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From: Andrew Bower <andrew@bower.uk>
Subject: Use empty memory table instead of failing to read empty file
Forwarded: https://github.com/thkukuk/wtmpdb/pull/39
Bug-Debian: https://bugs.debian.org/1094965
Last-Update: 2025-09-29
Previously, attempting to read an empty file gave an error
message and non-zero return code. Instead, when asked to open
an empty file as a read-only database, open a memory database
and populate it with an empty table. This avoids needing any
special case handling in calling code and matches the behaviour
of classic 'last' on an empty file.
---
lib/sqlite.c | 47 ++++++++++++++++++++++++++++++++---------------
1 file changed, 32 insertions(+), 15 deletions(-)
diff --git a/lib/sqlite.c b/lib/sqlite.c
index 001eb71..0f3090c 100644
--- a/lib/sqlite.c
+++ b/lib/sqlite.c
@@ -61,12 +61,37 @@ strip_extension(char *in_str)
}
}
+/* Creates the table if it does not exist.
+ * Returns 0 on success, -1 on failure. */
+static int64_t
+create_table (sqlite3 *db, char **error)
+{
+ char *err_msg = NULL;
+ char *sql_table = "CREATE TABLE IF NOT EXISTS wtmp(ID INTEGER PRIMARY KEY, Type INTEGER, User TEXT NOT NULL, Login INTEGER, Logout INTEGER, TTY TEXT, RemoteHost TEXT, Service TEXT) STRICT;";
+
+ if (sqlite3_exec (db, sql_table, 0, 0, &err_msg) != SQLITE_OK)
+ {
+ if (error)
+ if (asprintf (error, "SQL error creating table: %s", err_msg) < 0)
+ *error = strdup ("create_table: Out of memory");
+ sqlite3_free (err_msg);
+
+ return -1;
+ }
+ return 0;
+}
+
static int
open_database_ro (const char *path, sqlite3 **db, char **error)
{
+ struct stat statbuf;
+ int empty_file;
int r;
- r = sqlite3_open_v2 (path, db, SQLITE_OPEN_READONLY, NULL);
+ empty_file = stat(path, &statbuf) == 0 && statbuf.st_size == 0;
+ r = sqlite3_open_v2 (path, db, empty_file ?
+ SQLITE_OPEN_READWRITE | SQLITE_OPEN_MEMORY :
+ SQLITE_OPEN_READONLY, NULL);
if (r != SQLITE_OK)
{
if (error)
@@ -80,7 +105,10 @@ open_database_ro (const char *path, sqlite3 **db, char **error)
sqlite3_busy_timeout(*db, TIMEOUT);
- return 0;
+ if (empty_file)
+ r = create_table (*db, error);
+
+ return r == SQLITE_OK ? 0 : -1;
}
static int
@@ -114,7 +142,8 @@ open_database_rw (const char *path, sqlite3 **db, char **error)
sqlite3_busy_timeout(*db, TIMEOUT);
- return 0;
+ r = create_table (*db, error);
+ return r == SQLITE_OK ? 0 : -1;
}
/* Add a new entry. Returns ID (>=0) on success, -1 on failure. */
@@ -123,21 +152,9 @@ add_entry (sqlite3 *db, int type, const char *user,
uint64_t usec_login, const char *tty, const char *rhost,
const char *service, char **error)
{
- char *err_msg = NULL;
sqlite3_stmt *res;
- char *sql_table = "CREATE TABLE IF NOT EXISTS wtmp(ID INTEGER PRIMARY KEY, Type INTEGER, User TEXT NOT NULL, Login INTEGER, Logout INTEGER, TTY TEXT, RemoteHost TEXT, Service TEXT) STRICT;";
char *sql_insert = "INSERT INTO wtmp (Type,User,Login,TTY,RemoteHost,Service) VALUES(?,?,?,?,?,?);";
- if (sqlite3_exec (db, sql_table, 0, 0, &err_msg) != SQLITE_OK)
- {
- if (error)
- if (asprintf (error, "add_entry: SQL error: %s", err_msg) < 0)
- *error = strdup ("add_entry: Out of memory");
- sqlite3_free (err_msg);
-
- return -1;
- }
-
if (sqlite3_prepare_v2 (db, sql_insert, -1, &res, 0) != SQLITE_OK)
{
if (error)
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