Regular expression (regexp) matcher: initial commit

README.md

@@ -39,6 +39,7 @@ Current matchers:
 - **layer4.matchers.not** - matches connections that aren't matched by inner matcher sets.
 - **layer4.matchers.proxy_protocol** - matches connections that start with [HAPROXY proxy protocol](https://www.haproxy.org/download/1.8/doc/proxy-protocol.txt).
 - **layer4.matchers.rdp** - matches connections that look like [RDP](https://winprotocoldoc.blob.core.windows.net/productionwindowsarchives/MS-RDPBCGR/%5BMS-RDPBCGR%5D.pdf).
+- **layer4.matchers.regexp** - matches connections that have the first packet bytes matching a regular expression.
 - **layer4.matchers.socks4** - matches connections that look like [SOCKSv4](https://www.openssh.com/txt/socks4.protocol).
 - **layer4.matchers.socks5** - matches connections that look like [SOCKSv5](https://www.rfc-editor.org/rfc/rfc1928.html).
 - **layer4.matchers.xmpp** - matches connections that look like [XMPP](https://xmpp.org/about/technology-overview/).

imports.go

@@ -23,6 +23,7 @@ import (
 	_ "github.com/mholt/caddy-l4/modules/l4proxy"
 	_ "github.com/mholt/caddy-l4/modules/l4proxyprotocol"
 	_ "github.com/mholt/caddy-l4/modules/l4rdp"
+	_ "github.com/mholt/caddy-l4/modules/l4regexp"
 	_ "github.com/mholt/caddy-l4/modules/l4socks"
 	_ "github.com/mholt/caddy-l4/modules/l4ssh"
 	_ "github.com/mholt/caddy-l4/modules/l4subroute"

modules/l4regexp/matcher.go

@@ -0,0 +1,109 @@
+// Copyright 2024 VNXME
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package l4regexp
+
+import (
+	"io"
+	"regexp"
+	"strconv"
+
+	"github.com/caddyserver/caddy/v2"
+	"github.com/caddyserver/caddy/v2/caddyconfig/caddyfile"
+	"github.com/mholt/caddy-l4/layer4"
+)
+
+func init() {
+	caddy.RegisterModule(&MatchRegexp{})
+}
+
+// MatchRegexp is able to match any connections with regular expressions.
+type MatchRegexp struct {
+	Count   uint16 `json:"count,omitempty"`
+	Pattern string `json:"pattern,omitempty"`
+
+	compiled *regexp.Regexp
+}
+
+// CaddyModule returns the Caddy module information.
+func (m *MatchRegexp) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		ID:  "layer4.matchers.regexp",
+		New: func() caddy.Module { return new(MatchRegexp) },
+	}
+}
+
+// Match returns true if the connection bytes match the regular expression.
+func (m *MatchRegexp) Match(cx *layer4.Connection) (bool, error) {
+	// Read a number of bytes
+	buf := make([]byte, m.Count)
+	n, err := io.ReadFull(cx, buf)
+	if err != nil || n < int(m.Count) {
+		return false, nil
+	}
+
+	// Match these bytes against the regular expression
+	return m.compiled.Match(buf), nil
+}
+
+// Provision parses m's regular expression and sets m's minimum read bytes count.
+func (m *MatchRegexp) Provision(_ caddy.Context) (err error) {
+	if m.Count == 0 {
+		m.Count = minCount
+	}
+	m.compiled, err = regexp.Compile(m.Pattern)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+// UnmarshalCaddyfile sets up the MatchRegexp from Caddyfile tokens. Syntax:
+//
+//	regexp <pattern> [<count>]
+func (m *MatchRegexp) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
+	_, wrapper := d.Next(), d.Val() // consume wrapper name
+
+	// One or two same-line argument must be provided
+	if d.CountRemainingArgs() == 0 || d.CountRemainingArgs() > 2 {
+		return d.ArgErr()
+	}
+
+	_, m.Pattern = d.NextArg(), d.Val()
+	if d.NextArg() {
+		val, err := strconv.ParseUint(d.Val(), 10, 16)
+		if err != nil {
+			return d.Errf("parsing %s count: %v", wrapper, err)
+		}
+		m.Count = uint16(val)
+	}
+
+	// No blocks are supported
+	if d.NextBlock(d.Nesting()) {
+		return d.Errf("malformed %s option: blocks are not supported", wrapper)
+	}
+
+	return nil
+}
+
+// Interface guards
+var (
+	_ caddy.Provisioner     = (*MatchRegexp)(nil)
+	_ caddyfile.Unmarshaler = (*MatchRegexp)(nil)
+	_ layer4.ConnMatcher    = (*MatchRegexp)(nil)
+)
+
+const (
+	minCount uint16 = 4 // by default, read this many bytes to match against
+)

modules/l4regexp/matcher_test.go

@@ -0,0 +1,90 @@
+// Copyright 2024 VNXME
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package l4regexp
+
+import (
+	"context"
+	"io"
+	"net"
+	"testing"
+
+	"github.com/caddyserver/caddy/v2"
+	"github.com/mholt/caddy-l4/layer4"
+	"go.uber.org/zap"
+)
+
+func assertNoError(t *testing.T, err error) {
+	t.Helper()
+	if err != nil {
+		t.Fatalf("Unexpected error: %s\n", err)
+	}
+}
+
+func Test_MatchRegexp_Match(t *testing.T) {
+	type test struct {
+		matcher     *MatchRegexp
+		data        []byte
+		shouldMatch bool
+	}
+
+	tests := []test{
+		{matcher: &MatchRegexp{}, data: packet0123, shouldMatch: true},
+		{matcher: &MatchRegexp{Pattern: ""}, data: packet0123, shouldMatch: true},
+		{matcher: &MatchRegexp{Pattern: "12"}, data: packet0123, shouldMatch: true},
+		{matcher: &MatchRegexp{Pattern: "^0123$"}, data: packet0123, shouldMatch: true},
+		{matcher: &MatchRegexp{Pattern: "^012$"}, data: packet0123, shouldMatch: false},
+		{matcher: &MatchRegexp{Pattern: "^0123$", Count: 5}, data: packet0123, shouldMatch: false},
+		{matcher: &MatchRegexp{Pattern: "^012$", Count: 3}, data: packet0123, shouldMatch: true},
+		{matcher: &MatchRegexp{Pattern: "^\\d+$"}, data: packet0123, shouldMatch: true},
+		{matcher: &MatchRegexp{Pattern: "^\\d+$", Count: 0}, data: packet0123, shouldMatch: true},
+		{matcher: &MatchRegexp{Pattern: "^\x30\x31\x32(\x33|\x34)$", Count: 0}, data: packet0123, shouldMatch: true},
+	}
+
+	ctx, cancel := caddy.NewContext(caddy.Context{Context: context.Background()})
+	defer cancel()
+
+	for i, tc := range tests {
+		func() {
+			err := tc.matcher.Provision(ctx)
+			assertNoError(t, err)
+
+			in, out := net.Pipe()
+			defer func() {
+				_, _ = io.Copy(io.Discard, out)
+				_ = out.Close()
+			}()
+
+			cx := layer4.WrapConnection(out, []byte{}, zap.NewNop())
+			go func() {
+				_, err := in.Write(tc.data)
+				assertNoError(t, err)
+				_ = in.Close()
+			}()
+
+			matched, err := tc.matcher.Match(cx)
+			assertNoError(t, err)
+
+			if matched != tc.shouldMatch {
+				if tc.shouldMatch {
+					t.Fatalf("test %d: matcher did not match | %+v\n", i, tc.matcher)
+				} else {
+					t.Fatalf("test %d: matcher should not match | %+v\n", i, tc.matcher)
+				}
+			}
+		}()
+	}
+}
+
+var packet0123 = []byte{0x30, 0x31, 0x32, 0x33}