### Install gziphandler

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/vendor/github.com/NYTimes/gziphandler/README.md

Install the gziphandler package using go get.

```bash
go get -u github.com/NYTimes/gziphandler
```

--------------------------------

### Install Flect

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/vendor/github.com/gobuffalo/flect/README.md

Install the flect package using the go get command.

```console
$ go get github.com/gobuffalo/flect
```

--------------------------------

### Install Go Color Library

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/cppforlife/color/README.md

Install the color library using go get.

```bash
go get github.com/fatih/color
```

--------------------------------

### Define a WebService and Routes

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/emicklei/go-restful/v3/README.md

Example of setting up a new WebService, defining its path, supported content types, and a GET route for retrieving a user. This snippet demonstrates basic route configuration including path parameters and response types.

```go
ws := new(restful.WebService)
ws.
	Path("/users").
	Consumes(restful.MIME_XML, restful.MIME_JSON).
	Produces(restful.MIME_JSON, restful.MIME_XML)

ws.Route(ws.GET("/{user-id}").To(u.findUser).
	Doc("get a user").
	Param(ws.PathParameter("user-id", "identifier of the user").DataType("string")),
	Writes(User{}))		
...
	
func (u UserResource) findUser(request *restful.Request, response *restful.Response) {
	id := request.PathParameter("user-id")
	...
}
```

--------------------------------

### Install and Run Local Go Doc Site

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/vendor/go.opentelemetry.io/otel/CONTRIBUTING.md

Installs the pkgsite tool and runs a local Go documentation site. Ensure you have Go installed and configured.

```sh
go install golang.org/x/pkgsite/cmd/pkgsite@latest
pkgsite
```

--------------------------------

### Install go.yaml.in/yaml/v3

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/go.yaml.in/yaml/v3/README.md

Install the YAML package for Go using the go get command.

```bash
go get go.yaml.in/yaml/v3
```

--------------------------------

### Install json-iterator/go

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/json-iterator/go/README.md

Use the go get command to install the json-iterator/go library.

```go
go get github.com/json-iterator/go
```

--------------------------------

### Install Go Version Library

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/hashicorp/go-version/README.md

Install the go-version library using the standard Go toolchain.

```bash
$ go get github.com/hashicorp/go-version
```

--------------------------------

### Install and Import invopop/yaml

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/oasdiff/yaml/README.md

Install the package using go get and import it into your Go project.

```bash
$ go get github.com/invopop/yaml
```

```go
import "github.com/invopop/yaml"
```

--------------------------------

### Install uuid Package

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/google/uuid/README.md

Install the uuid package using the go get command.

```sh
go get github.com/google/uuid
```

--------------------------------

### Install etcd/client/v3

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/vendor/go.etcd.io/etcd/client/v3/README.md

Install the etcd client library using go modules.

```bash
go get go.etcd.io/etcd/client/v3
```

--------------------------------

### Install and Import YAML Package

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/sigs.k8s.io/yaml/README.md

Install the package using go get and import it into your Go project.

```bash
$ go get sigs.k8s.io/yaml
```

```go
import "sigs.k8s.io/yaml"
```

--------------------------------

### Install Cobra Library

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/spf13/cobra/README.md

Install the latest version of the Cobra library using go get.

```bash
go get -u github.com/spf13/cobra@latest
```

--------------------------------

### Install difflib Go Package

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/k14s/difflib/README.md

Use 'go get' to install the difflib library. This command fetches and installs the package and its dependencies.

```bash
go get github.com/aryann/difflib
```

--------------------------------

### Install Package

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/examples/local-kind-environment/README.md

Applies the package installation configuration using kubectl.

```sh
kubectl apply -f package_install.yml
```

--------------------------------

### Install go.uber.org/multierr

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/go.uber.org/multierr/README.md

Install the latest version of the multierr library using go get.

```bash
go get -u go.uber.org/multierr@latest
```

--------------------------------

### Install go-isatty Package

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/mattn/go-isatty/README.md

Use this command to install the go-isatty package into your Go project.

```bash
go get github.com/mattn/go-isatty
```

--------------------------------

### Install Marshmallow Go Package

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/perimeterx/marshmallow/README.md

Use go get to install the Marshmallow package. This command fetches and installs the latest version of the package.

```sh
go get -u github.com/perimeterx/marshmallow
```

--------------------------------

### Coexisting with klog/v1

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/k8s.io/klog/v2/README.md

Provides an example demonstrating how to use both klog/v1 and klog/v2 within the same project.

```go
// See examples/coexist_klog_v1_and_v2/
```

--------------------------------

### Basic Test Script Example

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/fsnotify/fsnotify/CONTRIBUTING.md

Illustrates creating a file and writing data to it, showing the expected fsnotify events.

```shell
# Create a new empty file with some data.
watch /
    echo data >/file

Output:
    create  /file
    write   /file
```

--------------------------------

### Install Package Repository

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/examples/local-kind-environment/README.md

Applies the package repository installation configuration using kubectl.

```sh
kubectl apply -f package_repository_install.yml
```

--------------------------------

### Install go-colorable Package

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/mattn/go-colorable/README.md

Use this command to install the go-colorable package into your Go project.

```bash
$ go get github.com/mattn/go-colorable
```

--------------------------------

### String Substring Examples

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/vendor/github.com/google/cel-go/ext/README.md

Shows how to extract substrings using start and optional end indices. Errors are raised for invalid ranges.

```cel
'tacocat'.substring(4)    // returns 'cat'
```

```cel
'tacocat'.substring(0, 4) // returns 'taco'
```

```cel
'tacocat'.substring(-1)   // error
```

```cel
'tacocat'.substring(2, 1) // error
```

--------------------------------

### Install Kapp Controller

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/examples/local-kind-environment/README.md

Installs the latest release of Kapp Controller using kubectl.

```sh
kubectl apply -f https://github.com/carvel-dev/kapp-controller/releases/latest/download/release.yml
```

--------------------------------

### Go Float16 Conversion Examples

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/x448/float16/README.md

Demonstrates converting between float32 and float16 using the float16 package. Includes examples for direct conversion and conditional conversion based on precision.

```Go
import (
	"math"
	"github.com/x448/float16"
)

// Convert float32 to float16
pi := float32(math.Pi)
pi16 := float16.Fromfloat32(pi)

// Convert float16 to float32
pi32 := pi16.Float32()

// PrecisionFromfloat32() is faster than the overhead of calling a function.
// This example only converts if there's no data loss and input is not a subnormal.
if float16.PrecisionFromfloat32(pi) == float16.PrecisionExact {
    pi16 := float16.Fromfloat32(pi)
}
```

--------------------------------

### Initialize Procfs and Get Stat

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/prometheus/procfs/README.md

Initializes the proc filesystem and retrieves CPU statistics from /proc/stat.

```go
fs, err := procfs.NewFS("/proc")
stats, err := fs.Stat()
```

--------------------------------

### String Split Examples

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/vendor/github.com/google/cel-go/ext/README.md

Illustrates the string split function with different separators and limits.

```cel
'hello hello hello'.split(' ')     // returns ['hello', 'hello', 'hello']
```

```cel
'hello hello hello'.split(' ', 0)  // returns []
```

```cel
'hello hello hello'.split(' ', 1)  // returns ['hello hello hello']
```

```cel
'hello hello hello'.split(' ', 2)  // returns ['hello', 'hello hello']
```

```cel
'hello hello hello'.split(' ', -1) // returns ['hello', 'hello', 'hello']
```

--------------------------------

### Platform-Specific Test Example

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/fsnotify/fsnotify/CONTRIBUTING.md

Demonstrates how to define platform-specific test outputs within a script.

```shell
watch /
touch /file

Output:
    # Tested if nothing else matches
    create    /file

    # Windows-specific test.
    windows:
        write  /file
```

--------------------------------

### Constructor Functions for Dog and Bird

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/vendor/go.opentelemetry.io/otel/CONTRIBUTING.md

Example constructor functions for 'Dog' and 'Bird' that accept specific options for their respective types.

```go
func NewDog(name string, o ...DogOption) Dog    {…}
func NewBird(name string, o ...BirdOption) Bird {…}
```

--------------------------------

### String Replace Examples

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/vendor/github.com/google/cel-go/ext/README.md

Demonstrates the string replace function with and without a replacement limit.

```cel
'hello hello'.replace('he', 'we')     // returns 'wello wello'
```

```cel
'hello hello'.replace('he', 'we', -1) // returns 'wello wello'
```

```cel
'hello hello'.replace('he', 'we', 1)  // returns 'wello hello'
```

```cel
'hello hello'.replace('he', 'we', 0)  // returns 'hello hello'
```

--------------------------------

### Add or Update Dependency

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/prometheus/procfs/CONTRIBUTING.md

Use 'go get' to add or update external package dependencies.

```bash
# Pick the latest tagged release.
go get example.com/some/module/pkg

# Pick a specific version.
go get example.com/some/module/pkg@vX.Y.Z
```

--------------------------------

### Enable gRPC-Go Logging

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/vendor/google.golang.org/grpc/README.md

Set environment variables to control the verbosity and severity of gRPC-Go logs. This example enables all logging.

```sh
export GRPC_GO_LOG_VERBOSITY_LEVEL=99
export GRPC_GO_LOG_SEVERITY_LEVEL=info
```

--------------------------------

### Basic fsnotify Watcher Example

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/fsnotify/fsnotify/README.md

Demonstrates how to create a new watcher, add a directory to watch, and listen for file system events (write, errors) in a separate goroutine. It's essential to close the watcher when done.

```go
package main

import (
    "log"

    "github.com/fsnotify/fsnotify"
)

func main() {
    // Create new watcher.
    watcher, err := fsnotify.NewWatcher()
    if err != nil {
        log.Fatal(err)
    }
    defer watcher.Close()

    // Start listening for events.
    go func() {
        for {
            select {
            case event, ok := <-watcher.Events:
                if !ok {
                    return
                }
                log.Println("event:", event)
                if event.Has(fsnotify.Write) {
                    log.Println("modified file:", event.Name)
                }
            case err, ok := <-watcher.Errors:
                if !ok {
                    return
                }
                log.Println("error:", err)
            }
        }
    }()

    // Add a path.
    err = watcher.Add("/tmp")
    if err != nil {
        log.Fatal(err)
    }

    // Block main goroutine forever.
    <-make(chan struct{}))
}
```

--------------------------------

### Define a WebService and Routes in Go

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/vendor/github.com/emicklei/go-restful/v3/README.md

Example demonstrating how to define a WebService with path, consumes, produces, and routes. Includes a handler function for finding a user by ID.

```go
ws := new(restful.WebService)
ws.
	Path("/users").
	Consumes(restful.MIME_XML, restful.MIME_JSON).
	Produces(restful.MIME_JSON, restful.MIME_XML)

ws.Route(ws.GET("/{user-id}").To(u.findUser).
	Doc("get a user").
	Param(ws.PathParameter("user-id", "identifier of the user").DataType("string")),
	Writes(User{}))		
...

func (u UserResource) findUser(request *restful.Request, response *restful.Response) {
	id := request.PathParameter("user-id")
	...
}
```

--------------------------------

### Create Root Logger in Go Application

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/go-logr/logr/README.md

Demonstrates how to create the initial 'root' logger instance in an application's main function, choosing a specific logging implementation like 'logimpl'. This setup is done early in the application's lifecycle.

```go
    func main() {
        // ... other setup code ...

        // Create the "root" logger.  We have chosen the "logimpl" implementation,
        // which takes some initial parameters and returns a logr.Logger.
        logger := logimpl.New(param1, param2)

        // ... other setup code ...

```

--------------------------------

### Install Latest JSON-Patch

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/gopkg.in/evanphx/json-patch.v4/README.md

Use this command to get the latest version of the jsonpatch library.

```bash
go get -u github.com/evanphx/json-patch/v5
```

--------------------------------

### Deploy a Sample MongoDB Replica Set

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/examples/package-authoring/mongodb-enterprise-operator/upstream/README.md

Applies a sample configuration to deploy a 3-member MongoDB Replica Set. Use the --namespace option if deploying to a specific namespace.

```shell
kubectl apply -f https://raw.githubusercontent.com/mongodb/mongodb-enterprise-kubernetes/master/samples/mongodb/minimal/replica-set.yaml [--namespace mongodb]
```

--------------------------------

### Install JSON-Patch v4

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/gopkg.in/evanphx/json-patch.v4/README.md

Use this command to get version 4 of the jsonpatch library if needed.

```bash
go get -u gopkg.in/evanphx/json-patch.v4
```

--------------------------------

### Example Go Module Requirement (Incorrect)

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/vendor/github.com/antlr4-go/antlr/v4/README.md

Illustrates the unclear module reference obtained when using `go get` directly from the deeply nested ANTLR4 repository.

```go
require (
	github.com/antlr/antlr4/runtime/Go/antlr/v4 v4.0.0-20230219212500-1f9a474dc2dc
)
```

--------------------------------

### Basic fsnotify Watcher Usage in Go

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/vendor/github.com/fsnotify/fsnotify/README.md

Demonstrates how to create a new watcher, listen for events and errors in a goroutine, add a directory to watch, and handle potential errors. It's recommended to ignore Chmod events as they can be noisy.

```go
package main

import (
    "log"

    "github.com/fsnotify/fsnotify"
)

func main() {
    // Create new watcher.
    watcher, err := fsnotify.NewWatcher()
    if err != nil {
        log.Fatal(err)
    }
    defer watcher.Close()

    // Start listening for events.
    go func() {
        for {
            select {
            case event, ok := <-watcher.Events:
                if !ok {
                    return
                }
                log.Println("event:", event)
                if event.Has(fsnotify.Write) {
                    log.Println("modified file:", event.Name)
                }
            case err, ok := <-watcher.Errors:
                if !ok {
                    return
                }
                log.Println("error:", err)
            }
        }
    }()

    // Add a path.
    err = watcher.Add("/tmp")
    if err != nil {
        log.Fatal(err)
    }

    // Block main goroutine forever.
    <-make(chan struct{})
}
```

--------------------------------

### Example using TagSet and TagOptions

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/fxamacker/cbor/v2/README.md

Shows how to create a TagSet, register a custom tag (COSE_Sign1 18) with a specific type, and then use this TagSet to create decoding and encoding modes.

```go
// Use signedCWT struct defined in "Decoding CWT" example.

// Create TagSet (safe for concurrency).
tags := cbor.NewTagSet()
// Register tag COSE_Sign1 18 with signedCWT type.
tags.Add(    
	cbor.TagOptions{EncTag: cbor.EncTagRequired, DecTag: cbor.DecTagRequired}, 
	reflect.TypeOf(signedCWT{}), 
	18)

// Create DecMode with immutable tags.
dm, _ := cbor.DecOptions{}.DecModeWithTags(tags)

// Unmarshal to signedCWT with tag support.
var v signedCWT
if err := dm.Unmarshal(data, &v); err != nil {
	return err
}

// Create EncMode with immutable tags.
em, _ := cbor.EncOptions{}.EncModeWithTags(tags)

// Marshal signedCWT with tag number.
if data, err := em.Marshal(v); err != nil {
	return err
}
```

--------------------------------

### Install Cobra CLI Generator

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/vendor/github.com/spf13/cobra/README.md

Installs the cobra-cli tool, used for scaffolding Cobra applications.

```bash
go install github.com/spf13/cobra-cli@latest
```

--------------------------------

### Initialize Package Build

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/examples/package-authoring/mongodb-enterprise-operator/README.md

Run `kctrl pkg init` to initialize the package build. This command reads configuration from `package-build.yml` and `vendir.yml` and prompts for default values, including the Helm Chart version.

```shell
cd cli/examples/mongodb-enterprise-operator
kctrl pkg init
```

--------------------------------

### Initialize Package with kctrl

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/examples/package-authoring/redis-enterprise-operator/README.md

Initializes the package for the Redis Enterprise Operator. Navigate to the example directory and run `kctrl pkg init`.

```shell
cd cli/examples/redis-enterprise-operator
kctrl pkg init
```

--------------------------------

### Find the first occurrence of a substring

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/vendor/github.com/google/cel-go/ext/README.md

Use indexOf to find the starting index of a substring within a string. Returns -1 if not found. An optional starting position can be provided. Returns the starting index if the search string is empty.

```cel
'hello mellow'.indexOf('')         // returns 0
'hello mellow'.indexOf('ello')     // returns 1
'hello mellow'.indexOf('jello')    // returns -1
'hello mellow'.indexOf('', 2)      // returns 2
'hello mellow'.indexOf('ello', 2)  // returns 7
'hello mellow'.indexOf('ello', 20) // returns -1
'hello mellow'.indexOf('ello', -1) // error
```

--------------------------------

### Run difflib Demo Application

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/k14s/difflib/README.md

Execute the difflib demo application by providing two file paths as arguments. The demo starts a web server to display diff results.

```bash
go run src/github.com/aryann/difflib/difflib_server/difflib_demo.go <file-1> <file-2>
```

--------------------------------

### Install Enterprise Operator in a Specific Namespace

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/examples/package-authoring/mongodb-enterprise-operator/upstream/README.md

Installs the Enterprise Operator in the 'mongodb' namespace, creating the namespace if it does not exist.

```shell
helm install enterprise-operator mongodb/enterprise-operator --namespace mongodb [--create-namespace]
```

--------------------------------

### Build Kapp-Controller Project

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/docs/dev.md

Run this script to build the kapp-controller project locally.

```bash
./hack/build.sh
```

--------------------------------

### Install Cobra CLI Generator

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/spf13/cobra/README.md

Install the cobra-cli command line program, used for generating Cobra application and command files.

```bash
go install github.com/spf13/cobra-cli@latest

```

--------------------------------

### Check Version Against Constraints in Go

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/hashicorp/go-version/README.md

Shows how to create a version constraint and check if a given version satisfies it. Assumes err is handled.

```go
v1, err := version.NewVersion("1.2")

// Constraints example.
constraints, err := version.NewConstraint(">= 1.0, < 1.4")
if constraints.Check(v1) {
	fmt.Printf("%s satisfies constraints %s", v1, constraints)
}
```

--------------------------------

### Install MongoDB Enterprise Operator

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/examples/package-authoring/mongodb-enterprise-operator/upstream/README.md

Installs the Enterprise Operator in the current namespace. Use the --namespace flag to specify a different namespace.

```shell
helm install enterprise-operator mongodb/enterprise-operator
```

--------------------------------

### Using Zapr with Logr

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/go-logr/zapr/README.md

Demonstrates how to initialize a logr.Logger using zapr and an Uber Zap logger. This is useful for projects already using the logr interface.

```go
package main

import (
    "fmt"

    "go.uber.org/zap"
    "github.com/go-logr/logr"
    "github.com/go-logr/zapr"
)

func main() {
    var log logr.Logger

    zapLog, err := zap.NewDevelopment()
    if err != nil {
        panic(fmt.Sprintf("who watches the watchmen (%v)?", err))
    }
    log = zapr.NewLogger(zapLog)

    log.Info("Logr in action!", "the answer", 42)
}
```

--------------------------------

### Start Local Docker Registry

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/test/e2e/assets/registry/instructions-for-one-time-setup.txt

Starts a Docker registry container in detached mode, mapping port 5000 and persisting data to /tmp/registry.

```bash
docker run -d -p 5000:5000 --restart=always -v/tmp/registry:/var/lib/registry --name registry registry:2
```

--------------------------------

### Get OpenTelemetry Go Module

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/vendor/go.opentelemetry.io/otel/CONTRIBUTING.md

Use `go get` to download the OpenTelemetry Go module, which places the project in your GOPATH. This command may print warnings that can be ignored.

```go
go get -d go.opentelemetry.io/otel
```

--------------------------------

### Build Package Repository Bundle

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/examples/local-kind-environment/README.md

Uses kbld to build the package repository bundle, outputting an imgpkg lock file.

```sh
kbld -f ./package-repository/packages --imgpkg-lock-output "./package-repository/.imgpkg/images.yml"
```

--------------------------------

### Parse and Compare Versions in Go

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/hashicorp/go-version/README.md

Demonstrates parsing version strings into Version objects and comparing them using LessThan. Assumes err is handled.

```go
v1, err := version.NewVersion("1.2")
v2, err := version.NewVersion("1.5+metadata")

// Comparison example. There is also GreaterThan, Equal, and just
// a simple Compare that returns an int allowing easy >=, <=, etc.
if v1.LessThan(v2) {
    fmt.Printf("%s is less than %s", v1, v2)
}
```

--------------------------------

### Gob Encoding Security Vulnerability Example

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/fxamacker/cbor/v2/README.md

Illustrates a 'fatal error: runtime: out of memory' when decoding malicious data using Go's encoding/gob. This example highlights the security risks associated with gob when handling untrusted inputs.

```Go
package main

import (
	"bytes"
	"encoding/gob"
	"encoding/hex"
	"fmt"
)

// Example data is from https://github.com/golang/go/issues/24446
// (shortened to 181 bytes).
const data = "4dffb503010102303001ff30000109010130010800010130010800010130"
	"01ffb80001014a01ffb60001014b01ff860001013001ff860001013001ff"
	"860001013001ff860001013001ffb80000001eff850401010e30303030"
	"303030303030303030303030303030303030303030303030303030303030"
	"303030303030303030303030303030303030303030303030303030303030"
	"30"

type X struct {
	J *X
	K map[string]int
}

func main() {
	raw, _ := hex.DecodeString(data)
	decoder := gob.NewDecoder(bytes.NewReader(raw))

	var x X
	decoder.Decode(&x) // fatal error: runtime: out of memory
	fmt.Println("Decoding finished.")
}

```

--------------------------------

### Base64.Encode Example

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/vendor/github.com/google/cel-go/ext/README.md

Encodes bytes to a base64-encoded string.

```cel
base64.encode(b'hello') // return 'aGVsbG8='
```

--------------------------------

### Example using Embedded JSON Tag for CBOR (tag 262)

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/cli/vendor/github.com/fxamacker/cbor/v2/README.md

Demonstrates encoding and decoding a CBOR data item with tag number 262, where the tag content is a JSON object embedded as a CBOR byte string. This example implements custom MarshalCBOR and UnmarshalCBOR methods.

```go
// https://github.com/fxamacker/cbor/issues/657

package cbor_test

// NOTE: RFC 8949 does not mention tag number 262. IANA assigned
// CBOR tag number 262 as "Embedded JSON Object" specified by the
// document Embedded JSON Tag for CBOR:
//
//	"Tag 262 can be applied to a byte string (major type 2) to indicate
//	that the byte string is a JSON Object. The length of the byte string
//	indicates the content."
//
// For more info, see Embedded JSON Tag for CBOR at:
// https://github.com/toravir/CBOR-Tag-Specs/blob/master/embeddedJSON.md

import (
	"bytes"
	"encoding/json"
	"fmt"

	"github.com/fxamacker/cbor/v2"
)

// cborTagNumForEmbeddedJSON is the CBOR tag number 262.
const cborTagNumForEmbeddedJSON = 262

// EmbeddedJSON represents a Go value to be encoded as a tagged CBOR data item
// with tag number 262 and the tag content is a JSON object "embedded" as a
// CBOR byte string (major type 2).
type EmbeddedJSON struct {
	any
}

func NewEmbeddedJSON(val any) EmbeddedJSON {
	return EmbeddedJSON{val}
}

// MarshalCBOR encodes EmbeddedJSON to a tagged CBOR data item with the
// tag number 262 and the tag content is a JSON object that is
// "embedded" as a CBOR byte string.
func (v EmbeddedJSON) MarshalCBOR() ([]byte, error) {
	// Encode v to JSON object.
	data, err := json.Marshal(v)
	if err != nil {
		return nil, err
	}

	// Create cbor.Tag representing a tagged CBOR data item.
	tag := cbor.Tag{
		Number:  cborTagNumForEmbeddedJSON,
		Content: data,
	}

	// Marshal to a tagged CBOR data item.
	return cbor.Marshal(tag)
}

// UnmarshalCBOR decodes a tagged CBOR data item to EmbeddedJSON.
// The byte slice provided to this function must contain a single
// tagged CBOR data item with the tag number 262 and tag content
// must be a JSON object "embedded" as a CBOR byte string.
func (v *EmbeddedJSON) UnmarshalCBOR(b []byte) error {
	// Unmarshal tagged CBOR data item.
	var tag cbor.Tag
	if err := cbor.Unmarshal(b, &tag); err != nil {
		return err
	}

	// Check tag number.
	if tag.Number != cborTagNumForEmbeddedJSON {
		return fmt.Errorf("got tag number %d, expect tag number %d", tag.Number, cborTagNumForEmbeddedJSON)
	}

	// Check tag content.
	jsonData, isByteString := tag.Content.([]byte)
	if !isByteString {
		return fmt.Errorf("got tag content type %T, expect tag content []byte", tag.Content)
	}

	// Unmarshal JSON object.
	return json.Unmarshal(jsonData, v)
}

// MarshalJSON encodes EmbeddedJSON to a JSON object.
func (v EmbeddedJSON) MarshalJSON() ([]byte, error) {
	return json.Marshal(v.any)
}

// UnmarshalJSON decodes a JSON object.
func (v *EmbeddedJSON) UnmarshalJSON(b []byte) error {
	dec := json.NewDecoder(bytes.NewReader(b))
	dec.UseNumber()
	return dec.Decode(&v.any)
}

func Example_embeddedJSONTagForCBOR() {
	value := NewEmbeddedJSON(map[string]any{
		"name": "gopher",
		"id":   json.Number("42"),
	})

	data, err := cbor.Marshal(value)
	if err != nil {
		panic(err)
	}

	fmt.Printf("cbor: %x\n", data)

	var v EmbeddedJSON
	err = cbor.Unmarshal(data, &v)
	if err != nil {
		panic(err)
	}

```

--------------------------------

### String Trim Example

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/vendor/github.com/google/cel-go/ext/README.md

Demonstrates removing leading and trailing whitespace from a string.

```cel
'  	trim
    '.trim() // returns 'trim'
```

--------------------------------

### TransformMap Map Value Example

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/vendor/github.com/google/cel-go/ext/README.md

Transforms the values of a map by appending a character to each value.

```cel
{'greeting': 'hello'}.transformMap(k, v, v + '!')
```

--------------------------------

### TransformList Map Values Example

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/vendor/github.com/google/cel-go/ext/README.md

Transforms a map into a list containing only the values of the map.

```cel
{'greeting': 'hello', 'farewell': 'goodbye'}
  .transformList(_, v, v)
```

--------------------------------

### Run Kapp-Controller Benchmark Tests Locally

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/docs/dev.md

Run benchmark tests locally using the go toolchain. Benchmark results are also graphed on GitHub pages.

```bash
go test ./test/bench/... -bench=.
```

--------------------------------

### TransformList Map Keys Example

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/vendor/github.com/google/cel-go/ext/README.md

Transforms a map into a list containing only the keys of the map.

```cel
{'greeting': 'hello', 'farewell': 'goodbye'}
  .transformList(k, _, k)
```

--------------------------------

### Run Standard Tests

Source: https://github.com/carvel-dev/kapp-controller/blob/develop/vendor/google.golang.org/grpc/CONTRIBUTING.md

Execute the Go tests with specified CPU configurations and timeout.

```bash
go test -cpu 1,4 -timeout 7m ./...
```