DiagramConverter ASP.NET Core Integration Guide

This guide shows how to integrate DiagramConverter into an ASP.NET Core application to expose Visio diagram conversion as an HTTP endpoint.

Prerequisites

Aspose.Diagram for .NET (version 26.4.0 or later)
ASP.NET Core 6.0 or later
License applied at application startup (see Step 1)

Step 1: Apply License at Startup

Apply your Aspose license once in Program.cs or Startup.cs before any conversions occur:

using Aspose.Diagram;

var builder = WebApplication.CreateBuilder(args);
// ... configure services

var app = builder.Build();

// Apply metered license before first request
var metered = new Metered();
metered.SetMeteredKey("publicKey", "privateKey");

app.Run();

Step 2: Create a Conversion Endpoint (Stream-Based)

Use stream-based conversion to avoid writing temporary files to disk:

using System.IO;
using Aspose.Diagram.LowCode;
using Microsoft.AspNetCore.Mvc;

[ApiController]
[Route("api/diagram")]
public class DiagramConverterController : ControllerBase
{
    [HttpPost("convert")]
    public IActionResult Convert(IFormFile visioFile, [FromQuery] string outputFormat = "vdx")
    {
        if (visioFile == null || visioFile.Length == 0)
            return BadRequest("No file uploaded.");

        var allowedFormats = new[] { "vsdx", "vdx", "vsd", "vssx", "vstx" };
        if (!Array.Exists(allowedFormats, f => f == outputFormat.ToLower()))
            return BadRequest($"Unsupported output format: {outputFormat}");

        using var outputStream = new MemoryStream();

        var loadOptions = new LowCodeLoadOptions();
        loadOptions.InputStream = visioFile.OpenReadStream();

        var saveOptions = new LowCodeSaveOptions();
        saveOptions.OutputStream = outputStream;
        saveOptions.OutputFile = $"output.{outputFormat}";

        DiagramConverter.Process(loadOptions, saveOptions);

        string contentType = "application/octet-stream";
        string fileName = Path.ChangeExtension(visioFile.FileName, outputFormat);
        return File(outputStream.ToArray(), contentType, fileName);
    }
}

Step 3: Handle Errors Gracefully

Add error handling to return appropriate HTTP status codes:

using System;
using System.IO;
using Aspose.Diagram.LowCode;
using Microsoft.AspNetCore.Mvc;

[HttpPost("convert")]
public IActionResult Convert(IFormFile visioFile, [FromQuery] string outputFormat = "vdx")
{
    if (visioFile == null || visioFile.Length == 0)
        return BadRequest("No file uploaded.");

    try
    {
        using var outputStream = new MemoryStream();

        var loadOptions = new LowCodeLoadOptions();
        loadOptions.InputStream = visioFile.OpenReadStream();

        var saveOptions = new LowCodeSaveOptions();
        saveOptions.OutputStream = outputStream;
        saveOptions.OutputFile = $"output.{outputFormat}";

        DiagramConverter.Process(loadOptions, saveOptions);

        string fileName = Path.ChangeExtension(visioFile.FileName, outputFormat);
        return File(outputStream.ToArray(), "application/octet-stream", fileName);
    }
    catch (Exception ex)
    {
        return StatusCode(500, $"Conversion failed: {ex.Message}");
    }
}

Troubleshooting

Problem	Likely Cause	Fix
Evaluation watermark in output	License not applied at startup	Apply `metered.SetMeteredKey()` in `Program.cs` before `app.Run()`
Empty output stream	Stream position not reset	Call `outputStream.Position = 0` before reading if needed
`ArgumentException` on output format	Unsupported extension passed	Validate `outputFormat` against allowed list before calling `Process()`
Upload file size limit exceeded	ASP.NET Core default 30MB limit	Configure `MaxRequestBodySize` in `Program.cs` for large files