Having issues with testing Lambda functions on AWS

Question

I have been trying to get my first lambda function in Go running via the Amazon API Gateway.

I have the following package set up in go. The goal is to send a JSON request and log and return the body of that request:

package main

import (
    "net/http"
    "log"
    "github.com/aws/aws-lambda-go/lambda"
    "github.com/aws/aws-lambda-go/events"
)

func Handler(request events.APIGatewayProxyRequest) (events.APIGatewayProxyResponse, error) {

    //These log statements return empty regardless of JSON input.
    log.Print(request.body)

    return events.APIGatewayProxyResponse{
        StatusCode: http.StatusOK,
        Body: request.Body
    }, nil
}

func main() {
    lambda.Start(Handler)
}

I can build and zip this and upload it to the AWS lambda manager. The AWS lambda manager contains an option to use a test event which I can configure with a JSON string

{
  "testint": 1,
  "teststring": "test"
}

However, if I run this test, I get the following result:

{
  "statusCode": 200,
  "headers": null,
  "body": ""
}

I would expect the body to actually contain the json I passed to the function, but clearly something is going wrong.

First, in your logging you have a typo: log.Print(request.body) should be log.Print(request.Body) — Derek Pollard
– Derek Pollard, Commented Jun 12, 2018 at 7:58
For example, your handler should be: Handler(ctx context.Context, request events.APIGatewayProxyRequest) — Derek Pollard
– Derek Pollard, Commented Jun 12, 2018 at 8:01
@Derek adding the context doesn't seem to make a difference. It still returns an empty body (even capitalized correctly). The Amazon example also doesn't list the context: aws.amazon.com/blogs/compute/… — matti0006
– matti0006, Commented Jun 12, 2018 at 9:30
In fact, the example on that website does not even work for me...it will return the error "no name was provided in the HTTP body" — matti0006
– matti0006, Commented Jun 12, 2018 at 9:37

Vorsprung · Accepted Answer · 2018-06-20 19:23:23Z

There's a few minor things I changed and then it works

First, log.Print(request.body) doesn't compile for me, but using request.Body is fine

Second, the type you are using for the request is

// APIGatewayProxyRequest contains data coming from the API Gateway proxy
type APIGatewayProxyRequest struct {
    Resource              string                        `json:"resource"` // The resource path defined in API Gateway
    Path                  string                        `json:"path"`     // The url path for the caller
    HTTPMethod            string                        `json:"httpMethod"`
    Headers               map[string]string             `json:"headers"`
    QueryStringParameters map[string]string             `json:"queryStringParameters"`
    PathParameters        map[string]string             `json:"pathParameters"`
    StageVariables        map[string]string             `json:"stageVariables"`
    RequestContext        APIGatewayProxyRequestContext `json:"requestContext"`
    Body                  string                        `json:"body"`
    IsBase64Encoded       bool                          `json:"isBase64Encoded,omitempty"`
}

and in this Body is a field "body" that's a string. So altering your test data to

{
  "body": "HELLO"

}

will give some data that passes through

Lastly, the parameters for the Handler in all the examples seems to include a context object, so I added that

func Handler(ctx context.Context, request events.APIGatewayProxyRequest)

Here is a complete version of your program that "worked for me"

package main

import (
    "context"
    "github.com/aws/aws-lambda-go/events"
    "github.com/aws/aws-lambda-go/lambda"
    "log"
    "net/http"
)

func Handler(ctx context.Context, request events.APIGatewayProxyRequest) (events.APIGatewayProxyResponse, error) {

    //These log statements return empty regardless of JSON input.
    log.Print(request.Body)

    return events.APIGatewayProxyResponse{
        StatusCode: http.StatusOK,
        Body:       request.Body}, nil
}

func main() {
    lambda.Start(Handler)
}

Thank you very much; this should give enough pointers to continue!

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