Defining policy settings

Firstly, you need to define the structure that holds the policy settings.

You do this by modifying the code in the settings.go file (from your local version of the Go policy template). You need to add two extra lines to the import section, change the Settings structure, and add the RegularExpression structure.

It should match the following code:

import (
    "encoding/json"
    "fmt"
    "regexp"

    mapset "github.com/deckarep/golang-set/v2"
    kubewarden "github.com/kubewarden/policy-sdk-go"
    kubewarden_protocol "github.com/kubewarden/policy-sdk-go/protocol"
)

type Settings struct {
    DeniedLabels      mapset.Set[string]            `json:"denied_labels"`
    ConstrainedLabels map[string]*RegularExpression `json:"constrained_labels"`
}

type RegularExpression struct {
    *regexp.Regexp
}

note

DeniedNames is no longer required in the Settings structure defined in settings.go.

As DeniedNames is no longer defined, you should also delete the function IsNameDefined in settings.go. You should also remove the function that references it in settings_test.go, TestIsNameDenied.

You're using the regexp package to handle regular expression objects and the mapset.Set type to store the list of denied labels.

Since regexp.Regexp doesn't handle deserialization, you need to define custom functions to handle marshaling and unmarshalling of regular expressions:

// UnmarshalText satisfies the encoding.TextMarshaler interface,
// also used by json.Unmarshal.
func (r *RegularExpression) UnmarshalText(text []byte) error {
    nativeRegExp, err := regexp.Compile(string(text))
    if err != nil {
        return err
    }
    r.Regexp = nativeRegExp
    return nil
}

// MarshalText satisfies the encoding.TextMarshaler interface,
// also used by json.Marshal.
func (r *RegularExpression) MarshalText() ([]byte, error) {
    if r.Regexp != nil {
        return []byte(r.Regexp.String()), nil
    }

    return nil, nil
}

Also, you need the UnmarshalJSON method to handle the deserialization of the Settings struct:

func (s *Settings) UnmarshalJSON(data []byte) error {
    rawSettings := struct {
        DeniedLabels      []string          `json:"denied_labels"`
        ConstrainedLabels map[string]*RegularExpression `json:"constrained_labels"`
    }{}

    err := json.Unmarshal(data, &rawSettings)
    if err != nil {
        return err
    }

    s.DeniedLabels = mapset.NewThreadUnsafeSet[string](rawSettings.DeniedLabels...)
    s.ConstrainedLabels = rawSettings.ConstrainedLabels

    return nil
}

Building Settings instances

A Kubewarden policy exposes two different functions that receive the policy settings as input:

• validate: Use this function when Kubernetes object requires validation by the policy. The settings are part of a ValidationRequest object.
• validate_settings: Call this function when the policy is first loaded by Kubewarden. The function receives the policy settings as input and checks validity.

You need to create a helper function that creates a Settings object starting from the JSON payload:

func NewSettingsFromValidationReq(validationReq *kubewarden_protocol.ValidationRequest) (Settings, error) {
    settings := Settings{}
    err := json.Unmarshal(validationReq.Settings, &settings)
    if err != nil {
        return Settings{}, err
    }

    return settings, nil
}

note

All the mapset.Set objects are created using the thread-unsafe variant. The WebAssembly code executes in a single thread, hence there are no concurrency issues.

The WebAssembly standard doesn't cover threads yet. See the official proposal for more details.

Implementing Settings validation

All Kubewarden policies have to implement settings validation.

You do this by adding a Valid method to the Settings instances:

func (s *Settings) Valid() (bool, error) {
    constrainedLabels := mapset.NewThreadUnsafeSet[string]()

    for label := range s.ConstrainedLabels {
        constrainedLabels.Add(label)
    }

    constrainedAndDenied := constrainedLabels.Intersect(s.DeniedLabels)
    if constrainedAndDenied.Cardinality() != 0 {
        return false,
            fmt.Errorf("These labels cannot be constrained and denied at the same time: %v", constrainedAndDenied)
    }

    return true, nil
}

The Valid method ensures no "denied" label is also part of the "constrained" map. Usage of the Intersect method provided by mapset.Set simplifies the check.

note

The Valid method invocation is on an already instantiated Setting object. This means the validation of the regular expression provided by the user already took place in of the Settings unmarshaller.

Finally, you need the validateSettings function, provided by the scaffolding, to change to look like this:

func validateSettings(payload []byte) ([]byte, error) {
    settings := Settings{}
    err := json.Unmarshal(payload, &settings)
    if err != nil {
        return kubewarden.RejectSettings(
            kubewarden.Message(fmt.Sprintf("Provided settings are not valid: %v", err)))
    }

    valid, err := settings.Valid()
    if valid {
        return kubewarden.AcceptSettings()
    }

    return kubewarden.RejectSettings(
        kubewarden.Message(fmt.Sprintf("Provided settings are not valid: %v", err)))
}

You can see the function takes advantage of the helper functions provided by Kubewarden's SDK.

Testing the settings code

It's important to have good test coverage of the code you write. The code you are using, from the scaffolding, comes with a series of unit tests defined in the settings_test.go file.

You have to change the contents of this file to reflect the new behavior of the Settings class.

Include the Go packages you are using:

import (
    "testing"

    "encoding/json"

    kubewarden_protocol "github.com/kubewarden/policy-sdk-go/protocol"
)

You can start by writing a unit test that ensures you can assign a Settings instance from a ValidationRequest object:

func TestParseValidSettings(t *testing.T) {
    settingsJSON := []byte(`
        {
            "denied_labels": [ "foo", "bar" ],
            "constrained_labels": {
                    "cost-center": "cc-\\d+"
            }
        }`)

    settings := Settings{}
    err := json.Unmarshal(settingsJSON, &settings)
    if err != nil {
        t.Errorf("Unexpected error %+v", err)
    }

    expected_denied_labels := []string{"foo", "bar"}
    for _, exp := range expected_denied_labels {
        if !settings.DeniedLabels.Contains(exp) {
            t.Errorf("Missing value %s", exp)
        }
    }

    re, found := settings.ConstrainedLabels["cost-center"]
    if !found {
        t.Error("Didn't find the expected constrained label")
    }

    expected_regexp := `cc-\d+`
    if re.String() != expected_regexp {
        t.Errorf("Expected regexp to be %v - got %v instead",
            expected_regexp, re.String())
    }
}

Next, you need a test that checks a Settings instance isn't generated when the user provides a broken regular expression:

func TestParseSettingsWithInvalidRegexp(t *testing.T) {
    settingsJSON := []byte(`
        {
            "denied_labels": [ "foo", "bar" ],
            "constrained_labels": {
                    "cost-center": "cc-[a+"
            }
        }`)

    err := json.Unmarshal(settingsJSON, &Settings{})
    if err == nil {
        t.Errorf("Didn't get expected error")
    }
}

Now, you can define a test that checks the behavior of the validate_settings entry point.

You look at the SettingsValidationResponse object returned by your validateSettings function:

func TestDetectValidSettings(t *testing.T) {
    settingsJSON := []byte(`
    {
        "denied_labels": [ "foo", "bar" ],
        "constrained_labels": {
            "cost-center": "cc-\\d+"
        }
    }`)

    responsePayload, err := validateSettings(settingsJSON)
    if err != nil {
        t.Errorf("Unexpected error %+v", err)
    }

    var response kubewarden_protocol.SettingsValidationResponse
    if err := json.Unmarshal(responsePayload, &response); err != nil {
        t.Errorf("Unexpected error: %+v", err)
    }

    if !response.Valid {
        t.Errorf("Expected settings to be valid: %s", *response.Message)
    }
}

Finally, you write two more tests to check the validateSettings function rejects invalid settings with the right messages:

func TestDetectNotValidSettingsDueToBrokenRegexp(t *testing.T) {
    settingsJSON := []byte(`
    {
        "denied_labels": [ "foo", "bar" ],
        "constrained_labels": {
            "cost-center": "cc-[a+"
        }
    }
    `)

    responsePayload, err := validateSettings(settingsJSON)
    if err != nil {
        t.Errorf("Unexpected error %+v", err)
    }

    var response kubewarden_protocol.SettingsValidationResponse
    if err := json.Unmarshal(responsePayload, &response); err != nil {
        t.Errorf("Unexpected error: %+v", err)
    }

    if response.Valid {
        t.Error("Expected settings to not be valid")
    }

    if *response.Message != "Provided settings are not valid: error parsing regexp: missing closing ]: `[a+`" {
        t.Errorf("Unexpected validation error message: %s", *response.Message)
    }
}

func TestDetectNotValidSettingsDueToConflictingLabels(t *testing.T) {
    settingsJSON := []byte(`
    {
        "denied_labels": [ "foo", "bar", "cost-center" ],
        "constrained_labels": {
            "cost-center": ".*"
        }
    }`)
    responsePayload, err := validateSettings(settingsJSON)
    if err != nil {
        t.Errorf("Unexpected error %+v", err)
    }

    var response kubewarden_protocol.SettingsValidationResponse
    if err := json.Unmarshal(responsePayload, &response); err != nil {
        t.Errorf("Unexpected error: %+v", err)
    }

    if response.Valid {
        t.Error("Expected settings to not be valid")
    }

    if *response.Message != "Provided settings are not valid: These labels cannot be constrained and denied at the same time: Set{cost-center}" {
        t.Errorf("Unexpected validation error message: %s", *response.Message)
    }
}

Now you can run the tests that you have defined so far by using the following command:

go test -v settings.go settings_test.go

All the tests will pass with the following output:

=== RUN   TestParseValidSettings
--- PASS: TestParseValidSettings (0.00s)
=== RUN   TestParseSettingsWithInvalidRegexp
--- PASS: TestParseSettingsWithInvalidRegexp (0.00s)
=== RUN   TestDetectValidSettings
--- PASS: TestDetectValidSettings (0.00s)
=== RUN   TestDetectNotValidSettingsDueToBrokenRegexp
--- PASS: TestDetectNotValidSettingsDueToBrokenRegexp (0.00s)
=== RUN   TestDetectNotValidSettingsDueToConflictingLabels
--- PASS: TestDetectNotValidSettingsDueToConflictingLabels (0.00s)
PASS
ok      command-line-arguments    0.002s

You can now implement the actual validation code in the next section.