federal habeas corpus

Although the circuit courts of the United States, and the several justices and judges thereof, have authority, under existing statutes, to discharge, upon habeas corpus, one held in custody by state authority in violation of the Constitution or of any treaty or law of the United States, the court, justice, or judge has a discretion as to the time and mode in which the power so conferred shall be exerted; and ... a Federal court or a Federal judge will not ordinarily interfere by habeas corpus with the regular course of procedure under state authority, but will leave the applicant for the writ of habeas corpus to exhaust the remedies afforded by the state for determining whether he is illegally restrained of his liberty.