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=========================
Nanopb: Encoding messages
=========================
The basic way to encode messages is to:
1) Write a callback function for whatever stream you want to write the message to.
2) Fill a structure with your data.
3) Call pb_encode with the stream, a pointer to *const pb_field_t* array and a pointer to your structure.
A few extra steps are necessary if you need to know the size of the message beforehand, or if you have dynamically sized fields.
Output streams
==============
This is the contents of *pb_ostream_t* structure::
typedef struct _pb_ostream_t pb_ostream_t;
struct _pb_ostream_t
{
bool (*callback)(pb_ostream_t *stream, const uint8_t *buf, size_t count);
void *state;
size_t max_size;
size_t bytes_written;
};
This, combined with the pb_write function, provides a light-weight abstraction
for whatever destination you want to write data to.
*callback* should be a pointer to your callback function. These are the rules for it:
1) Return false on IO errors. This will cause encoding to abort.
*
* 2) You can use state to store your own data (e.g. buffer pointer).
*
* 3) pb_write will update bytes_written after your callback runs.
*
* 4) Substreams will modify max_size and bytes_written. Don't use them to
* calculate any pointers.
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