如何使用AWS API Gateway将URL参数传递给Lambda函数？

Question

I am currently trying to create a Hello World Lambda function and test it through the API Gateway, as my intent is to provide a REST API using Lambda function. I have a very basic function handler that takes in an integer and outputs it as a string:

     public string FunctionHandler(int input, ILambdaContext context)
    {
        return input.ToString();
    }

I have published this code to AWS and it seems to work. I have tested it from Visual Studio using the AWS tools as well as from the AWS Console.

I have an API setup that has a POST method with a single resource parameter called "input". When creating the method I selected Lambda Expression for Integration Type.

When I use the API Test screen to test it out, I always receive a JSON exception. Here is the output:

{
"errorType": "JsonReaderException",
"errorMessage": "Unexpected character encountered while parsing value: {.   Path '', line 1, position 1.",
"stackTrace": [
"at Newtonsoft.Json.JsonTextReader.ReadNumberValue(ReadType readType)",
"at Newtonsoft.Json.JsonTextReader.ReadAsInt32()",
"at  Newtonsoft.Json.Serialization.JsonSerializerInternalReader.ReadForType(JsonReader reader, JsonContract contract, Boolean hasConverter)",
"at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)",
"at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)",
"at Newtonsoft.Json.JsonSerializer.Deserialize[T](JsonReader reader)",
"at lambda_method(Closure , Stream , Stream , ContextInfo )"
]
}

Here are the headers that are logged as well. They show the value that I am providing for input, in this case a 1:

Execution log for request test-request
Wed Jan 03 19:12:25 UTC 2018 : Starting execution for request: test-invoke-request
Wed Jan 03 19:12:25 UTC 2018 : HTTP Method: POST, Resource Path: /1
Wed Jan 03 19:12:25 UTC 2018 : Method request path: {input=1}
Wed Jan 03 19:12:25 UTC 2018 : Method request query string: {}
Wed Jan 03 19:12:25 UTC 2018 : Method request headers: {}

I dont really understand why I am receiving any sort of JSON errors. When I test via the console or Visual Studio, I simply provide a "1". No JSON formatting at all. When I test via the Console using path parameters it should essentially be a url like "mydomain.com/resource/1". It shouldnt need to parse it, but I am sure there is a good reason for it to try.

Is it even possible to pass path parameters to a Lambda function?

Thanks

Answer 1

I believe I have figured this out. I noticed that many people in similar threads were suggesting either using a Mapping Template to send the data in whatever format I wanted or selecting Use Lambda Proxy Integration . Either one of these suggestions will work, but what is confusing is how to handle it using the C# SDK.

The first parameter of your FunctionHandler will be a JObject containing the json in the request body. If you dont have a mapping template and you dont select Use Lambda Proxy Integration, this will always be empty. I decided to go with USe Lambda Proxy Integration because it seems to provide all of the details I need in well-formatted JSON.

The second important thing to note is that there is already a class that can be used to automatically deserialize the json. It provides the path params, querystring, body, and headers as simple properties that you can easily access. That is the Amazon.Lambda.APIGatewayEvents.APIGatewayProxyRequest (you will probably need to add the nuget package since it isnt a part of the default empty template).

So in the end my code looks like this:

    public APIGatewayProxyResponse FunctionHandler(APIGatewayProxyRequest request, ILambdaContext context)
    {

        context.Logger.LogLine("Get Request\n");
        var path = "none";
        if (request.PathParameters != null && request.PathParameters.Any())
        {
            path = request.PathParameters["input"];
        }
        var response = new APIGatewayProxyResponse
        {
            StatusCode = (int)HttpStatusCode.OK,
            Body = "Hello World. Here are is your path param: " + path,
            Headers = new Dictionary<string, string> { { "Content-Type", "application/json" }, { "Access-Control-Allow-Origin", "*" } }
        };
        return response;
    }