fix: harden flatfile backend, make SQLite optional

Build system:
- Add --without-sqlite configure flag (AM_CONDITIONAL BUILD_SQLITE)
- Guard database_sqlite.c with HAVE_SQLITE in Makefile.am, database.c,
  database.h and stub_database.c
- Fall back to flatfile when SQLite not compiled in

Security (database_flatfile.c):
- MAM dedup: skip incoming messages with duplicate stanza-id (archive_id)
- LMC sender validation: reject corrections from mismatched JIDs
- Add flock() advisory locking to prevent interleaved writes from
  concurrent instances
- Check fprintf return when writing file header

Autocomplete (cmd_ac.c):
- Add 'flatfile' to /privacy logging autocomplete
- Add dedicated /history autocomplete with on/off/verify (was boolean-only)

Code quality:
- Fix fwrite return type: size_t not ssize_t (database_flatfile_parser.c)
- Fix mixed allocators in ff_readline: use malloc() consistently for
  overlength-line fallback instead of g_strdup()
- Fix index alignment in _ff_state_extend: use local counter so index
  step doesn't depend on total_lines from initial build

Documentation:
- Fix page: correct directory structure (history.log not per-day files)
- Fix page: add aid:{archive_id} to line format example
- Fix page: missing newline before .SH BUGS

Makefile.am

@@ -3,7 +3,6 @@ core_sources = \
 	src/log.c src/common.c \
 	src/chatlog.c src/chatlog.h \
 	src/database.h src/database.c \
-	src/database_sqlite.c \
 	src/database_flatfile.c src/database_flatfile.h \
 	src/database_flatfile_parser.c \
 	src/database_flatfile_verify.c \
@@ -259,6 +258,12 @@ core_sources += $(omemo_sources)
 unittest_sources += $(omemo_unittest_sources)
 endif
 
+sqlite_sources = src/database_sqlite.c
+
+if BUILD_SQLITE
+core_sources += $(sqlite_sources)
+endif
+
 all_c_sources = $(core_sources) $(unittest_sources) \
 				$(pgp_sources) $(pgp_unittest_sources) \
 				$(otr4_sources) $(otr_unittest_sources) \

configure.ac

@@ -94,8 +94,17 @@ PKG_CHECK_MODULES([curl], [libcurl >= 7.62.0], [],
     [AC_CHECK_LIB([curl], [main], [],
         [AC_MSG_ERROR([libcurl 7.62.0 or higher is required])])])
 
-PKG_CHECK_MODULES([SQLITE], [sqlite3 >= 3.22.0], [],
+### sqlite (optional — can be disabled with --without-sqlite)
-    [AC_MSG_ERROR([sqlite3 3.22.0 or higher is required])])
+AC_ARG_WITH([sqlite],
+    [AS_HELP_STRING([--without-sqlite], [build without SQLite support (flat-file backend only)])],
+    [], [with_sqlite=yes])
+
+AS_IF([test "x$with_sqlite" != "xno"],
+    [PKG_CHECK_MODULES([SQLITE], [sqlite3 >= 3.22.0],
+        [AC_DEFINE([HAVE_SQLITE], [1], [SQLite support])],
+        [AC_MSG_ERROR([sqlite3 3.22.0 or higher is required (use --without-sqlite to disable)])])],
+    [AC_MSG_NOTICE([Building without SQLite — flat-file backend only])])
+AM_CONDITIONAL([BUILD_SQLITE], [test "x$with_sqlite" != "xno"])
 
 ACX_PTHREAD([], [AC_MSG_ERROR([pthread is required])])
 AS_IF([test "x$PTHREAD_CC" != x], [ CC="$PTHREAD_CC" ])
@@ -416,6 +425,7 @@ AC_OUTPUT
 AC_MSG_NOTICE([Summary of build options:
 PLATFORM                   : $target_os
 PACKAGE_STATUS             : $PACKAGE_STATUS
+SQLite support             : $with_sqlite
 GTK_VERSION                : $GTK_VERSION
 LIBS                       : $LIBS
 Install themes             : $THEMES_INSTALL

docs/profanity.1

@@ -215,17 +215,18 @@ Or use the command:
 Flat-file logs are stored under
 .IR $XDG_DATA_HOME/profanity/flatlog/ ,
 organized as
-.IR {account_jid}/{contact_jid}/{YYYY_MM_DD}.log .
+.IR {account_jid}/{contact_jid}/history.log .
 .PP
 Each line has the format:
 .br
 .EX
-{ISO8601} [{type}|{enc}|id:{id}|corrects:{id}] {sender}: {message}
+{ISO8601} [{type}|{enc}|id:{id}|aid:{archive_id}|corrects:{id}] {sender}: {message}
 .EE
 .PP
 Use
 .B /history verify
-to check integrity of stored history (both SQLite and flat-file)..SH BUGS
+to check integrity of stored history (both SQLite and flat-file).
+.SH BUGS
 Bugs can either be reported by raising an issue at the Github issue tracker:
 .br
 .PP

src/command/cmd_ac.c

@@ -275,6 +275,7 @@ static Autocomplete logging_ac;
 static Autocomplete logging_group_ac;
 static Autocomplete privacy_ac;
 static Autocomplete privacy_log_ac;
+static Autocomplete history_ac;
 static Autocomplete color_ac;
 static Autocomplete correction_ac;
 static Autocomplete avatar_ac;
@@ -429,6 +430,7 @@ static Autocomplete* all_acs[] = {
     &logging_group_ac,
     &privacy_ac,
     &privacy_log_ac,
+    &history_ac,
     &color_ac,
     &correction_ac,
     &avatar_ac,
@@ -1138,6 +1140,11 @@ cmd_ac_init(void)
     autocomplete_add(privacy_log_ac, "on");
     autocomplete_add(privacy_log_ac, "off");
     autocomplete_add(privacy_log_ac, "redact");
+    autocomplete_add(privacy_log_ac, "flatfile");
+
+    autocomplete_add(history_ac, "on");
+    autocomplete_add(history_ac, "off");
+    autocomplete_add(history_ac, "verify");
 
     autocomplete_add(logging_group_ac, "on");
     autocomplete_add(logging_group_ac, "off");
@@ -1776,7 +1783,7 @@ _cmd_ac_complete_params(ProfWin* window, const char* const input, gboolean previ
 
     // autocomplete boolean settings
     gchar* boolean_choices[] = { "/beep", "/states", "/outtype", "/flash", "/splash",
-                                 "/history", "/vercheck", "/privileges", "/wrap",
+                                 "/vercheck", "/privileges", "/wrap",
                                  "/carbons", "/slashguard", "/mam", "/silence" };
 
     for (int i = 0; i < ARRAY_SIZE(boolean_choices); i++) {
@@ -1786,6 +1793,11 @@ _cmd_ac_complete_params(ProfWin* window, const char* const input, gboolean previ
         }
     }
 
+    result = autocomplete_param_with_ac(input, "/history", history_ac, TRUE, previous);
+    if (result) {
+        return result;
+    }
+
     // autocomplete nickname in chat rooms
     if (window->type == WIN_MUC) {
         ProfMucWin* mucwin = (ProfMucWin*)window;

src/database.c

@@ -41,6 +41,7 @@
 
 #include "log.h"
 #include "common.h"
+#include "config.h"
 #include "database.h"
 #include "config/preferences.h"
 #include "ui/ui.h"
@@ -69,8 +70,13 @@ log_database_init(ProfAccount* account)
         active_db_backend = db_backend_flatfile();
         log_info("Using flat-file database backend");
     } else {
+#ifdef HAVE_SQLITE
         active_db_backend = db_backend_sqlite();
         log_info("Using SQLite database backend");
+#else
+        log_info("SQLite not compiled in, falling back to flat-file backend");
+        active_db_backend = db_backend_flatfile();
+#endif
     }
 
     if (!active_db_backend) {

src/database.h

@@ -85,7 +85,9 @@ typedef struct db_backend_t
 extern db_backend_t* active_db_backend;
 
 // Backend registry
+#ifdef HAVE_SQLITE
 db_backend_t* db_backend_sqlite(void);
+#endif
 db_backend_t* db_backend_flatfile(void);
 
 // Public API (dispatches to active_db_backend)

src/database_flatfile.c

@@ -33,6 +33,7 @@
 #include <unistd.h>
 #include <sys/stat.h>
 #include <sys/types.h>
+#include <sys/file.h>
 #include <glib.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -180,7 +181,9 @@ _ff_state_extend(ff_contact_state_t* state)
         }
     }
 
-    size_t msg_count = state->total_lines;
+    // Use a local counter for new messages so index step alignment
+    // doesn't depend on the total from the initial build.
+    size_t new_count = 0;
 
     while (1) {
         off_t pos = ftell(fp);
@@ -200,7 +203,7 @@ _ff_state_extend(ff_contact_state_t* state)
 
         state->total_lines++;
 
-        if (msg_count % FF_INDEX_STEP == 0) {
+        if (new_count % FF_INDEX_STEP == 0) {
             char* space = strchr(buf, ' ');
             if (space) {
                 char* ts_str = g_strndup(buf, space - buf);
@@ -219,7 +222,7 @@ _ff_state_extend(ff_contact_state_t* state)
                 g_free(ts_str);
             }
         }
-        msg_count++;
+        new_count++;
         free(buf);
     }
 
@@ -390,8 +393,17 @@ _ff_add_message(const char* type, const char* stanza_id, const char* archive_id,
         return;
     }
 
+    // Advisory lock to prevent interleaved writes from concurrent instances
+    if (flock(fd, LOCK_EX) != 0) {
+        log_warning("flatfile: flock(%s) failed (errno=%d: %s), writing anyway",
+                    log_path, errno, strerror(errno));
+    }
+
     if (is_new) {
-        fprintf(fp, "%s", FLATFILE_HEADER);
+        if (fprintf(fp, "%s", FLATFILE_HEADER) < 0) {
+            log_error("flatfile: failed to write header to %s (errno=%d)",
+                      log_path, errno);
+        }
     }
 
     ff_write_line(fp, date_fmt, type, ff_get_message_enc_str(enc),
@@ -399,6 +411,7 @@ _ff_add_message(const char* type, const char* stanza_id, const char* archive_id,
                   from_barejid, from_resource, effective_msg);
 
     fflush(fp);
+    // fclose also releases the flock
     fclose(fp);
     g_free(effective_msg);
 }
@@ -453,6 +466,82 @@ _flatfile_close(void)
 // Backend callbacks: add message
 // =========================================================================
 
+// =========================================================================
+// Incoming message validation helpers
+// =========================================================================
+
+// Search log file for a line containing aid:{archive_id}, return TRUE if found.
+static gboolean
+_ff_has_archive_id(const char* log_path, const char* archive_id)
+{
+    if (!log_path || !archive_id || strlen(archive_id) == 0)
+        return FALSE;
+
+    FILE* fp = fopen(log_path, "r");
+    if (!fp)
+        return FALSE;
+
+    auto_gchar gchar* needle = g_strdup_printf("aid:%s", archive_id);
+    gboolean found = FALSE;
+
+    while (!found) {
+        gboolean trunc = FALSE;
+        char* line = ff_readline(fp, &trunc);
+        if (!line)
+            break;
+        if (trunc) {
+            free(line);
+            break;
+        }
+        if (strstr(line, needle)) {
+            found = TRUE;
+        }
+        free(line);
+    }
+
+    fclose(fp);
+    return found;
+}
+
+// Search log file for a line with stanza id matching replace_id, return the
+// from_jid of the original message (caller must g_free). Returns NULL if not found.
+static char*
+_ff_find_original_sender(const char* log_path, const char* replace_id)
+{
+    if (!log_path || !replace_id || strlen(replace_id) == 0)
+        return NULL;
+
+    FILE* fp = fopen(log_path, "r");
+    if (!fp)
+        return NULL;
+
+    auto_gchar gchar* needle = g_strdup_printf("id:%s", replace_id);
+    char* sender = NULL;
+
+    while (!sender) {
+        gboolean trunc = FALSE;
+        char* line = ff_readline(fp, &trunc);
+        if (!line)
+            break;
+        if (trunc) {
+            free(line);
+            break;
+        }
+        if (strstr(line, needle)) {
+            ff_parsed_line_t* pl = ff_parse_line(line);
+            if (pl && pl->stanza_id && g_strcmp0(pl->stanza_id, replace_id) == 0) {
+                sender = g_strdup(pl->from_jid);
+            }
+            if (pl)
+                ff_parsed_line_free(pl);
+        }
+        free(line);
+    }
+
+    fclose(fp);
+    return sender;
+}
+
 static void
 _flatfile_add_incoming(ProfMessage* message)
 {
@@ -462,6 +551,39 @@ _flatfile_add_incoming(ProfMessage* message)
     const Jid* to_jid = message->to_jid ? message->to_jid : connection_get_jid();
     const char* type = ff_get_message_type_str(message->type);
 
+    // Determine contact JID for log path (same logic as _ff_add_message)
+    const char* contact = NULL;
+    const Jid* myjid = connection_get_jid();
+    if (myjid && myjid->barejid && g_strcmp0(message->from_jid->barejid, myjid->barejid) == 0) {
+        contact = to_jid->barejid;
+    } else {
+        contact = message->from_jid->barejid;
+    }
+    auto_gchar gchar* log_path = ff_get_log_path(contact);
+
+    // MAM dedup: skip if this stanza-id already exists in the log (XEP-0313 replay)
+    if (message->stanzaid && !message->is_mam && log_path) {
+        if (_ff_has_archive_id(log_path, message->stanzaid)) {
+            log_error("flatfile: duplicate stanza-id '%s' from %s, skipping",
+                      message->stanzaid, message->from_jid->barejid);
+            cons_show_error("Got a message with duplicate (server-generated) stanza-id from %s.",
+                            message->from_jid->fulljid);
+            return;
+        }
+    }
+
+    // LMC sender validation: verify the correction comes from the original sender
+    if (message->replace_id && log_path) {
+        auto_gchar gchar* original_sender = _ff_find_original_sender(log_path, message->replace_id);
+        if (original_sender && g_strcmp0(original_sender, message->from_jid->barejid) != 0) {
+            log_error("flatfile: LMC sender mismatch — corrected msg sender: %s, original: %s, replace-id: %s",
+                      message->from_jid->barejid, original_sender, message->replace_id);
+            cons_show_error("%s sent a message correction with mismatched sender. See log for details.",
+                            message->from_jid->barejid);
+            return;
+        }
+    }
+
     _ff_add_message(type, message->id, message->stanzaid, message->replace_id,
                     message->from_jid->barejid, message->from_jid->resourcepart,
                     to_jid->barejid, message->plain,

src/database_flatfile_parser.c

@@ -369,8 +369,11 @@ ff_readline(FILE* fp, gboolean* truncated)
         }
         if (truncated)
             *truncated = FALSE;
-        // Return empty string so caller's loop continues (parse will reject it)
+        // Return empty string so caller's loop continues (parse will reject it).
-        return g_strdup("");
+        // Use malloc() so callers can always use free() consistently.
+        char* empty = malloc(1);
+        if (empty) empty[0] = '\0';
+        return empty;
     }
     if (truncated)
         *truncated = FALSE;
@@ -450,9 +453,9 @@ ff_write_line(FILE* fp, const char* timestamp, const char* type, const char* enc
                     timestamp, meta->str, sender->str, safe_msg);
 
     size_t to_write = full_line->len;
-    ssize_t written = fwrite(full_line->str, 1, to_write, fp);
+    size_t written = fwrite(full_line->str, 1, to_write, fp);
-    if (written != (ssize_t)to_write) {
+    if (written != to_write) {
-        log_error("flatfile: partial write (%zd/%zu)", written, to_write);
+        log_error("flatfile: partial write (%zu/%zu)", written, to_write);
     }
 
     g_string_free(full_line, TRUE);

tests/unittests/database/stub_database.c

@@ -23,6 +23,7 @@
 #include <glib.h>
 #include "prof_cmocka.h"
 
+#include "config.h"
 #include "database.h"
 
 db_backend_t* active_db_backend = NULL;
@@ -66,11 +67,13 @@ integrity_issue_free(integrity_issue_t* issue)
         g_free(issue);
     }
 }
+#ifdef HAVE_SQLITE
 db_backend_t*
 db_backend_sqlite(void)
 {
     return NULL;
 }
+#endif
 db_backend_t*
 db_backend_flatfile(void)
 {