feat(flag): add schema validation for --server flag

pkg/flag/remote_flags.go

@@ -2,8 +2,11 @@ package flag
 
 import (
 	"net/http"
+	"net/url"
 	"strings"
 
+	"golang.org/x/xerrors"
+
 	"github.com/aquasecurity/trivy/pkg/log"
 )
 
@@ -112,6 +115,12 @@ func (f *RemoteFlagGroup) Flags() []Flagger {
 
 func (f *RemoteFlagGroup) ToOptions(opts *Options) error {
 	serverAddr := f.ServerAddr.Value()
+
+	// Validate server schema
+	if err := validateServerSchema(serverAddr); err != nil {
+		return err
+	}
+
 	customHeaders := splitCustomHeaders(f.CustomHeaders.Value())
 	listen := f.Listen.Value()
 	token := f.Token.Value()
@@ -159,3 +168,22 @@ func splitCustomHeaders(headers []string) http.Header {
 	}
 	return result
 }
+
+func validateServerSchema(serverAddr string) error {
+	if serverAddr == "" {
+		return nil
+	}
+
+	parsedURL, err := url.Parse(serverAddr)
+	if err != nil {
+		return xerrors.Errorf("invalid server address format: %w", err)
+	}
+
+	if parsedURL.Scheme == "" {
+		return xerrors.Errorf("server address must include HTTP or HTTPS schema (e.g., http://localhost:4954 or https://localhost:4954)")
+	} else if parsedURL.Scheme != "http" && parsedURL.Scheme != "https" {
+		return xerrors.Errorf("server address must use HTTP or HTTPS schema, got '%s' (e.g., use http://localhost:4954 instead of %s)", parsedURL.Scheme, serverAddr)
+	}
+
+	return nil
+}

pkg/flag/remote_flags_test.go

@@ -24,6 +24,7 @@ func TestRemoteFlagGroup_ToOptions(t *testing.T) {
 		fields   fields
 		want     flag.RemoteOptions
 		wantLogs []string
+		wantErr  string
 	}{
 		{
 			name: "happy",
@@ -93,6 +94,39 @@ func TestRemoteFlagGroup_ToOptions(t *testing.T) {
 				`"--token-header" should be used with "--token"`,
 			},
 		},
+		{
+			name: "server address without schema",
+			fields: fields{
+				Server: "localhost:8080",
+			},
+			wantErr: "server address must use HTTP or HTTPS schema, got 'localhost'",
+		},
+		{
+			name: "server address with invalid schema",
+			fields: fields{
+				Server: "ftp://localhost:8080",
+			},
+			wantErr: "server address must use HTTP or HTTPS schema, got 'ftp'",
+		},
+		{
+			name: "server address with malformed URL",
+			fields: fields{
+				Server: "http://[::1:8080",
+			},
+			wantErr: "invalid server address format",
+		},
+		{
+			name: "server address with https schema",
+			fields: fields{
+				Server:      "https://localhost:4954",
+				TokenHeader: "Trivy-Token",
+			},
+			want: flag.RemoteOptions{
+				CustomHeaders: http.Header{},
+				ServerAddr:    "https://localhost:4954",
+				TokenHeader:   "Trivy-Token",
+			},
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -112,6 +146,12 @@ func TestRemoteFlagGroup_ToOptions(t *testing.T) {
 			}
 			flags := flag.Flags{f}
 			got, err := flags.ToOptions(nil)
+
+			if tt.wantErr != "" {
+				assert.ErrorContains(t, err, tt.wantErr)
+				return
+			}
+
 			require.NoError(t, err)
 			assert.Equal(t, tt.want, got.RemoteOptions)