return &testOneByteReadNoEOF{false, data}
}

// testOneByteReadNoEOF - implements io.Reader which returns 1 byte and nil error, but
// returns io.EOF on the next Read().
type testOneByteReadNoEOF struct {
	eof  bool
	data []byte
}

func (r *testOneByteReadNoEOF) Read(p []byte) (n int, err error) {
	if r.eof {
		return 0, io.EOF
	}
	n = copy(p, r.data)
	r.eof = true
	return n, nil
}

We see that we are going to need some dependencies used in several places of the application.

So we put them in their own `dependencies` module (`app/dependencies.py`).

We will now use a simple dependency to read a custom `X-Token` header:

//// tab | Python 3.9+

```Python hl_lines="3  6-8" title="app/dependencies.py"
{!> ../../docs_src/bigger_applications/app_an_py39/dependencies.py!}
```

////

     *
     * <ul>
     *   <li>If this field's value == currentThread, we know that it's up to date, because write
     *       operations in a thread always happen-before subsequent read operations in the same
     *       thread
     *   <li>If this field's value == null because of unsafe publication, we know that it isn't the

      this.map =
          MapMakerInternalMap.createWithDummyValues(mapMaker.keyEquivalence(Equivalence.equals()));
    }

    @Override
    public E intern(E sample) {
      while (true) {
        // trying to read the canonical...
        @SuppressWarnings("rawtypes") // using raw types to avoid a bug in our nullness checker :(
        InternalEntry entry = map.getEntry(sample);
        if (entry != null) {

            }
        } else if (metadataFile.exists()) {
            try (InputStream input = Files.newInputStream(metadataFile.toPath())) {
                metadata = new Metadata(new MetadataStaxReader().read(input, false));
            }
        }

        boolean changed;

        // If file could not be found or was not valid, start from scratch
        if (metadata == null) {
            metadata = this.metadata;

	if err != nil {
		return nil, err
	}
	stream, err := algorithm.Stream(key.Plaintext)
	if err != nil {
		return nil, err
	}
	nonce := make([]byte, stream.NonceSize())
	if _, err := rand.Read(nonce); err != nil {
		return nil, err
	}

	const (
		MaxMetadataSize = 1 << 20 // max. size of the metadata
		Version         = 1
	)
	var (
		header [5]byte
		buffer bytes.Buffer
	)

# Convenient cache configurations
# Use a cache directory mounted to /tf/cache. Very useful!
build:sigbuild_local_cache --disk_cache=/tf/cache
# Use the public-access TF DevInfra cache (read only)
build:sigbuild_remote_cache --remote_cache="https://storage.googleapis.com/tensorflow-devinfra-bazel-cache/manylinux2014" --remote_upload_local_results=false

//     compress: true # S2/Snappy compressed archive
//     smallerThan: 5MiB # create archive for all objects smaller than 5MiB
//     skipErrs: false # skips any source side read() errors

// BatchJobSnowball describes the snowball feature when replicating objects from a local source to a remote target
type BatchJobSnowball struct {
	line, col   int

// ----------
// This implementation of the GET operation applies lambda functions and returns the
// response generated via the lambda functions. To use this API, you must have READ access
// to the object.
func (api objectAPIHandlers) GetObjectLambdaHandler(w http.ResponseWriter, r *http.Request) {
	ctx := newContext(r, w, "GetObjectLambda")

	var sub *subHandlerID
	if m.Payload == nil {
		m.Payload = GetByteBuffer()[:0]
	}
	h, err := m.UnmarshalMsg(b)
	if err != nil {
		return nil, nil, fmt.Errorf("read write: %v", err)
	}
	if len(m.Payload) == 0 && m.Flags&FlagPayloadIsZero == 0 {
		PutByteBuffer(m.Payload)
		m.Payload = nil
	}
	if m.Flags&FlagCRCxxh3 != 0 {
		const hashLen = 4
		if len(h) < hashLen {