Thanks to John Cummings.

src/cmd/upas/fs/tester.c

@@ -0,0 +1,81 @@
+#include <u.h>
+#include <libc.h>
+#include <ctype.h>
+#include <String.h>
+#include "message.h"
+
+Message *root;
+
+void
+prindent(int i)
+{
+	for(; i > 0; i--)
+		print(" ");
+}
+
+void
+prstring(int indent, char *tag, String *s)
+{
+	if(s == nil)
+		return;
+	prindent(indent+1);
+	print("%s %s\n", tag, s_to_c(s));
+}
+
+void
+info(int indent, int mno, Message *m)
+{
+	int i;
+	Message *nm;
+
+	prindent(indent);
+	print("%d%c %d ", mno, m->allocated?'*':' ', m->end - m->start);
+	if(m->unixfrom != nil)
+		print("uf %s ", s_to_c(m->unixfrom));
+	if(m->unixdate != nil)
+		print("ud %s ", s_to_c(m->unixdate));
+	print("\n");
+	prstring(indent, "from:", m->from822);
+	prstring(indent, "sender:", m->sender822);
+	prstring(indent, "to:", m->to822);
+	prstring(indent, "cc:", m->cc822);
+	prstring(indent, "reply-to:", m->replyto822);
+	prstring(indent, "subject:", m->subject822);
+	prstring(indent, "date:", m->date822);
+	prstring(indent, "filename:", m->filename);
+	prstring(indent, "type:", m->type);
+	prstring(indent, "charset:", m->charset);
+
+	i = 1;
+	for(nm = m->part; nm != nil; nm = nm->next){
+		info(indent+1, i++, nm);
+	}
+}
+	
+
+void
+main(int argc, char **argv)
+{
+	char *err;
+	char *mboxfile;
+
+	ARGBEGIN{
+	}ARGEND;
+
+	if(argc > 0)
+		mboxfile = argv[0];
+	else
+		mboxfile = "./mbox";
+
+	root = newmessage(nil);
+
+	err = readmbox(mboxfile, &root->part);
+	if(err != nil){
+		fprint(2, "boom: %s\n", err);
+		exits(0);
+	}
+
+	info(0, 1, root);
+
+	exits(0);
+}