.
├── cmd
│   └── main.go
├── funcy
│   └── function.json
├── go.mod
├── host.json
└── pkg
    └── function
        ├── function.go
        ├── giphy.go
        └── slack.go

{
    "bindings": [
        {
            "type": "httpTrigger",
            "direction": "in",
            "name": "req",
            "methods": [
                "get",
                "post"
            ]
        },
        {
            "type": "http",
            "direction": "out",
            "name": "res"
        }
    ]
}

{
    "version": "2.0",
    "extensionBundle": {
        "id": "Microsoft.Azure.Functions.ExtensionBundle",
        "version": "[1.*, 2.0.0)"
    },
    "customHandler": {
        "description": {
            "defaultExecutablePath": "go_funcy"
        },
        "enableForwardingHttpRequest": true
    },
    "logging": {
        "logLevel": {
            "default": "Trace"
        }
    }
}

func main() {
port, exists := os.LookupEnv("FUNCTIONS_CUSTOMHANDLER_PORT")
if !exists {
   port = "8080"
}
http.HandleFunc("/api/funcy", function.Funcy)
log.Fatal(http.ListenAndServe(":"+port, nil))
}

signingSecret := os.Getenv("SLACK_SIGNING_SECRET")
  apiKey := os.Getenv("GIPHY_API_KEY")
  if signingSecret == "" || apiKey == "" {
    http.Error(w, "Failed to process request. Please contact the admin", http.StatusUnauthorized)
    return
  }
  slackTimestamp := r.Header.Get("X-Slack-Request-Timestamp")
  b, err := ioutil.ReadAll(r.Body)
  if err != nil {
    http.Error(w, "Failed to process request", http.StatusBadRequest)
    return
  }
  slackSigningBaseString := "v0:" + slackTimestamp + ":" + string(b)
  slackSignature := r.Header.Get("X-Slack-Signature")
  if !matchSignature(slackSignature, signingSecret, slackSigningBaseString) {
    http.Error(w, "Function was not invoked by Slack", http.StatusForbidden)
    return
  }

vals, err := parse(b)
  if err != nil {
    http.Error(w, "Failed to process request", http.StatusBadRequest)
    return
  }
  giphyTag := vals.Get("text")

giphyResp, err := http.Get("http://api.giphy.com/v1/gifs/random?tag=" + giphyTag + "&api_key=" + apiKey)
  if err != nil {
    http.Error(w, "Failed to process request", http.StatusFailedDependency)
    return
  }
  resp, err := ioutil.ReadAll(giphyResp.Body)
  if err != nil {
    http.Error(w, "Failed to process request", http.StatusInternalServerError)
    return
  }

var gr GiphyResponse
json.Unmarshal(resp, &gr)
title := gr.Data.Title
url := gr.Data.Images.Downsized.URL
slackResponse := SlackResponse{Text: slackResponseStaticText, Attachments: []Attachment{{Text: title, ImageURL: url}}}
w.Header().Set("Content-Type", "application/json")
json.NewEncoder(w).Encode(slackResponse)
fmt.Println("Sent response to Slack")

git clone https://github.com/abhirockzz/serverless-go-slack-app
cd serverless-go-slack-app
GOOS=linux go build -o go_funcy cmd/main.go

func azure functionapp publish <enter name of the function app>