How to return a file that open in browser embed not download?

Question

I am using .net core web api and in a api there is return file (content-type:application/octet-stream)

but the browser will start download not open it.

in the html there is a form post to the web api.

I want to the file will open (pdf) not download

Answer 1

Hi @mc

You can use FileStreamResult to show pdf file, it will not start download.

You can change your code like below, and create a wwwroot folder in your project.

Program.cs

namespace SwaggerApi  
{  
    public class Program  
    {  
        public static void Main(string[] args)  
        {  
            var builder = WebApplication.CreateBuilder(args);  
  
            // Add services to the container.  
            // Add this line for show pdf  
            builder.Services.AddHttpClient("PdfDomain", client => {  
                client.BaseAddress = new Uri("https://localhost:7055/");  
            });  
            builder.Services.AddControllers();  
            // Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle  
            builder.Services.AddEndpointsApiExplorer();  
            builder.Services.AddSwaggerGen();  
  
            var app = builder.Build();  
  
            // Configure the HTTP request pipeline.  
            if (app.Environment.IsDevelopment())  
            {  
                app.UseSwagger();  
                app.UseSwaggerUI();  
            }  
            app.UseSwagger();  
            app.UseSwaggerUI();  
  
            app.UseHttpsRedirection();  
            // add this for access static files under wwwroot folder  
            app.UseStaticFiles();  
              
            app.UseAuthorization();  
  
            app.MapControllers();  
  
            app.Run();  
        }  
    }  
}  

PdfController.cs

using Microsoft.AspNetCore.Mvc;  
  
namespace SwaggerApi.Controllers  
{  
    [ApiController]  
    [Route("[controller]")]  
    public class PdfController : ControllerBase  
    {  
        private readonly IHttpClientFactory _httpClientFactory;  
        public PdfController(IHttpClientFactory httpClientFactory)  
        {  
            _httpClientFactory = httpClientFactory;  
        }  
        [HttpGet]  
        [Route("external-domain-pdf")]  
        public async Task<IActionResult> ExternlDomainPdf()  
        {  
            string url = "/images/sample.pdf";  
            var httpClient = _httpClientFactory.CreateClient("PdfDomain");  
            var response = await httpClient.GetAsync(url);  
            MemoryStream ms = new MemoryStream(await response.Content.ReadAsByteArrayAsync());  
            return new FileStreamResult(ms, "application/pdf");  
        }  
    }  
}  

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Best regards,
Jason

Answer 2

the Content-Disposition header control how the browser handle the download "inline" means open attachment means save.

// download  
Content-Disposition: attachment; filename=sample.pdf;  
  
// open  
Content-Disposition: inline; filename="sample.pdf"  
  

to know its a pdf file Content-Type should be application/pdf

so change your headers to:

Content-Type: application/pdf  
Content-Disposition: inline; filename="sample.pdf"