feat: Add H2C support

`podinfo --h2c` allows upgrading a HTTP/1.1 connection to HTTP/2 Cleartext.

This allows `podinfo` to be used in e.g. a H2C load-test like `echo "GET http://localhost:9898/status/200" | vegeta -h2c`, or a H2C connectivity test like done with `curl -v http2 http://localhost:9898/status/200`.

I have manually verified this to work by running `curl -v --http2` on macOS and seeing the H2C upgrade happens onl when `-h2c` is provided to `podinfo`.

Without `-h2c`:

```
$ curl -v --http2 localhost:9898/status/200
*   Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 9898 (#0)
> GET /status/200 HTTP/1.1
> Host: localhost:9898
> User-Agent: curl/7.54.0
> Accept: */*
> Connection: Upgrade, HTTP2-Settings
> Upgrade: h2c
> HTTP2-Settings: AAMAAABkAARAAAAAAAIAAAAA
>
< HTTP/1.1 200 OK
< Content-Type: application/json; charset=utf-8
< X-Content-Type-Options: nosniff
< Date: Mon, 04 Nov 2019 04:58:01 GMT
< Content-Length: 19
<
{
  "status": 200
* Connection #0 to host localhost left intact
}
```

With `-h2c`:

```
$ curl -v --http2 localhost:9898/status/200
*   Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 9898 (#0)
> GET /status/200 HTTP/1.1
> Host: localhost:9898
> User-Agent: curl/7.54.0
> Accept: */*
> Connection: Upgrade, HTTP2-Settings
> Upgrade: h2c
> HTTP2-Settings: AAMAAABkAARAAAAAAAIAAAAA
>
< HTTP/1.1 101 Switching Protocols
< Connection: Upgrade
< Upgrade: h2c
* Received 101
* Using HTTP2, server supports multi-use
* Connection state changed (HTTP/2 confirmed)
* Copying HTTP/2 data in stream buffer to connection buffer after upgrade: len=0
* Connection state changed (MAX_CONCURRENT_STREAMS updated)!
< HTTP/2 200
< content-type: application/json; charset=utf-8
< x-content-type-options: nosniff
< content-length: 19
< date: Mon, 04 Nov 2019 04:58:28 GMT
<
{
  "status": 200
* Connection #0 to host localhost left intact
}
`

cmd/podinfo/main.go

@@ -39,6 +39,7 @@ func main() {
 	fs.String("ui-logo", "", "UI logo")
 	fs.String("ui-color", "cyan", "UI color")
 	fs.String("ui-message", fmt.Sprintf("greetings from podinfo v%v", version.VERSION), "UI message")
+	fs.Bool("h2c", false, "Allow upgrading to H2C")
 	fs.Bool("random-delay", false, "between 0 and 5 seconds random delay")
 	fs.Bool("random-error", false, "1/3 chances of a random response error")
 	fs.Int("stress-cpu", 0, "Number of CPU cores with 100 load")

go.mod

@@ -47,6 +47,6 @@ require (
 	go.uber.org/atomic v1.3.2 // indirect
 	go.uber.org/multierr v1.1.0 // indirect
 	go.uber.org/zap v1.9.1
-	golang.org/x/net v0.0.0-20190724013045-ca1201d0de80 // indirect
+	golang.org/x/net v0.0.0-20190724013045-ca1201d0de80
 	google.golang.org/grpc v1.23.0
 )

pkg/api/server.go

@@ -4,6 +4,9 @@ import (
 	"context"
 	"fmt"
 	"github.com/swaggo/swag"
+	"golang.org/x/net/http2"
+	"golang.org/x/net/http2/h2c"
+
 	"net/http"
 	_ "net/http/pprof"
 	"os"
@@ -59,6 +62,7 @@ type Config struct {
 	Port                      string        `mapstructure:"port"`
 	PortMetrics               int           `mapstructure:"port-metrics"`
 	Hostname                  string        `mapstructure:"hostname"`
+	H2C                       bool          `mapstructure:"h2c"`
 	RandomDelay               bool          `mapstructure:"random-delay"`
 	RandomError               bool          `mapstructure:"random-error"`
 	JWTSecret                 string        `mapstructure:"jwt-secret"`
@@ -141,12 +145,19 @@ func (s *Server) ListenAndServe(stopCh <-chan struct{}) {
 	s.registerHandlers()
 	s.registerMiddlewares()
 
+	var handler http.Handler
+	if s.config.H2C {
+		handler = h2c.NewHandler(s.router, &http2.Server{})
+	} else {
+		handler = s.router
+	}
+
 	srv := &http.Server{
 		Addr:         ":" + s.config.Port,
 		WriteTimeout: s.config.HttpServerTimeout,
 		ReadTimeout:  s.config.HttpServerTimeout,
 		IdleTimeout:  2 * s.config.HttpServerTimeout,
-		Handler:      s.router,
+		Handler:      handler,
 	}
 
 	//s.printRoutes()