libc: Add a password file and pwd.h

initrd/etc/passwd

@@ -0,0 +1,2 @@
+root:toor:0:0:Administrator:/:/bin/sh
+selene:moon:1000:1000:User:/home/selene:/bin/sh

libc/CMakeLists.txt

@@ -16,6 +16,7 @@ set(SOURCES
     src/dirent.cpp
     src/setjmp.cpp
     src/env.cpp
+    src/pwd.cpp
     src/sys/stat.cpp
     src/sys/mman.cpp
     src/sys/wait.cpp

libc/include/pwd.h

@@ -0,0 +1,43 @@
+/* pwd.h: Password file parsing. */
+
+#ifndef _PWD_H
+#define _PWD_H
+
+#include <sys/types.h>
+
+struct passwd
+{
+    char* pw_name;
+    char* pw_passwd;
+    uid_t pw_uid;
+    gid_t pw_gid;
+    char* pw_gecos;
+    char* pw_dir;
+    char* pw_shell;
+};
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+    /* Read the next entry from the password file. */
+    struct passwd* getpwent(void);
+
+    /* Find the entry with a matching username in the password file. */
+    struct passwd* getpwnam(const char* name);
+
+    /* Find the entry with a matching user ID in the password file. */
+    struct passwd* getpwuid(uid_t uid);
+
+    /* Rewind the password file. */
+    void setpwent(void);
+
+    /* End password file parsing. */
+    void endpwent(void);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif

libc/src/pwd.cpp

@@ -0,0 +1,109 @@
+#include <pwd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static struct passwd pwd;
+static FILE* f { nullptr };
+static char buf[4096];
+
+extern "C"
+{
+    struct passwd* getpwent()
+    {
+        if (!f)
+        {
+            f = fopen("/etc/passwd", "r");
+            if (!f) return nullptr;
+        }
+
+        while (true)
+        {
+            char* rc = fgets(buf, sizeof(buf), f);
+            if (!rc) return nullptr;
+
+            char* name = strtok(rc, ":\n");
+            if (!name) continue;
+
+            char* passwd = strtok(nullptr, ":\n");
+            if (!passwd) continue;
+
+            char* uid = strtok(nullptr, ":\n");
+            if (!uid) continue;
+
+            char* gid = strtok(nullptr, ":\n");
+            if (!gid) continue;
+
+            char* gecos = strtok(nullptr, ":\n");
+            if (!gecos) continue;
+
+            char* dir = strtok(nullptr, ":\n");
+            if (!dir) continue;
+
+            char* shell = strtok(nullptr, ":\n");
+            if (!shell) continue;
+
+            pwd.pw_name = name;
+            pwd.pw_passwd = passwd;
+            pwd.pw_uid = (uid_t)strtoul(uid, NULL, 10);
+            pwd.pw_gid = (gid_t)strtoul(gid, NULL, 10);
+            pwd.pw_gecos = gecos;
+            pwd.pw_dir = dir;
+            pwd.pw_shell = shell;
+
+            return &pwd;
+        }
+    }
+
+    struct passwd* getpwnam(const char* name)
+    {
+        setpwent();
+
+        struct passwd* entry;
+
+        while ((entry = getpwent()))
+        {
+            if (!strcmp(entry->pw_name, name))
+            {
+                endpwent();
+                return entry;
+            }
+        }
+
+        endpwent();
+        return entry;
+    }
+
+    struct passwd* getpwuid(uid_t uid)
+    {
+        setpwent();
+
+        struct passwd* entry;
+
+        while ((entry = getpwent()))
+        {
+            if (entry->pw_uid == uid)
+            {
+                endpwent();
+                return entry;
+            }
+        }
+
+        endpwent();
+        return entry;
+    }
+
+    void setpwent()
+    {
+        if (f) rewind(f);
+    }
+
+    void endpwent()
+    {
+        if (f)
+        {
+            fclose(f);
+            f = nullptr;
+        }
+    }
+}