Amazon Lex postContent error "Failed to decode Session attributes." - php

Question

I am attempting to connect my webpage to my Lex bot using postContent from the AWS SDK for PHP.
I set the credentials and arguments then attempt postContent. Here is the relevant code:
$credentials = new \Aws\Credentials\Credentials('XXXXXXXX', 'XXXXXXXXXXXXXXXXXXXXXXXXXX');
$args = array(
'region' => 'us-east-1',
'version' => 'latest',
'debug' => true,
'credentials' => $credentials
);
$lex_client = new Aws\LexRuntimeService\LexRuntimeServiceClient($args);
$lex_response = $lex_client->postContent([
'accept' => 'text/plain; charset=utf-8',
'botAlias' => 'XXXX',
'botName' => 'XXXX',
'contentType' => 'text/plain; charset=utf-8',
'inputStream' => $userInput,
'requestAttributes' => "{}",
'sessionAttributes' => "{}",
'userId' => 'XXXXXXXXXXXX',
]);
This errors with:
'Error executing "PostContent" on "https://runtime.lex.us-east-1.amazonaws.com/bot/XXXX/alias/XXXX/user/XXXXXXXXXX/content";
AWS HTTP error: Client error: POST https://runtime.lex.us-east-1.amazonaws.com/bot/XXXX/alias/XXXX/user/XXXXXXXXXX/content resulted in a 400 Bad Request response:
{"message":"Invalid Request: Failed to decode Session attributes. Session Attributes should be a Base64 encoded json map of String to String"}' (length=142)
I have attempted using all kinds of JSON strings, JSON encoded strings, and Base64 encoded strings in the sessionAttributes but I continue to get this same error.

Answer 1

The LexRuntimeService in the AWS SDK automatically JSON encodes and Base64 encodes the postContent array. By passing it a JSON string, the json encoding in the SDK will place double quotes around the {} making it "{}" and that causes the error.
So simply pass the sessionAttributes and requestAttributes as PHP arrays.
$lex_response = $lex_client->postContent([
'accept' => 'text/plain; charset=utf-8',
'botAlias' => 'XXXX',
'botName' => 'XXXX',
'contentType' => 'text/plain; charset=utf-8',
'inputStream' => $userInput,
'requestAttributes' => array(),
'sessionAttributes' => array(), // <---- PHP Array not JSON
'userId' => 'XXXXXXXXXXXX',
]);