test: Add SPF integration test

This patch adds a new integration test to cover SPF checks. The main
goal is not to cover the SPF parsing, since that's handled by the
library already, but the higher level aspects: that the mails are indeed
rejected, that the DSN looks reasonable, etc.

test/t-16-spf/run.sh

@@ -0,0 +1,68 @@
+#!/bin/bash
+
+# Test SPF resolution, which requires overriding DNS server.
+# Note this aims at providing some general end to end coverage, as well as the
+# main gaps.
+
+set -e
+. $(dirname ${0})/../util/lib.sh
+
+init
+
+# Build with the DNS override, so we can fake DNS records.
+export GOTAGS="dnsoverride"
+
+# Two chasquid servers:
+# A - listens on :1025, hosts srv-A
+# B - listens on :2025, hosts srv-B
+
+CONFDIR=A generate_certs_for srv-A
+CONFDIR=A add_user userA@srv-A userA
+
+CONFDIR=B generate_certs_for srv-B
+CONFDIR=B add_user userB@srv-B userB
+
+rm -rf .data-A .data-B .mail .certs
+mkdir -p .logs-A .logs-B .mail .certs
+
+# Put public certs in .certs, and use it as our trusted cert dir.
+cp A/certs/srv-A/fullchain.pem .certs/srv-a.pem
+cp B/certs/srv-B/fullchain.pem .certs/srv-b.pem
+export SSL_CERT_DIR=$PWD/.certs/
+
+chasquid -v=2 --logfile=.logs-A/chasquid.log --config_dir=A \
+	--testing__dns_addr=127.0.0.1:9053 \
+	--testing__max_received_headers=5 \
+	--testing__outgoing_smtp_port=2025 &
+chasquid -v=2 --logfile=.logs-B/chasquid.log --config_dir=B \
+	--testing__dns_addr=127.0.0.1:9053 \
+	--testing__outgoing_smtp_port=1025 &
+
+wait_until_ready 1025
+wait_until_ready 2025
+
+function launch_minidns() {
+	if [ "$MINIDNS" != "" ]; then
+		kill $MINIDNS
+		wait $MINIDNS || true
+	fi
+	cp $1 .zones
+	minidns_bg --addr=":9053" -zones=.zones >> .minidns.log 2>&1
+	wait_until_ready 9053
+}
+
+# T0: Successful.
+launch_minidns zones.t0
+run_msmtp userB@srv-B < content
+wait_for_file .mail/userb@srv-b
+mail_diff content .mail/userb@srv-b
+
+# T1: A is not permitted to send to B.
+# Check that userA got a DSN about it.
+rm .mail/*
+launch_minidns zones.t1
+run_msmtp userB@srv-B < content
+wait_for_file .mail/usera@srv-a
+mail_diff expected_dsn .mail/usera@srv-a
+
+success