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