From 4bda74184186dd0e1d4657a0e6ff5c869ff6492c Mon Sep 17 00:00:00 2001
From: "Chloe M." <chloe@faracom.org>
Date: Tue, 28 Jul 2026 00:26:15 -0400
Subject: packer: Flush data descriptor table to output

Signed-off-by: Chloe M. <chloe@faracom.org>
---
 core/rdar.c | 99 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 91 insertions(+), 8 deletions(-)

diff --git a/core/rdar.c b/core/rdar.c
index b3a7c64..405bca0 100644
--- a/core/rdar.c
+++ b/core/rdar.c
@@ -13,6 +13,7 @@
 #include <stdint.h>
 #include <stddef.h>
 #include <stdlib.h>
+#include <stdbool.h>
 #include <dirent.h>
 #include <string.h>
 
@@ -37,7 +38,8 @@ struct idata_desc;
     (((VERSION) >> 8) & 0xFF)
 
 /* Pushes idata descriptor to table */
-#define IDATA_PUSH(IDATA_P) \
+#define IDATA_PUSH(IDATA_P)                             \
+    ++d_desc_count;                                     \
     TAILQ_INSERT_TAIL(&d_desc_table, (IDATA_P), link);
 
 /*
@@ -55,6 +57,19 @@ struct idata_desc;
 static const char *input_dir = NULL;
 static const char *output_path = NULL;
 static TAILQ_HEAD(, idata_desc) d_desc_table;
+static size_t d_desc_count = 1;
+
+/*
+ * The root data region (RDR) contains information about the
+ * entire archive.
+ *
+ * @desc_count:  Number of descriptors
+ * @revision:    Format revision
+ */
+struct root_data_region {
+    size_t desc_count;
+    uint16_t revision;
+};
 
 /*
  * Represents a file that has been mapped into memory
@@ -182,10 +197,11 @@ view_from_path(const char *path, struct file_view *result)
 /*
  * Allocate an internal data descriptor
  *
- * @path:   Path of file
+ * @path:     Path of file
+ * @is_root:  If set, don't create a view
  */
 static struct idata_desc *
-idata_from_file(const char *path)
+idata_from_file(const char *path, bool is_root)
 {
     struct idata_desc *idata_desc;
     struct data_desc *data_desc;
@@ -204,9 +220,11 @@ idata_from_file(const char *path)
         return NULL;
     }
 
-    if (view_from_path(path, &idata_desc->file) < 0) {
-        free(idata_desc);
-        return NULL;
+    if (!is_root) {
+        if (view_from_path(path, &idata_desc->file) < 0) {
+            free(idata_desc);
+            return NULL;
+        }
     }
 
     /* Initialize the data descriptor */
@@ -231,7 +249,7 @@ idata_push_root(void)
 {
     struct idata_desc *root;
 
-    root = idata_from_file("%root%");
+    root = idata_from_file("%root%", true);
     if (root == NULL) {
         return -1;
     }
@@ -257,6 +275,70 @@ idata_table_destroy(void)
     }
 }
 
+static void
+flush_root_desc(struct data_desc *d_desc, int out_fd)
+{
+    struct root_data_region rdr = {
+        .desc_count = d_desc_count,
+        .revision = RDAR_VERSION
+    };
+
+    d_desc->off = lseek(out_fd, 0, SEEK_CUR);
+    write(out_fd, &rdr, sizeof(rdr));
+}
+
+static void
+idata_table_flush(void)
+{
+    const struct file_view *view;
+    struct idata_desc *desc_iter;
+    struct data_desc *d_desc;
+    off_t new_off;
+    int fd;
+
+    fd = open(output_path, O_WRONLY | O_TRUNC | O_CREAT, 0666);
+    if (fd < 0) {
+        printf("fatal: failed to open output path\n");
+        perror("open");
+        return;
+    }
+
+    new_off = d_desc_count * sizeof(struct data_desc);
+    lseek(fd, new_off, SEEK_SET);
+
+    /* First pass write the file data */
+    TAILQ_FOREACH(desc_iter, &d_desc_table, link) {
+        view = &desc_iter->file;
+        d_desc = &desc_iter->data;
+
+        /*
+         * Check if we need to flush the root descriptor, we ignore any files that start
+         * with the '%' modifier.
+         */
+        if (d_desc->path[0] == '%') {
+            if (strcmp(d_desc->path, "%root%") == 0)
+                flush_root_desc(d_desc, fd);
+
+            continue;
+        }
+
+        d_desc->off = lseek(fd, 0, SEEK_CUR);
+        write(fd, view->data, view->length);
+    }
+
+    /* Data descriptors go at the start */
+    lseek(fd, 0, SEEK_SET);
+
+    /* Second pass write the data descriptors */
+    TAILQ_FOREACH(desc_iter, &d_desc_table, link) {
+        view = &desc_iter->file;
+        d_desc = &desc_iter->data;
+        write(fd, d_desc, sizeof(*d_desc));
+    }
+
+    close(fd);
+}
+
 static void
 recurse_dir(const char *dirpath)
 {
@@ -282,7 +364,7 @@ recurse_dir(const char *dirpath)
             snprintf(pathbuf, sizeof(pathbuf), "%s/%s", dirpath, dirent->d_name);
             printf("[f] %s\n", pathbuf);
 
-            idata_desc = idata_from_file(pathbuf);
+            idata_desc = idata_from_file(pathbuf, false);
             if (idata_desc == NULL) {
                 printf("warn: ignoring '%s'\n", pathbuf);
                 break;
@@ -352,6 +434,7 @@ main(int argc, char **argv)
     TAILQ_INIT(&d_desc_table);
     idata_push_root();
     recurse_dir(input_dir);
+    idata_table_flush();
     idata_table_destroy();
     return 0;
 }
-- 
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