Skip mitm for unsupported registries (#185)

* implement mitm decider for npm

* fix: Skip MITM for registries not supported for analysis

proxy/interceptors/npm_registry_test.go

@@ -0,0 +1,54 @@
+package interceptors
+
+import (
+	"testing"
+
+	"github.com/safedep/pmg/proxy"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNpmRegistryInterceptor_ShouldMITM(t *testing.T) {
+	interceptor := NewNpmRegistryInterceptor(nil, nil, nil, nil)
+
+	tests := []struct {
+		name     string
+		hostname string
+		wantMITM bool
+	}{
+		{"public registry is MITM'd", "registry.npmjs.org", true},
+		{"yarn registry is MITM'd", "registry.yarnpkg.com", true},
+		{"github packages is NOT MITM'd", "npm.pkg.github.com", false},
+		{"github blob storage is NOT MITM'd", "pkg-npm.githubusercontent.com", false},
+		{"unknown registry is NOT MITM'd", "registry.example.com", false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			ctx := &proxy.RequestContext{Hostname: tt.hostname}
+			assert.Equal(t, tt.wantMITM, interceptor.ShouldMITM(ctx))
+		})
+	}
+}
+
+func TestNpmRegistryInterceptor_ShouldIntercept(t *testing.T) {
+	interceptor := NewNpmRegistryInterceptor(nil, nil, nil, nil)
+
+	tests := []struct {
+		name          string
+		hostname      string
+		wantIntercept bool
+	}{
+		{"public registry", "registry.npmjs.org", true},
+		{"yarn registry", "registry.yarnpkg.com", true},
+		{"github packages", "npm.pkg.github.com", true},
+		{"github blob storage", "pkg-npm.githubusercontent.com", true},
+		{"unknown registry", "registry.example.com", false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			ctx := &proxy.RequestContext{Hostname: tt.hostname}
+			assert.Equal(t, tt.wantIntercept, interceptor.ShouldIntercept(ctx))
+		})
+	}
+}