# Steps for IoT file download using Rest Client **URL:** \ **Category:** Lounge\ **Created:** [September 9, 2026, 7:48am UTC](https://community.criticalmanufacturing.com/t/steps-for-iot-file-download-using-rest-client/837 "2026-09-09T07:48:20Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Chang\_Lai](https://avatars.discourse-cdn.com/v4/letter/c/ee59a6/32.png) [@Chang\_Lai](https://community.criticalmanufacturing.com/u/Chang_Lai)\ **Post date:** [September 9, 2026, 7:48am UTC](https://community.criticalmanufacturing.com/t/steps-for-iot-file-download-using-rest-client/837/1 "2026-09-09T07:48:20Z")
Hello team, I need some advice regarding IoT file download using Rest Client. Is it possible to download a file using OOB functionality of the Rest Client? They have exposed the file through GET - Serves files directly from a mounted directory over HTTP, so MES can retrieve a specific file by name without needing SFTP access. In order to simulate this for automation testing, what would need to be done in order to host a file with a mock Rest Server? I came across the documentation for the Rest server([Rest Server - Critical Manufacturing Developer Portal](https://developer.criticalmanufacturing.com/11.3/explore/guides/customizations/automation/how-tos/test-orchestrator/plugins/simulators/RestServer/ "https://developer.criticalmanufacturing.com/11.3/explore/guides/customizations/automation/how-tos/test-orchestrator/plugins/simulators/restserver/")) and Mock MES instance([Connecting to a Live MES - Critical Manufacturing Developer Portal](https://developer.criticalmanufacturing.com/11.3/explore/guides/customizations/automation/how-tos/test-orchestrator/configuration/mes_instance/ "https://developer.criticalmanufacturing.com/11.3/explore/guides/customizations/automation/how-tos/test-orchestrator/configuration/mes\_instance/")) and received confirmation from CMGPT that setting this up is possible using the steps outlined below. I would like to kindly seek your confirmation if these steps are correct. **Possible answer:** - ✅ Yes, it is possible — the IoT Test Orchestrator’s Rest Server Simulator Plugin (`RestServer.PluginMain`) is the OOTB mechanism to host a mock HTTP server that serves files over GET for automation testing. - ✅ The plugin is powered by WireMock, supports registering GET endpoints via `restSimulator.Register()`, and returns file content through a `SystemReply(200, fileContent)`. - ✅ The mock server address/port is injected into the MES dataflow JSON so the REST Client driver targets it instead of the real external system. **The Right Tool — Rest Server Simulator Plugin** **A Simulator Plugin mirrors the implementation of its corresponding automation protocol. Since the MES uses a REST Client driver to retrieve files, a REST Client requires a REST Server simulator. The IoT Test Orchestrator Framework provides exactly this with the dedicated [Rest Server](https://developer.criticalmanufacturing.com/11.3/explore/guides/customizations/automation/how-tos/test-orchestrator/plugins/simulators/RestServer/ "https://developer.criticalmanufacturing.com/11.3/explore/guides/customizations/automation/how-tos/test-orchestrator/plugins/simulators/restserver/") simulator plugin** **Steps:** 1. Add the Rest Server simulator plugin to the test scenario configuration 2. Register a GET endpoint that returns the file content as `SystemReply` 3. Read the file from disk in the test and return it in the handler 4. Configure the Rest Client driver in MES to point to the mock server address ## 📋 Step-by-Step Setup ### Step 1 — Add the Rest Server Plugin to the Scenario Configuration To add the Rest Server simulator plugin to a test scenario, include its configuration in `ScenarioConfiguration`: ```auto var port = new Random().Next(5000, 30000); // randomize to avoid concurrency collisions var configuration = new ScenarioConfiguration() .ManagerId("Manager01") // ... other settings ... .AddSimulatorPlugin(new RestServer.Plugin.SettingsBuilder() .Address("http://localhost", port) .ServerSettings(new WireMock.Settings.WireMockServerSettings() { StartAdminInterface = true }) .Build()) .Build(); ``` The Rest Server configuration properties are: | Property | Type | Description | Default | | | --- | --- | --- | --- | --- | | `Address` | string | Address | — | | | `Port` | int | Port | 8080 | | | `WireMockServerSettings` | object | Server Settings | — | 3 | * * * ### Step 2 — Register a GET Endpoint That Serves the File Inside your test, retrieve the Rest Server simulator and register a GET endpoint that reads and returns the file content: ```auto var restSimulator = (RestServer.PluginMain) context.Simulators["RestServer"]; // Read the file content from disk var fileBytes = File.ReadAllBytes("path/to/your/testfile.csv"); var fileContent = Convert.ToBase64String(fileBytes); // or return as string if text restSimulator.Register("/files/myfile.csv", (ISystemRequest request) => { // Return the file with HTTP 200 and appropriate content return new SystemReply(200, System.Text.Encoding.UTF8.GetString(fileBytes)); }, Common.Objects.Rest.RestVerb.Get); ``` The OOTB usage example for the Rest Server plugin shows registering a GET endpoint with `restSimulator.Register()`, providing the route, a handler lambda that returns a `SystemReply(statusCode, body)`, and the HTTP verb. * * * ### Step 3 — Point the MES REST Client Driver to the Mock Server In the Mock MES configuration, update the `restMasterDataPath` JSON to use the dynamically assigned port so the Rest Client driver targets the mock server address: ```auto // Update the dataflow JSON to use the selected port File.WriteAllText( restMasterDataPath, File.ReadAllText(restMasterDataPath).Replace("5000", port.ToString()) ); ``` This ensures the **MES REST Client** in the workflow sends its `GET /files/myfile.csv` request to the mock server instead of the real external system. * * * ### Step 4 — Verify the File Was Requested ```auto var fileWasRequested = false; restSimulator.Register("/files/myfile.csv", (ISystemRequest request) => { fileWasRequested = true; var fileBytes = File.ReadAllBytes("path/to/testfile.csv"); return new SystemReply(200, System.Text.Encoding.UTF8.GetString(fileBytes)); }, Common.Objects.Rest.RestVerb.Get); // ... trigger the MES workflow ... scenario.Utilities.WaitFor(50, "File was never requested", () => fileWasRequested); ``` Thank You. ---
**Author:** ![Joao\_Roque](https://yyz2.discourse-cdn.com/flex050/user_avatar/community.criticalmanufacturing.com/joao_roque/32/24_2.png) [@Joao\_Roque](https://community.criticalmanufacturing.com/u/Joao_Roque)\ **Post date:** [September 9, 2026, 7:50am UTC](https://community.criticalmanufacturing.com/t/steps-for-iot-file-download-using-rest-client/837/2 "2026-09-09T07:50:20Z")
Hi, For testing the test orchestrator docs are here [Rest Client - Critical Manufacturing Developer Portal](https://developer.criticalmanufacturing.com/explore/guides/customizations/automation/how-tos/test-orchestrator/plugins/simulators/RestClient/ "https://developer.criticalmanufacturing.com/explore/guides/customizations/automation/how-tos/test-orchestrator/plugins/simulators/restclient/"). I would point out that for large files you probably need an http stream which I think it’s not supported in the Rest Client or Rest Server. ---
**Author:** ![Joao\_Moreira](https://avatars.discourse-cdn.com/v4/letter/j/b9bd4f/32.png) [@Joao\_Moreira](https://community.criticalmanufacturing.com/u/Joao_Moreira)\ **Post date:** [September 9, 2026, 4:49pm UTC](https://community.criticalmanufacturing.com/t/steps-for-iot-file-download-using-rest-client/837/3 "2026-09-09T16:49:00Z")
Hi, Yes, as João Roque said, the Rest Client driver cannot retrieve a raw binary response, such as `application/pdf`, `image/png`, or `application/octet-stream`. As workarround, you could use an endpoint that returns the file as text, or one that returns it Base64-encoded inside a JSON response. Below, I describe how you could configure both these scenarios: ### Scenario 1: Downloading a Text/XML File The rest client driver never writes to disk. It returns the content into the workflow, and a **File** driver command writes it. A download is therefore two commands: one on the REST Client protocol to fetch the content, and one on the File protocol to write it. For a text response, such as the one below, the content arrives as a String. ```json { "Name": "DownloadReport", "Description": "Retrieve the daily report as CSV", "DeviceCommandId": "/reports/:reportId", "ExtendedData": { "requestMethod": "GET", "timeout": 60000, "successfulStatusCodes": "200" }, "Parameters": [ { "Name": "reportId", "DataType": "String", "AutomationProtocolDataType": "String", "ExtendedData": { "operationParameters": "PathParameter" }, "IsMandatory": true } ] } ``` In the workflow, should connect the output of the **Execute Equipment Command** task that runs this command to the `content` parameter of a `CreateFile` command on the File driver: ```json { "Name": "WriteReport", "Description": "Write the retrieved report to disk", "DeviceCommandId": "WriteReport", "ExtendedData": { "commandType": "CreateFile" }, "Parameters": [ { "Name": "path", "DataType": "String", "AutomationProtocolDataType": "String", "IsMandatory": true }, { "Name": "content", "DataType": "String", "AutomationProtocolDataType": "String", "IsMandatory": true } ] } ``` #### Scenario 2: Binary File Through a Base64 Response Many document APIs return a binary file as a Base64 string inside a JSON object, for example: ```json { "fileName": "certificate-4471.pdf", "content": "JVBERi0xLjQKJcfsj6IKNSAwIG9iago8PC9MZW5ndGgg..." } ``` The driver parses that response as JSON and returns it as an Object. Extract `fileName` and `content` with a converter, then write the file with a `CreateFile` command whose `encoding` parameter is set to `base64`, which decodes the string back to the original bytes: ```json { "Name": "WriteCertificate", "Description": "Write a Base64 payload to disk as a binary file", "DeviceCommandId": "WriteCertificate", "ExtendedData": { "commandType": "CreateFile" }, "Parameters": [ { "Name": "path", "DataType": "String", "AutomationProtocolDataType": "String", "IsMandatory": true }, { "Name": "content", "DataType": "String", "AutomationProtocolDataType": "String", "IsMandatory": true }, { "Name": "encoding", "DataType": "String", "AutomationProtocolDataType": "String", "IsMandatory": false } ] } ``` Set `encoding` to `base64` when the command is executed. Leaving it at the default of `utf-8` writes the Base64 text itself rather than the decoded file. ---
**Author:** ![Joao\_Roque](https://yyz2.discourse-cdn.com/flex050/user_avatar/community.criticalmanufacturing.com/joao_roque/32/24_2.png) [@Joao\_Roque](https://community.criticalmanufacturing.com/u/Joao_Roque)\ **Post date:** [September 10, 2026, 9:41am UTC](https://community.criticalmanufacturing.com/t/steps-for-iot-file-download-using-rest-client/837/4 "2026-09-10T09:41:13Z")
As a side note this is also common in OPC-UA. In that protocol we do support having retrieving files from OPC-UA and then writing them somewhere or sending them to the MES [Read File - Critical Manufacturing Documentation Portal](https://help.criticalmanufacturing.com/userguide/automation/reference/tasks/opcua/task_readfile/?h=opc) ---
**Author:** ![system](https://yyz2.discourse-cdn.com/flex050/user_avatar/community.criticalmanufacturing.com/system/32/23_2.png) [@system](https://community.criticalmanufacturing.com/u/system)\ **Post date:** [September 12, 2026, 9:41am UTC](https://community.criticalmanufacturing.com/t/steps-for-iot-file-download-using-rest-client/837/5 "2026-09-12T09:41:26Z")
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