code: func mutualCipherSuite(have []uint16, want uint16) *cipherSuite {
  	for _, id := range have {
  		if id == want {
  			for _, suite := range cipherSuites {
  				if suite.id == want {
  					return suite
  				}
  			}
  			return nil
  		}
  	}
  	return nil
  }
docs: // mutualCipherSuite returns a cipherSuite given a list of supported
  // ciphersuites and the id requested by the peer.