Retrieve `matchinfo` from FTS4 table on SQLite.

sqlite_matchinfo.go

package main

import (
	"bytes"
	"database/sql"
	"encoding/binary"
	_ "github.com/mattn/go-sqlite3"
	"log"
)

func loadDB() *sql.DB {
	db, err := sql.Open("sqlite3", ":memory:")
	if err != nil {
		log.Fatal(err)
	}

	var sqliteVersion string
	err = db.QueryRow("select sqlite_version()").Scan(&sqliteVersion)
	if err != nil {
		log.Fatal(err)
	}
	log.Println("SQLite version:", sqliteVersion)

	log.Println("creating FTS index...")
	_, err = db.Exec("CREATE VIRTUAL TABLE dict USING fts4(key, entry)")
	if err != nil {
		log.Fatal(err)
	}
	insertStmt, err := db.Prepare("INSERT INTO dict(key, entry) VALUES(?, ?)")
	if err != nil {
		log.Fatal(err)
	}
	defer insertStmt.Close()
	dict := map[string]string{
		"Russia": "Moscow",
		"Poland": "Warsaw",
	}
	for key, entry := range dict {
		insertStmt.Exec(key, entry)
	}
	log.Printf("indexed %d entries\n", len(dict))

	return db
}

type MatchInfo struct {
	P, C uint32
	X    []uint32
}

func (mi *MatchInfo) Read(b []byte) {
	buf := bytes.NewBuffer(b)
	binary.Read(buf, binary.LittleEndian, &mi.P)
	binary.Read(buf, binary.LittleEndian, &mi.C)
	mi.X = make([]uint32, 3*mi.P*mi.C)
	binary.Read(buf, binary.LittleEndian, &mi.X)
}

func search(db *sql.DB, term string) map[int]MatchInfo {
	rows, err := db.Query("SELECT docid, matchinfo(dict) FROM dict WHERE entry MATCH ?", term)
	if err != nil {
		log.Fatal(err)
	}
	defer rows.Close()
	results := make(map[int]MatchInfo)
	for rows.Next() {
		var (
			docid   int
			miBytes *[]byte
			mi      MatchInfo
		)
		if err := rows.Scan(&docid, &miBytes); err != nil {
			log.Fatal(err)
		}
		mi.Read(*miBytes)
		//log.Println("****", docid, mi)
		results[docid] = mi
	}
	return results
}

func main() {
	db := loadDB()
	defer db.Close()
	log.Println("results:", search(db, "Warsaw"))
}

I observe segmentation violation when db.Close() is called. Tested in two environments:

Env 1:

• Mac OS X 10.6.8
• go1.1 darwin/amd64
• mattn/go-sqlite3@dc751dd

Env 2:

• Cent OS 6 - 2.6.32-358.6.2.el6.x86_64
• go1.1.1 linux/amd64
• mattn/go-sqlite3@dc751dd