Allow for configuration policies

Summary:
Implements a rough interface for validating configuration against
arbitrary policy rules. Policies are provided as YAML and passed via the
command line as file paths or remote URIs.

The format of policies is:

    enforcements:
      - path: <path>
        rule: <rule>

Where `<path>` is a YAML-ish path to a config field and `<rule>` is any
expression our config validator understands (expressions built in by the
validator library and custom tags defined in `config.validation.go`).

Example policy:

    enforcements:
      - path: variants.production.base
        rule: oneof=debian:jessie debian:stretch
      - path: variants.production.runs.as
        rule: ne=foo
      - path: variants.production.node.dependencies
        rule: isfalse

Command flag parsing was implemented in `main.go` to support the new
`--policy=uri` flag and improve existing handling of `--version` and the
usage statement.

Test Plan: Run `go test ./...`.

Reviewers: thcipriani, demon, hashar, mmodell, #release-engineering-team

Reviewed By: thcipriani, #release-engineering-team

Tags: #release-engineering-team

Differential Revision: https://phabricator.wikimedia.org/D999

1 files changed, 117 insertions, 0 deletions

diff --git a/config/policy_test.go b/config/policy_test.go
new file mode 100644
index 0000000..2d7a3a7
--- /dev/null
+++ b/config/policy_test.go
@@ -0,0 +1,117 @@
+package config_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"phabricator.wikimedia.org/source/blubber/config"
+)
+
+func TestPolicyRead(t *testing.T) {
+	policy, err := config.ReadPolicy([]byte(`---
+    enforcements:
+      - path: variants.production.runs.as
+        rule: ne=root
+      - path: base
+        rule: oneof=debian:jessie debian:stretch`))
+
+	if assert.NoError(t, err) {
+		if assert.Len(t, policy.Enforcements, 2) {
+			assert.Equal(t, "variants.production.runs.as", policy.Enforcements[0].Path)
+			assert.Equal(t, "ne=root", policy.Enforcements[0].Rule)
+
+			assert.Equal(t, "base", policy.Enforcements[1].Path)
+			assert.Equal(t, "oneof=debian:jessie debian:stretch", policy.Enforcements[1].Rule)
+		}
+	}
+}
+
+func TestPolicyValidate(t *testing.T) {
+	cfg := config.Config{
+		CommonConfig: config.CommonConfig{
+			Base: "foo:tag",
+		},
+		Variants: map[string]config.VariantConfig{
+			"foo": config.VariantConfig{
+				CommonConfig: config.CommonConfig{
+					Runs: config.RunsConfig{
+						UserConfig: config.UserConfig{
+							As: "root",
+						},
+					},
+				},
+			},
+		},
+	}
+
+	policy := config.Policy{
+		Enforcements: []config.Enforcement{
+			{Path: "variants.foo.runs.as", Rule: "ne=root"},
+		},
+	}
+
+	assert.EqualError(t,
+		policy.Validate(cfg),
+		`value for "variants.foo.runs.as" violates policy rule "ne=root"`,
+	)
+
+	policy = config.Policy{
+		Enforcements: []config.Enforcement{
+			{Path: "base", Rule: "oneof=debian:jessie debian:stretch"},
+		},
+	}
+
+	assert.EqualError(t,
+		policy.Validate(cfg),
+		`value for "base" violates policy rule "oneof=debian:jessie debian:stretch"`,
+	)
+}
+
+func TestEnforcementOnFlag(t *testing.T) {
+	cfg := config.Config{
+		Variants: map[string]config.VariantConfig{
+			"production": config.VariantConfig{
+				CommonConfig: config.CommonConfig{
+					Node: config.NodeConfig{
+						Dependencies: config.Flag{True: true},
+					},
+				},
+			},
+		},
+	}
+
+	policy := config.Policy{
+		Enforcements: []config.Enforcement{
+			{Path: "variants.production.node.dependencies", Rule: "isfalse"},
+		},
+	}
+
+	assert.Error(t,
+		policy.Validate(cfg),
+		`value for "variants.production.node.dependencies" violates policy rule "isfalse"`,
+	)
+
+}
+
+func TestResolveYAMLPath(t *testing.T) {
+	cfg := config.Config{
+		Variants: map[string]config.VariantConfig{
+			"foo": config.VariantConfig{
+				CommonConfig: config.CommonConfig{
+					Runs: config.RunsConfig{
+						UserConfig: config.UserConfig{
+							As: "root",
+						},
+					},
+				},
+			},
+		},
+	}
+
+	val, err := config.ResolveYAMLPath("variants.foo.runs.as", cfg)
+
+	if assert.NoError(t, err) {
+		assert.Equal(t, "root", val)
+	}
+}