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I have a stock aspnetcore and reactjs app, generated from the starter template (dotnet new react). I would like the SPA app to be served from a subpath off the root url; e.g. instead of the sample app being https://localhost:5001/counter I'm looking for it to instead be served from https://localhost:5001/myapp/counter.

I changed the Startup.cs from:

app.UseSpa(spa =>
            {
                spa.Options.SourcePath = "ClientApp";

                if (env.IsDevelopment())
                {
                    spa.UseReactDevelopmentServer(npmScript: "start");
                }
            });

to this:

app.Map(new Microsoft.AspNetCore.Http.PathString("/myapp"), appMember =>
            {
                appMember.UseSpa(spa =>
                {
                    spa.Options.SourcePath = "ClientApp";

                    if (env.IsDevelopment())
                    {
                        spa.UseReactDevelopmentServer(npmScript: "start");
                    }
                });
            });

This sort of works. If I browse to https://localhost:5001/myapp/ it appears to load the index.html, but the static files are attempting to load from the root path and not the subpath.

What needs to be changed so that the react app uses the subpath as the root? I'd like this to work both in the interactive VS dev environment and when deployed, likely on IIS. It seems like it's close but I'm missing something.

Sample demo of the solution is available here: https://github.com/petertirrell/mvc-spa-demo/tree/master/mvc-spa-demo

Thanks!

Answers

Start with moving app to sub-path by adding this to top of package.json:

"homepage": "/myapp/", 

When running npm start inside ClientApp folder, app is now serving http://localhost:3000/myapp

Then change Startup.cs like this:

First remove

app.UseSpaStaticFiles()

then add

        const string spaPath = "/myapp";
        if (env.IsDevelopment())
        {
            app.MapWhen(ctx => ctx.Request.Path.StartsWithSegments(spaPath)
                               || ctx.Request.Path.StartsWithSegments("/sockjs-node"),
                client =>
            {
                client.UseSpa(spa =>
                {
                    spa.Options.SourcePath = "ClientApp";
                    spa.UseReactDevelopmentServer(npmScript: "start");
                });
            });
        }
        else
        {
            app.Map(new PathString(spaPath), client =>
            {
                // `https://github.com/dotnet/aspnetcore/issues/3147`
                client.UseSpaStaticFiles(new StaticFileOptions()
                {
                    OnPrepareResponse = ctx =>
                    {
                        if (ctx.Context.Request.Path.StartsWithSegments($"{spaPath}/static"))
                        {
                            // Cache all static resources for 1 year (versioned file names)
                            var headers = ctx.Context.Response.GetTypedHeaders();
                            headers.CacheControl = new CacheControlHeaderValue
                            {
                                Public = true,
                                MaxAge = TimeSpan.FromDays(365)
                            };
                        }
                        else
                        {
                            // Do not cache explicit `/index.html` or any other files.  See also: `DefaultPageStaticFileOptions` below for implicit "/index.html"
                            var headers = ctx.Context.Response.GetTypedHeaders();
                            headers.CacheControl = new CacheControlHeaderValue
                            {
                                Public = true,
                                MaxAge = TimeSpan.FromDays(0)
                            };
                        }
                    }
                });

                client.UseSpa(spa =>
                {
                    spa.Options.SourcePath = "ClientApp";
                    spa.Options.DefaultPageStaticFileOptions = new StaticFileOptions()
                    {
                        OnPrepareResponse = ctx => {
                            // Do not cache implicit `/index.html`.  See also: `UseSpaStaticFiles` above
                            var headers = ctx.Context.Response.GetTypedHeaders();
                            headers.CacheControl = new CacheControlHeaderValue
                            {
                                Public = true,
                                MaxAge = TimeSpan.FromDays(0)
                            };
                        }
                    };
                });
            });
        }

Don't forget to clear browser history before testing changes for the first time on e.g. Azure.