add support for defining an "eponymous only" virtual table (#885)

* add support for defining an "eponymous only" virtual table

As suggested here: https://github.com/mattn/go-sqlite3/issues/846#issuecomment-736206222

* add an example of an eponymous only vtab module

* add a test case for an eponymous only vtab module

_example/vtable_eponymous_only/main.go

@@ -0,0 +1,33 @@
+package main
+
+import (
+	"database/sql"
+	"fmt"
+	"log"
+
+	"github.com/mattn/go-sqlite3"
+)
+
+func main() {
+	sql.Register("sqlite3_with_extensions", &sqlite3.SQLiteDriver{
+		ConnectHook: func(conn *sqlite3.SQLiteConn) error {
+			return conn.CreateModule("series", &seriesModule{})
+		},
+	})
+	db, err := sql.Open("sqlite3_with_extensions", ":memory:")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer db.Close()
+
+	rows, err := db.Query("select * from series")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer rows.Close()
+	for rows.Next() {
+		var value int
+		rows.Scan(&value)
+		fmt.Printf("value: %d\n", value)
+	}
+}

_example/vtable_eponymous_only/vtable.go

@@ -0,0 +1,118 @@
+package main
+
+import (
+	"fmt"
+
+	"github.com/mattn/go-sqlite3"
+)
+
+type seriesModule struct{}
+
+func (m *seriesModule) EponymousOnlyModule() {}
+
+func (m *seriesModule) Create(c *sqlite3.SQLiteConn, args []string) (sqlite3.VTab, error) {
+	err := c.DeclareVTab(fmt.Sprintf(`
+		CREATE TABLE %s (
+			value INT,
+			start HIDDEN,
+			stop HIDDEN,
+			step HIDDEN
+		)`, args[0]))
+	if err != nil {
+		return nil, err
+	}
+	return &seriesTable{0, 0, 1}, nil
+}
+
+func (m *seriesModule) Connect(c *sqlite3.SQLiteConn, args []string) (sqlite3.VTab, error) {
+	return m.Create(c, args)
+}
+
+func (m *seriesModule) DestroyModule() {}
+
+type seriesTable struct {
+	start int64
+	stop  int64
+	step  int64
+}
+
+func (v *seriesTable) Open() (sqlite3.VTabCursor, error) {
+	return &seriesCursor{v, 0}, nil
+}
+
+func (v *seriesTable) BestIndex(csts []sqlite3.InfoConstraint, ob []sqlite3.InfoOrderBy) (*sqlite3.IndexResult, error) {
+	used := make([]bool, len(csts))
+	for c, cst := range csts {
+		if cst.Usable && cst.Op == sqlite3.OpEQ {
+			used[c] = true
+		}
+	}
+
+	return &sqlite3.IndexResult{
+		IdxNum: 0,
+		IdxStr: "default",
+		Used:   used,
+	}, nil
+}
+
+func (v *seriesTable) Disconnect() error { return nil }
+func (v *seriesTable) Destroy() error    { return nil }
+
+type seriesCursor struct {
+	*seriesTable
+	value int64
+}
+
+func (vc *seriesCursor) Column(c *sqlite3.SQLiteContext, col int) error {
+	switch col {
+	case 0:
+		c.ResultInt64(vc.value)
+	case 1:
+		c.ResultInt64(vc.seriesTable.start)
+	case 2:
+		c.ResultInt64(vc.seriesTable.stop)
+	case 3:
+		c.ResultInt64(vc.seriesTable.step)
+	}
+	return nil
+}
+
+func (vc *seriesCursor) Filter(idxNum int, idxStr string, vals []interface{}) error {
+	switch {
+	case len(vals) < 1:
+		vc.seriesTable.start = 0
+		vc.seriesTable.stop = 1000
+		vc.value = vc.seriesTable.start
+	case len(vals) < 2:
+		vc.seriesTable.start = vals[0].(int64)
+		vc.seriesTable.stop = 1000
+		vc.value = vc.seriesTable.start
+	case len(vals) < 3:
+		vc.seriesTable.start = vals[0].(int64)
+		vc.seriesTable.stop = vals[1].(int64)
+		vc.value = vc.seriesTable.start
+	case len(vals) < 4:
+		vc.seriesTable.start = vals[0].(int64)
+		vc.seriesTable.stop = vals[1].(int64)
+		vc.seriesTable.step = vals[2].(int64)
+	}
+
+	return nil
+}
+
+func (vc *seriesCursor) Next() error {
+	vc.value += vc.step
+	return nil
+}
+
+func (vc *seriesCursor) EOF() bool {
+	return vc.value > vc.stop
+}
+
+func (vc *seriesCursor) Rowid() (int64, error) {
+	return int64(vc.value), nil
+}
+
+func (vc *seriesCursor) Close() error {
+	return nil
+}

sqlite3_opt_vtable.go

@@ -226,11 +226,43 @@ static sqlite3_module goModule = {
 	0	                     // xRollbackTo
 };
 
+// See https://sqlite.org/vtab.html#eponymous_only_virtual_tables
+static sqlite3_module goModuleEponymousOnly = {
+	0,                       // iVersion
+	0,                       // xCreate - create a table, which here is null
+	cXConnect,               // xConnect - connect to an existing table
+	cXBestIndex,             // xBestIndex - Determine search strategy
+	cXDisconnect,            // xDisconnect - Disconnect from a table
+	cXDestroy,               // xDestroy - Drop a table
+	cXOpen,                  // xOpen - open a cursor
+	cXClose,                 // xClose - close a cursor
+	cXFilter,                // xFilter - configure scan constraints
+	cXNext,                  // xNext - advance a cursor
+	cXEof,                   // xEof
+	cXColumn,                // xColumn - read data
+	cXRowid,                 // xRowid - read data
+	cXUpdate,                // xUpdate - write data
+// Not implemented
+	0,                       // xBegin - begin transaction
+	0,                       // xSync - sync transaction
+	0,                       // xCommit - commit transaction
+	0,                       // xRollback - rollback transaction
+	0,                       // xFindFunction - function overloading
+	0,                       // xRename - rename the table
+	0,                       // xSavepoint
+	0,                       // xRelease
+	0	                     // xRollbackTo
+};
+
 void goMDestroy(void*);
 
 static int _sqlite3_create_module(sqlite3 *db, const char *zName, uintptr_t pClientData) {
   return sqlite3_create_module_v2(db, zName, &goModule, (void*) pClientData, goMDestroy);
 }
+
+static int _sqlite3_create_module_eponymous_only(sqlite3 *db, const char *zName, uintptr_t pClientData) {
+  return sqlite3_create_module_v2(db, zName, &goModuleEponymousOnly, (void*) pClientData, goMDestroy);
+}
 */
 import "C"
 
@@ -595,6 +627,13 @@ type Module interface {
 	DestroyModule()
 }
 
+// EponymousOnlyModule is a "virtual table module" (as above), but
+// for defining "eponymous only" virtual tables See: https://sqlite.org/vtab.html#eponymous_only_virtual_tables
+type EponymousOnlyModule interface {
+	Module
+	EponymousOnlyModule()
+}
+
 // VTab describes a particular instance of the virtual table.
 // See: http://sqlite.org/c3ref/vtab.html
 type VTab interface {
@@ -652,9 +691,19 @@ func (c *SQLiteConn) CreateModule(moduleName string, module Module) error {
 	mname := C.CString(moduleName)
 	defer C.free(unsafe.Pointer(mname))
 	udm := sqliteModule{c, moduleName, module}
-	rv := C._sqlite3_create_module(c.db, mname, C.uintptr_t(uintptr(newHandle(c, &udm))))
-	if rv != C.SQLITE_OK {
-		return c.lastError()
+	switch module.(type) {
+	case EponymousOnlyModule:
+		rv := C._sqlite3_create_module_eponymous_only(c.db, mname, C.uintptr_t(uintptr(newHandle(c, &udm))))
+		if rv != C.SQLITE_OK {
+			return c.lastError()
+		}
+		return nil
+	case Module:
+		rv := C._sqlite3_create_module(c.db, mname, C.uintptr_t(uintptr(newHandle(c, &udm))))
+		if rv != C.SQLITE_OK {
+			return c.lastError()
+		}
+		return nil
 	}
 	return nil
 }

sqlite3_opt_vtable_test.go

@@ -484,3 +484,125 @@ func (c *vtabUpdateCursor) Rowid() (int64, error) {
 func (c *vtabUpdateCursor) Close() error {
 	return nil
 }
+
+type testModuleEponymousOnly struct {
+	t        *testing.T
+	intarray []int
+}
+
+type testVTabEponymousOnly struct {
+	intarray []int
+}
+
+type testVTabCursorEponymousOnly struct {
+	vTab  *testVTabEponymousOnly
+	index int
+}
+
+func (m testModuleEponymousOnly) EponymousOnlyModule() {}
+
+func (m testModuleEponymousOnly) Create(c *SQLiteConn, args []string) (VTab, error) {
+	err := c.DeclareVTab("CREATE TABLE x(test INT)")
+	if err != nil {
+		return nil, err
+	}
+	return &testVTabEponymousOnly{m.intarray}, nil
+}
+
+func (m testModuleEponymousOnly) Connect(c *SQLiteConn, args []string) (VTab, error) {
+	return m.Create(c, args)
+}
+
+func (m testModuleEponymousOnly) DestroyModule() {}
+
+func (v *testVTabEponymousOnly) BestIndex(cst []InfoConstraint, ob []InfoOrderBy) (*IndexResult, error) {
+	used := make([]bool, 0, len(cst))
+	for range cst {
+		used = append(used, false)
+	}
+	return &IndexResult{
+		Used:           used,
+		IdxNum:         0,
+		IdxStr:         "test-index",
+		AlreadyOrdered: true,
+		EstimatedCost:  100,
+		EstimatedRows:  200,
+	}, nil
+}
+
+func (v *testVTabEponymousOnly) Disconnect() error {
+	return nil
+}
+
+func (v *testVTabEponymousOnly) Destroy() error {
+	return nil
+}
+
+func (v *testVTabEponymousOnly) Open() (VTabCursor, error) {
+	return &testVTabCursorEponymousOnly{v, 0}, nil
+}
+
+func (vc *testVTabCursorEponymousOnly) Close() error {
+	return nil
+}
+
+func (vc *testVTabCursorEponymousOnly) Filter(idxNum int, idxStr string, vals []interface{}) error {
+	vc.index = 0
+	return nil
+}
+
+func (vc *testVTabCursorEponymousOnly) Next() error {
+	vc.index++
+	return nil
+}
+
+func (vc *testVTabCursorEponymousOnly) EOF() bool {
+	return vc.index >= len(vc.vTab.intarray)
+}
+
+func (vc *testVTabCursorEponymousOnly) Column(c *SQLiteContext, col int) error {
+	if col != 0 {
+		return fmt.Errorf("column index out of bounds: %d", col)
+	}
+	c.ResultInt(vc.vTab.intarray[vc.index])
+	return nil
+}
+
+func (vc *testVTabCursorEponymousOnly) Rowid() (int64, error) {
+	return int64(vc.index), nil
+}
+
+func TestCreateModuleEponymousOnly(t *testing.T) {
+	tempFilename := TempFilename(t)
+	defer os.Remove(tempFilename)
+	intarray := []int{1, 2, 3}
+	sql.Register("sqlite3_TestCreateModuleEponymousOnly", &SQLiteDriver{
+		ConnectHook: func(conn *SQLiteConn) error {
+			return conn.CreateModule("test", testModuleEponymousOnly{t, intarray})
+		},
+	})
+	db, err := sql.Open("sqlite3_TestCreateModuleEponymousOnly", tempFilename)
+	if err != nil {
+		t.Fatalf("could not open db: %v", err)
+	}
+
+	var i, value int
+	rows, err := db.Query("SELECT rowid, * FROM test")
+	if err != nil {
+		t.Fatalf("couldn't select from virtual table: %v", err)
+	}
+	for rows.Next() {
+		err := rows.Scan(&i, &value)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if intarray[i] != value {
+			t.Fatalf("want %v but %v", intarray[i], value)
+		}
+	}
+
+	_, err = db.Exec("DROP TABLE test")
+	if err != nil {
+		t.Fatalf("couldn't drop virtual table: %v", err)
+	}
+}