github.com/cncf/xds/go v0.0.0-20250501225837-2ac532fd4443: v3.ResourceLocator_Directive_Alt

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify github.com/cncf/xds/go/xds/core/v3.ResourceLocator_Directive_Alt in pkg:golang/github.com/cncf/xds/go@v0.0.0-20250501225837-2ac532fd4443
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/cncf/xds/go@v0.0.0-20250501225837-2ac532fd4443
Demonstrate these symbols/APIs:
  - github.com/cncf/xds/go/xds/core/v3.ResourceLocator_Directive_Alt

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:63b0ad9b191e514941e2102e22b696b11b132e6b280164e5506eb10d042180fb","contract":["ResourceLocator_Directive initializes with ResourceLocator_Directive_Alt wrapping an alternate ResourceLocator","ResourceLocator_Directive GetAlt accessor returns the inner ResourceLocator instance","ResourceLocator_Directive GetDirective enables type assertion to *ResourceLocator_Directive_Alt","ResourceLocator containing ResourceLocator_Directive_Alt passes Validate and ValidateAll checks","ResourceLocator_Directive validation rejects ResourceLocator_Directive_Alt with invalid nested ResourceLocator"],"goal":"verify github.com/cncf/xds/go/xds/core/v3.ResourceLocator_Directive_Alt in pkg:golang/github.com/cncf/xds/go@v0.0.0-20250501225837-2ac532fd4443","kind":"HOW","packages":["pkg:golang/github.com/cncf/xds/go@v0.0.0-20250501225837-2ac532fd4443"],"schemaVersion":1,"symbols":["github.com/cncf/xds/go/xds/core/v3.ResourceLocator_Directive_Alt"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/github.com/cncf/xds/go@v0.0.0-20250501225837-2ac532fd4443"],"schemaVersion":1,"subject":"pkg:golang/github.com/cncf/xds/go@v0.0.0-20250501225837-2ac532fd4443","symbols":["github.com/cncf/xds/go/xds/core/v3.ResourceLocator_Directive_Alt"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

require github.com/cncf/xds/go v0.0.0-20250501225837-2ac532fd4443

require (
	github.com/envoyproxy/protoc-gen-validate v1.0.4 // indirect
	google.golang.org/protobuf v1.33.0 // indirect
)

github.com/cncf/xds/go v0.0.0-20250501225837-2ac532fd4443 h1:aQ3y1lwWyqYPiWZThqv1aFbZMiM9vblcSArJRf2Irls=
github.com/cncf/xds/go v0.0.0-20250501225837-2ac532fd4443/go.mod h1:W+zGtBO5Y1IgJhy4+A9GOqVhqLpfZi+vwmdNXUehLA8=
github.com/envoyproxy/protoc-gen-validate v1.0.4 h1:gVPz/FMfvh57HdSJQyvBtF00j8JU4zdyUgIUNhlgg0A=
github.com/envoyproxy/protoc-gen-validate v1.0.4/go.mod h1:qys6tmnRsYrQqIhm2bvKZH4Blx/1gTIZ2UKVY1M+Yew=
github.com/google/go-cmp v0.5.5 h1:Khx7svrCpmxxtHBq5j2mp/xVjsi8hQMfNLvJFAlrGgU=
github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543 h1:E7g+9GITq07hpfrRu66IVDexMakfv52eLZ2CXBWiKr4=
golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
google.golang.org/protobuf v1.33.0 h1:uNO2rsAINq/JlFpSdYEKIZ0uKD/R9cpdv0T+yoGwGmI=
google.golang.org/protobuf v1.33.0/go.mod h1:c6P6GXX6sHbq/GpV6MGZEdwhWPcYBgnhAHhKbcUYpos=

{
  "schemaVersion": 1,
  "goal": "verify github.com/cncf/xds/go/xds/core/v3.ResourceLocator_Directive_Alt in pkg:golang/github.com/cncf/xds/go@v0.0.0-20250501225837-2ac532fd4443",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/cncf/xds/go@v0.0.0-20250501225837-2ac532fd4443"
  ],
  "symbols": [
    "github.com/cncf/xds/go/xds/core/v3.ResourceLocator_Directive_Alt"
  ]
}

package main

import (
	"fmt"

	v3 "github.com/cncf/xds/go/xds/core/v3"
)

func main() {
	// 1. Construct alternate ResourceLocator
	altLocator := &v3.ResourceLocator{
		Scheme:       v3.ResourceLocator_XDSTP,
		Id:           "fallback-cluster",
		Authority:    "example.com",
		ResourceType: "envoy.config.cluster.v3.Cluster",
	}

	// 2. Wrap within ResourceLocator_Directive_Alt oneof variant
	altDirective := &v3.ResourceLocator_Directive_Alt{
		Alt: altLocator,
	}

	directive := &v3.ResourceLocator_Directive{
		Directive: altDirective,
	}

	// 3. Verify GetAlt accessor returns the wrapped ResourceLocator
	if got := directive.GetAlt(); got != altLocator {
		panic(fmt.Sprintf("GetAlt mismatch: expected %v, got %v", altLocator, got))
	}
	if got := directive.GetEntry(); got != "" {
		panic(fmt.Sprintf("GetEntry on Alt directive expected empty string, got %q", got))
	}

	// 4. Verify type assertion on the underlying oneof interface
	switch d := directive.GetDirective().(type) {
	case *v3.ResourceLocator_Directive_Alt:
		if d.Alt.GetId() != "fallback-cluster" {
			panic(fmt.Sprintf("expected alt locator ID fallback-cluster, got %s", d.Alt.GetId()))
		}
	default:
		panic("expected *v3.ResourceLocator_Directive_Alt from GetDirective()")
	}

	// 5. Verify parent ResourceLocator containing the Alt directive validates successfully
	parentLocator := &v3.ResourceLocator{
		Scheme:       v3.ResourceLocator_XDSTP,
		Id:           "primary-cluster",
		Authority:    "example.com",
		ResourceType: "envoy.config.cluster.v3.Cluster",
		Directives: []*v3.ResourceLocator_Directive{
			directive,
		},
	}

	if err := parentLocator.Validate(); err != nil {
		panic(fmt.Sprintf("parent locator validation failed: %v", err))
	}
	if err := parentLocator.ValidateAll(); err != nil {
		panic(fmt.Sprintf("parent locator ValidateAll failed: %v", err))
	}

	// 6. Verify validation catches an invalid nested ResourceLocator inside ResourceLocator_Directive_Alt
	invalidAlt := &v3.ResourceLocator{
		Scheme:       v3.ResourceLocator_XDSTP,
		Id:           "invalid-cluster",
		Authority:    "example.com",
		ResourceType: "", // violates min_len: 1 rule
	}
	invalidDirective := &v3.ResourceLocator_Directive{
		Directive: &v3.ResourceLocator_Directive_Alt{
			Alt: invalidAlt,
		},
	}
	if err := invalidDirective.Validate(); err == nil {
		panic("expected validation failure for ResourceLocator_Directive_Alt wrapping invalid ResourceLocator")
	}

	fmt.Println("PASS: ResourceLocator_Directive_Alt verification succeeded")
}