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367 lines
17 KiB
C++
367 lines
17 KiB
C++
/*
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* Copyright The Mbed TLS Contributors
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* SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
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*/
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/**
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* \file mps_reader.h
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*
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* \brief This file defines reader objects, which together with their
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* sibling writer objects form the basis for the communication
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* between the various layers of the Mbed TLS messaging stack,
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* as well as the communication between the messaging stack and
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* the (D)TLS handshake protocol implementation.
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*
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* Readers provide a means of transferring incoming data from
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* a 'producer' providing it in chunks of arbitrary size, to
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* a 'consumer' which fetches and processes it in chunks of
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* again arbitrary, and potentially different, size.
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*
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* Readers can thus be seen as datagram-to-stream converters,
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* and they abstract away the following two tasks from the user:
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* 1. The pointer arithmetic of stepping through a producer-
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* provided chunk in smaller chunks.
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* 2. The merging of incoming data chunks in case the
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* consumer requests data in larger chunks than what the
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* producer provides.
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*
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* The basic abstract flow of operation is the following:
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* - Initially, the reader is in 'producing mode'.
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* - The producer hands an incoming data buffer to the reader,
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* moving it from 'producing' to 'consuming' mode.
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* - The consumer subsequently fetches and processes the buffer
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* content. Once that's done -- or partially done and a consumer's
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* request can't be fulfilled -- the producer revokes the reader's
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* access to the incoming data buffer, putting the reader back to
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* producing mode.
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* - The producer subsequently gathers more incoming data and hands
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* it to the reader until it switches back to consuming mode
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* if enough data is available for the last consumer request to
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* be satisfiable.
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* - Repeat the above.
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*
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* The abstract states of the reader from the producer's and
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* consumer's perspective are as follows:
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*
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* - From the perspective of the consumer, the state of the
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* reader consists of the following:
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* - A byte stream representing (concatenation of) the data
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* received through calls to mbedtls_mps_reader_get(),
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* - A marker within that byte stream indicating which data
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* can be considered processed, and hence need not be retained,
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* when the reader is passed back to the producer via
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* mbedtls_mps_reader_reclaim().
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* The marker is set via mbedtls_mps_reader_commit()
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* which places it at the end of the current byte stream.
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* The consumer need not be aware of the distinction between consumer
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* and producer mode, because it only interfaces with the reader
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* when the latter is in consuming mode.
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*
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* - From the perspective of the producer, the reader's state is one of:
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* - Attached: The reader is in consuming mode.
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* - Unset: No incoming data buffer is currently managed by the reader,
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* and all previously handed incoming data buffers have been
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* fully processed. More data needs to be fed into the reader
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* via mbedtls_mps_reader_feed().
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*
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* - Accumulating: No incoming data buffer is currently managed by the
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* reader, but some data from the previous incoming data
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* buffer hasn't been processed yet and is internally
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* held back.
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* The Attached state belongs to consuming mode, while the Unset and
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* Accumulating states belong to producing mode.
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*
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* Transitioning from the Unset or Accumulating state to Attached is
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* done via successful calls to mbedtls_mps_reader_feed(), while
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* transitioning from Attached to either Unset or Accumulating (depending
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* on what has been processed) is done via mbedtls_mps_reader_reclaim().
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*
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* The following diagram depicts the producer-state progression:
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*
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* +------------------+ reclaim
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* | Unset +<-------------------------------------+ get
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* +--------|---------+ | +------+
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* | | | |
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* | | | |
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* | feed +---------+---+--+ |
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* +--------------------------------------> <---+
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* | Attached |
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* +--------------------------------------> <---+
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* | feed, enough data available +---------+---+--+ |
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* | to serve previous consumer request | | |
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* | | | |
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* +--------+---------+ | +------+
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* +----> Accumulating |<-------------------------------------+ commit
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* | +---+--------------+ reclaim, previous read request
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* | | couldn't be fulfilled
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* | |
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* +--------+
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* feed, need more data to serve
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* previous consumer request
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* |
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* |
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* producing mode | consuming mode
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* |
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*
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*/
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#ifndef MBEDTLS_READER_H
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#define MBEDTLS_READER_H
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#include <stdio.h>
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#include "mps_common.h"
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#include "mps_error.h"
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struct mbedtls_mps_reader;
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typedef struct mbedtls_mps_reader mbedtls_mps_reader;
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/*
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* Structure definitions
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*/
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struct mbedtls_mps_reader {
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unsigned char *frag; /*!< The fragment of incoming data managed by
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* the reader; it is provided to the reader
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* through mbedtls_mps_reader_feed(). The reader
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* does not own the fragment and does not
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* perform any allocation operations on it,
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* but does have read and write access to it.
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*
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* The reader is in consuming mode if
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* and only if \c frag is not \c NULL. */
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mbedtls_mps_stored_size_t frag_len;
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/*!< The length of the current fragment.
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* Must be 0 if \c frag == \c NULL. */
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mbedtls_mps_stored_size_t commit;
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/*!< The offset of the last commit, relative
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* to the first byte in the fragment, if
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* no accumulator is present. If an accumulator
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* is present, it is viewed as a prefix to the
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* current fragment, and this variable contains
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* an offset from the beginning of the accumulator.
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*
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* This is only used when the reader is in
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* consuming mode, i.e. \c frag != \c NULL;
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* otherwise, its value is \c 0. */
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mbedtls_mps_stored_size_t end;
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/*!< The offset of the end of the last chunk
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* passed to the user through a call to
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* mbedtls_mps_reader_get(), relative to the first
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* byte in the fragment, if no accumulator is
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* present. If an accumulator is present, it is
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* viewed as a prefix to the current fragment, and
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* this variable contains an offset from the
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* beginning of the accumulator.
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*
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* This is only used when the reader is in
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* consuming mode, i.e. \c frag != \c NULL;
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* otherwise, its value is \c 0. */
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mbedtls_mps_stored_size_t pending;
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/*!< The amount of incoming data missing on the
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* last call to mbedtls_mps_reader_get().
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* In particular, it is \c 0 if the last call
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* was successful.
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* If a reader is reclaimed after an
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* unsuccessful call to mbedtls_mps_reader_get(),
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* this variable is used to have the reader
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* remember how much data should be accumulated
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* so that the call to mbedtls_mps_reader_get()
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* succeeds next time.
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* This is only used when the reader is in
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* consuming mode, i.e. \c frag != \c NULL;
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* otherwise, its value is \c 0. */
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/* The accumulator is only needed if we need to be able to pause
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* the reader. A few bytes could be saved by moving this to a
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* separate struct and using a pointer here. */
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unsigned char *acc; /*!< The accumulator is used to gather incoming
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* data if a read-request via mbedtls_mps_reader_get()
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* cannot be served from the current fragment. */
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mbedtls_mps_stored_size_t acc_len;
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/*!< The total size of the accumulator. */
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mbedtls_mps_stored_size_t acc_available;
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/*!< The number of bytes currently gathered in
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* the accumulator. This is both used in
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* producing and in consuming mode:
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* While producing, it is increased until
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* it reaches the value of \c acc_remaining below.
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* While consuming, it is used to judge if a
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* get request can be served from the
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* accumulator or not.
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* Must not be larger than \c acc_len. */
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union {
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mbedtls_mps_stored_size_t acc_remaining;
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/*!< This indicates the amount of data still
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* to be gathered in the accumulator. It is
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* only used in producing mode.
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* Must be at most acc_len - acc_available. */
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mbedtls_mps_stored_size_t frag_offset;
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/*!< If an accumulator is present and in use, this
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* field indicates the offset of the current
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* fragment from the beginning of the
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* accumulator. If no accumulator is present
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* or the accumulator is not in use, this is \c 0.
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* It is only used in consuming mode.
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* Must not be larger than \c acc_available. */
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} acc_share;
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};
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/*
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* API organization:
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* A reader object is usually prepared and maintained
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* by some lower layer and passed for usage to an upper
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* layer, and the API naturally splits according to which
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* layer is supposed to use the respective functions.
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*/
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/*
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* Maintenance API (Lower layer)
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*/
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/**
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* \brief Initialize a reader object
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*
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* \param reader The reader to be initialized.
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* \param acc The buffer to be used as a temporary accumulator
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* in case get requests through mbedtls_mps_reader_get()
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* exceed the buffer provided by mbedtls_mps_reader_feed().
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* This buffer is owned by the caller and exclusive use
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* for reading and writing is given to the reader for the
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* duration of the reader's lifetime. It is thus the caller's
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* responsibility to maintain (and not touch) the buffer for
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* the lifetime of the reader, and to properly zeroize and
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* free the memory after the reader has been destroyed.
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* \param acc_len The size in Bytes of \p acc.
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*
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* \return \c 0 on success.
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* \return A negative \c MBEDTLS_ERR_READER_XXX error code on failure.
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*/
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int mbedtls_mps_reader_init(mbedtls_mps_reader *reader,
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unsigned char *acc,
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mbedtls_mps_size_t acc_len);
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/**
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* \brief Free a reader object
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*
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* \param reader The reader to be freed.
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*
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* \return \c 0 on success.
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* \return A negative \c MBEDTLS_ERR_READER_XXX error code on failure.
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*/
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int mbedtls_mps_reader_free(mbedtls_mps_reader *reader);
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/**
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* \brief Pass chunk of data for the reader to manage.
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*
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* \param reader The reader context to use. The reader must be
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* in producing mode.
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* \param buf The buffer to be managed by the reader.
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* \param buflen The size in Bytes of \p buffer.
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*
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* \return \c 0 on success. In this case, the reader will be
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* moved to consuming mode and obtains read access
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* of \p buf until mbedtls_mps_reader_reclaim()
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* is called. It is the responsibility of the caller
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* to ensure that the \p buf persists and is not changed
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* between successful calls to mbedtls_mps_reader_feed()
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* and mbedtls_mps_reader_reclaim().
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* \return \c MBEDTLS_ERR_MPS_READER_NEED_MORE if more input data is
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* required to fulfill a previous request to mbedtls_mps_reader_get().
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* In this case, the reader remains in producing mode and
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* takes no ownership of the provided buffer (an internal copy
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* is made instead).
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* \return Another negative \c MBEDTLS_ERR_READER_XXX error code on
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* different kinds of failures.
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*/
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int mbedtls_mps_reader_feed(mbedtls_mps_reader *reader,
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unsigned char *buf,
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mbedtls_mps_size_t buflen);
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/**
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* \brief Reclaim reader's access to the current input buffer.
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*
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* \param reader The reader context to use. The reader must be
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* in consuming mode.
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* \param paused If not \c NULL, the integer at address \p paused will be
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* modified to indicate whether the reader has been paused
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* (value \c 1) or not (value \c 0). Pausing happens if there
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* is uncommitted data and a previous request to
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* mbedtls_mps_reader_get() has exceeded the bounds of the
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* input buffer.
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*
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* \return \c 0 on success.
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* \return A negative \c MBEDTLS_ERR_READER_XXX error code on failure.
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*/
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int mbedtls_mps_reader_reclaim(mbedtls_mps_reader *reader,
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int *paused);
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/*
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* Usage API (Upper layer)
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*/
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/**
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* \brief Request data from the reader.
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*
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* \param reader The reader context to use. The reader must
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* be in consuming mode.
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* \param desired The desired amount of data to be read, in Bytes.
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* \param buffer The address to store the buffer pointer in.
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* This must not be \c NULL.
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* \param buflen The address to store the actual buffer
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* length in, or \c NULL.
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*
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* \return \c 0 on success. In this case, \c *buf holds the
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* address of a buffer of size \c *buflen
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* (if \c buflen != \c NULL) or \c desired
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* (if \c buflen == \c NULL). The user has read access
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* to the buffer and guarantee of stability of the data
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* until the next call to mbedtls_mps_reader_reclaim().
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* \return #MBEDTLS_ERR_MPS_READER_OUT_OF_DATA if there is not enough
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* data available to serve the get request. In this case, the
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* reader remains intact and in consuming mode, and the consumer
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* should retry the call after a successful cycle of
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* mbedtls_mps_reader_reclaim() and mbedtls_mps_reader_feed().
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* If, after such a cycle, the consumer requests a different
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* amount of data, the result is implementation-defined;
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* progress is guaranteed only if the same amount of data
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* is requested after a mbedtls_mps_reader_reclaim() and
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* mbedtls_mps_reader_feed() cycle.
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* \return Another negative \c MBEDTLS_ERR_READER_XXX error
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* code for different kinds of failure.
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*
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* \note Passing \c NULL as \p buflen is a convenient way to
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* indicate that fragmentation is not tolerated.
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* It's functionally equivalent to passing a valid
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* address as buflen and checking \c *buflen == \c desired
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* afterwards.
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*/
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int mbedtls_mps_reader_get(mbedtls_mps_reader *reader,
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mbedtls_mps_size_t desired,
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unsigned char **buffer,
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mbedtls_mps_size_t *buflen);
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/**
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* \brief Mark data obtained from mbedtls_mps_reader_get() as processed.
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*
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* This call indicates that all data received from prior calls to
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* mbedtls_mps_reader_get() has been or will have been
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* processed when mbedtls_mps_reader_reclaim() is called,
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* and thus need not be backed up.
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*
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* This function has no user observable effect until
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* mbedtls_mps_reader_reclaim() is called. In particular,
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* buffers received from mbedtls_mps_reader_get() remain
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* valid until mbedtls_mps_reader_reclaim() is called.
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*
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* \param reader The reader context to use.
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*
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* \return \c 0 on success.
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* \return A negative \c MBEDTLS_ERR_READER_XXX error code on failure.
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*
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*/
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int mbedtls_mps_reader_commit(mbedtls_mps_reader *reader);
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#endif /* MBEDTLS_READER_H */
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