# Middleware { #middleware }

You can add middleware to **FastAPI** applications.

A "middleware" is a function that works with every **request** before it is processed by any specific *path operation*. And also with every **response** before returning it.

* It takes each **request** that comes to your application.
* It can then do something to that **request** or run any needed code.

class SecurityScopes:
    """
    This is a special class that you can define in a parameter in a dependency to
    obtain the OAuth2 scopes required by all the dependencies in the same chain.

    This way, multiple dependencies can have different scopes, even when used in the
    same *path operation*. And with this, you can access all the scopes required in
    all those dependencies in a single place.

    # o targetProcedureNameList: (NotRequired - Default list:{})
    #  You can specify target name of generated parameter bean for procedure.
    #  This property is valid only when isGenerateProcedureParameterBean is valid.
    #   e.g. list:{prefix:SP_}
    #  And you can specify procedures through DB link.
    #  This is treated as additional setting

In 12 drive example above, with MinIO server running in the default configuration, you can lose any of the six drives and still reconstruct the data reliably from the remaining drives.

## Why is Erasure Code useful?

      if (compareAndSet(currentRunner, blocker)) {
        // Thread.interrupt can throw arbitrary exceptions due to the nio InterruptibleChannel API
        // This will make sure that tasks don't get stuck busy waiting.
        // Some of this is fixed in jdk11 (see https://bugs.openjdk.org/browse/JDK-8198692) but
        // not all.  See the test cases for examples on how this can happen.
        try {
          ((Thread) currentRunner).interrupt();

/// warning

This is a more or less advanced section. If you are just starting, you can skip it.

You don't necessarily need OAuth2 scopes, and you can handle authentication and authorization however you want.

But OAuth2 with scopes can be nicely integrated into your API (with OpenAPI) and your API docs.

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    /**
     * Gets the decrypted proxies.
     *
     * @return The decrypted proxy, can be empty but never {@code null}.
     */
    List<Proxy> getProxies();

    /**
     * Gets the problems that were encountered during the settings decryption.
     *
     * @return The problems that were encountered during the decryption, can be empty but never {@code null}.
     */
    List<SettingsProblem> getProblems();

    // merged into POM being built. Once the POM builder has this plugin information, versions can be assigned
    // by the POM builder because they will have to be defined in plugin management. Once this is setComplete then it
    // can be passed back so that the default configuration information can be populated.
    //
    // We need to know the specific version so that we can look up the right version of the plugin descriptor

So we have a dedicated thread for every socket that just reads frames and dispatches them.

The reader thread must never run application-layer code. Otherwise one slow stream can hold up the entire connection.