From b251117ddd460bb2209f565d71121b17b4385881 Mon Sep 17 00:00:00 2001
From: Patrick McDermott <patrick.mcdermott@libiquity.com>
Date: Wed, 10 May 2023 06:11:03 -0400
Subject: dirent: Fix separators and length limits

---
diff --git a/src/dirent.c b/src/dirent.c
index b918a0d..7f361da 100644
--- a/src/dirent.c
+++ b/src/dirent.c
@@ -30,30 +30,43 @@ _opkg_opk_dirent_name_prefix(struct opkg_opk_dirent *dirent, char **name_buf,
 {
 	size_t   len;
 	char   **buf;
+	int      sep;
 
 	len = strlen(dirent->name);
-	if (*name_len + len <= *name_buf_len) {
+	if (*name_len > 0 && *name_len + len + 1 <= *name_buf_len) {
+		/* Space available in name buffer.  Not last node, so append
+		 * separator. */
 		buf = name_buf;
-		if (*buf == NULL) {
-			return OPKG_OPK_ERROR;
-		}
-		if (**buf != '\0') {
-			++len;
-		}
-		*name_buf_len -= len;
-	} else if (*pref_len + len <= *pref_buf_len) {
+		*name_len += len + 1;
+		sep = 1;
+	} else if (*name_len == 0 && *name_len + len <= *name_buf_len) {
+		/* Space available in name buffer.  Last node (first in
+		 * recursion), so don't append separator. */
+		buf = name_buf;
+		*name_len += len;
+		sep = 0;
+	} else if (*pref_len > 0 && *pref_len + len + 1 <= *pref_buf_len) {
+		/* Space available in prefix buffer.  Not last node, so append
+		 * separator. */
+		buf = pref_buf;
+		*pref_len += len + 1;
+		sep = 1;
+	} else if (*pref_len == 0 && *pref_len + len <= *pref_buf_len) {
+		/* Space available in prefix buffer.  Last node (first in
+		 * recursion), so don't append separator. */
 		buf = pref_buf;
-		if (*buf == NULL) {
-			return OPKG_OPK_ERROR;
-		}
-		if (**buf != '\0') {
-			++len;
-		}
-		*pref_buf_len -= len;
+		*pref_len += len;
+		sep = 0;
 	} else {
+		/* Both buffers full. */
+		return OPKG_OPK_ERROR;
+	}
+	if (*buf == NULL) {
+		/* Caller provided a NULL buffer pointer. */
 		return OPKG_OPK_ERROR;
 	}
 
+	/* Recurse. */
 	if (dirent->parent != NULL &&
 			_opkg_opk_dirent_name_prefix(dirent->parent,
 				name_buf, name_buf_len, pref_buf, pref_buf_len,
@@ -61,13 +74,13 @@ _opkg_opk_dirent_name_prefix(struct opkg_opk_dirent *dirent, char **name_buf,
 		return OPKG_OPK_ERROR;
 	}
 
-	if (**buf != '\0') {
+	/* Copy node name and possibly separator suffix. */
+	memcpy(*buf, dirent->name, len);
+	*buf += len;
+	if (sep == 1) {
 		**buf = '/';
 		*buf += 1;
-		--len;
 	}
-	memcpy(*buf, dirent->name, len);
-	*buf += len;
 
 	return OPKG_OPK_OK;
 }
@@ -76,18 +89,24 @@ int
 opkg_opk_dirent_name_prefix(struct opkg_opk_dirent *dirent, char *name_buf,
 		size_t name_buf_len, char *pref_buf, size_t pref_buf_len)
 {
-	size_t name_len = 0;
-	size_t pref_len = 0;
+	size_t  name_len = 0;
+	size_t  pref_len = 0;
+	char   *name     = name_buf;
+	char   *pref     = pref_buf;
+
+	/* NUL bytes */
+	--name_buf_len;
+	--pref_buf_len;
 
-	name_buf[0] = '\0';
-	pref_buf[0] = '\0';
 	if (_opkg_opk_dirent_name_prefix(dirent, &name_buf, &name_buf_len,
 				&pref_buf, &pref_buf_len, &name_len, &pref_len)
 			== OPKG_OPK_ERROR) {
 		return OPKG_OPK_ERROR;
 	}
-	name_buf[name_len] = '\0';
-	pref_buf[pref_len] = '\0';
+
+	name[name_len] = '\0';
+	pref[pref_len] = '\0';
+
 	return OPKG_OPK_OK;
 }
 
@@ -107,10 +126,10 @@ main()
 		.parent = &bar,
 	};
 	char  name[8];
-	char  pref[5];
+	char  pref[4];
 
-	if (opkg_opk_dirent_name_prefix(&baz, name, 8, pref, 5) != OPKG_OPK_OK)
-	{
+	if (opkg_opk_dirent_name_prefix(&baz, name, sizeof(name),
+				pref, sizeof(pref)) != OPKG_OPK_OK) {
 		puts("Error building name parts");
 		return EXIT_FAILURE;
 	}
--
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