SimpleCloudNotifier/scnserver/db/dbtools/preprocessor.go

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package dbtools
import (
"context"
"errors"
"fmt"
"github.com/rs/zerolog/log"
"gogs.mikescher.com/BlackForestBytes/goext/langext"
"gogs.mikescher.com/BlackForestBytes/goext/sq"
"regexp"
"strings"
"sync"
)
//
// This is..., not good...
//
// for sq.ScanAll to work with (left-)joined tables _need_ to get column names aka "alias.column"
// But sqlite (and all other db server) only return "column" if we don't manually specify `alias.column as "alias.columnname"`
// But always specifying all columns (and their alias) would be __very__ cumbersome...
//
// The "solution" is this preprocessor, which translates queries of the form `SELECT tab1.*, tab2.* From tab1` into `SELECT tab1.col1 AS "tab1.col1", tab1.col2 AS "tab1.col2" ....`
//
// Prerequisites:
// - all aliased tables must be written as `tablename AS alias` (the variant without the AS keyword is invalid)
// - a star only expands to the (single) table in FROM. Use *, table2.* if there exists a second (joined) table
// - No weird SQL syntax, this "parser" is not very robust...
//
type DBPreprocessor struct {
db sq.DB
lock sync.Mutex
cacheColumns map[string][]string
cacheQuery map[string]string
}
var regexAlias = regexp.MustCompile("([A-Za-z_\\-0-9]+)\\s+AS\\s+([A-Za-z_\\-0-9]+)")
func NewDBPreprocessor(db sq.DB) *DBPreprocessor {
return &DBPreprocessor{
db: db,
lock: sync.Mutex{},
cacheColumns: make(map[string][]string),
cacheQuery: make(map[string]string),
}
}
func (pp *DBPreprocessor) PrePing(ctx context.Context) error {
return nil
}
func (pp *DBPreprocessor) PreTxBegin(ctx context.Context, txid uint16) error {
return nil
}
func (pp *DBPreprocessor) PreTxCommit(txid uint16) error {
return nil
}
func (pp *DBPreprocessor) PreTxRollback(txid uint16) error {
return nil
}
func (pp *DBPreprocessor) PreQuery(ctx context.Context, txID *uint16, sql *string, params *sq.PP) error {
sqlOriginal := *sql
pp.lock.Lock()
v, ok := pp.cacheQuery[sqlOriginal]
pp.lock.Unlock()
if ok {
*sql = v
return nil
}
if !strings.HasPrefix(sqlOriginal, "SELECT ") {
return nil
}
idxFrom := strings.Index(sqlOriginal, " FROM ")
if idxFrom < 0 {
return nil
}
fromTableName := strings.Split(strings.TrimSpace(sqlOriginal[idxFrom+len(" FROM"):]), " ")[0]
sels := strings.TrimSpace(sqlOriginal[len("SELECT "):idxFrom])
split := strings.Split(sels, ",")
newsel := make([]string, 0)
aliasMap := make(map[string]string)
for _, v := range regexAlias.FindAllStringSubmatch(sqlOriginal, idxFrom+len(" FROM")) {
aliasMap[strings.TrimSpace(v[2])] = strings.TrimSpace(v[1])
}
for _, expr := range split {
expr = strings.TrimSpace(expr)
if expr == "*" {
columns, err := pp.getTableColumns(ctx, fromTableName)
if err != nil {
return err
}
for _, colname := range columns {
newsel = append(newsel, fmt.Sprintf("%s.%s AS \"%s\"", fromTableName, colname, colname))
}
} else if strings.HasSuffix(expr, ".*") {
tableName := expr[0 : len(expr)-2]
if tableRealName, ok := aliasMap[tableName]; ok {
columns, err := pp.getTableColumns(ctx, tableRealName)
if err != nil {
return err
}
for _, colname := range columns {
newsel = append(newsel, fmt.Sprintf("%s.%s AS \"%s.%s\"", tableName, colname, tableName, colname))
}
} else if tableName == fromTableName {
columns, err := pp.getTableColumns(ctx, tableName)
if err != nil {
return err
}
for _, colname := range columns {
newsel = append(newsel, fmt.Sprintf("%s.%s AS \"%s\"", tableName, colname, colname))
}
} else {
columns, err := pp.getTableColumns(ctx, tableName)
if err != nil {
return err
}
for _, colname := range columns {
newsel = append(newsel, fmt.Sprintf("%s.%s AS \"%s.%s\"", tableName, colname, tableName, colname))
}
}
} else {
return nil
}
}
newSQL := "SELECT " + strings.Join(newsel, ", ") + sqlOriginal[idxFrom:]
pp.lock.Lock()
pp.cacheQuery[sqlOriginal] = newSQL
pp.lock.Unlock()
log.Debug().Msgf("Preprocessed SQL statement from '%s' --to--> '%s'", sqlOriginal, newSQL)
*sql = newSQL
return nil
}
func (pp *DBPreprocessor) PreExec(ctx context.Context, txID *uint16, sql *string, params *sq.PP) error {
return nil
}
func (pp *DBPreprocessor) PostPing(result error) {
//
}
func (pp *DBPreprocessor) PostTxBegin(txid uint16, result error) {
//
}
func (pp *DBPreprocessor) PostTxCommit(txid uint16, result error) {
//
}
func (pp *DBPreprocessor) PostTxRollback(txid uint16, result error) {
//
}
func (pp *DBPreprocessor) PostQuery(txID *uint16, sqlOriginal string, sqlReal string, params sq.PP) {
//
}
func (pp *DBPreprocessor) PostExec(txID *uint16, sqlOriginal string, sqlReal string, params sq.PP) {
//
}
func (pp *DBPreprocessor) getTableColumns(ctx context.Context, tablename string) ([]string, error) {
pp.lock.Lock()
v, ok := pp.cacheColumns[tablename]
pp.lock.Unlock()
if ok {
return v, nil
}
type res struct {
CID int64 `db:"cid"`
Name string `db:"name"`
Type string `db:"type"`
NotNull int `db:"notnull"`
DFLT *string `db:"dflt_value"`
PK int `db:"pk"`
}
rows, err := pp.db.Query(ctx, "PRAGMA table_info('"+tablename+"');", sq.PP{})
if err != nil {
return nil, err
}
resrows, err := sq.ScanAll[res](rows, true)
if err != nil {
return nil, err
}
columns := langext.ArrMap(resrows, func(v res) string { return v.Name })
if len(columns) == 0 {
return nil, errors.New("no columns in table '" + tablename + "' (table does not exist?)")
}
pp.lock.Lock()
pp.cacheColumns[tablename] = columns
pp.lock.Unlock()
return columns, nil
}