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+/* Copyright (c) 2001 Matej Pfajfar.
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+ * Copyright (c) 2001-2004, Roger Dingledine.
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+ * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
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+ * Copyright (c) 2007-2017, The Tor Project, Inc. */
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+/* See LICENSE for licensing information */
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+
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+#ifndef DOWNLOAD_STATUS_ST_H
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+#define DOWNLOAD_STATUS_ST_H
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+
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+/** Information about our plans for retrying downloads for a downloadable
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+ * directory object.
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+ * Each type of downloadable directory object has a corresponding retry
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+ * <b>schedule</b>, which can be different depending on whether the object is
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+ * being downloaded from an authority or a mirror (<b>want_authority</b>).
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+ * <b>next_attempt_at</b> contains the next time we will attempt to download
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+ * the object.
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+ * For schedules that <b>increment_on</b> failure, <b>n_download_failures</b>
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+ * is used to determine the position in the schedule. (Each schedule is a
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+ * smartlist of integer delays, parsed from a CSV option.) Every time a
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+ * connection attempt fails, <b>n_download_failures</b> is incremented,
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+ * the new delay value is looked up from the schedule, and
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+ * <b>next_attempt_at</b> is set delay seconds from the time the previous
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+ * connection failed. Therefore, at most one failure-based connection can be
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+ * in progress for each download_status_t.
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+ * For schedules that <b>increment_on</b> attempt, <b>n_download_attempts</b>
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+ * is used to determine the position in the schedule. Every time a
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+ * connection attempt is made, <b>n_download_attempts</b> is incremented,
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+ * the new delay value is looked up from the schedule, and
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+ * <b>next_attempt_at</b> is set delay seconds from the time the previous
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+ * connection was attempted. Therefore, multiple concurrent attempted-based
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+ * connections can be in progress for each download_status_t.
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+ * After an object is successfully downloaded, any other concurrent connections
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+ * are terminated. A new schedule which starts at position 0 is used for
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+ * subsequent downloads of the same object.
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+ */
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+struct download_status_t {
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+ time_t next_attempt_at; /**< When should we try downloading this object
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+ * again? */
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+ uint8_t n_download_failures; /**< Number of failed downloads of the most
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+ * recent object, since the last success. */
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+ uint8_t n_download_attempts; /**< Number of (potentially concurrent) attempts
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+ * to download the most recent object, since
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+ * the last success. */
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+ download_schedule_bitfield_t schedule : 8; /**< What kind of object is being
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+ * downloaded? This determines the
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+ * schedule used for the download.
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+ */
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+ download_want_authority_bitfield_t want_authority : 1; /**< Is the download
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+ * happening from an authority
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+ * or a mirror? This determines
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+ * the schedule used for the
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+ * download. */
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+ download_schedule_increment_bitfield_t increment_on : 1; /**< does this
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+ * schedule increment on each attempt,
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+ * or after each failure? */
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+ uint8_t last_backoff_position; /**< number of attempts/failures, depending
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+ * on increment_on, when we last recalculated
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+ * the delay. Only updated if backoff
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+ * == 1. */
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+ int last_delay_used; /**< last delay used for random exponential backoff;
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+ * only updated if backoff == 1 */
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+};
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+
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+#endif
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+
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