Users (Linux): adds systemd fallback for user detection on Linux

Fixes #2064

src/detection/users/users_linux.c

@@ -1,6 +1,10 @@
+#include "common/io/io.h"
+#include "common/properties.h"
 #include "fastfetch.h"
 #include "users.h"
 
+#include <unistd.h>
+
 #if FF_HAVE_UTMPX
     #include <utmpx.h>
 #else
@@ -15,7 +19,111 @@
     #include <arpa/inet.h>
 #endif
 
-const char* ffDetectUsers(FFUsersOptions* options, FFlist* users)
+#if __linux__
+bool detectUserBySystemd(const FFstrbuf* pathUsers, FFlist* users)
+{
+    FF_STRBUF_AUTO_DESTROY state = ffStrbufCreate();
+    FF_STRBUF_AUTO_DESTROY userName = ffStrbufCreate();
+    FF_STRBUF_AUTO_DESTROY loginTime = ffStrbufCreate();
+    FF_STRBUF_AUTO_DESTROY sessions = ffStrbufCreate();
+
+    // WARNING: This is private data. Do not parse
+    if (!ffParsePropFileValues(pathUsers->chars, 4, (FFpropquery[]) {
+        {"NAME=", &userName},
+        {"STATE=", &state},
+        {"REALTIME=", &loginTime},
+        {"ONLINE_SESSIONS=", &sessions},
+    }) || !ffStrbufEqualS(&state, "active"))
+        return false;
+
+    FFUserResult* user = FF_LIST_ADD(FFUserResult, *users);
+    ffStrbufInitMove(&user->name, &userName);
+    ffStrbufInit(&user->hostName);
+    ffStrbufInit(&user->sessionName);
+    ffStrbufInit(&user->clientIp);
+    ffStrbufSubstrBefore(&loginTime, loginTime.length - 3); // converts us to ms
+    user->loginTime = ffStrbufToUInt(&loginTime, 0);
+
+    FF_STRBUF_AUTO_DESTROY pathSessions = ffStrbufCreateS("/run/systemd/sessions/");
+    const uint32_t pathSessionsBaseLen = pathSessions.length;
+
+    FF_STRBUF_AUTO_DESTROY tty = ffStrbufCreate();
+    FF_STRBUF_AUTO_DESTROY remoteHost = ffStrbufCreate();
+    FF_STRBUF_AUTO_DESTROY service = ffStrbufCreate();
+
+    char* token = NULL;
+    size_t n = 0;
+    while (ffStrbufGetdelim(&token, &n, ' ', &sessions))
+    {
+        ffStrbufSubstrBefore(&pathSessions, pathSessionsBaseLen);
+        ffStrbufAppendS(&pathSessions, token);
+
+        ffStrbufClear(&remoteHost);
+        ffStrbufClear(&service);
+        ffStrbufClear(&tty);
+        ffStrbufClear(&loginTime);
+
+        // WARNING: This is private data. Do not parse
+        if (ffParsePropFileValues(pathSessions.chars, 4, (FFpropquery[]) {
+            {"REMOTE_HOST=", &remoteHost},
+            {"TTY=", &tty},
+            {"SERVICE=", &service},
+            {"REALTIME=", &loginTime},
+        }) && !ffStrbufEqualS(&service, "systemd-user"))
+        {
+            if (remoteHost.length)
+            {
+                ffStrbufTrimRight(&remoteHost, ']');
+                ffStrbufTrimLeft(&remoteHost, '[');
+                ffStrbufInitMove(&user->hostName, &remoteHost);
+            }
+            else
+                ffStrbufSetStatic(&user->hostName, "localhost");
+            ffStrbufInitMove(&user->sessionName, tty.length ? &tty : &service);
+            if (loginTime.length)
+            {
+                ffStrbufSubstrBefore(&loginTime, loginTime.length - 3); // converts us to ms
+                user->loginTime = ffStrbufToUInt(&loginTime, 0);
+            }
+            break;
+        }
+    }
+
+    return true;
+}
+
+const char* detectBySystemd(FFUsersOptions* options, FFlist* users)
+{
+    // For some reason, debian/ubuntu no longer updates `/var/run/utmp` (#2064)
+    // Query systemd instead
+    FF_STRBUF_AUTO_DESTROY pathUsers = ffStrbufCreateS("/run/systemd/users/");
+
+    if (options->myselfOnly)
+    {
+        ffStrbufAppendUInt(&pathUsers, getuid());
+        detectUserBySystemd(&pathUsers, users);
+    }
+    else
+    {
+        const uint32_t pathUsersBaseLen = pathUsers.length;
+        FF_AUTO_CLOSE_DIR DIR* dirp = opendir(pathUsers.chars);
+        if (!dirp) return "opendir(\"/run/systemd/users/\") failed";
+
+        struct dirent* entry;
+        while ((entry = readdir(dirp)))
+        {
+            if (entry->d_type != DT_REG) continue;
+
+            ffStrbufAppendS(&pathUsers, entry->d_name);
+            detectUserBySystemd(&pathUsers, users);
+            ffStrbufSubstrBefore(&pathUsers, pathUsersBaseLen);
+        }
+    }
+    return NULL;
+}
+#endif
+
+const char* detectByUtmp(FFUsersOptions* options, FFlist* users)
 {
     struct utmpx* n = NULL;
     setutxent();
@@ -35,7 +143,7 @@ next:
                 goto next;
         }
 
-        FFUserResult* user = (FFUserResult*) ffListAdd(users);
+        FFUserResult* user = FF_LIST_ADD(FFUserResult, *users);
         ffStrbufInitS(&user->name, n->ut_user);
         ffStrbufInitS(&user->hostName, n->ut_host);
         ffStrbufInitS(&user->sessionName, n->ut_line);
@@ -68,3 +176,15 @@ next:
 
     return NULL;
 }
+
+const char* ffDetectUsers(FFUsersOptions* options, FFlist* users)
+{
+    const char* err = detectByUtmp(options, users);
+    if (err) return err;
+
+    #if __linux__
+    if (users->length == 0) detectBySystemd(options, users);
+    #endif
+
+    return NULL;
+}