From: Rafael Sadowski <rafael@sizeofvoid.org>
Subject: Re: httpd: remove MAX_IMSG_DATA_SIZE
To: tech@openbsd.org
Date: Sat, 17 Oct 2026 09:03:48 +0200

On Sat Oct 17, 2026 at 09:02:27AM +0200, Rafael Sadowski wrote:
> Remove MAX_IMSG_DATA_SIZE and we avoid having to calculate the length
> over and over again in a loop.
> 
> OK?
> 

Full diff ...

commit ff40a9b7c2f4879c791074d9e609ed97c8e28781
Author: Rafael Sadowski <rafael@sizeofvoid.org>
Date:   Sat Oct 17 08:59:57 2026 +0200

    httpd: remove MAX_IMSG_DATA_SIZE

diff --git a/config.c b/config.c
index 957da66..23a7042 100644
--- a/config.c
+++ b/config.c
@@ -320,7 +320,7 @@ config_settls(struct httpd *env, struct server *srv, enum tls_config_type type,
 	struct server_config	*srv_conf = &srv->srv_conf;
 	struct tls_config	 tls;
 	struct iovec		 iov[2];
-	size_t			 c;
+	size_t			 c, maxchunk;
 
 	if (data == NULL || len == 0)
 		return (0);
@@ -335,10 +335,13 @@ config_settls(struct httpd *env, struct server *srv, enum tls_config_type type,
 	tls.tls_len = len;
 	tls.tls_chunk_offset = 0;
 
+	/* largest chunk that fits next to the header into one imsg */
+	maxchunk = MAX_IMSGSIZE - IMSG_HEADER_SIZE - sizeof(tls);
+
 	while (len > 0) {
 		tls.tls_chunk_len = len;
-		if (tls.tls_chunk_len > (MAX_IMSG_DATA_SIZE - sizeof(tls)))
-			tls.tls_chunk_len = MAX_IMSG_DATA_SIZE - sizeof(tls);
+		if (tls.tls_chunk_len > maxchunk)
+			tls.tls_chunk_len = maxchunk;
 
 		c = 0;
 		iov[c].iov_base = &tls;
diff --git a/httpd.h b/httpd.h
index e238e04..381f8da 100644
--- a/httpd.h
+++ b/httpd.h
@@ -165,7 +165,6 @@ struct imsgev {
 };
 
 #define IMSG_DATA_SIZE(imsg)	((imsg)->hdr.len - IMSG_HEADER_SIZE)
-#define MAX_IMSG_DATA_SIZE	(MAX_IMSGSIZE - IMSG_HEADER_SIZE)
 
 enum imsg_type {
 	IMSG_NONE,