libc: Implement setenv() and unsetenv()

apps/su.cpp

@@ -92,8 +92,14 @@ Result<int> luna_main(int argc, char** argv)
     setuid(entry->pw_uid);
 
     chdir(entry->pw_dir);
+    if (setenv("HOME", entry->pw_dir, 1) < 0)
+    {
+        perror("setenv");
+        return 1;
+    }
 
     execl(entry->pw_shell, entry->pw_shell, NULL);
 
+    perror("execl");
     return 1;
 }

libc/include/stdlib.h

@@ -106,6 +106,12 @@ extern "C"
     /* Get the value of an environment variable. */
     char* getenv(const char* key);
 
+    /* Set the value of an environment variable. */
+    int setenv(const char* key, const char* value, int overwrite);
+
+    /* Remove a variable from the environment. */
+    int unsetenv(const char* key);
+
     void qsort(void*, size_t, size_t, int (*)(const void*, const void*));
     void* bsearch(const void*, const void*, size_t, size_t, int (*)(const void*, const void*));
 

libc/src/env.cpp

@@ -1,11 +1,17 @@
-#include <string.h>
+#include <luna/ScopeGuard.h>
+#include <luna/Vector.h>
 
-extern "C"
+#include <errno.h>
+#include <stdlib.h>
+
+extern "C" char** environ;
+Vector<char*> g_dynamic_env = {};
+bool env_is_dynamic { false };
+
+/* If an environment variable matching key is found, stores its value in value and returns its index. Otherwise,
+ * returns -1. */
+static isize _findenv(const char* key, char** value)
 {
-    char** environ = nullptr;
-
-    char* getenv(const char* key)
-    {
     char** env = environ;
     size_t len = strlen(key);
 
@@ -23,9 +29,145 @@ extern "C"
         if (len != key_length) continue;
 
         // If the keys match, we found it! Return the value (which is just after the equals sign)
-            if (!memcmp(key, var, key_length)) { return delim + 1; }
+        if (!memcmp(key, var, key_length))
+        {
+            if (value) *value = delim + 1;
+            return (env - environ) - 1;
+        }
     }
 
-        return nullptr;
+    return -1;
+}
+
+/* Move environ to a heap-allocated array. */
+static Result<void> _try_move_env()
+{
+    char** env = environ;
+    g_dynamic_env.clear();
+    auto guard = make_scope_guard([] {
+        for (auto element : g_dynamic_env)
+        {
+            if (element) free(element);
+        }
+    });
+
+    while (*env)
+    {
+        char* ptr = strdup(*(env++));
+        if (!ptr) return err(errno);
+
+        auto ptr_guard = make_scope_guard([=] { free(ptr); });
+        TRY(g_dynamic_env.try_append(ptr));
+        ptr_guard.deactivate();
+    }
+
+    TRY(g_dynamic_env.try_append(nullptr));
+
+    guard.deactivate();
+
+    env_is_dynamic = true;
+    environ = g_dynamic_env.data();
+
+    return {};
+}
+
+static int _move_env()
+{
+    auto rc = _try_move_env();
+    if (rc.has_error())
+    {
+        errno = rc.error();
+        return -1;
+    }
+    return 0;
+}
+
+static void _update_env()
+{
+    environ = g_dynamic_env.data();
+}
+
+extern "C"
+{
+    char** environ = nullptr;
+
+    int unsetenv(const char* key)
+    {
+        if (!key || *key == 0 || strchr(key, '='))
+        {
+            errno = EINVAL;
+            return -1;
+        }
+
+        auto index = _findenv(key, nullptr);
+        if (index < 0) return 0;
+
+        if (!env_is_dynamic)
+        {
+            if (_move_env() < 0) return -1;
+        }
+
+        g_dynamic_env.remove_at(index);
+        _update_env();
+
+        return 0;
+    }
+
+    int setenv(const char* key, const char* value, int overwrite)
+    {
+        if (!key || *key == 0 || strchr(key, '='))
+        {
+            errno = EINVAL;
+            return -1;
+        }
+
+        auto index = _findenv(key, nullptr);
+        if (index >= 0 && !overwrite) return 0;
+
+        if (!env_is_dynamic)
+        {
+            if (_move_env() < 0) return -1;
+        }
+
+        usize len = strlen(key) + strlen(value) + 2;
+
+        char* str = (char*)calloc(len, 1);
+        if (!str) return -1;
+        auto guard = make_scope_guard([=] { free(str); });
+
+        strncpy(str, key, strlen(key) + 1);
+        strncat(str, "=", 2);
+        strncat(str, value, strlen(value) + 1);
+
+        if (index >= 0)
+        {
+            free(environ[index]);
+            environ[index] = str;
+            guard.deactivate();
+            return 0;
+        }
+
+        // Add a new NULL at the end of the array and replace the previous one with our string.
+        index = g_dynamic_env.size() - 1;
+
+        auto rc = g_dynamic_env.try_append(nullptr);
+        if (rc.has_error())
+        {
+            errno = rc.error();
+            return -1;
+        }
+        guard.deactivate();
+        _update_env();
+
+        environ[index] = str;
+
+        return 0;
+    }
+
+    char* getenv(const char* key)
+    {
+        char* result;
+        if (_findenv(key, &result) < 0) return nullptr;
+        return result;
     }
 }