Add Docker container support

Adding a containerized version to this repo.

The main additions here are the Dockerfile and docker-compose.yml.
But also, I changed the default port to run on :5000.

Dockerfile

@@ -0,0 +1,12 @@
+FROM golang:1.14
+
+WORKDIR /go/src/app
+
+COPY . /go/src/app
+
+RUN env GOOS=linux go build gohang.go
+RUN go install .
+
+ENTRYPOINT /go/src/app/gohang
+
+EXPOSE 5000

README.md

@@ -12,7 +12,7 @@ Run `gohang`
 ### /
 
 ```
-curl -I localhost:80/
+curl -I localhost:5000/
 HTTP/1.1 200 OK
 Date: Sun, 04 Oct 2020 01:38:03 GMT
 Content-Length: 19
@@ -22,7 +22,7 @@ Content-Type: text/plain; charset=utf-8
 ### /404
 
 ```
-$ curl -I localhost:80/404
+$ curl -I localhost:5000/404
 HTTP/1.1 404 Not Found
 Date: Sun, 04 Oct 2020 01:37:17 GMT
 Content-Length: 26
@@ -32,7 +32,7 @@ Content-Type: text/plain; charset=utf-8
 ### /500
 
 ```
-$ curl -I localhost:80/500
+$ curl -I localhost:5000/500
 HTTP/1.1 500 Internal Server Error
 Date: Sun, 04 Oct 2020 01:34:28 GMT
 Content-Length: 38
@@ -42,9 +42,56 @@ Content-Type: text/plain; charset=utf-8
 ### /slow
 
 ```
-$ time curl localhost:80/slow
+$ time curl localhost:5000/slow
 { "data": "slow response"}
 real    0m5.023s
 user    0m0.006s
 sys     0m0.006s
 ```
+
+## Build a Docker container
+
+Did you want to run this in a Docker container?
+Simply run `docker-compose build` and then `docker-compose up`.
+
+### docker-compose build
+
+```
+$ docker-compose build
+Building web
+Step 1/7 : FROM golang:1.14
+ ---> d6747a138341
+Step 2/7 : WORKDIR /go/src/app
+ ---> Using cache
+ ---> e0c45301390b
+Step 3/7 : COPY . /go/src/app
+ ---> 8baa0d29af0d
+Step 4/7 : RUN env GOOS=linux go build gohang.go
+ ---> Running in bde0f5e072ab
+Removing intermediate container bde0f5e072ab
+ ---> 0a454230e0c5
+Step 5/7 : RUN go install .
+ ---> Running in 9701cb98bf9a
+Removing intermediate container 9701cb98bf9a
+ ---> c2b7cf38e979
+Step 6/7 : ENTRYPOINT /go/src/app/gohang
+ ---> Running in 60bbd1397191
+Removing intermediate container 60bbd1397191
+ ---> ad4f7bc0dbe0
+Step 7/7 : EXPOSE 5000
+ ---> Running in e56fedc7f4d6
+Removing intermediate container e56fedc7f4d6
+ ---> a15ced7b2772
+
+Successfully built a15ced7b2772
+Successfully tagged gohang_web:latest
+```
+
+### docker-compose up
+
+```
+$ docker-compose up
+Recreating gohang_web_1 ... done
+Attaching to gohang_web_1
+web_1  | 2020/10/04 21:16:09 [INFO] Now listening on :5000
+```

docker-compose.yml

@@ -0,0 +1,6 @@
+version: "3.8"
+services:
+  web:
+    build: .
+    ports:
+      - "5000:5000"

gohang.go

@@ -6,6 +6,8 @@ import (
 	"time"
 )
 
+const DEFAULT_PORT string = ":5000"
+
 func okTwoHundred(w http.ResponseWriter, r *http.Request) {
 	w.Write([]byte("{ \"data\": \"200 OK\"}"))
 }
@@ -32,6 +34,6 @@ func main() {
 	mux.HandleFunc("/404", notFound)
 	mux.HandleFunc("/slow", slowResponse)
 
-	log.Println("[INFO] Now listening on :80")
-	http.ListenAndServe(":80", mux)
+	log.Printf("[INFO] Now listening on %s", DEFAULT_PORT)
+	http.ListenAndServe(DEFAULT_PORT, mux)
 }