lib: libc: Introduce POSIX getlogin()

Signed-off-by: Ian Moffett <ian@osmora.org>

1 files changed, 109 insertions, 0 deletions

diff --git a/lib/libc/src/unistd/getlogin.c b/lib/libc/src/unistd/getlogin.c
new file mode 100644
index 0000000..91f326c
--- /dev/null
+++ b/lib/libc/src/unistd/getlogin.c
@@ -0,0 +1,109 @@
+/*
+ * Copyright (c) 2023-2025 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <sys/types.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <string.h>
+
+#define UNKNOWN_USER "unknown"
+
+static char *ucache = NULL;
+
+static int
+match_entry(uid_t uid, char *entry)
+{
+    char uidstr[16];
+    static char *username = NULL;
+    char *p;
+    size_t len;
+    uint8_t row = 0;
+
+    if (itoa(uid, uidstr, 10) == NULL) {
+        return -1;
+    }
+
+    p = strtok(entry, ":");
+    if (p == NULL) {
+        return -1;
+    }
+
+    while (p != NULL) {
+        switch (row) {
+        case 0:
+            username = p;
+            break;
+        case 2:
+            /*
+             * If the user ID matches, we'll cache the
+             * username.
+             */
+            if (strcmp(uidstr, p) == 0) {
+                ucache = username;
+                return 0;
+            }
+            break;
+        }
+
+        p = strtok(NULL, ":");
+        ++row;
+    }
+
+    return -1;
+}
+
+char *
+getlogin(void)
+{
+    FILE *fp;
+    char entry[256];
+    int retval;
+    uid_t uid = getuid();
+
+    /* Get the user from the cache */
+    if (ucache != NULL) {
+        return ucache;
+    }
+
+    fp = fopen("/etc/passwd", "r");
+    if (fp == NULL) {
+        return UNKNOWN_USER;
+    }
+
+    while (fgets(entry, sizeof(entry), fp) != NULL) {
+        if (match_entry(uid, entry) == 0) {
+            fclose(fp);
+            return ucache;
+        }
+    }
+
+    fclose(fp);
+    return UNKNOWN_USER;
+}