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