Added host substitution in MTProxy match type #189

A host substitution functionality has been added to the match logic for the MTProxy match type. This allows for more flexible routing rules, enabling the replacement of "$host" and "${host}" placeholders in the destination URL with the server name, before performing the regex match. Updated corresponding tests to reflect this change.

app/discovery/discovery.go

@@ -165,6 +165,15 @@ func (s *Service) Run(ctx context.Context) error {
 // For MTStatic always a single match because fail-over doesn't supported for assets
 func (s *Service) Match(srv, src string) (res Matches) {
 
+	replaceHost := func(dest, srv string) string {
+		// $host or ${host} in dest replaced by srv
+		dest = strings.ReplaceAll(dest, "$host", srv)
+		if strings.Contains(dest, "${host}") {
+			dest = strings.ReplaceAll(dest, "${host}", srv)
+		}
+		return dest
+	}
+
 	s.lock.RLock()
 	defer s.lock.RUnlock()
 
@@ -179,8 +188,9 @@ func (s *Service) Match(srv, src string) (res Matches) {
 
 			switch m.MatchType {
 			case MTProxy:
-				dest := m.SrcMatch.ReplaceAllString(src, m.Dst)
-				if src != dest { // regex matched
+				dest := replaceHost(m.Dst, srv) // replace $host and ${host} in dest first, before regex match
+				dest = m.SrcMatch.ReplaceAllString(src, dest)
+				if src != dest { // regex matched because dest changed after replacement
 					lastSrcMatch = m.SrcMatch.String()
 					res.MatchType = MTProxy
 					res.Routes = append(res.Routes, MatchedRoute{Destination: dest, Alive: m.IsAlive(), Mapper: m})

app/discovery/discovery_test.go

@@ -164,7 +164,6 @@ func TestService_Match(t *testing.T) {
 	}
 
 	for i, tt := range tbl {
-		tt := tt
 		t.Run(strconv.Itoa(i)+"-"+tt.server, func(t *testing.T) {
 			res := svc.Match(tt.server, tt.src)
 			require.Equal(t, len(tt.res.Routes), len(res.Routes), res.Routes)
@@ -192,8 +191,8 @@ func TestService_MatchServerRegex(t *testing.T) {
 					Dst: "http://127.0.0.10:8080/", MatchType: MTProxy, dead: false},
 
 				// regex servers
-				{Server: "test-prefix\\.(.*)", SrcMatch: *regexp.MustCompile("^/"),
-					Dst: "http://127.0.0.1:8080/", MatchType: MTProxy, dead: false},
+				{Server: "test-prefix\\.(.*)", SrcMatch: *regexp.MustCompile("^/(.*)"),
+					Dst: "http://127.0.0.1:8080/$host/blah/$1", MatchType: MTProxy, dead: false},
 				{Server: "(.*)\\.test-domain\\.(com|org)", SrcMatch: *regexp.MustCompile("^/"),
 					Dst: "http://127.0.0.2:8080/", MatchType: MTProxy, dead: false},
 
@@ -212,21 +211,43 @@ func TestService_MatchServerRegex(t *testing.T) {
 	assert.Equal(t, context.DeadlineExceeded, err)
 
 	tbl := []struct {
+		name        string
 		server, src string
 		res         Matches
 	}{
-		// strict match should take priority
-		{"test-prefix.exact.com", "/", Matches{MTProxy, []MatchedRoute{{Destination: "http://127.0.0.4:8080/", Alive: true}}}},
-
-		// regex servers
-		{"test-prefix.example.com", "/", Matches{MTProxy, []MatchedRoute{{Destination: "http://127.0.0.1:8080/", Alive: true}}}},
-		{"another-prefix.example.com", "/", Matches{MTProxy, nil}},
-		{"another-prefix.test-domain.org", "/", Matches{MTProxy, []MatchedRoute{{Destination: "http://127.0.0.2:8080/", Alive: true}}}},
-		{"another-prefix.test-domain.net", "/", Matches{MTProxy, nil}},
+		{
+			name:   "strict match",
+			server: "test-prefix.exact.com",
+			src:    "/",
+			res:    Matches{MTProxy, []MatchedRoute{{Destination: "http://127.0.0.4:8080/", Alive: true}}},
+		},
+		{
+			name:   "regex server with host match",
+			server: "test-prefix.example.com",
+			src:    "/some",
+			res:    Matches{MTProxy, []MatchedRoute{{Destination: "http://127.0.0.1:8080/test-prefix.example.com/blah/some", Alive: true}}},
+		},
+		{
+			name:   "regex server without a match",
+			server: "another-prefix.example.com",
+			src:    "/",
+			res:    Matches{MTProxy, nil},
+		},
+		{
+			name:   "regex server with test-domain.org match",
+			server: "another-prefix.test-domain.org",
+			src:    "/",
+			res:    Matches{MTProxy, []MatchedRoute{{Destination: "http://127.0.0.2:8080/", Alive: true}}},
+		},
+		{
+			name:   "regex server with test-domain.net mismatch",
+			server: "another-prefix.test-domain.net",
+			src:    "/",
+			res:    Matches{MTProxy, nil},
+		},
 	}
 
 	for i, tt := range tbl {
-		tt := tt
 		t.Run(strconv.Itoa(i)+"-"+tt.server, func(t *testing.T) {
 			res := svc.Match(tt.server, tt.src)
 			require.Equal(t, len(tt.res.Routes), len(res.Routes), res.Routes)
@@ -374,7 +395,6 @@ func TestService_Servers(t *testing.T) {
 }
 
 func TestService_extendRule(t *testing.T) {
-
 	tbl := []struct {
 		inp URLMapper
 		out URLMapper
@@ -411,11 +431,9 @@ func TestService_extendRule(t *testing.T) {
 			assert.Equal(t, tt.out, res)
 		})
 	}
-
 }
 
 func TestService_redirects(t *testing.T) {
-
 	tbl := []struct {
 		inp URLMapper
 		out URLMapper