## Composition by architecture modules

Each [architecture module and platform](platforms.md) can contribute code to any of the runtimes.
Not every module contributes to every runtime.

The core-runtime module defines each runtime:

- The target JVM for the runtime. Each runtime has its own JVM compatibility constraints.
- Some base services that are available to code hosted by the runtime. This varies by runtime.

  newline-terminated lines in the byte slice s.
- [SplitSeq] returns an iterator over
  all substrings of s separated by sep.
- [SplitAfterSeq] returns an iterator
  over substrings of s split after each instance of sep.
- [FieldsSeq] returns an iterator over
  substrings of s split around runs of whitespace characters,
  as defined by unicode.IsSpace.
- [FieldsFuncSeq] returns an iterator

    /**
     * Returns model source identified by a path relative to this model source POM. Implementation <strong>MUST</strong>
     * be able to accept <code>relPath</code> parameter values that
     * <ul>
     * <li>use either / or \ file path separator</li>
     * <li>have .. parent directory references</li>
     * <li>point either at file or directory, in the latter case POM file name 'pom.xml' needs to be used by the
     * requested model source.</li>

# Using the Request Directly

Up to now, you have been declaring the parts of the request that you need with their types.

Taking data from:

* The path as parameters.
* Headers.
* Cookies.
* etc.

And by doing so, **FastAPI** is validating that data, converting it and generating documentation for your API automatically.

But there are situations where you might need to access the `Request` object directly.

   * Reads a count corresponding to a serialized map, multiset, or multimap. It returns the size of
   * a map serialized by {@link #writeMap(Map, ObjectOutputStream)}, the number of distinct elements
   * in a multiset serialized by {@link #writeMultiset(Multiset, ObjectOutputStream)}, or the number
   * of distinct keys in a multimap serialized by {@link #writeMultimap(Multimap,
   * ObjectOutputStream)}.
   */

      and distribution as defined by Sections 1 through 9 of this document.

      "Licensor" shall mean the copyright owner or entity authorized by
      the copyright owner that is granting the License.

      "Legal Entity" shall mean the union of the acting entity and all
      other entities that control, are controlled by, or are under common

# Custom Request and APIRoute class

In some cases, you may want to override the logic used by the `Request` and `APIRoute` classes.

In particular, this may be a good alternative to logic in a middleware.

For example, if you want to read or manipulate the request body before it is processed by your application.

/// danger

This is an "advanced" feature.

If you are just starting with **FastAPI** you might want to skip this section.

///

      and distribution as defined by Sections 1 through 9 of this document.

      "Licensor" shall mean the copyright owner or entity authorized by
      the copyright owner that is granting the License.

      "Legal Entity" shall mean the union of the acting entity and all
      other entities that control, are controlled by, or are under common

      and distribution as defined by Sections 1 through 9 of this document.

      "Licensor" shall mean the copyright owner or entity authorized by
      the copyright owner that is granting the License.

      "Legal Entity" shall mean the union of the acting entity and all
      other entities that control, are controlled by, or are under common

      and distribution as defined by Sections 1 through 9 of this document.

      "Licensor" shall mean the copyright owner or entity authorized by
      the copyright owner that is granting the License.

      "Legal Entity" shall mean the union of the acting entity and all
      other entities that control, are controlled by, or are under common