From 63c984b897f009c07a73c3aaf11a24ecf9876411 Mon Sep 17 00:00:00 2001
From: David Woodhouse <dwmw2@infradead.org>
Date: Wed, 19 May 2021 10:45:39 +0100
Subject: [PATCH] Add more buf_append_base64() tests... and fix it.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
---
 tests/buftest.c | 15 +++++++++++++++
 textbuf.c       | 21 +++++++++++++++++----
 2 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/tests/buftest.c b/tests/buftest.c
index a15cb2ef..25bd20f7 100644
--- a/tests/buftest.c
+++ b/tests/buftest.c
@@ -101,6 +101,7 @@ struct oc_text_buf {
 	int error;
 };
 
+#define BUFTEST
 #include "../textbuf.c"
 
 #define assert(x) if (!(x)) {						\
@@ -133,6 +134,20 @@ int main(void)
 	buf_append_base64(buf, testbytes, -1, 0);
 	assert(buf_error(buf) == -EINVAL);
 
+	buf->error = 0;
+	buf_truncate(buf);
+
+	int ll;
+
+	for (ll = 0; ll < 128; ll += 4) {
+		for (len = 0; len < 16384; len++) {
+			buf_truncate(buf);
+			buf_append_base64(buf, testbytes, len, ll);
+			assert(!buf_error(buf));
+			if (len > 128)
+				len += len/2;
+		}
+	}
 	buf_free(buf);
 	return 0;
 }
diff --git a/textbuf.c b/textbuf.c
index a8b22a48..05d0bcc2 100644
--- a/textbuf.c
+++ b/textbuf.c
@@ -418,14 +418,17 @@ void buf_append_base64(struct oc_text_buf *buf, const void *bytes, int len,
 	if (!buf || buf->error)
 		return;
 
-	if (len < 0 || line_len < 0 || (line_len % 3)) {
+	if (len < 0 || line_len < 0 || (line_len & 3)) {
 		buf->error = -EINVAL;
 		return;
 	}
 
-	unsigned int needed = ((len + 2u) / 3) * 4 + 1;
-	if (line_len)
-		needed += needed / line_len;
+	unsigned int needed = ((len + 2u) / 3) * 4;
+
+	/* Line endings, but not for the last line if it reaches line_len */
+	if (line_len && needed)
+		needed += (needed - 1) / line_len;
+	needed++; /* Allow for the trailing NUL */
 
 	if (needed >= (unsigned)(OC_BUF_MAX - buf->pos)) {
 		buf->error = -E2BIG;
@@ -435,6 +438,9 @@ void buf_append_base64(struct oc_text_buf *buf, const void *bytes, int len,
 	if (buf_ensure_space(buf, needed))
 		return;
 
+#ifdef BUFTEST
+	int orig_len = len, orig_pos = buf->pos;
+#endif
 	int ll = 0;
 	while (len > 0) {
 		if (line_len) {
@@ -465,5 +471,12 @@ void buf_append_base64(struct oc_text_buf *buf, const void *bytes, int len,
 		in += 3;
 		len -= 3;
 	}
+#ifdef BUFTEST
+	if (buf->pos != orig_pos + needed - 1) {
+		printf("Used %d instead of calculated %d for %d bytes at line len %d\n",
+		       buf->pos - orig_pos, needed, orig_len, line_len);
+		buf->error = -EIO;
+	}
+#endif
 	buf->data[buf->pos] = 0;
 }
-- 
2.49.0