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