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Diffstat (limited to 'docs')
| -rw-r--r-- | docs/reference.rst | 118 |
1 files changed, 32 insertions, 86 deletions
diff --git a/docs/reference.rst b/docs/reference.rst index 3331c6d3..7dd08edd 100644 --- a/docs/reference.rst +++ b/docs/reference.rst @@ -320,16 +320,6 @@ In addition to EOF, the pb_decode implementation supports terminating a message For optional fields, this function applies the default value and sets *has_<field>* to false if the field is not present. -pb_decode_varint ----------------- -Read and decode a varint_ encoded integer. :: - - bool pb_decode_varint(pb_istream_t *stream, uint64_t *dest); - -:stream: Input stream to read from. 1-10 bytes will be read. -:dest: Storage for the decoded integer. Value is undefined on error. -:returns: True on success, false if value exceeds uint64_t range or an IO error happens. - pb_skip_varint -------------- Skip a varint_ encoded integer without decoding it. :: @@ -373,48 +363,41 @@ Remove the data for a field from the stream, without actually decoding it:: :wire_type: Type of field to skip. :returns: True on success, false on IO error. -.. sidebar:: Field decoders +.. sidebar:: Decoding fields manually - The functions with names beginning with *pb_dec_* are called field decoders. Each PB_LTYPE has an own field decoder, which handles translating from Protocol Buffers data to C data. + The functions with names beginning with *pb_decode_* are used when dealing with callback fields. The typical reason for using callbacks is to have an array of unlimited size. In that case, `pb_decode`_ will call your callback function repeatedly, which can then store the values into e.g. filesystem in the order received in. - Each field decoder reads and decodes a single value. For arrays, the decoder is called repeatedly. + For decoding numeric (including enumerated and boolean) values, use `pb_decode_varint`_, `pb_decode_svarint`_, `pb_decode_fixed32`_ and `pb_decode_fixed64`_. They take a pointer to a 32- or 64-bit C variable, which you may then cast to smaller datatype for storage. - You can use the decoders from your callbacks. Just be aware that the pb_field_t passed to the callback is not directly compatible - with the *varint* field decoders. Instead, you must create a new pb_field_t structure and set the data_size according to the data type - you pass to *dest*, e.g. *field.data_size = sizeof(int);*. Other fields in the *pb_field_t* don't matter. + For decoding strings and bytes fields, the length has already been decoded. You can therefore check the total length in *stream->state* and read the data using `pb_read`_. - The field decoder interface is a bit messy as a result of the interface required inside the nanopb library. - Eventually they may be replaced by separate wrapper functions with a more friendly interface. + Finally, for decoding submessages in a callback, simply use `pb_decode`_ and pass it the *SubMessage_fields* descriptor array. -pb_dec_varint -------------- -Field decoder for PB_LTYPE_VARINT. :: +pb_decode_varint +---------------- +Read and decode a varint_ encoded integer. :: - bool pb_dec_varint(pb_istream_t *stream, const pb_field_t *field, void *dest) + bool pb_decode_varint(pb_istream_t *stream, uint64_t *dest); :stream: Input stream to read from. 1-10 bytes will be read. -:field: Field description structure. Only *field->data_size* matters. -:dest: Pointer to destination integer. Must have size of *field->data_size* bytes. -:returns: True on success, false on IO errors or if `pb_decode_varint`_ fails. - -This function first calls `pb_decode_varint`_. It then copies the first bytes of the 64-bit result value to *dest*, or on big endian architectures, the last bytes. +:dest: Storage for the decoded integer. Value is undefined on error. +:returns: True on success, false if value exceeds uint64_t range or an IO error happens. -pb_dec_svarint --------------- -Field decoder for PB_LTYPE_SVARINT. Similar to `pb_dec_varint`_, except that it performs zigzag-decoding on the value. :: +pb_decode_svarint +----------------- +Similar to `pb_decode_varint`_, except that it performs zigzag-decoding on the value. This corresponds to the Protocol Buffers *sint32* and *sint64* datatypes. :: - bool pb_dec_svarint(pb_istream_t *stream, const pb_field_t *field, void *dest); + bool pb_decode_svarint(pb_istream_t *stream, int64_t *dest); -(parameters are the same as `pb_dec_varint`_) +(parameters are the same as `pb_decode_varint`_) -pb_dec_fixed32 --------------- -Field decoder for PB_LTYPE_FIXED32. :: +pb_decode_fixed32 +----------------- +Decode a *fixed32*, *sfixed32* or *float* value. :: - bool pb_dec_fixed32(pb_istream_t *stream, const pb_field_t *field, void *dest); + bool pb_decode_fixed32(pb_istream_t *stream, void *dest); :stream: Input stream to read from. 4 bytes will be read. -:field: Not used. :dest: Pointer to destination *int32_t*, *uint32_t* or *float*. :returns: True on success, false on IO errors. @@ -422,9 +405,9 @@ This function reads 4 bytes from the input stream. On big endian architectures, it then reverses the order of the bytes. Finally, it writes the bytes to *dest*. -pb_dec_fixed64 --------------- -Field decoder for PB_LTYPE_FIXED64. :: +pb_decode_fixed64 +----------------- +Decode a *fixed64*, *sfixed64* or *double* value. :: bool pb_dec_fixed(pb_istream_t *stream, const pb_field_t *field, void *dest); @@ -433,53 +416,16 @@ Field decoder for PB_LTYPE_FIXED64. :: :dest: Pointer to destination *int64_t*, *uint64_t* or *double*. :returns: True on success, false on IO errors. -Same as `pb_dec_fixed32`_, except this reads 8 bytes. - -pb_dec_bytes ------------- -Field decoder for PB_LTYPE_BYTES. Reads a length-prefixed block of bytes. :: - - bool pb_dec_bytes(pb_istream_t *stream, const pb_field_t *field, void *dest); +Same as `pb_decode_fixed32`_, except this reads 8 bytes. -**Note:** This is an internal function that is not useful in decoder callbacks. To read bytes fields in callbacks, use -*stream->bytes_left* and `pb_read`_. - -:stream: Input stream to read from. -:field: Field description structure. Only *field->data_size* matters. -:dest: Pointer to a structure similar to pb_bytes_array_t. -:returns: True on success, false on IO error or if length exceeds the array size. - -This function expects a pointer to a structure with a *size_t* field at start, and a variable sized byte array after it. It will deduce the maximum size of the array from *field->data_size*. - -pb_dec_string -------------- -Field decoder for PB_LTYPE_STRING. Reads a length-prefixed string. :: +pb_make_string_substream +------------------------ +Decode the length for a field with wire type *PB_WT_STRING* and create a substream for reading the data. :: - bool pb_dec_string(pb_istream_t *stream, const pb_field_t *field, void *dest); - -**Note:** This is an internal function that is not useful in decoder callbacks. To read string fields in callbacks, use -*stream->bytes_left* and `pb_read`_. - -:stream: Input stream to read from. -:field: Field description structure. Only *field->data_size* matters. -:dest: Pointer to a character array of size *field->data_size*. -:returns: True on success, false on IO error or if length exceeds the array size. - -This function null-terminates the string when successful. On error, the contents of the destination array is undefined. - -pb_dec_submessage ------------------ -Field decoder for PB_LTYPE_SUBMESSAGE. Calls `pb_decode`_ to perform the actual decoding. :: - - bool pb_dec_submessage(pb_istream_t *stream, const pb_field_t *field, void *dest) - -**Note:** This is an internal function that is not useful in decoder callbacks. To read submessage fields in callbacks, use -`pb_decode`_ directly. - -:stream: Input stream to read from. -:field: Field description structure. Only *field->ptr* matters. -:dest: Pointer to the destination structure. -:returns: True on success, false on IO error or if `pb_decode`_ fails. + bool pb_make_string_substream(pb_istream_t *stream, pb_istream_t *substream); -The *field->ptr* should be a pointer to *pb_field_t* array describing the submessage. +:stream: Original input stream to read the length and data from. +:substream: New substream that has limited length. Filled in by the function. +:returns: True on success, false if reading the length fails. +This function uses `pb_decode_varint`_ to read an integer from the stream. This is interpreted as a number of bytes, and the substream is set up so that its `bytes_left` is initially the same as the length. The substream has a wrapper callback that in turn reads from the parent stream. |