The Microsoft.Azure.WebJobs.Script encountered an issue while attempting to cast an object of type 'System.String' to type 'Microsoft.AspNetCore.Http.HttpRequest' during the return process

Question

The Microsoft.Azure.WebJobs.Script encountered an issue while attempting to cast an object of type 'System.String' to type 'Microsoft.AspNetCore.Http.HttpRequest' during the return process

I recently encountered an issue with my Azure Function written in JS that is triggered by the Service Bus and generates files to Blob Storage. When attempting to return an HTTP result, I received the following error message:

System.Private.CoreLib: Exception while executing function: Functions.categoryMessageConsumer. Microsoft.Azure.WebJobs.Script: Unable to cast object of type 'System.String' to type 'Microsoft.AspNetCore.Http.HttpRequest'.

It's perplexing why the result is being mapped to the HttpRequest object.

index.ts:

import { AzureFunction, Context, HttpRequest } from '@azure/functions';
...

const serviceBusTopicTrigger: AzureFunction = async function(context: Context, req: HttpRequest) {
    let categoryMessage: CategoryMessage = Object.assign(new CategoryMessage(), req);
    let messageValidationResult = await categoryMessage.validate();
    if(!messageValidationResult.isValid) {
        context.log.error(messageValidationResult.errors);
        return {
            status: 400,
            body: "Unexpected error"
        };
    }

    ...
}

function.json output binding:

...
    {
      "type": "http",
      "direction": "out",
      "name": "$return"
    }
...

host.json

{
  "version": "2.0",
  "logging": {
    "applicationInsights": {
      "samplingSettings": {
        "isEnabled": true,
        "excludedTypes": "Request"
      }
    }
  },
  "extensionBundle": {
    "id": "Microsoft.Azure.Functions.ExtensionBundle",
    "version": "[1.*, 2.0.0)"
  }
}

javascript typescript azure azure-blob-storage

Answer 1

Answer №1

const axios = require('axios');

module.exports = function (context, eventHubMessages) {
    context.log(`Triggering JavaScript eventhub function for message array ${eventHubMessages}`);

    eventHubMessages.forEach((message, index) => {

        function callWebService(msg) {
            let promise = new Promise((resolve, reject) => {
                const options = {
                    host: process.env["HOST"],
                    port: process.env["PORT"],
                    path: process.env["PATH"],
                    method: process.env["WEBSERVICE_METHOD"],
                    headers: {
                        'Content-Type': process.env["WEBSERVICE_CONTENT_TYPE"],
                        'x-api-key': process.env["WEBSERVICE_API_KEY"]
                    }
                };

                axios(options)
                    .then(res => {
                        context.res = { body: res.data };
                        resolve(res.data);
                    })
                    .catch(error => {
                        context.log.error(error);
                        reject(error);
                        context.done();
                    });
            });

            promise.then(response => {
                context.log(`Message sent: ${msg}`);
                context.log(`Response: ${response}`);
                context.done();
            });

        }

        callWebService(message);
    });
};

This used to be my index.js file.

And now it has been refactored into my function.js:

{
  "bindings": [
    {
      "type": "eventHubTrigger",
      "name": "eventHubMessages",
      "direction": "in",
      "eventHubName": "event-hub-name",
      "connection": "CONNECTION_EVENT_HUB",
      "cardinality": "many",
      "consumerGroup": "$Default",
      "dataType": "string"
    },
    {
      "type": "http",
      "direction": "out",
      "name": "$return"
    }
  ]
}

In the local.settings.json file, all necessary environment variables like HOST, PORT, CONNECTION_EVENT_HUB, etc., have been properly declared.

Answer 2

const axios = require('axios');

module.exports = function (context, eventHubMessages) {
    context.log(`Triggering JavaScript eventhub function for message array ${eventHubMessages}`);

    eventHubMessages.forEach((message, index) => {

        function callWebService(msg) {
            let promise = new Promise((resolve, reject) => {
                const options = {
                    host: process.env["HOST"],
                    port: process.env["PORT"],
                    path: process.env["PATH"],
                    method: process.env["WEBSERVICE_METHOD"],
                    headers: {
                        'Content-Type': process.env["WEBSERVICE_CONTENT_TYPE"],
                        'x-api-key': process.env["WEBSERVICE_API_KEY"]
                    }
                };

                axios(options)
                    .then(res => {
                        context.res = { body: res.data };
                        resolve(res.data);
                    })
                    .catch(error => {
                        context.log.error(error);
                        reject(error);
                        context.done();
                    });
            });

            promise.then(response => {
                context.log(`Message sent: ${msg}`);
                context.log(`Response: ${response}`);
                context.done();
            });

        }

        callWebService(message);
    });
};

This used to be my index.js file.

And now it has been refactored into my function.js:

{
  "bindings": [
    {
      "type": "eventHubTrigger",
      "name": "eventHubMessages",
      "direction": "in",
      "eventHubName": "event-hub-name",
      "connection": "CONNECTION_EVENT_HUB",
      "cardinality": "many",
      "consumerGroup": "$Default",
      "dataType": "string"
    },
    {
      "type": "http",
      "direction": "out",
      "name": "$return"
    }
  ]
}

In the local.settings.json file, all necessary environment variables like HOST, PORT, CONNECTION_EVENT_HUB, etc., have been properly declared.

Answer 3

Answer №2

We were able to resolve the issue by deleting the following binding from function.json:

{
 "type": "http",
 "direction": "out",
 "name": "res"
}

As a result, if you are executing the function using a timingTrigger, the configuration should look like this:

{
  "scriptFile": "index.js",
  "bindings": [
    {
      "name": "myTimer",
      "type": "timerTrigger",
      "direction": "in",
      "schedule": "0 */1 * * * *"
    }
  ]
}

If you switch back to using HTTP or another trigger type, remember to fill out the bindings completely and remove any references to the timer trigger:

{
  "scriptFile": "index.js",
  "bindings": [
    {
      "authLevel": "function",
      "type": "httpTrigger",
      "direction": "in",
      "name": "req",
      "methods": [
        "get",
        "post"
      ]
    },
    {
      "type": "http",
      "direction": "out",
      "name": "res"
    }
  ]
}

Answer 4

We were able to resolve the issue by deleting the following binding from function.json:

{
 "type": "http",
 "direction": "out",
 "name": "res"
}

As a result, if you are executing the function using a timingTrigger, the configuration should look like this:

{
  "scriptFile": "index.js",
  "bindings": [
    {
      "name": "myTimer",
      "type": "timerTrigger",
      "direction": "in",
      "schedule": "0 */1 * * * *"
    }
  ]
}

If you switch back to using HTTP or another trigger type, remember to fill out the bindings completely and remove any references to the timer trigger:

{
  "scriptFile": "index.js",
  "bindings": [
    {
      "authLevel": "function",
      "type": "httpTrigger",
      "direction": "in",
      "name": "req",
      "methods": [
        "get",
        "post"
      ]
    },
    {
      "type": "http",
      "direction": "out",
      "name": "res"
    }
  ]
}

Answer 5

Answer №3

Your function may be encountering unexpected object creation, leading to errors.

If you specified the response variable as $return, ensure your function is coded accordingly:

function.json:

{
    "disabled": false,    
    "bindings": [
        {
            "authLevel": "function",
            "type": "httpTrigger",
            "direction": "in",
            "name": "req"
        },
        {
            "type": "http",
            "direction": "out",
            "name": "res"
        }
    ]
}

JS code:

module.exports = function(context, req) {
    context.log('Node.js HTTP trigger function processed a request. RequestUri=%s', req.originalUrl);

    if (req.query.name || (req.body && req.body.name)) {
        context.res = {
            // status defaults to 200 */
            body: "Hello " + (req.query.name || req.body.name)
        };
    }
    else {
        context.res = {
            status: 400,
            body: "Please pass a name on the query string or in the request body"
        };
    }
    context.done();
};

For additional configuration options in function.json, explore resources here and here.

Answer 6

Your function may be encountering unexpected object creation, leading to errors.

If you specified the response variable as $return, ensure your function is coded accordingly:

function.json:

{
    "disabled": false,    
    "bindings": [
        {
            "authLevel": "function",
            "type": "httpTrigger",
            "direction": "in",
            "name": "req"
        },
        {
            "type": "http",
            "direction": "out",
            "name": "res"
        }
    ]
}

JS code:

module.exports = function(context, req) {
    context.log('Node.js HTTP trigger function processed a request. RequestUri=%s', req.originalUrl);

    if (req.query.name || (req.body && req.body.name)) {
        context.res = {
            // status defaults to 200 */
            body: "Hello " + (req.query.name || req.body.name)
        };
    }
    else {
        context.res = {
            status: 400,
            body: "Please pass a name on the query string or in the request body"
        };
    }
    context.done();
};

For additional configuration options in function.json, explore resources here and here.

The Microsoft.Azure.WebJobs.Script encountered an issue while attempting to cast an object of type 'System.String' to type 'Microsoft.AspNetCore.Http.HttpRequest' during the return process

Answer №1

Answer №2

Answer №3

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