mirror of
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350 lines
16 KiB
C
350 lines
16 KiB
C
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/*
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* Copyright The Mbed TLS Contributors
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* SPDX-License-Identifier: Apache-2.0
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*
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* Licensed under the Apache License, Version 2.0 (the "License"); you may
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* not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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* This file is part of mbed TLS (https://tls.mbed.org)
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*/
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/**
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* \file 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 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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* requests 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 reader until the latter 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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* From the perspective of the consumer, the state of the
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* reader is a potentially empty list of input buffers that
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* the reader has provided to the consumer.
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* New buffers can be requested through calls to mbedtls_reader_get(),
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* while previously obtained input buffers can be marked processed
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* through calls to mbedtls_reader_consume(), emptying the list of
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* input buffers and invalidating them from the consumer's perspective.
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* The consumer need not be aware of the distinction between consumer
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* and producer mode, because he 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 state of the reader
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* is one of the following:
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* - Attached: An incoming data buffer is currently
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* being managed by the reader, and
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* - Unset: No incoming data buffer is currently
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* managed by the reader, and all previously
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* handed incoming data buffers have been
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* fully processed.
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* - Accumulating: No incoming data buffer is currently
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* managed by the reader, but some data
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* from the previous incoming data buffer
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* hasn't been processed yet and is internally
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* held back.
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* The Unset and Accumulating states belong to producing mode,
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* while the Attached state belongs to consuming mode.
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*
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* Transitioning from Unset or Accumulating to Attached is
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* done via calls to mbedtls_reader_feed(), while transitioning
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* from Consuming to either Unset or Accumulating (depending
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* on what has been processed) is done via mbedtls_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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* +--------------------------------------> Attached <---+
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* | / |
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* +--------------------------------------> Consuming <---+
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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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#ifndef MBEDTLS_READER_H
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#define MBEDTLS_READER_H
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#include <stdio.h>
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#include "common.h"
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#include "error.h"
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struct mbedtls_reader;
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typedef struct mbedtls_reader mbedtls_reader;
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/*
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* Structure definitions
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*/
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struct mbedtls_reader
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{
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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_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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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 accumulator.
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* This is only used when the reader is in
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* consuming mode, i.e. frag != 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_reader_get(), relative to the first
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* byte in the accumulator.
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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_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_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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* before the reader can be passed back to
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* the user again.
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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_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_avail;
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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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* read request can be served from the
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* accumulator or not.
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* Must not be larger than acc_len. */
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union
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{
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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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/*!< This indicates the offset of the current
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* fragment from the beginning of the
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* accumulator.
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* It is only used in consuming mode.
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* Must not be larger than \c acc_avail. */
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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 read requests through mbedtls_reader_get()
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* exceed the buffer provided by mbedtls_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 reade 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_reader_init( mbedtls_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_reader_free( mbedtls_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 state.
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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 state, and ownership of \p buf
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* will be passed to the reader until mbedtls_reader_reclaim()
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* is called.
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* \return \c MBEDTLS_ERR_READER_NEED_MORE if more input data is
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* required to fulfill a previous request to mbedtls_reader_get().
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* In this case, the reader remains in producing state 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_reader_feed( mbedtls_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 producing state.
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* \param paused If not \c NULL, the intger 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_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_reader_reclaim( mbedtls_reader *reader,
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mbedtls_mps_size_t *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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* in consuming state.
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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 hass ownership
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* of the buffer until the next call to mbedtls_reader_commit().
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* or mbedtls_reader_reclaim().
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* \return #MBEDTLS_ERR_READER_OUT_OF_DATA if there is not enough
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* data available to serve the read request. In this case,
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* the reader remains intact, and additional data can be
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* provided by reclaiming the current input buffer via
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* mbedtls_reader_reclaim() and feeding a new one via
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* mbedtls_reader_feed().
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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_reader_get( mbedtls_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 Signal that all input buffers previously obtained
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* from mbedtls_writer_get() are fully processed.
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*
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* This function marks the previously fetched data as fully
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* processed and invalidates their respective buffers.
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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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* \warning Once this function is called, you must not use the
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* pointers corresponding to the committed data anymore.
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*
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*/
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int mbedtls_reader_commit( mbedtls_reader *reader );
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#endif /* MBEDTLS_READER_H */
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