Vanilla NodeJS Appsync client error while making queries/mutations

Question

I'm trying to hit my Appsync GraphQL endpoint with a plain nodejs client that signs and sends the requests. There it is:

var https = require("https");
let AWS = require("aws-sdk");
let urlParse = require("url").URL;
require("dotenv").config();

const throwOnErrors = ({ query, variables, errors }) => {
  if (errors) {
    const errorMessage = `
        query: ${query.substr(0, 100)}

        variables: ${JSON.stringify(variables, null, 4)}

        error: ${JSON.stringify(errors, null, 4)}
        `;
    throw new Error(errorMessage);
  }
};

module.exports = async (
  url,
  credentials,
  query,
  operationName,
  variables = {}
) => {
  
  AWS.config.update({
    region: process.env.AWS_REGION,
    credentials: new AWS.Credentials(
      credentials.accessKeyId,
      credentials.secretAccessKey,
      credentials.sessionToken
    ),
  });

  let endpoint = new urlParse(url).hostname.toString();
  const item = {
    input: variables
  };
  let req = new AWS.HttpRequest(url, process.env.AWS_REGION);
  req.method = "POST";
  req.headers.host = endpoint;
  req.headers["Content-Type"] = "application/json";
  req.body = JSON.stringify({
    query: query,  
    operationName: operationName,
    variables: item
  });

  let signer = new AWS.Signers.V4(req, "appsync", true);
  signer.addAuthorization(AWS.config.credentials, AWS.util.date.getDate());

  const data = await new Promise((resolve, reject) => {
    const httpRequest = https.request({ ...req, host: endpoint }, (result) => {
      result.on("data", (data) => {
        
        resultdata = JSON.parse(data.toString());
        if (resultdata.errors != null) {
          throwOnErrors(query, variables, data);
          reject(resultdata);
        } else {
          resolve(resultdata);
        }
      });

      result.on("errors", (data) => {
        reject(() => {
          throwOnErrors(query, variables, data)
          return JSON.parse(data.toString())
        });
      });
    });
    
    httpRequest.write(req.body);
    httpRequest.end();
  });

  return data.data
};

Unfortunately, sometimes, the response does get rejected and the error is always something like this:

SyntaxError: Unexpected token , in JSON at position 0
        at JSON.parse (<anonymous>)

      56 |       result.on("data", (data) => {
      57 |         
    > 58 |         resultdata = JSON.parse(data.toString());
         |                           ^
      59 |         if (resultdata.errors != null) {
      60 |           throwOnErrors(query, variables, data);
      61 |           reject(resultdata);

      at IncomingMessage.<anonymous> (_tests/lib/graphql.js:58:27)

I really have no clue on how to solve this, because sometimes the promise gets resolved and sometimes not.

Do you guys have any tips for me?

Thanks in advance!

check network tab - response not in json format – xadm May 07 '21 at 21:04 — xadm, May 07 '21 at 21:04

score 0 · Answer 1 · answered May 07 '21 at 21:25

Your 'data' callback can run many times, result is a stream, so

const httpRequest = https.request({ ...req, host: endpoint }, (result) => {
  result.on("data", (data) => {
    
    resultdata = JSON.parse(data.toString());
    if (resultdata.errors != null) {
      throwOnErrors(query, variables, data);
      reject(resultdata);
    } else {
      resolve(resultdata);
    }
  });

  result.on("errors", (data) => {
    reject(() => {
      throwOnErrors(query, variables, data)
      return JSON.parse(data.toString())
    });
  });
});

needs to be more like

const httpRequest = https.request({ ...req, host: endpoint }, (response) => {
  const chunks = [];
  response.on("data", (data) => { chunks.push(data); });
  response.on("end", () => {        
    resultdata = JSON.parse(Buffer.concat(chunks).toString());
    if (resultdata.errors != null) {
      throwOnErrors(query, variables, data);
      reject(resultdata);
    } else {
      resolve(resultdata);
    }
  });
  response.on("error", err => {
    reject(() => {
      throwOnErrors(query, variables, data)
      return JSON.parse(data.toString())
    });
  });
});

Vanilla NodeJS Appsync client error while making queries/mutations

1 Answers1