APIGW Response using Lambda custom (non-proxy) integration

[ymwjbxxq]

Hello all,

we have 2 libs:

• lambda_http
• lambda_runtime

And you cannot mix them, and I have a third case, which I can only solve with lambda_runtime trying to return a lambda_http response.

PROBLEM:
My APIGW has a Lambda Request Authorizer. The output of the Authorizer is a context, for example:
context: { email: [email protected] }

To pass the context to Lambda, you must disable the LambdaProxy and create an integration template.
Using the default one from AWS, I end up having a payload that is not compatible with the types of lambda_http

##  See http://docs.aws.amazon.com/apigateway/latest/developerguide/api-gateway-mapping-template-reference.html
##  This template will pass through all parameters including path, querystring, header, stage variables, and context through to the integration endpoint via the body/payload
#set($allParams = $input.params())
{
"body" : $input.json('$'),
"params" : {
#foreach($type in $allParams.keySet())
    #set($params = $allParams.get($type))
"$type" : {
    #foreach($paramName in $params.keySet())
    "$paramName" : "$util.escapeJavaScript($params.get($paramName))"
        #if($foreach.hasNext),#end
    #end
}
    #if($foreach.hasNext),#end
#end
},
"stage-variables" : {
#foreach($key in $stageVariables.keySet())
"$key" : "$util.escapeJavaScript($stageVariables.get($key))"
    #if($foreach.hasNext),#end
#end
},
"auth" : {
    "email" : "$context.authorizer.email"
    }
}

Because of this, I need to create my custom structure and switch to lambda_runtime.

LINKS:

• https://docs.aws.amazon.com/apigateway/latest/developerguide/api-gateway-lambda-authorizer-output.html
• https://aws.amazon.com/premiumsupport/knowledge-center/custom-headers-api-gateway-lambda/#:~:text=To%20pass%20custom%20headers%20from,from%20the%20original%20API%20request

using lambda_http:

 lambda_http::run(service_fn(|event: Request| {
        execute(event)
    }))
    .await?;
...

pub async fn execute(event: Request) -> Result<impl IntoResponse, Error> {
     let request = MyStruct::deserialize(MapDeserializer::new(result.body.into_iter())).unwrap();
    ...my code...
    
    Ok(response)

I get this error:
ERROR lambda_runtime: Error("data did not match any variant of untagged enum LambdaRequest", line: 0, column: 0)

using lambda_runtime:

#[derive(Debug, Serialize, Deserialize)]
pub struct Payload {
    #[serde(rename = "auth")]
    #[serde(skip_serializing_if = "Option::is_none")]
    pub auth: Option<Auth>,

    #[serde(rename = "body")]
    pub body: HashMap<String, Value>,

    #[serde(rename = "params")]
    #[serde(skip_serializing_if = "Option::is_none")]
    pub params: Option<Params>,
}

 lambda_runtime::run(service_fn(|event: LambdaEvent<Value>| {
        execute(event)
    }))
    .await?;

pub async fn execute(event: LambdaEvent<Value>) -> Result<Value, Error> {
     let request = MyStruct::deserialize(MapDeserializer::new(result.body.into_iter())).unwrap();
    ...my code...
    
    Ok(response)

The problem is the response. End of the day, I need to return something like the:

{
  "statusCode": 200,
  "body": "ok",
  "headers": { 
    "Access-Control-Allow-Origin": "*",
    ...
    "Accept": "application/json"
  }
}

If I use:
serde_json::from_str(response)?

It will return all as JSON in the body, and so it will skip the headers (see images)

Question is:

• how can I do it?

If I return Result<Response<String>, Error lambda_runtime complain

 the trait bound `lambda_http::Response<std::string::String>: Serialize` is not satisfied
the following other types implement trait `Serialize`:

[calavera]

lambda_http is an abstraction that takes payloads from different services and turns them into http objects. If you remove the abstraction, you need to return something that the service that you're using expects.

If you're using APIGW Rest, you probably need to return a ProxyResponse object:

https://github.com/LegNeato/aws-lambda-events/blob/master/aws_lambda_events/src/apigw/mod.rs#L60

If you're using APIGW Http, you probably need to return a HttpResponse object:

https://github.com/LegNeato/aws-lambda-events/blob/master/aws_lambda_events/src/apigw/mod.rs#L295

[bnusunny]

Are you having issues with the response for Lambda Authorizer or that for a Lambda function as an integration target?

[ymwjbxxq]

The Lambda Authorizer is fine to return the correct type (ApiGatewayCustomAuthorizerResponse).
The APIGW pass the output of the Lambda Authorizer to the Lambda and I can read it.

because I created a mapping template:

I am having issues with the integration response

trying mapping the Header Mappings and status from the Lambda response (ApiGatewayProxyResponse)

[bnusunny]

Okay. Got it. Creating a generic response mapping from lambda proxy response to APIGW response sounds like a good idea.

[ymwjbxxq]

I made it with lambda_runtime

 lambda_runtime::run(service_fn(|event: LambdaEvent<Value>| {
        execute(event)
    }))
    .await?;

pub async fn execute(event: LambdaEvent<Value>) -> Result<Value, MyCustomError> {
     let result: Payload = serde_json::from_value(event.payload).unwrap();
     let request = MyStruct::deserialize(MapDeserializer::new(result.body.into_iter())).unwrap();
    //handler logic

    //return 200
    return Ok(json!({ "message": "all good" }));
    
    // imagine 404
    Err(ApplicationError::InternalError(format!(
        "errors: {:?}",
        errors.join("##")
    )))
}

#[derive(Debug, Serialize, Deserialize)]
pub struct Payload {
    #[serde(rename = "auth")]
    #[serde(skip_serializing_if = "Option::is_none")]
    pub auth: Option<Auth>,

    #[serde(rename = "body")]
    pub body: HashMap<String, Value>,

    #[serde(rename = "params")]
    #[serde(skip_serializing_if = "Option::is_none")]
    pub params: Option<Params>,
}

Now we must have 2 mapping templates in the APIGW:

• integration request
• integration response

Integration request:

#set($allParams = $input.params())
"body": $input.json('$'),
"params" : {
#foreach($type in $allParams.keySet())
   #set($params = $allParams.get($type))
   "$type" : {
        #foreach($paramName in $params.keySet())
              "$paramName" : "$util.escapeJavaScript($params.get($paramName))"
               #if($foreach.hasNext),#end
       #end 
    }
    #if($foreach.hasNext),#end
#end 
},
"stage-variables" : {
#foreach($key in $stageVariables.keySet())
  "$key" : "$util.escapeJavaScript($stageVariables.get($key))"
    #if($foreach.hasNext),#end
#end},
"auth" : {
    "myprop":"$context.authorizer.myprop" ##custom output from the Lambda Authorizer
}
}"

Integration response:

• Here you need to map all the status code that the Lambda return, for example, 200 and 404
• For errors, you need to match the string of the error message, so I solve putting a text specifically for the error code that I will remove in the mapping. And with replacing and split I will construct the output JSON that I want.
  Maybe there is a better way to do it but I could not find it. At least you have the idea ;)

#set( $response = $input.path('$.errorMessage').replace("errors: ", ""))
#set( $errors = $response.replace('\"', ""))
{ 
"errors": [
#foreach($item in $errors.split('##'))
       "$item"
      #if($foreach.hasNext),#end
#end  
]
}

[calavera]

that's awesome! @ymwjbxxq what do you think about creating an example in the examples directory, I'm sure other people would appreciate it, it they might not be able to find it here.