internal/openvex: add vex types

updates golang/go#62486

Change-Id: I550ca00f1209e21ee3fef91128d0522494b9d994
Reviewed-on: https://go-review.googlesource.com/c/vuln/+/575857
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Zvonimir Pavlinovic <zpavlinovic@google.com>

Author: Maceo Thompson

internal/openvex/vex.go

@@ -0,0 +1,105 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package vex defines the Vulnerability EXchange Format (VEX) types
+// supported by govulncheck.
+//
+// These types match the OpenVEX standard. See https://github.com/openvex for
+// more information on VEX and OpenVEX.
+package openvex
+
+import "time"
+
+const (
+	ContextURI = "https://openvex.dev/ns/v0.2.0"
+	Tooling    = "https://pkg.go.dev/golang.org/x/vuln/cmd/govulncheck"
+	Impact     = "Govulncheck determined that the vulnerable code isn't called"
+
+	DefaultAuthor = "Unknown Author"
+	DefaultPID    = "Unknown Product"
+
+	// The following are defined by the VEX standard.
+	StatusAffected    = "affected"
+	StatusNotAffected = "not_affected"
+
+	// The following are defined by the VEX standard.
+	JustificationNotExecuted = "vulnerable_code_not_in_execute_path"
+	JustificationNotPresent  = "vulnerable_code_not_present"
+)
+
+// Document is the top-level struct for a VEX document.
+type Document struct {
+	// Context is an IRI pointing to the version of openVEX being used by the doc
+	// For govulncheck, it will always be https://openvex.dev/ns/v0.2.0
+	Context string `json:"@context,omitempty"`
+
+	// ID is the identifying string for the VEX document.
+	// govulncheck/vex-[content-based-hash]
+	ID string `json:"@id,omitempty"`
+
+	// Author is the identifier for the author of the VEX statement.
+	// Govulncheck will leave this field default (Unknown author) to be filled in by the user.
+	Author string `json:"author,omitempty"`
+
+	// Timestamp defines the time at which the document was issued.
+	Timestamp time.Time `json:"timestamp,omitempty"`
+
+	// Version is the document version. For govulncheck's output, this will always be 1.
+	Version int `json:"version,omitempty"`
+
+	// Tooling expresses how the VEX document and contained VEX statements were
+	// generated. In this case, it will always be:
+	// "https://pkg.go.dev/golang.org/x/vuln/cmd/govulncheck"
+	Tooling string `json:"tooling,omitempty"`
+
+	// Statements are all statements for a given govulncheck output.
+	// Each OSV emitted by govulncheck will have a corresponding statement.
+	Statements []Statement `json:"statements,omitempty"`
+}
+
+// Statement conveys a single status for a single vulnerability for one or more products.
+type Statement struct {
+	// Vulnerability is the vuln being referenced by the statement.
+	Vulnerability Vulnerability `json:"vulnerability,omitempty"`
+
+	// Products are the products associated with the given vulnerability in the statement.
+	Products []Product `json:"products,omitempty"`
+
+	// The status of the vulnerability. Will be either not_affected or affected for govulncheck.
+	Status string `json:"status,omitempty"`
+
+	// If the status is not_affected, this must be filled. The official VEX justification that
+	// best matches govulncheck's vuln filtering is "vulnerable_code_not_in_execute_path"
+	Justification string `json:"justification,omitempty"`
+
+	// If the status is not_affected, this must be filled. For govulncheck, this will always be:
+	// "Govulncheck determined that the vulnerable code isn't called"
+	ImpactStatement string `json:"impact_statement,omitempty"`
+}
+
+// Vulnerability captures a vulnerability and its identifiers/aliases.
+type Vulnerability struct {
+	// ID is a URI that in govulncheck's case points to the govulndb link for the vulnerability.
+	// I.E. https://pkg.go.dev/vuln/GO-2024-2497
+	ID string `json:"@id,omitempty"`
+
+	// Name is the main identifier for the vulnerability (GO-YYYY-XXXX)
+	Name string `json:"name,omitempty"`
+
+	// Description is a short text description of the vulnerability.
+	// It will be populated from the 'summary' field of the vuln's OSV if it exists,
+	// and the 'description' field of the osv if a summary isn't present.
+	Description string `json:"description,omitempty"`
+
+	// Aliases a list of identifiers that other systems are using to track the vulnerability.
+	// I.E. GHSA or CVE ids.
+	Aliases []string `json:"aliases,omitempty"`
+}
+
+// Product identifies the products associated with the given vuln.
+type Product struct {
+	// For now, the ID will always be "Unknown product".
+	// This is temporary and is subject to change.
+	ID string `json:"@id,omitempty"`
+}