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To: 9front@9front.org
Subject: Re: [9front] [Bug] [PATCH] Mail cannot cope with multi-line header fields
Date: Fri, 11 Sep 2020 23:08:06 +0200
From: theinicke@bss-wf.de
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X-Bullshit: virtual virtual method-oriented locator 

Then the simplest way to do that might be something like the following (remove all line breaks from info fields, preserving it everywhere else).
But maybe we would like to take into account the fact that some info fields never contain line breaks or remove them not just in info file but earlier by stripping them in copy822,..

diff -r d8b6a8706f51 sys/src/cmd/upas/fs/fs.c
--- a/sys/src/cmd/upas/fs/fs.c	Mon Sep 07 19:32:50 2020 -0700
+++ b/sys/src/cmd/upas/fs/fs.c	Fri Sep 11 23:03:08 2020 +0200
@@ -387,6 +387,33 @@
 	return s;
 }
 
+int
+unfold(char *s, int len, char **pp)
+{
+	int i, u;
+	char c;
+	char *p;
+
+	if(s == nil) {
+		return 0;
+	}
+
+	p = malloc(len);
+	*pp = p;
+	u = 0;
+	for(i = 0; i < len; i++) {
+		c = s[i];
+		if(c != '\n') {
+			p[u++] = c;
+		}
+	}
+	if(u < len) {
+		p[u] = '\0';
+	}
+
+	return u;
+}
+
 static int
 fileinfo(Mailbox *mb, Message *m, int t, char **pp)
 {
@@ -568,7 +595,7 @@
 int
 readinfo(Mailbox *mb, Message *m, char *buf, long off, int count)
 {
-	char *s, *p, *e;
+	char *s, *p, *e, *q;
 	int i, n;
 	long off0;
 
@@ -584,18 +611,22 @@
 		}
 		if((n = fileinfo(mb, m, infofields[i], &p)) < 0)
 			return -1;
+		/* remove line breaks in fields s.t. consumers of info
+		can rely on finding particular field at certain line */
+		n = unfold(p, n, &q);
 		if(off > n){
 			off -= n + 1;
 			continue;
 		}
 		if(off){
 			n -= off;
-			p += off;
+			q += off;
 			off = 0;
 		}
 		if(s + n > e)
 			n = e - s;
-		memcpy(s, p, n);
+		memcpy(s, q, n);
+		free(q);
 		s += n;
 		if(s < e)
 			*s++ = '\n';