📝Coding Notes

[crupest]

I love and hate coding at the same time! 🤣

[crupest]

Forwarded Headers And Docker

When you deploy aspnet core app with docker and use reverse proxy with forwarded header middleware in app, there is a problem that forwarded header middleware may not regard forwarded headers or replace the http context.

I made a basic investigation. Here is the reason I figure out and it may not be completely correct.

Aspnet core began to ignore forwarded headers when the original request ip is not in the allowed list from some version. By default allowed ip is only loopback. However it seems when running in docker a individual network is established and requests from proxy server are like external requests so aspnet core ignore forwarded headers.

The solution is to explicitly make aspnet core trust the requests. Like this

if (string.Equals(System.Environment.GetEnvironmentVariable("ASPNETCORE_FORWARDEDHEADERS_ENABLED"), "true", StringComparison.OrdinalIgnoreCase))
{
    var options = new ForwardedHeadersOptions
    {
        ForwardedHeaders = ForwardedHeaders.XForwardedFor |
        ForwardedHeaders.XForwardedProto
    };
    // Only loopback proxies are allowed by default.
    // Clear that restriction because forwarders are enabled by explicit 
    // configuration.
    options.KnownNetworks.Clear();
    options.KnownProxies.Clear();
    app.UseForwardedHeaders(options);
}

Remember to define environment variable ASPNETCORE_FORWARDEDHEADERS_ENABLED as true in docker image!

[crupest]

Guess what? They do not define the environment variable in official base docker image in fact.

[crupest]

The source map generated with eval-source-map in webpack is totally a mass and not even able to be used.
Use eval-cheap-module-source-map instead and at least you can make breakpoint line by line.

[crupest]

Be careful when using react hooks and rxjs. Hooks may create a new observable for each update making some function like throttle not work properly.

[crupest]

Be careful with signalr behind nginx. It needs special configuration. See this for example.

[crupest]

A lesson learned at the cost of blood, never refactor thoroughly at one time. Do it slowly and progressively!

[crupest]

There is currently a bug in parceljs. If you want to proxy ws in dev server, you should use a different hmr port from dev server port. See details in parcel-bundler/parcel#6994. Hope the bug can be fixed soon.

(I won't tell you that I spent several hours to find the problem.😭)

[crupest]

Some tips about reactjs:

• When your array state variable does not work well, try to figure out it is a new array or an old array with different elements. Although experienced developer knows this rule very much, there are cases you make such mistake carelessly.
• Events of elements in reactjs are bubbled as in jsx. If you use a portal, they are still bubbled as the structure in jsx because reactjs will do the magic for you.
• If you can't use jsx, check if your file is .tsx or .ts.

[crupest]

No longer record it here.