### Install protobuf compiler (protoc)

Source: https://github.com/go-kit/kit/blob/master/transport/grpc/README.md

Steps to install the protobuf compiler (protoc) from source using Homebrew and Git. This is necessary for compiling .proto files.

```sh
brew install autoconf automake libtool
git clone https://github.com/google/protobuf
cd protobuf
./autogen.sh ; ./configure ; make ; make install
```

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

### Trace Database Query with Zipkin in Go-kit

Source: https://github.com/go-kit/kit/blob/master/tracing/zipkin/README.md

Provides an example of how to trace a database query using Zipkin within a Go-kit service. It shows how to start a span, annotate it with query details and timing, and finish it.

```go
import (
	zipkin "github.com/openzipkin/zipkin-go"
)

func (svc *Service) GetMeSomeExamples(ctx context.Context, ...) ([]Examples, error) {
  // Example of annotating a database query:
  var (
    spanContext model.SpanContext
    serviceName = "MySQL"
    serviceHost = "mysql.example.com:3306"
    queryLabel  = "GetExamplesByParam"
    query       = "select * from example where param = :value"
  )

  // retrieve the parent span from context to use as parent if available.
  if parentSpan := zipkin.SpanFromContext(ctx); parentSpan != nil {
    spanContext = parentSpan.Context()
  }

  // create the remote Zipkin endpoint
  ep, _ := zipkin.NewEndpoint(serviceName, serviceHost)

  // create a new span to record the resource interaction
  span := zipkin.StartSpan(
    queryLabel,
    zipkin.Parent(parentSpan.Context()),
    zipkin.WithRemoteEndpoint(ep),
  )

	// add interesting key/value pair to our span
	span.SetTag("query", query)

	// add interesting timed event to our span
	span.Annotate(time.Now(), "query:start")

	// do the actual query...

	// let's annotate the end...
	span.Annotate(time.Now(), "query:end")

	// we're done with this span.
	span.Finish()

	// do other stuff
	...
}
```

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

### Contextual Loggers with Go-Kit

Source: https://github.com/go-kit/kit/blob/master/log/README.md

Illustrates creating contextual loggers in Go-Kit by adding key-value pairs to a base logger. This example adds 'instance_id' and 'component' to log messages.

```Go
func main() {
	var logger log.Logger
	logger = log.NewLogfmtLogger(log.NewSyncWriter(os.Stderr))
	logger = log.With(logger, "instance_id", 123)

	logger.Log("msg", "starting")
	NewWorker(log.With(logger, "component", "worker")).Run()
	NewSlacker(log.With(logger, "component", "slacker")).Run()
}

// Output:
// instance_id=123 msg=starting
// instance_id=123 component=worker msg=running
// instance_id=123 component=slacker msg=running
```

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

### Go-Kit JSON RPC Server Setup

Source: https://github.com/go-kit/kit/blob/master/transport/http/jsonrpc/README.md

Demonstrates how to set up a Go-Kit JSON RPC server. It involves creating an EndpointCodecMap to route incoming JSON RPC methods to specific endpoints, decoders, and encoders. The server is then registered as an HTTP handler.

```Go
handler := jsonrpc.NewServer(jsonrpc.EndpointCodecMap{
		"sum": jsonrpc.EndpointCodec{
			Endpoint: sumEndpoint,
			Decode:   decodeSumRequest,
			Encode:   encodeSumResponse,
		},
	})
	http.Handle("/rpc", handler)
	http.ListenAndServe(":80", nil)
```

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

### Compile Thrift IDL to Go

Source: https://github.com/go-kit/kit/blob/master/transport/thrift/README.md

This command compiles a Thrift IDL file into Go source code. It uses the Thrift compiler with specific generation flags, including a package prefix for the generated Go code. Ensure you have the Thrift compiler installed and the .thrift file is correctly defined.

```Shell
thrift -r --gen go:package_prefix=github.com/my-org/my-repo/thrift/gen-go/ add.thrift
```

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

### Go-Kit JSON RPC EndpointCodecMap Example

Source: https://github.com/go-kit/kit/blob/master/transport/http/jsonrpc/README.md

Illustrates the structure of an `EndpointCodecMap` in Go-Kit for JSON RPC. It maps a JSON RPC method name (e.g., "sum") to an `EndpointCodec`, which bundles the endpoint logic with request decoding and response encoding functions.

```Go
jsonrpc.EndpointCodecMap{
		"sum": jsonrpc.EndpointCodec{
			Endpoint: sumEndpoint,
			Decode:   decodeSumRequest,
			Encode:   encodeSumResponse,
		},
	}
```

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

### Go-Kit: Monitoring and Instrumentation with spacemonkeygo/monitor

Source: https://github.com/go-kit/kit/blob/master/README.md

Uses spacemonkeygo/monitor for data collection, monitoring, and instrumentation, including a Zipkin client library. This facilitates performance tracking and distributed tracing.

```Go
package main

import (
	"fmt"
	"github.com/spacemonkeygo/monitor/monitorlib"
	"github.com/spacemonkeygo/monitor/tracing/zipkin"
	"time"
)

func main() {
	// Initialize monitor with Zipkin tracing
	zipkinClient, err := zipkin.NewClient("my-service", "localhost:9411") // Zipkin collector address
	if err != nil {
		panic(err)
	}

	monitorlib.SetGlobalMonitor(monitorlib.NewMonitor(zipkinClient))

	// Start a trace span
	span := monitorlib.NewSpan("process_request")
	defer span.Finish()

	// Simulate work
	time.Sleep(100 * time.Millisecond)

	fmt.Println("Request processed with monitoring.")
}
```

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

### Go-Kit: Application Tracing with Appdash

Source: https://github.com/go-kit/kit/blob/master/README.md

Integrates Appdash for application tracing, inspired by Google's Dapper. It helps visualize request flows and identify performance bottlenecks in distributed systems.

```Go
package main

import (
	"fmt"
	"net/http"

	"sourcegraph.com/sourcegraph/appdash"
	"sourcegraph.com/sourcegraph/appdash/traceapp"
)

func main() {
	// Set up the Appdash collector
	collector := appdash.NewMemoryCollector()
	tracer := appdash.NewTracer(collector)

	// Start the trace viewer web UI
	go traceapp.RunTraceApp(collector, ":63730")

	// Example: Trace an HTTP request
	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		span, ok := appdash.SpanFromContext(r.Context())
		if !ok {
			span = tracer.StartSpan("root")
			defer span.Finish()
			r = r.WithContext(appdash.NewContext(r.Context(), span))
		}

		fmt.Fprintf(w, "Hello from Go-Kit!")
		subSpan := span.NewChild("response_written")
		subSpan.Finish()
	})

	fmt.Println("Starting server on :8080, trace viewer on :63730")
	// http.ListenAndServe(":8080", nil)
}
```

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

### Go: Counter using expvar

Source: https://github.com/go-kit/kit/blob/master/metrics/README.md

Demonstrates how to create and use a simple counter metric exported via expvar. This involves initializing the counter and adding a value to it.

```go
import (
	"github.com/go-kit/kit/metrics"
	"github.com/go-kit/kit/metrics/expvar"
)

func main() {
	var myCount metrics.Counter
	myCount = expvar.NewCounter("my_count")
	myCount.Add(1)
}
```

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

### Go-Kit: Structured Logging with logrus

Source: https://github.com/go-kit/kit/blob/master/README.md

Leverages logrus for structured, pluggable logging in Go. It offers flexibility with different output formats and hooks for custom processing.

```Go
package main

import (
	"github.com/sirupsen/logrus"
)

func main() {
	// Create a new logger instance
	log := logrus.New()

	// Set output to stdout
	log.SetOutput(os.Stdout)

	// Set formatter (e.g., JSONFormatter)
	log.SetFormatter(&logrus.JSONFormatter{})

	// Log messages with fields
	log.WithFields(logrus.Fields{
		"event": "login",
		"user_id": 42,
	}).Info("User successfully logged in")

	log.Warn("Potential issue detected")
}
```

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

### Go-Kit: Structured Logging with log15

Source: https://github.com/go-kit/kit/blob/master/README.md

Employs the log15 library for simple and powerful structured logging in Go applications. It supports various handlers for outputting logs.

```Go
package main

import (
	"github.com/inconshreveable/log15"
	"os"
)

func main() {
	// Create a logger with a handler that writes to stdout
	log := log15.New()
	log.SetHandler(log15.StreamHandler(os.Stdout, log15.LogfmtFormat()))

	// Log messages with context
	log.Info("User logged in", "user_id", 123, "ip", "192.168.1.1")
	log.Error("Failed to process request", "error", "timeout", "request_id", "abc")
}
```

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

### Go-Kit: Nanomsg Implementation with mangos

Source: https://github.com/go-kit/kit/blob/master/README.md

Provides a pure Go implementation of Nanomsg (nanomsg) messaging patterns using the mangos library. It enables high-performance asynchronous messaging.

```Go
package main

import (
	"fmt"
	"log"

	"github.com/gdamore/mangos"
	_ "github.com/gdamore/mangos/protocol/reqrep"
	_ "github.com/gdamore/mangos/transport/tcp"
)

func main() {
	sock, err := mangos.NewSocket(mangos.REQ)
	if err != nil {
		log.Fatalf("cannot create new socket: %v", err)
	}

	// Ensure socket is closed
	defer sock.Close()

	// Connect to the address
	if err = sock.Dial("tcp://localhost:8081"); err != nil {
		log.Fatalf("cannot dial: %v", err)
	}

	// Send a message
	msg := []byte("Hello Nanomsg!")
	if err = sock.Send(msg);
		err != nil {
		log.Fatalf("cannot send: %v", err)
	}

	// Receive a reply
	reply, err := sock.Recv()
	if err != nil {
		log.Fatalf("cannot recv: %v", err)
	}

	fmt.Printf("Received reply: %s\n", reply)
}
```

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

### Basic Logfmt Logger Usage in Go-Kit

Source: https://github.com/go-kit/kit/blob/master/log/README.md

Shows how to create and use a basic logfmt logger with Go-Kit. It logs a question and answer to standard error.

```Go
w := log.NewSyncWriter(os.Stderr)
logger := log.NewLogfmtLogger(w)
logger.Log("question", "what is the meaning of life?", "answer", 42)

// Output:
// question="what is the meaning of life?" answer=42
```

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

### Go-Kit: HTTP Handler Filters with handy

Source: https://github.com/go-kit/kit/blob/master/README.md

Applies net/http handler filters using the handy library. This allows for middleware-like functionality to wrap HTTP handlers for cross-cutting concerns.

```Go
package main

import (
	"fmt"
	"net/http"

	"github.com/streadway/handy"
)

func main() {
	// Define a simple handler
	mainHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		fmt.Fprintln(w, "Hello from main handler!")
	})

	// Create a filter (e.g., logging)
	loggingFilter := handy.LoggingHandler(os.Stdout, mainHandler)

	// Create another filter (e.g., method check)
	methodFilter := handy.MethodHandler("GET", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		fmt.Fprintln(w, "This is a GET request.")
	}))

	// Chain filters
	chainedHandler := handy.Chain(loggingFilter, methodFilter)

	http.Handle("/", chainedHandler)

	fmt.Println("Server starting on :8080...")
	// http.ListenAndServe(":8080", nil)
}
```

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

### Go: Histogram using Prometheus Summary

Source: https://github.com/go-kit/kit/blob/master/metrics/README.md

Shows how to create a histogram for request duration using a Prometheus Summary. It includes setting up the SummaryOpts with namespace, subsystem, name, and help text, and observing the duration.

```go
import (
	time "time"

	stdprometheus "github.com/prometheus/client_golang/prometheus"

	"github.com/go-kit/kit/metrics"
	"github.com/go-kit/kit/metrics/prometheus"
)

func main() {
	var dur metrics.Histogram = prometheus.NewSummaryFrom(stdprometheus.SummaryOpts{
		Namespace: "myservice",
		Subsystem: "api",
		Name:     "request_duration_seconds",
		Help:     "Total time spent serving requests.",
	}, []string{})
	// ...
}

func handleRequest(dur metrics.Histogram) {
	defer func(begin time.Time) { dur.Observe(time.Since(begin).Seconds()) }(time.Now())
	// handle request
}
```

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

### Go-Kit: Client-side Fault Tolerance with Hystrix-Go

Source: https://github.com/go-kit/kit/blob/master/README.md

Integrates the hystrix-go library for implementing client-side latency and fault tolerance patterns within Go applications. This helps manage failures and improve system resilience.

```Go
package main

import (
	"fmt"
	"github.com/afex/hystrix-go/hystrix"
)

func main() {
	// Configure a circuit breaker
	hystrix.ConfigureCommand("my_command", hystrix.CommandConfig{
		Timeout:               1000,
		MaxConcurrentRequests: 100,
		ErrorPercentThreshold: 25,
	})

	// Execute a command
	err := hystrix.Do("my_command", func() error {
		// Your command logic here
		fmt.Println("Executing command...")
		return nil
	}, func(err error) error {
		// Fallback logic here
		fmt.Println("Executing fallback...")
		return nil
	})

	if err != nil {
		fmt.Printf("Error executing command: %v\n", err)
	}
}
```

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

### Go-Kit HTTP Basic Auth Middleware Usage

Source: https://github.com/go-kit/kit/blob/master/auth/basic/README.md

Demonstrates how to integrate the Basic Authentication middleware into a Go-Kit HTTP server. It shows the necessary import, the middleware's placement in the server creation, and the requirement for context population.

```go
import httptransport "github.com/go-kit/kit/transport/http"

httptransport.NewServer(
		AuthMiddleware(cfg.auth.user, cfg.auth.password, "Example Realm")(makeUppercaseEndpoint()),
		decodeMappingsRequest,
		httptransport.EncodeJSONResponse,
		httptransport.ServerBefore(httptransport.PopulateRequestContext),
	)
```

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

### Structured vs. Unstructured Logging in Go-Kit

Source: https://github.com/go-kit/kit/blob/master/log/README.md

Demonstrates the difference between unstructured and structured logging using the Go-Kit log package. Structured logging uses key-value pairs for contextual information.

```Go
// Unstructured
log.Printf("HTTP server listening on %s", addr)

// Structured
logger.Log("transport", "HTTP", "addr", addr, "msg", "listening")
```

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

### Go-Kit: Metrics Exporting with go-metrics

Source: https://github.com/go-kit/kit/blob/master/README.md

Utilizes the go-metrics library to export performance and runtime metrics to external systems. This enables monitoring and analysis of application behavior.

```Go
package main

import (
	"fmt"
	"github.com/armon/go-metrics"
	"time"
)

func main() {
	// Initialize metrics registry
	metrics.NewGlobalMetricRegistry(nil)

	// Create a counter
	requests, _ := metrics.NewCounter("requests_total")

	// Increment the counter
	requests.Inc(1)

	// Create a timer
	latency, _ := metrics.NewTimer("request_latency_seconds")

	// Record a duration
	latency.Record(50 * time.Millisecond)

	fmt.Println("Metrics recorded.")
}
```

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

### Redirecting Go-Kit Logger to Stdlib Logger

Source: https://github.com/go-kit/kit/blob/master/log/README.md

Shows how to pipe Go-Kit logger output through the standard library's log package for legacy systems.

```Go
logger := kitlog.NewLogfmtLogger(kitlog.StdlibWriter{})
logger.Log("legacy", true, "msg", "at least it's something")

// Output:
// 2016/01/01 12:34:56 legacy=true msg="at least it's something"
```

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

### Redirecting Stdlib Logger to Go-Kit JSON Logger

Source: https://github.com/go-kit/kit/blob/master/log/README.md

Demonstrates how to redirect the standard library's log output to a Go-Kit JSON logger using an adapter.

```Go
import (
	os
	stdlog "log"
	kitlog "github.com/go-kit/kit/log"
)

func main() {
	logger := kitlog.NewJSONLogger(kitlog.NewSyncWriter(os.Stdout))
	stdlog.SetOutput(kitlog.NewStdlibAdapter(logger))
	stdlog.Print("I sure like pie")
}

// Output:
// {"msg":"I sure like pie","ts":"2016/01/01 12:34:56"}
```

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

### Go-Kit: RPC with context.Context using rpcplus

Source: https://github.com/go-kit/kit/blob/master/README.md

Utilizes the rpcplus package for enhanced RPC functionality, including support for context.Context. This allows for request-scoped values and cancellation propagation.

```Go
package main

import (
	"context"
	"fmt"
	"net/rpc"

	"github.com/youtube/vitess/go/rpcplus"
)

// Define arguments and results for the RPC method
type Args struct { A, B int }

type Reply struct {
	C int
}

// Define a service
type MathService int

func (t *MathService) Add(ctx context.Context, args *Args, reply *Reply) error {
	reply.C = args.A + args.B
	return nil
}

func main() {
	// Register the service
	math := new(MathService)
	rpcplus.Register(math)

	// Example of calling the service (typically done client-side)
	client, err := rpcplus.Dial("tcp", "localhost:1234")
	if err != nil {
		fmt.Printf("dialing %v\n", err)
		return
	}

	args := &Args{1, 2}
	reply := new(Reply)

	// Call the Add method with context
	ctx := context.Background()
	err = client.Call(ctx, "MathService.Add", args, reply)
	if err != nil {
		fmt.Printf("Error calling Add: %v\n", err)
	} else {
		fmt.Printf("Math: %d + %d = %d\n", args.A, args.B, reply.C)
	}
}
```

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

### Configure Zipkin HTTP Reporter in Go-kit

Source: https://github.com/go-kit/kit/blob/master/tracing/zipkin/README.md

Demonstrates how to configure the Zipkin HTTP reporter in a Go-kit service. It involves creating a reporter, defining the service's local endpoint, and initializing the tracer.

```go
var (
  serviceName        = "MyService"
  serviceHostPort    = "localhost:8000"
  zipkinHTTPEndpoint = "http://localhost:9411/api/v2/spans"
)

// create an instance of the HTTP Reporter.
reporter := zipkin.NewReporter(zipkinHTTPEndpoint)

// create our tracer's local endpoint (how the service is identified in Zipkin).
localEndpoint, err := zipkin.NewEndpoint(serviceName, serviceHostPort)

// create our tracer instance.
tracer, err = zipkin.NewTracer(reporter, zipkin.WithLocalEndpoint(localEndpoint))
...
```

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

### Go-Kit Zipkin Tracing

Source: https://github.com/go-kit/kit/blob/master/tracing/README.md

Provides bindings to the native Go tracing implementation for Zipkin. This is the preferred binding for polyglot microservices environments. Instrumentation exists for kit/transport/http and kit/transport/grpc.

```Go
package tracing

// Zipkin provides bindings to the native Go tracing implementation [zipkin-go].
// Instrumentation exists for `kit/transport/http` and `kit/transport/grpc`.
```

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

### Go-Kit: RPC with gRPC-Go

Source: https://github.com/go-kit/kit/blob/master/README.md

Utilizes gRPC-Go for building high-performance, HTTP/2-based Remote Procedure Call (RPC) services. It supports features like protocol buffers for efficient data serialization.

```Go
package main

import (
	"context"
	"fmt"
	"log"

	"google.golang.org/grpc"
	"google.golang.org/grpc/credentials/insecure"

	// Assuming you have a protobuf generated package
	// "path/to/your/proto"
)

func main() {
	// Set up a connection to the server.
	conn, err := grpc.Dial("localhost:50051", grpc.WithTransportCredentials(insecure.NewCredentials()))
	if err != nil {
		log.Fatalf("did not connect: %v", err)
	}
	defer conn.Close()

	// Create a client
	// client := pb.NewYourServiceClient(conn)

	// Call a remote procedure
	// resp, err := client.YourMethod(context.Background(), &pb.YourRequest{Name: "Go-Kit"})
	// if err != nil {
	// 	log.Fatalf("could not greet: %v", err)
	// }
	// fmt.Printf("Response: %s\n", resp.GetMessage())
	fmt.Println("gRPC client setup complete (example).")
}
```

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

### Go-Kit: Resiliency Patterns with go-resiliency

Source: https://github.com/go-kit/kit/blob/master/README.md

Implements various resiliency patterns using the go-resiliency library. This includes strategies like retries, timeouts, and circuit breakers to enhance application robustness.

```Go
package main

import (
	"fmt"
	"github.com/eapache/go-resiliency/retrier"
	"time"
)

func main() {
	// Configure a retrier
	r := retrier.New(2*time.Second, 3) // 2-second delay, 3 retries

	// Attempt an operation with retries
	err := r.Run(func() error {
		// Your operation that might fail
		fmt.Println("Attempting operation...")
		return fmt.Errorf("operation failed")
	})

	if err != nil {
		fmt.Printf("Operation failed after multiple retries: %v\n", err)
	} else {
		fmt.Println("Operation succeeded.")
	}
}
```

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

### Go-Kit OpenTracing Tracing

Source: https://github.com/go-kit/kit/blob/master/tracing/README.md

Supports the OpenTracing API and uses the opentracing-go package to provide tracing middlewares for its servers and clients. Instrumentation exists for kit/transport/http and kit/transport/grpc. Supports multiple tracing backends through the OpenTracing interface.

```Go
package tracing

// Go kit supports the [OpenTracing] API and uses the [opentracing-go] package to provide tracing middlewares for its servers and clients.
// Currently OpenTracing instrumentation exists for `kit/transport/http` and `kit/transport/grpc`.
```

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

### Go-Kit OpenCensus Tracing

Source: https://github.com/go-kit/kit/blob/master/tracing/README.md

Supports transport and endpoint middlewares for the OpenCensus instrumentation library. OpenCensus provides a cross-language consistent data model and instrumentation libraries for tracing and metrics, allowing exports to various backends.

```Go
package tracing

// Go kit supports transport and endpoint middlewares for the [OpenCensus] instrumentation library.
// Go kit uses the [opencensus-go] implementation to power its middlewares.
```

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

### Run Zipkin with Docker

Source: https://github.com/go-kit/kit/blob/master/tracing/zipkin/README.md

This snippet shows how to run a Zipkin server using a Docker container. It exposes the default HTTP collector and web UI on port 9411.

```bash
docker run -d -p 9411:9411 openzipkin/zipkin
```

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

### Compile protobuf to Go with gRPC

Source: https://github.com/go-kit/kit/blob/master/transport/grpc/README.md

Command to compile a .proto file into Go source files with gRPC support using the protoc compiler. This generates the necessary Go code for gRPC communication.

```sh
protoc add.proto --go_out=plugins=grpc:.
```

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

### Go: Gauge using StatsD

Source: https://github.com/go-kit/kit/blob/master/metrics/README.md

Illustrates creating a gauge to track the number of goroutines, exported via StatsD. It sets up a StatsD client, a send loop, and a goroutine to periodically update the gauge with the current goroutine count.

```go
import (
	"context"
	"net"
	"os"
	"runtime"
	"time"

	"github.com/go-kit/kit/metrics"
	"github.com/go-kit/kit/metrics/statsd"
)

func main() {
	statsd := statsd.New("foo_svc.", log.NewNopLogger())
	report := time.NewTicker(5 * time.Second)
	defer report.Stop()
	go statsd.SendLoop(context.Background(), report.C, "tcp", "statsd.internal:8125")
	goroutines := statsd.NewGauge("goroutine_count")
	go exportGoroutines(goroutines)
	// ...
}

func exportGoroutines(g metrics.Gauge) {
	for range time.Tick(time.Second) {
		g.Set(float64(runtime.NumGoroutine()))
	}
}
```

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

### Go-Kit OpenTelemetry Tracing

Source: https://github.com/go-kit/kit/blob/master/tracing/README.md

Provides Go kit instrumentation through the opentelemetry-go-contrib repository, which is a central repository of instrumentation libraries. OpenTelemetry merged OpenCensus and OpenTracing.

```Go
package tracing

// Go kit instrumentation can be found in [opentelemetry-go-contrib]
// which is a central repository of instrumentation libraries.
```

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

### Go: JWT Signing Middleware

Source: https://github.com/go-kit/kit/blob/master/auth/jwt/README.md

Creates an endpoint middleware that signs JWTs for outgoing requests. It takes a key ID header, signing key, signing method, and claims object to construct the token.

```go
import (
	stdjwt "github.com/golang-jwt/jwt/v4"

	"github.com/go-kit/kit/auth/jwt"
	"github.com/go-kit/kit/endpoint"
)

func main() {
	var exampleEndpoint endpoint.Endpoint
	{
		exampleEndpoint = grpctransport.NewClient(...).Endpoint()
		exampleEndpoint = jwt.NewSigner(
			"kid-header",
			[]byte("SigningString"),
			stdjwt.SigningMethodHS256,
			jwt.Claims{},
		)(exampleEndpoint)
	}
}
```

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

### Adding Timestamps and Callers with Go-Kit Logger

Source: https://github.com/go-kit/kit/blob/master/log/README.md

Configures a Go-Kit logger to automatically include UTC timestamps and caller information in log messages.

```Go
var logger log.Logger
logger = log.NewLogfmtLogger(log.NewSyncWriter(os.Stderr))
logger = log.With(logger, "ts", log.DefaultTimestampUTC, "caller", log.DefaultCaller)

logger.Log("msg", "hello")

// Output:
// ts=2016-01-01T12:34:56Z caller=main.go:15 msg=hello
```

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

### Go-Kit Logger Interface Definition

Source: https://github.com/go-kit/kit/blob/master/log/README.md

Defines the core Logger interface in the Go-Kit log package, which accepts a variable number of key-value pairs.

```Go
type Logger interface {
	Log(keyvals ...interface{}) error
}
```

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

### Go: JWT Token Parsing Middleware

Source: https://github.com/go-kit/kit/blob/master/auth/jwt/README.md

Creates an endpoint middleware that parses a JWT from the request context. It requires a key function to verify the token's signature and an expected signing method. Valid claims are added to the context.

```go
import (
	stdjwt "github.com/golang-jwt/jwt/v4"

	"github.com/go-kit/kit/auth/jwt"
	"github.com/go-kit/kit/endpoint"
)

func main() {
	var exampleEndpoint endpoint.Endpoint
	{
		kf := func(token *stdjwt.Token) (interface{}, error) { return []byte("SigningString"), nil }
		exampleEndpoint = MakeExampleEndpoint(service)
		exampleEndpoint = jwt.NewParser(kf, stdjwt.SigningMethodHS256, jwt.StandardClaimsFactory)(exampleEndpoint)
	}
}
```

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

### Go: JWT Context to gRPC Transport

Source: https://github.com/go-kit/kit/blob/master/auth/jwt/README.md

Helper function to transfer JWT information from the context to the gRPC transport layer. Used as a ClientBefore option for gRPC clients.

```go
import (
	stdjwt "github.com/golang-jwt/jwt/v4"

	grpctransport "github.com/go-kit/kit/transport/grpc"
	"github.com/go-kit/kit/auth/jwt"
	"github.com/go-kit/kit/endpoint"
)

func main() {

	options := []httptransport.ClientOption{}
	var exampleEndpoint endpoint.Endpoint
	{
		exampleEndpoint = grpctransport.NewClient(..., grpctransport.ClientBefore(jwt.ContextToGRPC())).Endpoint()
		exampleEndpoint = jwt.NewSigner(
			"kid-header",
			[]byte("SigningString"),
			stdjwt.SigningMethodHS256,
			jwt.Claims{},
		)(exampleEndpoint)
	}
}
```

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

### Go: JWT gRPC Transport to Context

Source: https://github.com/go-kit/kit/blob/master/auth/jwt/README.md

Helper function to transfer JWT information from the gRPC transport layer to the context. Used as a ServerBefore option for gRPC servers.

```go
import (
	"context"

	"github.com/go-kit/kit/auth/jwt"
	"github.com/go-kit/log"
	grpctransport "github.com/go-kit/kit/transport/grpc"
)

func MakeGRPCServer(ctx context.Context, endpoints Endpoints, logger log.Logger) pb.ExampleServer {
	options := []grpctransport.ServerOption{grpctransport.ServerErrorLogger(logger)}

	return &grpcServer{
		createUser: grpctransport.NewServer(
			ctx,
			endpoints.CreateUserEndpoint,
			DecodeGRPCCreateUserRequest,
			EncodeGRPCCreateUserResponse,
			append(options, grpctransport.ServerBefore(jwt.GRPCToContext())).
		),
		getUser: grpctransport.NewServer(
			ctx,
			endpoints.GetUserEndpoint,
			DecodeGRPCGetUserRequest,
			EncodeGRPCGetUserResponse,
			options
		),
	}
}
```

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

### Go-Kit JSON RPC Request Decoder

Source: https://github.com/go-kit/kit/blob/master/transport/http/jsonrpc/README.md

Defines a `DecodeRequestFunc` for Go-Kit's JSON RPC server. This function takes raw JSON parameters from a JSON RPC request, unmarshals them into a specific Go struct (e.g., `SumRequest`), and returns it as an interface{}.

```Go
type SumRequest struct {
	A, B int
}

func decodeSumRequest(ctx context.Context, msg json.RawMessage) (interface{}, error) {
	var req SumRequest
	err := json.Unmarshal(msg, &req)
	if err != nil {
		return nil, err
	}
	return req, nil
}
```

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

### Go-Kit JSON RPC Response Encoder

Source: https://github.com/go-kit/kit/blob/master/transport/http/jsonrpc/README.md

Defines an `EncodeResponseFunc` for Go-Kit's JSON RPC server. This function takes the result from an endpoint (expected to be an int in this case), marshals it into JSON, and returns it as `json.RawMessage` to be included in the JSON RPC response.

```Go
func encodeSumResponse(ctx context.Context, result interface{}) (json.RawMessage, error) {
	sum, ok := result.(int)
	if !ok {
		return nil, errors.New("result is not an int")
	}
	b, err := json.Marshal(sum)
	if err != nil {
		return nil, err
	}
	return b, nil
}
```

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