upas/fs: header ignores

[ori@eigenstate.org]

Now that the release is out, I'm going to
look at more email stuff. So, here's the
first bit of work, which does threee things:

- Remove /mail/lib/ignore, which filters
  the headers we show.
- Add /mail/lib/filterheaders, which has
  a new syntax: lines default to keep, but
  '!' can be used to drop a header:
- Add defaults.

The last time this came up, some people had
opinions on what reasonable defaults are,
so if you care, speak up.

Otherwise, the default behavior will be
unchanged from what we have today, since
I have no strong feelings on the matter.

diff -r 0281cd6caa8c sys/src/cmd/upas/fs/fs.c
--- a/sys/src/cmd/upas/fs/fs.c	Sat Oct 24 17:24:59 2020 -0700
+++ b/sys/src/cmd/upas/fs/fs.c	Sat Oct 24 17:46:15 2020 -0700
@@ -1500,11 +1500,31 @@
 typedef struct Ignorance Ignorance;
 struct Ignorance
 {
-	Ignorance *next;
+	int	drop;
+	int	len;
 	char	*str;
-	int	len;
 };
 static Ignorance *ignorance;
+static int nignorance;
+static Ignorance defaultignorance[] = {
+	{.drop=1, .len=13,	.str="Mime-Version:"},
+	{.drop=1, .len=8,	.str="Content-"},
+	{.drop=1, .len=11,	.str="Message-Id:"},
+	{.drop=1, .len=9,	.str="Received:"},
+	{.drop=1, .len=7,	.str="Mailer:"},
+	{.drop=1, .len=11,	.str="References:"},
+	{.drop=1, .len=11,	.str="Precedence:"},
+	{.drop=1, .len=2,	.str="X-"},
+	{.drop=1, .len=5,	.str="X400-"},
+	{.drop=1, .len=2,	.str="O-"},
+	{.drop=1, .len=5,	.str="List-"},
+	{.drop=1, .len=13,	.str="Organization:"},
+	{.drop=1, .len=11,	.str="User-Agent:"},
+	{.drop=1, .len=12,	.str="In-Reply-To:"},
+	{.drop=1, .len=13,	.str="Delivered-To:"},
+	{.drop=1, .len=20,	.str="DomainKey-Signature:"},
+	{.drop=1, .len=15,	.str="DKIM-Signature:"},
+};
 
 /*
  *  read the file of headers to ignore
@@ -1515,28 +1535,32 @@
 	char *p;
 	Ignorance *i;
 	Biobuf *b;
+	int drop;
 
 	if(ignorance != nil)
 		return;
 
-	b = Bopen("/mail/lib/ignore", OREAD);
-	if(b == 0)
+	b = Bopen("/mail/lib/filterheaders", OREAD);
+	if(b == nil){
+		ignorance = defaultignorance;
+		nignorance = nelem(defaultignorance);
 		return;
+	}
 	while(p = Brdline(b, '\n')){
 		p[Blinelen(b) - 1] = 0;
 		while(*p && (*p == ' ' || *p == '\t'))
 			p++;
-		if(*p == '#')
+		if(*p == '#' || *p == '\0')
 			continue;
-		i = emalloc(sizeof *i);
+		if(drop = (*p == '!'))
+			p++;
+		ignorance = erealloc(ignorance, ++nignorance*sizeof(*i));
+		i = &ignorance[nignorance - 1];
+		i->drop = drop;
 		i->len = strlen(p);
 		i->str = strdup(p);
-		if(i->str == 0){
-			free(i);
-			break;
-		}
-		i->next = ignorance;
-		ignorance = i;
+		if(i->str == nil)
+			sysfatal("strdup: %r");
 	}
 	Bterm(b);
 }
@@ -1547,9 +1571,9 @@
 	Ignorance *i;
 
 	readignore();
-	for(i = ignorance; i != nil; i = i->next)
+	for(i = ignorance; i != &ignorance[nignorance]; i++)
 		if(i->len <= n && cistrncmp(i->str, p, i->len) == 0)
-			return 1;
+			return i->drop;
 	return 0;
 }