checking it is safe to write to that file
+func removeFile(path string) error {
+	err := checkCanWrite(path)
+	if err != nil {
+		return err
+	}
+
+	err = os.Remove(path)
+	if e, ok := err.(*os.PathError); ok && os.IsNotExist(e.Err) {
+		err = nil
+	}
+	return err
+}
+
+// Program represents loaded program for tracepoint analysis.			XXX
+//
+// It is generalization of loader.Program due to loader not allowing to
+// construct programs incrementally.
+type Program struct {
+	// list of loader.Programs in use
+	//
+	// We generally need to have several programs because a package can
+	// trace:import another package which is not otherwise imported by
+	// original program.
+	//
+	// Since go/loader does not support incrementally augmenting loaded
+	// program with more packages, we work-around it with having several
+	// progs.
+	progv []*loader.Program
+
+	// config for loading programs
+	loaderConf *loader.Config
+}
+
+// NewProgram constructs new empty Program ready to load packages according to specified build context
+func NewProgram(ctxt *build.Context, cwd string) *Program {
+	// adjust build context to filter-out zquery* files when discovering packages
+	//
+	// we don't load what should be generated by us for 2 reasons:
+	// - code generated could be wrong with older version of the
+	//   tool - it should not prevent from regenerating.
+	// - generated code imports packages which might be not there
+	//   yet in gopath (lab.nexedi.com/kirr/go123/tracing)
+	ctxtReadDir := ctxt.ReadDir
+	if ctxtReadDir == nil {
+		ctxtReadDir = ioutil.ReadDir
+	}
+	ctxtNoZTrace := *ctxt
+	ctxtNoZTrace.ReadDir = func(dir string) ([]os.FileInfo, error) {
+		fv, err := ctxtReadDir(dir)
+		okv := fv[:0]
+		for _, f := range fv {
+			if !strings.HasPrefix(f.Name(), "zquery") {
+				okv = append(okv, f)
+			}
+		}
+		return okv, err
+	}
+
+	p := &Program{}
+	p.loaderConf = &loader.Config{
+		ParserMode:          parser.ParseComments,
+		TypeCheckFuncBodies: func(path string) bool { return false },
+		Build:               &ctxtNoZTrace,
+		Cwd:                 cwd,
+	}
+
+	return p
+}
+
+// Import imports a package and returns associated package info and program
+// under which it was loaded.
+func (p *Program) Import(pkgpath string) (prog *loader.Program, pkgi *loader.PackageInfo, err error) {
+	// let's see - maybe it is already there
+	for _, prog := range p.progv {
+		pkgi := prog.Package(pkgpath)
+		if pkgi != nil {
+			return prog, pkgi, nil
+		}
+	}
+
+	// not found - we have to load new program rooted at pkgpath
+	p.loaderConf.ImportPkgs = nil
+	p.loaderConf.Import(pkgpath)
+
+	prog, err = p.loaderConf.Load()
+	if err != nil {
+		return nil, nil, err
+	}
+
+	if !(len(prog.Created) == 0 && len(prog.Imported) == 1) {
+		panic("import")
+	}
+
+	p.progv = append(p.progv, prog)
+	pkgi = prog.InitialPackages()[0]
+	return prog, pkgi, nil
+}
+
+
+// ---- `goquery gen` ----
+
+// querygen generates code according to query directives in a package @ pkgpath.
+//
+// ctxt is build context for discovering packages
+// cwd is "current" directory for resolving local imports (e.g. packages like "./some/package")
+func querygen(pkgpath string, ctxt *build.Context, cwd string) error {
+	P := NewProgram(ctxt, cwd)
+
+	lprog, pkgi, err := P.Import(pkgpath)
+	if err != nil {
+		return err
+	}
+
+	// determine package directory
+	if len(pkgi.Files) == 0 {
+		return fmt.Errorf("package %s is empty", pkgi.Pkg.Path())
+	}
+
+	pkgdir := filepath.Dir(lprog.Fset.File(pkgi.Files[0].Pos()).Name())
+
+	// query info for this specified package
+	qpkg, err := packageSQL(lprog, pkgi)
+	if err != nil {
+		return err // XXX err ctx
+	}
+
+	// write zquery.{go,c} with code generated for queries
+	zquery_go := filepath.Join(pkgdir, "zquery.go")
+	zquery_h  := filepath.Join(pkgdir, "zquery.h")	// XXX -> .cinc ?
+	if len(qpkg.Queryv) == 0 {
+		err1 := removeFile(zquery_go)
+		err2 := removeFile(zquery_h)
+		return xerr.Merge(err1, err2)
+	}
+
+	// ---- zquery.go ----
+
+	// prologue
+	prologue := &Buffer{}
+	prologue.WriteString(magic)
+	prologue.emit("\npackage %v", qpkg.Pkgi.Pkg.Name())
+	prologue.emit(`// Go code generated for queries.
+
+// #cgo pkg-config: sqlite3
+// #include "./zquery.h"
+import "C"
+
+import (`)
+
+	// pkgpaths of all packages needed for used types
+	needPkg := StrSet{}
+
+	// some packages are imported with explicit name
+	importedAs := map[string]string{} // pkgpath -> pkgname
+
+	text := &Buffer{}
+
+	// code for query definitions
+	for _, query := range qpkg.Queryv {
+		needPkg.Add(query.NeedPkgv()...)
+		err = query1GoTmpl.Execute(text, query)
+		if err != nil {
+			panic(err)
+		}
+	}
+
+	needPkg.Delete(qpkg.Pkgi.Pkg.Path()) // our pkg - no need to import
+	needPkgv := needPkg.Itemv()
+	if len(needPkgv) > 0 {
+		prologue.emit("")
+	}
+
+	for _, needpkg := range needPkgv {
+		pkgname := importedAs[needpkg]
+		if pkgname != "" {
+			pkgname += " "
+		}
+		prologue.emit("\t%s%q", pkgname, needpkg)
+	}
+	prologue.emit(")")
+
+// XXX needed?
+//	// export something so that cgo generates _cgo_export.h
+//	prologue.emit("\n//export _")
+//	prologue.emit("func _() {}")
+
+	prologue.emit(`
+type conn C.Conn
+
+// db represents interface for accessing the database.
+//
+// Database connections can be opened (getConn) and put back to reuse (putConn).
+type db interface {
+	getConn() (*conn, error)
+	putConn(*conn)
+}
+
+func openConn(...) (*conn, error) {
+	// XXX
+}
+
+func (conn *conn) Close() error {
+	// XXX
+}
+`)
+
+	// write output
+	fulltext := append(prologue.Bytes(), text.Bytes()...)
+	err = writeFile(zquery_go, fulltext)
+	if err != nil {
+		return err
+	}
+
+	// ---- zquery.h ----
+
+	// prologue
+	prologue = &Buffer{}
+	prologue.WriteString(magic)
+	prologue.emit(`// C code generated for queries.
+
+#include <sqlite3.h>
+#include <stdint.h>
+#include <string.h>
+#include <assert.h>
+
+//#include "_cgo_export.h"
+
+#define OK(RC) if ((RC) != SQLITE_OK) {	\
+	r.rc = (RC);	\
+	goto out;	\
+}
+
+// cgo does not give us _GoStringPtr & friends in non-preamble.
+// we take it ourselves:
+static inline const char *gostr_ptr(_GoString_ s) { return s.p; }
+static inline size_t      gostr_len(_GoString_ s) { return s.n; }
+
+// Conn represents connection to sqlite database.
+//
+// Conn can be used by only one goroutine simultaneously.
+typedef struct {
+	sqlite3	*db;
+
+	// cached query statements`)
+
+	text = &Buffer{}
+
+	// code for query definitions
+	for _, query := range qpkg.Queryv {
+		needPkg.Add(query.NeedPkgv()...)
+		err = query1CTmpl.Execute(text, query)
+		if err != nil {
+			panic(err)
+		}
+
+		prologue.emit("\tsqlite3_stmt *_qstmt_%s;", query.Name)
+	}
+
+	prologue.emit(`} Conn;`)
+
+	// write output
+	fulltext = append(prologue.Bytes(), text.Bytes()...)
+	err = writeFile(zquery_h, fulltext)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+const genSummary = "generate code according to query annotations"
+
+func genUsage(w io.Writer) {
+	fmt.Fprintf(w,
+		`Usage: goquery gen <package>
+Generate code according to query annotations
+
+  options:
+
+        -h --help       this help text.
+`)
+}
+
+func genMain(argv []string) {
+	flags := flag.FlagSet{Usage: func() { genUsage(os.Stderr) }}
+	flags.Init("", flag.ExitOnError)
+	flags.Parse(argv[1:])
+
+	argv = flags.Args()
+	if len(argv) < 1 {
+		flags.Usage()
+		prog.Exit(2)
+	}
+	pkgpath := argv[0]
+
+	cwd, err := os.Getwd()
+	if err != nil {
+		prog.Fatal(err)
+	}
+
+	err = querygen(pkgpath, &build.Default, cwd)
+	if err != nil {
+		prog.Fatal(err)
+	}
+}
+
+
+// ---- `goquery list` ----
+
+// querylist lists queries defined by a package @ pkgpath.
+//
+// ctxt and cwd are tunables for discovering packages. See querygen for details.
+//
+// TODO support listing by pkgspec (e.g. "./...")
+func querylist(w io.Writer, pkgpath string, ctxt *build.Context, cwd string, verbose bool) error {
+	P := NewProgram(ctxt, cwd)
+
+	// NOTE only listing queries provided by main package, not tests or xtest
+	lprog, pkgi, err := P.Import(pkgpath)
+	if err != nil {
+		return err
+	}
+
+	qpkg, err := packageSQL(lprog, pkgi)
+	if err != nil {
+		return err // XXX err ctx
+	}
+
+	for _, query := range qpkg.Queryv {
+		_, err = fmt.Fprintf(w, "%s:%s\n", query.Pkgq.Pkgi.Pkg.Path(), query.Name)
+		if err != nil {
+			return err
+		}
+		if verbose {
+			// XXX indent sql
+			_, err = fmt.Fprintf(w, "%s\n", query.Sql)
+			if err != nil {
+				return err
+			}
+		}
+	}
+
+	return nil
+}
+
+const listSummary = "lists queries defined by a package"
+
+func listUsage(w io.Writer) {
+	fmt.Fprintf(w,
+		`Usage: goquery list <package>
+List queries defined by a package
+
+  options:
+
+	-v		verbose output.
+	-h --help       this help text.
+`)
+}
+
+func listMain(argv []string) {
+	var verbose bool
+	flags := flag.FlagSet{Usage: func() { listUsage(os.Stderr) }}
+	flags.Init("", flag.ExitOnError)
+	flags.BoolVar(&verbose, "v", verbose, "verbose mode")
+	flags.Parse(argv[1:])
+
+	argv = flags.Args()
+	if len(argv) < 1 {
+		flags.Usage()
+		prog.Exit(2)
+	}
+	pkgpath := argv[0]
+
+	cwd, err := os.Getwd()
+	if err != nil {
+		prog.Fatal(err)
+	}
+
+	err = querylist(os.Stdout, pkgpath, &build.Default, cwd, verbose)
+	if err != nil {
+		prog.Fatal(err)
+	}
+}
+
+// ---- main driver ----
+
+var commands = prog.CommandRegistry{
+	{"gen", genSummary, genUsage, genMain},
+	{"list", listSummary, listUsage, listMain},
+}
+
+var goquery = prog.MainProg{
+	Name:     "goquery",
+	Summary:  "Goquery is a program to XXX", // XXX
+	Commands: commands,
+}
+
+func main() {
+	log.SetFlags(0)
+	log.SetPrefix("goquery: ")
+	goquery.Main()
+}
+
+// ---- from gotrace/util.go ----
+
+// Buffer is bytes.Buffer + syntatic sugar
+type Buffer struct {
+	bytes.Buffer
+}
+
+func (b *Buffer) emit(format string, argv ...interface{}) {
+	fmt.Fprintf(b, format+"\n", argv...)
+}
+
+// StrSet is set<string>
+type StrSet map[string]struct{}
+
+func (s StrSet) Add(itemv ...string) {
+	for _, item := range itemv {
+		s[item] = struct{}{}
+	}
+}
+
+func (s StrSet) Delete(item string) {
+	delete(s, item)
+}
+
+func (s StrSet) Has(item string) bool {
+	_, has := s[item]
+	return has
+}
+
+// Itemv returns ordered slice of set items
+func (s StrSet) Itemv() []string {
+	itemv := make([]string, 0, len(s))
+	for item := range s {
+		itemv = append(itemv, item)
+	}
+	sort.Strings(itemv)
+	return itemv
+}
+diff --git a/go/neo/storage/sqlite/pool.go b/go/neo/storage/sqlite/pool.go
+index afbed66c..2e608314 100644
+--- a/go/neo/storage/sqlite/pool.go
+++ b/go/neo/storage/sqlite/pool.go
+@@ -25,21 +25,19 @@ import (
+ 	"sync"
+ 
+ 	"lab.nexedi.com/kirr/go123/xerr"
+-
+-	sqlite3 "github.com/gwenn/gosqlite"
+ )
+ 
+-// connPool is a pool of sqlite3.Conn
+// connPool is a pool of connections.
+ type connPool struct {
+-	factory func() (*sqlite3.Conn, error) // =nil if pool closed
+	factory func() (*conn, error) // =nil if pool closed
+ 
+ 	mu     sync.Mutex
+-	connv  []*sqlite3.Conn // operated as stack
+	connv  []*conn // operated as stack
+ }
+ 
+ // newConnPool creates new connPool that will be using factory to create new
+ // connections.
+-func newConnPool(factory func() (*sqlite3.Conn, error)) *connPool {
+func newConnPool(factory func() (*conn, error)) *connPool {
+ 	return &connPool{factory: factory}
+ }
+ 
+@@ -64,7 +62,7 @@ var errClosedPool = errors.New("sqlite: pool: getConn on closed pool")
+ 
+ // getConn returns a connection - either from pool, or newly created if the
+ // pool was empty.
+-func (p *connPool) getConn() (conn *sqlite3.Conn, _ error) {
+func (p *connPool) getConn() (conn *conn, _ error) {
+ 	p.mu.Lock()
+ 
+ 	factory := p.factory
+@@ -93,10 +91,14 @@ func (p *connPool) getConn() (conn *sqlite3.Conn, _ error) {
+ // putConn puts a connection to pool.
+ //
+ // Caller must not directly use conn after call to putConn anymore.
+-func (p *connPool) putConn(conn *sqlite3.Conn) {
+func (p *connPool) putConn(conn *conn) {
+ 	p.mu.Lock()
+ 	if p.factory != nil { // forgiving putConn after close
+ 		p.connv = append(p.connv, conn)
+ 	}
+ 	p.mu.Unlock()
+ }
+
+
+
+// TODO +singleConn that exposes single connection via pool interface.
+diff --git a/go/neo/storage/sqlite/sqlite.go b/go/neo/storage/sqlite/sqlite.go
+index 4aae47b3..d935d66c 100644
+--- a/go/neo/storage/sqlite/sqlite.go
+++ b/go/neo/storage/sqlite/sqlite.go
+@@ -21,6 +21,8 @@
+ // Package sqlite provides NEO storage backend that uses SQLite database for persistence.
+ package sqlite
+ 
+//go:generate go run goquery.go gen .
+
+ import (
+ 	"context"
+ 	"errors"
+@@ -316,14 +318,9 @@ func (b *Backend) load(xid zodb.Xid) (*proto.AnswerObject, error) {
+ 	//var data sql.RawBytes
+ 	var data []byte
+ 
+-	// XXX recheck vvv with sqlite3 direct
+-	// hash is variable-length BLOB - Scan refuses to put it into [20]byte
+-	//var hash sql.RawBytes
+-	var hash []byte
+-
+ 	// obj.value_tid can be null
+ 	//var valueTid sql.NullInt64	// XXX ok not to uint64 - max tid is max signed int64
+-	var valueTid int64	// XXX ok not to uint64 - max tid is max signed int64
+	var valueTid zodb.Tid	// XXX ok not to uint64 - max tid is max signed int64
+ 
+ 	// FIXME pid = getReadablePartition (= oid % Np; error if pid not readable)
+ 	pid := 0
+@@ -333,13 +330,18 @@ func (b *Backend) load(xid zodb.Xid) (*proto.AnswerObject, error) {
+ 
+ 	// XXX use conn for several query1 (see below) without intermediate returns to pool?
+ 
+-	err := b.query1(
+-		"SELECT tid, compression, data.hash, value, value_tid" +
+-		" FROM obj LEFT JOIN data ON obj.data_id = data.id" +
+-		" WHERE partition=? AND oid=? AND tid<=?" +
+-		" ORDER BY tid DESC LIMIT 1",
+-		pid, xid.Oid, xid.At).
+-		Scan(&obj.Serial, &obj.Compression, &hash, &data, &valueTid)
+
+//sql:query1 sql_getObject(pid int, oid zodb.Oid, at zodb.Tid) (serial zodb.Tid, compression int, hash  proto.Checksum, value []byte, dataSerial zodb.Tid)
+//	SELECT tid, compression, data.hash, value, value_tid
+//		FROM obj LEFT JOIN data ON obj.data_id = data.id
+//		WHERE partition=? AND oid=? AND tid<=?
+//		ORDER BY tid DESC LIMIT 1
+//
+
+	var compression int
+	var err error
+	obj.Serial, compression, obj.Checksum, data, valueTid, err =
+		sql_getObject(b.pool, pid, xid.Oid, xid.At)
+ 
+ 	if err != nil {
+ 		if err == errNoRows {
+@@ -365,11 +367,7 @@ func (b *Backend) load(xid zodb.Xid) (*proto.AnswerObject, error) {
+ 		return nil, err
+ 	}
+ 
+-	// hash -> obj.Checksum
+-	if len(hash) != len(obj.Checksum) {
+-		return nil, fmt.Errorf("data corrupt: len(hash) = %d", len(hash))
+-	}
+-	copy(obj.Checksum[:], hash)
+	obj.Compression = (compression != 0)
+ 
+ 	// valueTid -> obj.DataSerial
+ 	if valueTid != 0 {
+@@ -377,7 +375,7 @@ func (b *Backend) load(xid zodb.Xid) (*proto.AnswerObject, error) {
+ 	}
+ 
+ 
+-	// data -> obj.Data
+	// data -> obj.Data	XXX do this directly in query
+ 	obj.Data = mem.BufAlloc(len(data))
+ 	copy(obj.Data.Data, data)
+ 
+@@ -403,6 +401,9 @@ func (b *Backend) load(xid zodb.Xid) (*proto.AnswerObject, error) {
+ 
+ 
+ func (b *Backend) config(key string, pvalue *string) error {
+//sql:query1 sql_getConfig(name string) (value string)
+//	SELECT value FROM config WHERE name=?
+
+ 	return b.query1("SELECT value FROM config WHERE name=?", key).Scan(pvalue)
+ }
+ 
+diff --git a/go/neo/storage/sqlite/zquery.go b/go/neo/storage/sqlite/zquery.go
+new file mode 100644
+index 00000000..3d5d049c
+--- /dev/null
+++ b/go/neo/storage/sqlite/zquery.go
+@@ -0,0 +1,53 @@
+// Code generated by lab.nexedi.com/kirr/neo/.../goquery; DO NOT EDIT.
+
+package sqlite
+// Go code generated for queries.
+
+// #cgo pkg-config: sqlite3
+// #include "./zquery.h"
+import "C"
+
+import (
+
+	"lab.nexedi.com/kirr/neo/go/neo/proto"
+	"lab.nexedi.com/kirr/neo/go/zodb"
+)
+
+type conn C.Conn
+
+// db represents interface for accessing the database.
+//
+// Database connections can be opened (getConn) and put back to reuse (putConn).
+type db interface {
+	getConn() (*conn, error)
+	putConn(*conn)
+}
+
+
+// query1: sql_getConfig(name) (value)
+func sql_getConfig(_db db, name string) (value string, err error) {
+	_conn, err := _db.getConn()
+	if err != nil {
+		return
+	}
+
+	_r := C.sql_getConfig(_conn, name)
+
+	_ = _r
+	_cp.putConn(_conn)
+	panic("TODO")
+}
+
+// query1: sql_getObject(pid, oid, at) (serial, compression, hash, value, dataSerial)
+func sql_getObject(_db db, pid int, oid zodb.Oid, at zodb.Tid) (serial zodb.Tid, compression int, hash proto.Checksum, value []byte, dataSerial zodb.Tid, err error) {
+	_conn, err := _db.getConn()
+	if err != nil {
+		return
+	}
+
+	_r := C.sql_getObject(_conn, C.int(pid), C.uint64_t(oid), C.uint64_t(at))
+
+	_ = _r
+	_cp.putConn(_conn)
+	panic("TODO")
+}
+diff --git a/go/neo/storage/sqlite/zquery.h b/go/neo/storage/sqlite/zquery.h
+new file mode 100644
+index 00000000..fa562837
+--- /dev/null
+++ b/go/neo/storage/sqlite/zquery.h
+@@ -0,0 +1,265 @@
+// Code generated by lab.nexedi.com/kirr/neo/.../goquery; DO NOT EDIT.
+// C code generated for queries.
+
+#include <sqlite3.h>
+#include <stdint.h>
+#include <string.h>
+#include <assert.h>
+
+//#include "_cgo_export.h"
+
+#define OK(RC) if ((RC) != SQLITE_OK) {	\
+	r.rc = (RC);	\
+	goto out;	\
+}
+
+// cgo does not give us _GoStringPtr & friends in non-preamble.
+// we take it ourselves:
+static inline const char *gostr_ptr(_GoString_ s) { return s.p; }
+static inline size_t      gostr_len(_GoString_ s) { return s.n; }
+
+// Conn represents connection to sqlite database.
+//
+// Conn can be used by only one goroutine simultaneously.
+typedef struct {
+	sqlite3	*db;
+
+	// cached query statements
+	sqlite3_stmt *_qstmt_sql_getConfig;
+	sqlite3_stmt *_qstmt_sql_getObject;
+} Conn;
+
+// query1: sql_getConfig(name) (value)
+
+typedef struct {
+	const char *	value_ptr;
+	size_t	value_len;
+
+	int rc;
+} sql_getConfig_ret;
+
+sql_getConfig_ret sql_getConfig(Conn *conn, _GoString_ name) {
+	sql_getConfig_ret r;
+	sqlite3_stmt *qstmt;
+	int rc;
+
+	qstmt = conn->_qstmt_sql_getConfig;
+	conn->_qstmt_sql_getConfig = NULL;	// XXX just in case
+	if (!qstmt) {
+		rc = sqlite3_prepare_v2(conn->db,
+"SELECT value FROM config WHERE name=?", -1, &qstmt, NULL);
+		if (rc != SQLITE_OK) {
+			r.rc = rc;
+			return r;
+		}
+	}
+
+	// bind arguments
+	//
+	// NOTE for strings we pass SQLITE_STATIC which means to SQLite "that
+	// the content pointer is constant and will never change". It is valid
+	// to do so because we'll unbind all arguments when returning.
+	rc = sqlite3_bind_text(qstmt, 1, gostr_ptr(name), gostr_len(name), SQLITE_STATIC);
+	OK(rc);
+
+	// run the query
+	rc = sqlite3_step(qstmt);
+	switch (rc) {
+	case SQLITE_ROW:
+		break;	// ok
+
+	case SQLITE_DONE:
+		r.rc = rc;
+		goto out;
+
+	default:
+		r.rc = rc;
+		goto out;
+	}
+
+	// we got data -> read columns
+	// ... value
+	switch ( sqlite3_column_type(qstmt, 1) ) {
+	case SQLITE_TEXT:
+		// XXX also NULL?
+		break;
+
+	default:
+		r.rc = SQLITE_MISMATCH;		// XXX details
+		return r;
+	}
+
+	r.value_ptr = sqlite3_column_text (qstmt, 1);
+	r.value_len = sqlite3_column_bytes(qstmt, 1);
+
+
+	r.rc = SQLITE_OK;
+
+out:
+	// clear bindings so that we put qstmt back with all arguments cleared.
+	// in particular we HAVE to unbind go strings memory (see bind part for why).
+	//
+	// ignore rc - sqlite3_clear_bindings always returns SQLITE_OK.
+	rc = sqlite3_clear_bindings(qstmt);
+	assert(rc == SQLITE_OK);
+
+	// reset the statement so it can be executed again.
+	// ignore rc as sqlite3_reset returns error of last sqlite3_step.
+	(void)sqlite3_reset(qstmt);
+
+	// put statment back to conn for reuse
+	conn->_qstmt_sql_getConfig = qstmt;
+
+	return r;
+}
+
+// query1: sql_getObject(pid, oid, at) (serial, compression, hash, value, dataSerial)
+
+typedef struct {
+	uint64_t	serial;
+	int	compression;
+	uint8_t	hash[20];
+	const char *	value_ptr;
+	size_t	value_len;
+	uint64_t	dataSerial;
+
+	int rc;
+} sql_getObject_ret;
+
+sql_getObject_ret sql_getObject(Conn *conn, int pid, uint64_t oid, uint64_t at) {
+	sql_getObject_ret r;
+	sqlite3_stmt *qstmt;
+	int rc;
+
+	qstmt = conn->_qstmt_sql_getObject;
+	conn->_qstmt_sql_getObject = NULL;	// XXX just in case
+	if (!qstmt) {
+		rc = sqlite3_prepare_v2(conn->db,
+"SELECT tid, compression, data.hash, value, value_tid"
+"	FROM obj LEFT JOIN data ON obj.data_id = data.id"
+"	WHERE partition=? AND oid=? AND tid<=?"
+"	ORDER BY tid DESC LIMIT 1", -1, &qstmt, NULL);
+		if (rc != SQLITE_OK) {
+			r.rc = rc;
+			return r;
+		}
+	}
+
+	// bind arguments
+	//
+	// NOTE for strings we pass SQLITE_STATIC which means to SQLite "that
+	// the content pointer is constant and will never change". It is valid
+	// to do so because we'll unbind all arguments when returning.
+	rc = sqlite3_bind_int64(qstmt, 1, pid);
+	OK(rc);
+	rc = sqlite3_bind_int64(qstmt, 2, oid);
+	OK(rc);
+	rc = sqlite3_bind_int64(qstmt, 3, at);
+	OK(rc);
+
+	// run the query
+	rc = sqlite3_step(qstmt);
+	switch (rc) {
+	case SQLITE_ROW:
+		break;	// ok
+
+	case SQLITE_DONE:
+		r.rc = rc;
+		goto out;
+
+	default:
+		r.rc = rc;
+		goto out;
+	}
+
+	// we got data -> read columns
+	// ... serial
+	switch ( sqlite3_column_type(qstmt, 1) ) {
+	case SQLITE_INTEGER:
+		// XXX also NULL?
+		break;
+
+	default:
+		r.rc = SQLITE_MISMATCH;		// XXX details
+		return r;
+	}
+
+	r.serial = sqlite3_column_int64(qstmt, 1);
+
+	// ... compression
+	switch ( sqlite3_column_type(qstmt, 2) ) {
+	case SQLITE_INTEGER:
+		// XXX also NULL?
+		break;
+
+	default:
+		r.rc = SQLITE_MISMATCH;		// XXX details
+		return r;
+	}
+
+	r.compression = sqlite3_column_int64(qstmt, 2);
+
+	// ... hash
+	switch ( sqlite3_column_type(qstmt, 3) ) {
+	case SQLITE_BLOB:
+		// XXX also NULL?
+		break;
+
+	default:
+		r.rc = SQLITE_MISMATCH;		// XXX details
+		return r;
+	}
+
+	// array - check lenght matching + read directly here
+	if (20 != sqlite3_column_bytes(qstmt, 3)) {
+		r.rc = SQLITE_MISMATCH;		// XXX detail
+		goto out;
+	}
+	memcpy(r.hash, sqlite3_column_blob(qstmt, 3), 20);
+
+	// ... value
+	switch ( sqlite3_column_type(qstmt, 4) ) {
+	case SQLITE_BLOB:
+		// XXX also NULL?
+		break;
+
+	default:
+		r.rc = SQLITE_MISMATCH;		// XXX details
+		return r;
+	}
+
+	// TODO blob
+
+	// ... dataSerial
+	switch ( sqlite3_column_type(qstmt, 5) ) {
+	case SQLITE_INTEGER:
+		// XXX also NULL?
+		break;
+
+	default:
+		r.rc = SQLITE_MISMATCH;		// XXX details
+		return r;
+	}
+
+	r.dataSerial = sqlite3_column_int64(qstmt, 5);
+
+
+	r.rc = SQLITE_OK;
+
+out:
+	// clear bindings so that we put qstmt back with all arguments cleared.
+	// in particular we HAVE to unbind go strings memory (see bind part for why).
+	//
+	// ignore rc - sqlite3_clear_bindings always returns SQLITE_OK.
+	rc = sqlite3_clear_bindings(qstmt);
+	assert(rc == SQLITE_OK);
+
+	// reset the statement so it can be executed again.
+	// ignore rc as sqlite3_reset returns error of last sqlite3_step.
+	(void)sqlite3_reset(qstmt);
+
+	// put statment back to conn for reuse
+	conn->_qstmt_sql_getObject = qstmt;
+
+	return r;
+}