CLI/insert: escape envelope from

The idea is to do as little parsing and modification of the delivered
message as possible. Luckily the position of the "envelope header"
lets us escape it by replacing the first 5 characters of the stream
with a regular header name (with ':').

notmuch-insert.c

@@ -269,10 +269,13 @@ static bool
 copy_fd (int fdout, int fdin)
 {
     bool empty = true;
+    bool first = true;
+    const char *header = "X-Envelope-From: ";
 
     while (! interrupted) {
 	ssize_t remain;
 	char buf[4096];
+	const char *p = buf;
 
 	remain = read (fdin, buf, sizeof (buf));
 	if (remain == 0)
@@ -284,7 +287,17 @@ copy_fd (int fdout, int fdin)
 		     strerror (errno));
 	    return false;
 	}
-	if (! write_buf (buf, fdout, remain))
+
+	if (first && remain >= 5 && 0 == strncmp (buf, "From ", 5)) {
+	    if (! write_buf (header, fdout, strlen (header)))
+		return false;
+	    p += 5;
+	    remain -= 5;
+	}
+
+	first = false;
+
+	if (! write_buf (p, fdout, remain))
 	    return false;
 	empty = false;
     }

test/T070-insert.sh

@@ -293,7 +293,6 @@ for code in OUT_OF_MEMORY XAPIAN_EXCEPTION ; do
 done
 
 test_begin_subtest "insert converts mboxes on delivery"
-test_subtest_known_broken
 notmuch insert +unmboxed < "${TEST_DIRECTORY}"/corpora/indexing/mbox-attachment.eml
 output=$(notmuch count tag:unmboxed)
 test_expect_equal "${output}" 1