target/ignore_error: add wrapper target to ignore delivery errors

.mkdocs.yml

@@ -37,6 +37,7 @@ nav:
             - reference/blob/s3.md
       - reference/smtp-pipeline.md
       - SMTP targets:
+          - reference/targets/ignore_error.md
           - reference/targets/queue.md
           - reference/targets/remote.md
           - reference/targets/smtp.md

docs/reference/targets/ignore_error.md

@@ -0,0 +1,26 @@
+# Ignore delivery errors
+
+Module that wraps another delivery target and turns any delivery error into a
+logged warning instead of propagating it.
+
+This is useful for non-critical `deliver_to` copies (e.g. push notifications)
+where a failure should not abort the rest of the pipeline.
+
+```
+deliver_to ignore_error smtp tcp://127.0.0.1:2525
+```
+
+The wrapped target is given inline, exactly as it would be written after
+`deliver_to`. Any configuration block attached to the directive belongs to the
+wrapped target and is forwarded as-is:
+
+```
+deliver_to ignore_error smtp tcp://127.0.0.1:2525 {
+    connect_timeout 5s
+}
+```
+
+Errors from every delivery stage of the wrapped target (connection, RCPT, body
+and commit) are logged and then discarded, so the message is always reported as
+delivered to the pipeline. If the wrapped target cannot be started at all, the
+whole delivery becomes a no-op.

internal/target/ignore_error/ignore_error.go

@@ -0,0 +1,141 @@
+/*
+Maddy Mail Server - Composable all-in-one email server.
+Copyright © 2019-2025 Max Mazurov <fox.cpp@disroot.org>, Maddy Mail Server contributors
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
+/*
+Package ignore_error implements a delivery target that wraps another target and
+turns any delivery error into a logged warning instead of propagating it.
+
+It is meant for non-critical deliver_to copies (e.g. push notifications) where a
+failure should not affect the rest of the pipeline. The wrapped target is given
+inline:
+
+	deliver_to ignore_error smtp tcp://127.0.0.1:2525
+
+Any configuration block attached to the directive belongs to the wrapped target
+and is forwarded as-is.
+*/
+package ignore_error
+
+import (
+	"context"
+
+	"github.com/emersion/go-message/textproto"
+	"github.com/emersion/go-smtp"
+	"github.com/foxcpp/maddy/framework/buffer"
+	"github.com/foxcpp/maddy/framework/config"
+	modconfig "github.com/foxcpp/maddy/framework/config/module"
+	"github.com/foxcpp/maddy/framework/container"
+	"github.com/foxcpp/maddy/framework/log"
+	"github.com/foxcpp/maddy/framework/module"
+	"github.com/foxcpp/maddy/framework/module/modules"
+	"github.com/foxcpp/maddy/internal/target"
+)
+
+const modName = "target.ignore_error"
+
+type Target struct {
+	instName string
+	log      *log.Logger
+	wrapped  module.DeliveryTarget
+}
+
+func New(c *container.C, _, instName string) (module.Module, error) {
+	return &Target{
+		instName: instName,
+		log:      c.DefaultLogger.Sublogger(modName),
+	}, nil
+}
+
+func (t *Target) Configure(inlineArgs []string, cfg *config.Map) error {
+	// The wrapped target is defined inline, so its name and arguments arrive as
+	// inlineArgs and any attached block belongs to it. Forward both to the
+	// module loader instead of consuming them here.
+	return modconfig.ModuleFromNode("target", inlineArgs, cfg.Block, cfg.Globals, &t.wrapped)
+}
+
+func (t *Target) Name() string {
+	return modName
+}
+
+func (t *Target) InstanceName() string {
+	return t.instName
+}
+
+func (t *Target) StartDelivery(ctx context.Context, msgMeta *module.MsgMetadata, mailFrom string) (module.Delivery, error) {
+	d := &delivery{
+		log: target.DeliveryLogger(t.log, msgMeta),
+	}
+
+	wrapped, err := t.wrapped.StartDelivery(ctx, msgMeta, mailFrom)
+	if err != nil {
+		// Leave d.wrapped nil so the rest of the delivery is a no-op.
+		d.log.Error("ignored error from wrapped target", err)
+		return d, nil
+	}
+	d.wrapped = wrapped
+	return d, nil
+}
+
+type delivery struct {
+	wrapped module.Delivery
+	log     *log.Logger
+}
+
+func (d *delivery) AddRcpt(ctx context.Context, rcptTo string, opts smtp.RcptOptions) error {
+	if d.wrapped == nil {
+		return nil
+	}
+	if err := d.wrapped.AddRcpt(ctx, rcptTo, opts); err != nil {
+		d.log.Error("ignored error from wrapped target", err, "rcpt", rcptTo)
+	}
+	return nil
+}
+
+func (d *delivery) Body(ctx context.Context, header textproto.Header, body buffer.Buffer) error {
+	if d.wrapped == nil {
+		return nil
+	}
+	if err := d.wrapped.Body(ctx, header, body); err != nil {
+		d.log.Error("ignored error from wrapped target", err)
+	}
+	return nil
+}
+
+func (d *delivery) Abort(ctx context.Context) error {
+	if d.wrapped == nil {
+		return nil
+	}
+	if err := d.wrapped.Abort(ctx); err != nil {
+		d.log.Error("ignored error from wrapped target", err)
+	}
+	return nil
+}
+
+func (d *delivery) Commit(ctx context.Context) error {
+	if d.wrapped == nil {
+		return nil
+	}
+	if err := d.wrapped.Commit(ctx); err != nil {
+		d.log.Error("ignored error from wrapped target", err)
+	}
+	return nil
+}
+
+func init() {
+	modules.Register(modName, New)
+}

internal/target/ignore_error/ignore_error_test.go

@@ -0,0 +1,73 @@
+/*
+Maddy Mail Server - Composable all-in-one email server.
+Copyright © 2019-2025 Max Mazurov <fox.cpp@disroot.org>, Maddy Mail Server contributors
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
+package ignore_error
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/foxcpp/maddy/framework/config"
+	"github.com/foxcpp/maddy/internal/testutils"
+)
+
+func wrap(t *testing.T, inner *testutils.Target) *Target {
+	return &Target{
+		instName: "test",
+		log:      testutils.Logger(t, modName),
+		wrapped:  inner,
+	}
+}
+
+func TestPassthroughOnSuccess(t *testing.T) {
+	inner := &testutils.Target{}
+	tgt := wrap(t, inner)
+
+	testutils.DoTestDelivery(t, tgt, "from@example.org", []string{"to@example.org"})
+
+	testutils.CheckTestMessage(t, inner, 0, "from@example.org", []string{"to@example.org"})
+}
+
+func TestIgnoredErrors(t *testing.T) {
+	boom := errors.New("boom")
+
+	cases := map[string]*testutils.Target{
+		"StartDelivery": {StartErr: boom},
+		"AddRcpt":       {RcptErr: map[string]error{"to@example.org": boom}},
+		"Body":          {BodyErr: boom},
+		"Commit":        {CommitErr: boom},
+	}
+
+	for name, inner := range cases {
+		t.Run(name, func(t *testing.T) {
+			tgt := wrap(t, inner)
+
+			if _, err := testutils.DoTestDeliveryErr(t, tgt, "from@example.org", []string{"to@example.org"}); err != nil {
+				t.Errorf("wrapped %s error was not ignored: %v", name, err)
+			}
+		})
+	}
+}
+
+func TestConfigureRequiresTarget(t *testing.T) {
+	tgt := &Target{instName: "test", log: testutils.Logger(t, modName)}
+
+	if err := tgt.Configure(nil, config.NewMap(nil, config.Node{})); err == nil {
+		t.Error("expected an error when no wrapped target is given")
+	}
+}

maddy.go

@@ -77,6 +77,7 @@ import (
 	_ "github.com/foxcpp/maddy/internal/table"
 	_ "github.com/foxcpp/maddy/internal/table/file"
 	_ "github.com/foxcpp/maddy/internal/table/sql"
+	_ "github.com/foxcpp/maddy/internal/target/ignore_error"
 	_ "github.com/foxcpp/maddy/internal/target/queue"
 	_ "github.com/foxcpp/maddy/internal/target/remote"
 	_ "github.com/foxcpp/maddy/internal/target/smtp"