pb_decode.h

/* pb_decode.h: Functions to decode protocol buffers. Depends on pb_decode.c.
 * The main function is pb_decode. You also need an input stream, and the
 * field descriptions created by nanopb_generator.py.
 */

#ifndef _PB_DECODE_H_
#define _PB_DECODE_H_

#include "pb.h"

#ifdef __cplusplus
extern "C" {
#endif

/* Structure for defining custom input streams. You will need to provide
 * a callback function to read the bytes from your storage, which can be
 * for example a file or a network socket.
 * 
 * The callback must conform to these rules:
 *
 * 1) Return false on IO errors. This will cause decoding to abort.
 * 2) You can use state to store your own data (e.g. buffer pointer),
 *    and rely on pb_read to verify that no-body reads past bytes_left.
 * 3) Your callback may be used with substreams, in which case bytes_left
 *    is different than from the main stream. Don't use bytes_left to compute
 *    any pointers.
 */
struct _pb_istream_t
{
#ifdef PB_BUFFER_ONLY
    /* Callback pointer is not used in buffer-only configuration.
     * Having an int pointer here allows binary compatibility but
     * gives an error if someone tries to assign callback function.
     */
    int *callback;
#else
    bool (*callback)(pb_istream_t *stream, uint8_t *buf, size_t count);
#endif

    void *state; /* Free field for use by callback implementation */
    size_t bytes_left;
    
#ifndef PB_NO_ERRMSG
    const char *errmsg;
#endif
};

/***************************
 * Main decoding functions *
 ***************************/
 
/* Decode a single protocol buffers message from input stream into a C structure.
 * Returns true on success, false on any failure.
 * The actual struct pointed to by dest must match the description in fields.
 * Callback fields of the destination structure must be initialized by caller.
 * All other fields will be initialized by this function.
 *
 * Example usage:
 *    MyMessage msg = {};
 *    uint8_t buffer[64];
 *    pb_istream_t stream;
 *    
 *    // ... read some data into buffer ...
 *
 *    stream = pb_istream_from_buffer(buffer, count);
 *    pb_decode(&stream, MyMessage_fields, &msg);
 */
bool pb_decode(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct);

/* Same as pb_decode, except does not initialize the destination structure
 * to default values. This is slightly faster if you need no default values
 * and just do memset(struct, 0, sizeof(struct)) yourself.
 *
 * This can also be used for 'merging' two messages, i.e. update only the
 * fields that exist in the new message.
 */
bool pb_decode_noinit(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct);

/* Same as pb_decode, except expects the stream to start with the message size
 * encoded as varint. Corresponds to parseDelimitedFrom() in Google's
 * protobuf API.
 */
bool pb_decode_delimited(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct);


/**************************************
 * Functions for manipulating streams *
 **************************************/

/* Create an input stream for reading from a memory buffer.
 *
 * Alternatively, you can use a custom stream that reads directly from e.g.
 * a file or a network socket.
 */
pb_istream_t pb_istream_from_buffer(uint8_t *buf, size_t bufsize);

/* Function to read from a pb_istream_t. You can use this if you need to
 * read some custom header data, or to read data in field callbacks.
 */
bool pb_read(pb_istream_t *stream, uint8_t *buf, size_t count);


/************************************************
 * Helper functions for writing field callbacks *
 ************************************************/

/* Decode the tag for the next field in the stream. Gives the wire type and
 * field tag. At end of the message, returns false and sets eof to true. */
bool pb_decode_tag(pb_istream_t *stream, pb_wire_type_t *wire_type, uint32_t *tag, bool *eof);

/* Skip the field payload data, given the wire type. */
bool pb_skip_field(pb_istream_t *stream, pb_wire_type_t wire_type);

/* Decode an integer in the varint format. This works for bool, enum, int32,
 * int64, uint32 and uint64 field types. */
bool pb_decode_varint(pb_istream_t *stream, uint64_t *dest);

/* Decode an integer in the zig-zagged svarint format. This works for sint32
 * and sint64. */
bool pb_decode_svarint(pb_istream_t *stream, int64_t *dest);

/* Decode a fixed32, sfixed32 or float value. You need to pass a pointer to
 * a 4-byte wide C variable. */
bool pb_decode_fixed32(pb_istream_t *stream, void *dest);

/* Decode a fixed64, sfixed64 or double value. You need to pass a pointer to
 * a 8-byte wide C variable. */
bool pb_decode_fixed64(pb_istream_t *stream, void *dest);

/* Make a limited-length substream for reading a PB_WT_STRING field. */
bool pb_make_string_substream(pb_istream_t *stream, pb_istream_t *substream);
void pb_close_string_substream(pb_istream_t *stream, pb_istream_t *substream);

#ifdef __cplusplus
} /* extern "C" */
#endif

#endif