Create and deploy a HTTP Cloud Function by using Go

This guide takes you through the process of writing a Cloud Function using the Go runtime. There are two types of Cloud Functions:

An HTTP function, which you invoke from standard HTTP requests.
An event-driven function, which you use to handle events from your Cloud infrastructure, such as messages on a Cloud Pub/Sub topic, or changes in a Cloud Storage bucket.

The sample shows how to create a simple HTTP function.

Guide structure

Creating a GCP project using gcloud CLI

Sign in to your Google Cloud account. If you're new to Google Cloud, create an account to evaluate how our products perform in real-world scenarios. New customers also get $300 in free credits to run, test, and deploy workloads.

In the Google Cloud console, on the project selector page, select or create a Google Cloud project.

Go to project selector

Make sure that billing is enabled for your Google Cloud project. Learn how to check if billing is enabled on a project.

Enable the Cloud Functions and Cloud Build APIs.

Enable the APIs

In the Google Cloud console, on the project selector page, select or create a Google Cloud project.

Go to project selector

Make sure that billing is enabled for your Google Cloud project. Learn how to check if billing is enabled on a project.

Enable the Cloud Functions and Cloud Build APIs.

Enable the APIs

Install and initialize the gcloud CLI.
Update and install gcloud components:
```
gcloud components update
```

Prepare your development environment.
Go to the Go setup guide

Creating a function

Create a directory on your local system for the function code:

Linux or Mac OS X

mkdir ~/helloworld
cd ~/helloworld

Windows

mkdir %HOMEPATH%\helloworld
cd %HOMEPATH%\helloworld

Create a file called hello_http.go in the helloworld directory with the following contents:

functions/helloworld/hello_http.go

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// Package helloworld provides a set of Cloud Functions samples.
package helloworld

import (
	"encoding/json"
	"fmt"
	"html"
	"net/http"

	"github.com/GoogleCloudPlatform/functions-framework-go/functions"
)

func init() {
	functions.HTTP("HelloHTTP", HelloHTTP)
}

// HelloHTTP is an HTTP Cloud Function with a request parameter.
func HelloHTTP(w http.ResponseWriter, r *http.Request) {
	var d struct {
		Name string `json:"name"`
	}
	if err := json.NewDecoder(r.Body).Decode(&d); err != nil {
		fmt.Fprint(w, "Hello, World!")
		return
	}
	if d.Name == "" {
		fmt.Fprint(w, "Hello, World!")
		return
	}
	fmt.Fprintf(w, "Hello, %s!", html.EscapeString(d.Name))
}

This example function takes a name supplied in the HTTP request and returns a greeting, or "Hello, World!" when no name is supplied.

Specifying dependencies

This example function only uses Go standard library packages, so you don't need to declare any dependencies beyond just importing the packages.

For functions that require dependencies outside of the standard library, you must provide the dependencies via either a go.mod file or a vendor directory. For more details, read Specifying dependencies in Go.

Deploying the function

To deploy the function with an HTTP trigger, run the following command in the helloworld directory, specifying either go113 or go111 as the value for the --runtime flag, depending on which version you are using:

gcloud functions deploy HelloHTTP --runtime go120 --trigger-http --allow-unauthenticated

The --allow-unauthenticated flag lets you reach the function without authentication. To require authentication, omit the flag.

Testing the function

When the function finishes deploying, take note of the httpsTrigger.url property or find it using the following command:
```
gcloud functions describe HelloHTTP
```
It should look like this:
```
https://GCP_REGION-PROJECT_ID.cloudfunctions.net/HelloHTTP
```
Visit this URL in your browser, or use cURL by running the command:
```
curl https://GCP_REGION-PROJECT_ID.cloudfunctions.net/HelloHTTP
```
You should see a "Hello, World!" message. Try passing a name in the HTTP request by running the following command:
```
curl -X POST https://GCP_REGION-PROJECT_ID.cloudfunctions.net/HelloHTTP -H "Content-Type:application/json"  -d '{"name":"NAME"}'
```
You should see the message "Hello, NAME!"

Viewing logs

Using the command-line tool

Logs for Cloud Functions are viewable in the Cloud Logging UI, and via the Google Cloud CLI.

To view logs for your function with the gcloud CLI, use the logs read command, followed by the name of the function:

gcloud functions logs read HelloHTTP

The output should resemble the following:

LEVEL  NAME        EXECUTION_ID  TIME_UTC                 LOG
D      HelloHTTP  buv9ej2k1a7r  2019-09-20 13:23:18.910  Function execution started
D      HelloHTTP  buv9ej2k1a7r  2019-09-20 13:23:18.913  Function execution took 4 ms, finished with status code: 200

Using the Logging dashboard

You can also view logs for Cloud Functions from the Google Cloud console.