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.

///

## Use cases { #use-cases }

Some use cases include:

}

// NewDummyDataGen returns a ReadSeeker over the first `totalLength`
// bytes from the infinite stream consisting of repeated
// concatenations of `alphabets`.
//
// The skipOffset (generally = 0) can be used to skip a given number
// of bytes from the beginning of the infinite stream. This is useful
// to compare such streams of bytes that may be split up, because:
//
// Given the function:
//
//	f := func(r io.Reader) string {

        // Validate compression count
        if (compressionCount < 0 || compressionCount > 16) {
            throw new SMBProtocolDecodingException("Invalid compression count: " + compressionCount);
        }

        // Skip padding
        bufferIndex += 2;

        // Read flags
        this.flags = SMBUtil.readInt4(buffer, bufferIndex);
        bufferIndex += 4;

        // Validate remaining buffer size for algorithms

            // Verify the path is correctly encoded in UTF-16LE
            ByteBuffer bb = ByteBuffer.wrap(dst).order(ByteOrder.LITTLE_ENDIAN);
            bb.getShort(); // Skip referral level

            byte[] pathBytes = path.getBytes(StandardCharsets.UTF_16LE);
            byte[] encodedPath = new byte[pathBytes.length];
            bb.get(encodedPath);

## Dependencies with `yield`, `HTTPException`, `except` and Background Tasks { #dependencies-with-yield-httpexception-except-and-background-tasks }

/// warning

You most probably don't need these technical details, you can skip this section and continue below.

These details are useful mainly if you were using a version of FastAPI prior to 0.106.0 and used resources from dependencies with `yield` in background tasks.

///

	buf, err := io.ReadAll(io.LimitReader(r, maxSpecialFileSize+1))
	if len(buf) > maxSpecialFileSize {
		return nil, ErrFieldTooLong
	}
	return buf, err
}

// discard skips n bytes in r, reporting an error if unable to do so.
func discard(r io.Reader, n int64) error {
	// If possible, Seek to the last byte before the end of the data section.

			}

			for k, v := range userAccounts {
				if k == siteReplicatorSvcAcc {
					// skip the site replicate svc account as it is
					// already replicated.
					continue
				}

				if v.Credentials.ParentUser != "" && v.Credentials.ParentUser == globalActiveCred.AccessKey {
					// skip all root user service accounts.
					continue
				}

				info.UserInfoMap[k] = madmin.UserInfo{

But first, let's check some small concepts.

## In a hurry? { #in-a-hurry }

If you don't care about any of these terms and you just need to add security with authentication based on username and password *right now*, skip to the next chapters.

## OAuth2 { #oauth2 }

OAuth2 is a specification that defines several ways to handle authentication and authorization.

It is quite an extensive specification and covers several complex use cases.

	newMeta.Version = poolMetaVersion
	for idx, pool := range z.serverPools {
		var skip bool
		for _, currentPool := range prevMeta.Pools {
			// Preserve any current pool status.
			if currentPool.CmdLine == pool.endpoints.CmdLine {
				newMeta.Pools = append(newMeta.Pools, currentPool)
				skip = true
				break
			}
		}
		if skip {
			continue
		}
		newMeta.Pools = append(newMeta.Pools, PoolStatus{

    delegate.add(checkNotNull(first));
    do {
      delegate.add(checkNotNull(elements.next()));
    } while (elements.hasNext());

    return unsafeDelegate(delegate);
  }

  // Factory methods that skips the null checks on elements, only used when
  // the elements are known to be non-null.
  static <E> ImmutableSet<E> unsafeDelegate(Set<E> delegate) {
    switch (delegate.size()) {
      case 0:
        return of();