core: Add support for pointer boxes

Pointer boxes are a way to manage memory and have all references
released after operation, this way they do not need to be manually
managed.

Signed-off-by: Chloe M. <chloe@aptel.org>

5 files changed, 170 insertions, 2 deletions

diff --git a/core/lexer.c b/core/lexer.c
index 2eb50a1..e93c629 100644
--- a/core/lexer.c
+++ b/core/lexer.c
@@ -3,6 +3,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include "defconf/lexer.h"
+#include "defconf/ptrbox.h"
 
 /* Constants */
 #define MAX_KW_LEN 32
@@ -109,7 +110,7 @@ lexer_scan_ident(struct defconf_state *state, int lc)
         if (!isalnum(c) && c != '_') {
             lexer_putback(state, c);
             buf[bufind] = '\0';
-            return strdup(buf);
+            return ptrbox_strdup(&state->ptrbox, buf);
         }
 
         buf[bufind++] = c;
@@ -177,7 +178,6 @@ lexer_scan(struct defconf_state *state, struct token *result)
     /* Scan for an identifier */
     if ((ident = lexer_scan_ident(state, c)) != NULL) {
         if (lexer_check_kw(ident, result) == 0) {
-            free(ident);
             return 0;
         }
 
diff --git a/core/ptrbox.c b/core/ptrbox.c
new file mode 100644
index 0000000..f6e2254
--- /dev/null
+++ b/core/ptrbox.c
@@ -0,0 +1,98 @@
+/*
+ * Copyright (c) 2026, Apollo Telephone Laboratories.
+ * Provided under the BSD-3 clause.
+ */
+
+#include <stdlib.h>
+#include <string.h>
+#include "defconf/ptrbox.h"
+
+static inline void
+ptrbox_insert(struct ptrbox *ptrbox, struct ptrbox_entry *entry)
+{
+    if (ptrbox == NULL || entry == NULL) {
+        return;
+    }
+
+    TAILQ_INSERT_TAIL(&ptrbox->entries, entry, link);
+    ++ptrbox->entry_count;
+}
+
+/*
+ * Allocate a new pointer box entry
+ *
+ * @data:  Data to be associated with pointer box entry
+ */
+static struct ptrbox_entry *
+ptrbox_alloc_entry(void *data)
+{
+    struct ptrbox_entry *entry;
+
+    if (data == NULL) {
+        return NULL;
+    }
+
+    entry = malloc(sizeof(*entry));
+    if (entry == NULL) {
+        return NULL;
+    }
+
+    entry->data = data;
+    return entry;
+}
+
+char *
+ptrbox_strdup(struct ptrbox *ptrbox, const char *s)
+{
+    struct ptrbox_entry *entry;
+    char *dup;
+
+    if (ptrbox == NULL || s == NULL) {
+        return NULL;
+    }
+
+    if ((dup = strdup(s)) == NULL) {
+        return NULL;
+    }
+
+    if ((entry = ptrbox_alloc_entry(dup)) == NULL) {
+        free(dup);
+        return NULL;
+    }
+
+    ptrbox_insert(ptrbox, entry);
+    return dup;
+}
+
+int
+ptrbox_init(struct ptrbox *ptrbox)
+{
+    if (ptrbox == NULL) {
+        return -1;
+    }
+
+    TAILQ_INIT(&ptrbox->entries);
+    ptrbox->entry_count = 0;
+    return 0;
+}
+
+void
+ptrbox_destroy(struct ptrbox *ptrbox)
+{
+    struct ptrbox_entry *entry, *tmp;
+
+    if (ptrbox == NULL) {
+        return;
+    }
+
+    entry = TAILQ_FIRST(&ptrbox->entries);
+    while (entry != NULL) {
+        if (entry->data != NULL) {
+            free(entry->data);
+        }
+
+        tmp = entry;
+        entry = TAILQ_NEXT(entry, link);
+        free(tmp);
+    }
+}
diff --git a/core/state.c b/core/state.c
index ce1c286..c55a5be 100644
--- a/core/state.c
+++ b/core/state.c
@@ -9,6 +9,8 @@
 int
 defconf_state_init(const char *in_path, struct defconf_state *state)
 {
+    int error;
+
     if (in_path == NULL || state == NULL) {
         return -1;
     }
@@ -19,6 +21,12 @@ defconf_state_init(const char *in_path, struct defconf_state *state)
         return -1;
     }
 
+    if ((error = ptrbox_init(&state->ptrbox)) < 0) {
+        fclose(state->in_fp);
+        printf("fatal: failed to create pointer box\n");
+        return error;
+    }
+
     state->lex_cache = '\0';
     return 0;
 }
@@ -32,4 +40,5 @@ defconf_state_destroy(struct defconf_state *state)
 
     fclose(state->in_fp);
     state->in_fp = NULL;
+    ptrbox_destroy(&state->ptrbox);
 }
diff --git a/head/defconf/ptrbox.h b/head/defconf/ptrbox.h
new file mode 100644
index 0000000..3358595
--- /dev/null
+++ b/head/defconf/ptrbox.h
@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2026, Apollo Telephone Laboratories.
+ * Provided under the BSD-3 clause.
+ */
+
+#ifndef DEFCONF_PTRBOX_H
+#define DEFCONF_PTRBOX_H 1
+
+#include <sys/queue.h>
+#include <stdint.h>
+#include <stddef.h>
+
+/*
+ * Represents a pointer box entry
+ *
+ * @data:  Allocated data
+ * @link:  TAILQ link
+ */
+struct ptrbox_entry {
+    void *data;
+    TAILQ_ENTRY(ptrbox_entry) link;
+};
+
+/*
+ * A pointer box stores references to memory to be freed later on
+ *
+ * @entries:        Entries within pointer box
+ * @entry_count:    Number of pointer box entries
+ */
+struct ptrbox {
+    TAILQ_HEAD(, ptrbox_entry) entries;
+    size_t entry_count;
+};
+
+/*
+ * Wrapper over strdup() but saved in a pointer box
+ *
+ * @ptrbox:  Pointer box to allocate into
+ * @s:       String to dup
+ *
+ * Returns the base of the dup'd string on success, otherwise
+ * NULL on failure.
+ */
+char *ptrbox_strdup(struct ptrbox *ptrbox, const char *s);
+
+/*
+ * Initialize a pointer box
+ */
+int ptrbox_init(struct ptrbox *ptrbox);
+
+/*
+ * Destroy a pointer box and all of its entries
+ *
+ * @ptrbox: Pointer box to destroy
+ */
+void ptrbox_destroy(struct ptrbox *ptrbox);
+
+#endif  /* !DEFCONF_PTRBOX_H */
diff --git a/head/defconf/state.h b/head/defconf/state.h
index 524af3b..aa99105 100644
--- a/head/defconf/state.h
+++ b/head/defconf/state.h
@@ -9,16 +9,19 @@
 #include <stdint.h>
 #include <stddef.h>
 #include <stdio.h>
+#include "defconf/ptrbox.h"
 
 /*
  * DEFCONF state machine
  *
  * @in_fp:      Input file pointer
  * @lex_cache:  Putback cache
+ * @ptrbox:     Global pointer box
  */
 struct defconf_state {
     FILE *in_fp;
     int lex_cache;
+    struct ptrbox ptrbox;
 };
 
 /*