Provide more detailed error messages

Use the sqlite3_errmsg() API to retrieve more specific error
messages.

eg. Attempting to exec 'CREATE TABLE ExistingTableName (...)'
will now report 'table already exists: ExistingTableName' rather
than 'SQL logic error or missing database'

error.go

@@ -4,6 +4,12 @@ import "C"
 
 type ErrNo int
 
+type Error struct {
+	Code ErrNo  /* The error code returned by SQLite */
+	err  string /* The error string returned by sqlite3_errmsg(),
+	this usually contains more specific details. */
+}
+
 // result codes from http://www.sqlite.org/c3ref/c_abort.html
 var (
 	ErrError      error = ErrNo(1)  /* SQL error or missing database */
@@ -37,5 +43,13 @@ var (
 )
 
 func (err ErrNo) Error() string {
-	return errorString(err)
+	return Error{Code: err}.Error()
+}
+
+func (err Error) Error() string {
+	if err.err != "" {
+		return err.err
+	} else {
+		return errorString(err)
+	}
 }

error_test.go

@@ -27,7 +27,7 @@ func TestFailures(t *testing.T) {
 	if err == nil {
 		_, err = db.Exec("drop table foo")
 	}
-	if err != ErrNotADB {
+	if err.Code != ErrNotADB {
 		t.Error("wrong error code for corrupted DB")
 	}
 	if err.Error() == "" {

sqlite3.go

@@ -138,6 +138,12 @@ func (c *SQLiteConn) AutoCommit() bool {
 	return int(C.sqlite3_get_autocommit(c.db)) != 0
 }
 
+func (c *SQLiteConn) lastError() Error {
+	return Error{Code: ErrNo(C.sqlite3_errcode(c.db)),
+		err: C.GoString(C.sqlite3_errmsg(c.db)),
+	}
+}
+
 // TODO: Execer & Queryer currently disabled
 // https://github.com/mattn/go-sqlite3/issues/82
 //// Implements Execer
@@ -205,7 +211,7 @@ func (c *SQLiteConn) exec(cmd string) error {
 	defer C.free(unsafe.Pointer(pcmd))
 	rv := C.sqlite3_exec(c.db, pcmd, nil, nil, nil)
 	if rv != C.SQLITE_OK {
-		return ErrNo(rv)
+		return c.lastError()
 	}
 	return nil
 }
@@ -218,8 +224,8 @@ func (c *SQLiteConn) Begin() (driver.Tx, error) {
 	return &SQLiteTx{c}, nil
 }
 
-func errorString(err ErrNo) string {
-	return C.GoString(C.sqlite3_errstr(C.int(err)))
+func errorString(err Error) string {
+	return C.GoString(C.sqlite3_errstr(C.int(err.Code)))
 }
 
 // Open database and return a new connection.
@@ -242,7 +248,7 @@ func (d *SQLiteDriver) Open(dsn string) (driver.Conn, error) {
 			C.SQLITE_OPEN_CREATE,
 		nil)
 	if rv != 0 {
-		return nil, ErrNo(rv)
+		return nil, Error{Code: ErrNo(rv)}
 	}
 	if db == nil {
 		return nil, errors.New("sqlite succeeded without returning a database")
@@ -250,7 +256,7 @@ func (d *SQLiteDriver) Open(dsn string) (driver.Conn, error) {
 
 	rv = C.sqlite3_busy_timeout(db, 5000)
 	if rv != C.SQLITE_OK {
-		return nil, ErrNo(rv)
+		return nil, Error{Code: ErrNo(rv)}
 	}
 
 	conn := &SQLiteConn{db}
@@ -295,7 +301,7 @@ func (d *SQLiteDriver) Open(dsn string) (driver.Conn, error) {
 func (c *SQLiteConn) Close() error {
 	rv := C.sqlite3_close_v2(c.db)
 	if rv != C.SQLITE_OK {
-		return ErrNo(rv)
+		return c.lastError()
 	}
 	c.db = nil
 	return nil
@@ -309,7 +315,7 @@ func (c *SQLiteConn) Prepare(query string) (driver.Stmt, error) {
 	var tail *C.char
 	rv := C.sqlite3_prepare_v2(c.db, pquery, -1, &s, &tail)
 	if rv != C.SQLITE_OK {
-		return nil, ErrNo(rv)
+		return nil, c.lastError()
 	}
 	var t string
 	if tail != nil && C.strlen(tail) > 0 {
@@ -329,7 +335,7 @@ func (s *SQLiteStmt) Close() error {
 	}
 	rv := C.sqlite3_finalize(s.s)
 	if rv != C.SQLITE_OK {
-		return ErrNo(rv)
+		return s.c.lastError()
 	}
 	return nil
 }
@@ -342,7 +348,7 @@ func (s *SQLiteStmt) NumInput() int {
 func (s *SQLiteStmt) bind(args []driver.Value) error {
 	rv := C.sqlite3_reset(s.s)
 	if rv != C.SQLITE_ROW && rv != C.SQLITE_OK && rv != C.SQLITE_DONE {
-		return ErrNo(rv)
+		return s.c.lastError()
 	}
 
 	for i, v := range args {
@@ -387,7 +393,7 @@ func (s *SQLiteStmt) bind(args []driver.Value) error {
 			rv = C._sqlite3_bind_text(s.s, n, (*C.char)(unsafe.Pointer(&b[0])), C.int(len(b)))
 		}
 		if rv != C.SQLITE_OK {
-			return ErrNo(rv)
+			return s.c.lastError()
 		}
 	}
 	return nil
@@ -418,7 +424,7 @@ func (s *SQLiteStmt) Exec(args []driver.Value) (driver.Result, error) {
 	}
 	rv := C.sqlite3_step(s.s)
 	if rv != C.SQLITE_ROW && rv != C.SQLITE_OK && rv != C.SQLITE_DONE {
-		return nil, ErrNo(rv)
+		return nil, s.c.lastError()
 	}
 
 	res := &SQLiteResult{
@@ -435,7 +441,7 @@ func (rc *SQLiteRows) Close() error {
 	}
 	rv := C.sqlite3_reset(rc.s.s)
 	if rv != C.SQLITE_OK {
-		return ErrNo(rv)
+		return rc.s.c.lastError()
 	}
 	return nil
 }
@@ -460,7 +466,7 @@ func (rc *SQLiteRows) Next(dest []driver.Value) error {
 	if rv != C.SQLITE_ROW {
 		rv = C.sqlite3_reset(rc.s.s)
 		if rv != C.SQLITE_OK {
-			return ErrNo(rv)
+			return rc.s.c.lastError()
 		}
 		return nil
 	}