AWS Lambda Go function not getting request body when called via API GW

Question

First off, one might say this question is very similar to HTTP request body not getting to AWS lambda function via AWS API Gateway or Getting json body in aws Lambda via API gateway

However, none of these questions address using Golang, and the problem I have been having is finding an equivalent of the event parameter used everywhere in the Node.js documentation.

Here's my Lambda Function:

package main

import (
    "context"
    "encoding/json"
    "github.com/aws/aws-lambda-go/lambda"
    "github.com/aws/aws-lambda-go/events"
    "log"
)

type MyReturn struct {
    Response string `json:"response"`
}

type APIGWResponse struct {
    IsBase64Encoded bool              `json:"isBase64Encoded"`
    StatusCode      int               `json:"statusCode"`
    Headers         map[string]string `json:"headers"`
    Body            string            `json:"body"`
}

func handle(ctx context.Context, name MyReturn) (APIGWResponse, error) {
    log.Print("Called by ", name)
    log.Print("context ", ctx)
    headers := map[string]string{"Access-Control-Allow-Origin": "*", "Access-Control-Allow-Headers": "Origin, X-Requested-With, Content-Type, Accept"}

    code := 200
    response, error := json.Marshal(myReturn{Response:"Hello, " + name.Body})
    if error != nil {
        log.Println(error)
        response = []byte("Internal Server Error")
        code = 500
    }

    return APIGWResponse{true, code, headers, string(response)}, nil
}

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

Problem: the MyReturn object is not being filled with any value when called from API GW. The line log.Print("Called by ", name) results in nothing being appended to the Called by string.

Request to API GW:

 POST -> body: '{"name":"Bob"}', headers: {'Content-Type': 'application/json'}

This is being performed in pure JS as follows:

const BASE_URL = "https://my_api_id.execute-api.us-east-1.amazonaws.com/prod/";
const TRIGGER_URL = "my_lambda_function";

function toGW() {
    fetch(BASE_URL + TRIGGER_URL, {
        method: 'POST',
        body: '{"name":"Bimesh"}',
        headers:{
            'Content-Type': 'application/json'
        }
    })
    .then(data => data.json())
    .then(json => console.log(json))
    .catch(error => console.log(error));
}

And yet, the exact same body works when testing it from the AWS Lambda console.

Body:

{"name":"Bob"}

Farouche

Answer 1

Turns out, even though I wasn't able to find any documentation on this on a user-facing website, documentation does exist. Read this: https://github.com/aws/aws-lambda-go/blob/master/events/README_ApiGatewayEvent.md

Here's the simplest way I've figured out so far to receive data from and respond to a request from API GW:

package main

import (
    "context"
    "encoding/json"
    "github.com/aws/aws-lambda-go/lambda"
    "github.com/aws/aws-lambda-go/events"
    "log"
)

type myReturn struct {
    Response string `json:"response"`
}

func handle(ctx context.Context, name events.APIGatewayProxyRequest) (events.APIGatewayProxyResponse, error) {
    log.Print("Request body: ", name)
    log.Print("context ", ctx)
    headers := map[string]string{"Access-Control-Allow-Origin": "*", "Access-Control-Allow-Headers": "Origin, X-Requested-With, Content-Type, Accept"}

    code := 200
    response, error := json.Marshal(myReturn{Response:"Hello, " + name.Body})
    if error != nil {
        log.Println(error)
        response = []byte("Internal Server Error")
        code = 500
    }

    return events.APIGatewayProxyResponse {code, headers, string(response), false}, nil
}

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

In this case, the log.Print("Request body: ", name) line results in the exact request body being logged. Problem solved.

Note: Also I didn't have to create that APIGWResponse object from the question, the events.APIGatewayProxyResponse is the exact same thing, already made for you. These objects are all inside this class: https://github.com/aws/aws-lambda-go/blob/master/events/apigw.go

Farouche

Thank you, this really saved me from a headache :) The only downside is taking an events.APIGatewayProxyRequest as an input means writing pure json for the AWS Console "Test" functionality doesn't work anymore - I guess I need to wrap the request somehow, have you found a way around that? – Subdelirium