You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: hkdf.go
    path of file: ./repos/go-starter-kit/vendor/golang.org/x/crypto/hkdf
    
    the code of the file until where you have to start completion: // Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package hkdf implements the HMAC-based Extract-and-Expand Key Derivation
// Function (HKDF) as defined in RFC 5869.
//
// HKDF is a cryptographic key derivation function (KDF) with the goal of
// expanding limited input keying material into one or more cryptographically
// strong secret keys.
//
// RFC 5869: https://tools.ietf.org/html/rfc5869
package hkdf // import "golang.org/x/crypto/hkdf"

import (
	"crypto/hma
    
func (f *hkdf) Read(p []byte) (int, error) {
	// Check whether enough data can be generated
	need := len(p)
	remains := len(f.cache) + int(255-f.counter+1)*f.size
	if remains < need {
		return 0, errors.New("hkdf: entropy limit reached")
	}
	// Read from the cache, if enough data is present
	n := copy(p, f.cache)
	p = p[n:]

	// Fill the buffer
	for len(p) > 0 {
		f.expander.Reset()
		f.expander.Write(f.prev)
		f.expander.Write(f.info)
		f.expander.Write([]byte{f.counter})
		f.prev = f.expander.Sum(f.prev[:0])
		f.counter++

		// Copy the new batch into p
		f.cache = f.prev
		n = copy(p, f.cache)
		p = p[n:]
	}
	// Save leftovers for next run
	f.cache = f.cache[n:]

	return need, nil
}