3

I have a Lambda function that is tied to API Gateway and i am trying to fetch the path and stage from either event or context object that are passed to the Lambda function.

The mapping template generated by the AWS console is below: 

##  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-json" : $input.json('$'),
"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
},
"context" : {
"stage" : "$context.stage",
    "source-ip" : "$context.identity.sourceIp",
    "user" : "$context.identity.user",
    "user-agent" : "$context.identity.userAgent",
    "user-arn" : "$context.identity.userArn",
    "request-id" : "$context.requestId",
    "resource-id" : "$context.resourceId",
    "resource-path" : "$context.resourcePath",
    "account-id" : "$context.identity.accountId",
    "api-id" : "$context.apiId",
    "api-key" : "$context.identity.apiKey",
    "authorizer-principal-id" : "$context.authorizer.principalId",
    "caller" : "$context.identity.caller",
    "cognito-authentication-provider" : "$context.identity.cognitoAuthenticationProvider",
    "cognito-authentication-type" : "$context.identity.cognitoAuthenticationType",
    "cognito-identity-id" : "$context.identity.cognitoIdentityId",
    "cognito-identity-pool-id" : "$context.identity.cognitoIdentityPoolId",
    "http-method" : "$context.httpMethod"
    }
}

I am trying to get the stage from the context object like this:

exports.handler = function(event, context) {
 console.log("Stage: " + context.stage);
 ...
}

but the logcat shows as Stage : undefined.

I have other query parameters that i am able to extract from params of event object like this

var id = event.params.querystring.id;
var publisher_id = event.params.querystring.publisher_id;

How can i extract the path and stage values from context with the above mapping template?

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2
  • Have you tried logging the entire context to see what is in there? If you changed the mapping template, make sure you "deploy" the API Gateway afterwards in order to make the template take effect. Commented Feb 12, 2020 at 14:11
  • Found a way to get it from the event object.. of course not what i would have wanted, but still have to see why context didn't give it. Commented Feb 12, 2020 at 16:04

3 Answers 3

Reset to default
2

The stage value is available in event.context.stage. So change your code to this:

exports.handler = function(event, context) {
 console.log("Stage: " + event.context.stage);
 ...
}

We are using a basic mapping template listed here:

##  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-json" : $input.json('$'),
"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
},
"context" : {
    "account-id" : "$context.identity.accountId",
    "api-id" : "$context.apiId",
    "api-key" : "$context.identity.apiKey",
    "authorizer-principal-id" : "$context.authorizer.principalId",
    "caller" : "$context.identity.caller",
    "cognito-authentication-provider" : "$context.identity.cognitoAuthenticationProvider",
    "cognito-authentication-type" : "$context.identity.cognitoAuthenticationType",
    "cognito-identity-id" : "$context.identity.cognitoIdentityId",
    "cognito-identity-pool-id" : "$context.identity.cognitoIdentityPoolId",
    "http-method" : "$context.httpMethod",
    "stage" : "$context.stage",
    "source-ip" : "$context.identity.sourceIp",
    "user" : "$context.identity.user",
    "user-agent" : "$context.identity.userAgent",
    "user-arn" : "$context.identity.userArn",
    "request-id" : "$context.requestId",
    "resource-id" : "$context.resourceId",
    "resource-path" : "$context.resourcePath"
    }
}
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1 Comment

Yes this will also solve the issue without need to add the extra "stage" to the mapping template
1

I added this line "stage":"$context:stage", in the mapping template and used event[stage] to retrieve the value. This worked. Don't forget to re-deploy the api.

Changed Mapping Template:

##  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-json" : $input.json('$'),
"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
},
"stage" : "$context.stage", // added this line
"context" : {
"stage" : "$context.stage",
    "source-ip" : "$context.identity.sourceIp",
    "user" : "$context.identity.user",
    "user-agent" : "$context.identity.userAgent",
    "user-arn" : "$context.identity.userArn",
    "request-id" : "$context.requestId",
    "resource-id" : "$context.resourceId",
    "resource-path" : "$context.resourcePath",
    "account-id" : "$context.identity.accountId",
    "api-id" : "$context.apiId",
    "api-key" : "$context.identity.apiKey",
    "authorizer-principal-id" : "$context.authorizer.principalId",
    "caller" : "$context.identity.caller",
    "cognito-authentication-provider" : "$context.identity.cognitoAuthenticationProvider",
    "cognito-authentication-type" : "$context.identity.cognitoAuthenticationType",
    "cognito-identity-id" : "$context.identity.cognitoIdentityId",
    "cognito-identity-pool-id" : "$context.identity.cognitoIdentityPoolId",
    "http-method" : "$context.httpMethod"
    }
}

and code:

exports.handler = function(event, context) {
 console.log("Stage: " + event[stage]);
 ...
}
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Comments

0

You must check "Lambda Proxy Integration" in your method integration on API gateway, to receive the stage information.

enter image description here

To use a stage variable to customize the HTTP integration endpoint, you must first configure a stage variable of a specified name, e.g., url, and then assign it a value, e.g., example.com. Next, from your method configuration, set up an HTTP proxy integration, and instead of entering the endpoint's URL, you can tell API Gateway to use the stage variable value, http://${stageVariables.url}. This value tells API Gateway to substitute your stage variable ${} at runtime, depending on which stage your API is running. You can reference stage variables in a similar way to specify a Lambda function name, an AWS Service Proxy path, or an AWS role ARN in the credentials field.

Reference: https://docs.aws.amazon.com/apigateway/latest/developerguide/stage-variables.html

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4 Comments

That is incorrect. The stage information is available in API Gateway mapping templates docs.aws.amazon.com/apigateway/latest/developerguide/…
docs.aws.amazon.com/apigateway/latest/developerguide/… - to use the stage variable you need the integration mapping
That's only to follow the example given on that page. API Gateway supported stage variables before Lambda proxy integration was even a thing. If you had to use Proxy integration to use stage variables then why would stage variables be available in the custom API Gateway mapping templates, which are only used in non-proxy integrations?
I will try the Lambda Proxy again, but when the mapping says the value will be in the context, why can't i retrieve it?

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