14 Defines the encoder/decoder behaviour that should be used for a field. ::
16 typedef enum { ... } pb_type_t;
18 The low-order byte of the enumeration values defines the function that can be used for encoding and decoding the field data:
20 ==================== ===== ================================================
21 LTYPE identifier Value Storage format
22 ==================== ===== ================================================
23 PB_LTYPE_VARINT 0x00 Integer.
24 PB_LTYPE_SVARINT 0x01 Integer, zigzag encoded.
25 PB_LTYPE_FIXED 0x02 Integer or floating point.
26 PB_LTYPE_BYTES 0x03 Structure with *size_t* field and byte array.
27 PB_LTYPE_STRING 0x04 Null-terminated string.
28 PB_LTYPE_SUBMESSAGE 0x05 Submessage structure.
29 ==================== ===== ================================================
31 The high-order byte defines whether the field is required, optional, repeated or callback:
33 ==================== ===== ================================================
34 HTYPE identifier Value Field handling
35 ==================== ===== ================================================
36 PB_HTYPE_REQUIRED 0x00 Verify that field exists in decoded message.
37 PB_HTYPE_OPTIONAL 0x10 Use separate *has_<field>* boolean to specify
38 whether the field is present.
39 PB_HTYPE_ARRAY 0x20 A repeated field with preallocated array.
40 Separate *<field>_count* for number of items.
41 PB_HTYPE_CALLBACK 0x30 A field with dynamic storage size, data is
42 actually a pointer to a structure containing a
44 ==================== ===== ================================================
48 Describes a single structure field with memory position in relation to others. The descriptions are usually autogenerated. ::
50 typedef struct _pb_field_t pb_field_t;
61 :tag: Tag number of the field or 0 to terminate a list of fields.
62 :type: LTYPE and HTYPE of the field.
63 :data_offset: Offset of field data, relative to the end of the previous field.
64 :size_offset: Offset of *bool* flag for optional fields or *size_t* count for arrays, relative to field data.
65 :data_size: Size of a single data entry, in bytes. For PB_LTYPE_BYTES, the size of the byte array inside the containing structure. For PB_HTYPE_CALLBACK, size of the C data type if known.
66 :array_size: Maximum number of entries in an array, if it is an array type.
67 :ptr: Pointer to default value for optional fields, or to submessage description for PB_LTYPE_SUBMESSAGE.
69 The *uint8_t* datatypes limit the maximum size of a single item to 255 bytes and arrays to 255 items. Compiler will warn "Initializer too large for type" if the limits are exceeded. The types can be changed to larger ones if necessary.
73 An byte array with a field for storing the length::
80 In an actual array, the length of *bytes* may be different.
84 Part of a message structure, for fields with type PB_HTYPE_CALLBACK::
86 typedef struct _pb_callback_t pb_callback_t;
87 struct _pb_callback_t {
89 bool (*decode)(pb_istream_t *stream, const pb_field_t *field, void *arg);
90 bool (*encode)(pb_ostream_t *stream, const pb_field_t *field, const void *arg);
96 The *arg* is passed to the callback when calling. It can be used to store any information that the callback might need.
98 When calling `pb_encode`_, *funcs.encode* is used, and similarly when calling `pb_decode`_, *funcs.decode* is used. The function pointers are stored in the same memory location but are of incompatible types. You can set the function pointer to NULL to skip the field.
102 Protocol Buffers wire types. These are used with `pb_encode_tag`_. ::
114 pb_ostream_from_buffer
115 ----------------------
116 Constructs an output stream for writing into a memory buffer. This is just a helper function, it doesn't do anything you couldn't do yourself in a callback function. It uses an internal callback that stores the pointer in stream *state* field. ::
118 pb_ostream_t pb_ostream_from_buffer(uint8_t *buf, size_t bufsize);
120 :buf: Memory buffer to write into.
121 :bufsize: Maximum number of bytes to write.
122 :returns: An output stream.
124 After writing, you can check *stream.bytes_written* to find out how much valid data there is in the buffer.
128 Writes data to an output stream. Always use this function, instead of trying to call stream callback manually. ::
130 bool pb_write(pb_ostream_t *stream, const uint8_t *buf, size_t count);
132 :stream: Output stream to write to.
133 :buf: Pointer to buffer with the data to be written.
134 :count: Number of bytes to write.
135 :returns: True on success, false if maximum length is exceeded or an IO error happens.
137 If an error happens, *bytes_written* is not incremented. Depending on the callback used, calling pb_write again after it has failed once may be dangerous. Nanopb itself never does this, instead it returns the error to user application. The builtin pb_ostream_from_buffer is safe to call again after failed write.
141 Encodes the contents of a structure as a protocol buffers message and writes it to output stream. ::
143 bool pb_encode(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct);
145 :stream: Output stream to write to.
146 :fields: A field description array, usually autogenerated.
147 :src_struct: Pointer to the data that will be serialized.
148 :returns: True on success, false on IO error, on detectable errors in field description, or if a field encoder returns false.
150 Normally pb_encode simply walks through the fields description array and serializes each field in turn. However, submessages must be serialized twice: first to calculate their size and then to actually write them to output. This causes some constraints for callback fields, which must return the same data on every call.
154 Encodes an unsigned integer in the varint_ format. ::
156 bool pb_encode_varint(pb_ostream_t *stream, uint64_t value);
158 :stream: Output stream to write to. 1-10 bytes will be written.
159 :value: Value to encode.
160 :returns: True on success, false on IO error.
162 .. _varint: http://code.google.com/apis/protocolbuffers/docs/encoding.html#varints
166 Starts a field in the Protocol Buffers binary format: encodes the field number and the wire type of the data. ::
168 bool pb_encode_tag(pb_ostream_t *stream, pb_wire_type_t wiretype, int field_number);
170 :stream: Output stream to write to. 1-5 bytes will be written.
171 :wiretype: PB_WT_VARINT, PB_WT_64BIT, PB_WT_STRING or PB_WT_32BIT
172 :field_number: Identifier for the field, defined in the .proto file.
173 :returns: True on success, false on IO error.
175 pb_encode_tag_for_field
176 -----------------------
177 Same as `pb_encode_tag`_, except takes the parameters from a *pb_field_t* structure. ::
179 bool pb_encode_tag_for_field(pb_ostream_t *stream, const pb_field_t *field);
181 :stream: Output stream to write to. 1-5 bytes will be written.
182 :field: Field description structure. Usually autogenerated.
183 :returns: True on success, false on IO error or unknown field type.
185 This function only considers the LTYPE of the field. You can use it from your field callbacks, because the source generator writes correct LTYPE also for callback type fields.
187 Wire type mapping is as follows:
189 ========================= ============
191 ========================= ============
192 VARINT, SVARINT PB_WT_VARINT
194 STRING, BYTES, SUBMESSAGE PB_WT_STRING
196 ========================= ============
200 Writes the length of a string as varint and then contents of the string. Used for writing fields with wire type PB_WT_STRING. ::
202 bool pb_encode_string(pb_ostream_t *stream, const uint8_t *buffer, size_t size);
204 :stream: Output stream to write to.
205 :buffer: Pointer to string data.
206 :size: Number of bytes in the string.
207 :returns: True on success, false on IO error.
209 .. sidebar:: Field encoders
211 The functions with names beginning with *pb_enc_* are called field encoders. Each PB_LTYPE has an own field encoder, which handles translating from C data into Protocol Buffers data.
213 By using the *data_size* in the field description and by taking advantage of C casting rules, it has been possible to combine many data types to a single LTYPE. For example, *int32*, *uint32*, *int64*, *uint64*, *bool* and *enum* are all handled by *pb_enc_varint*.
215 Each field encoder only encodes the contents of the field. The tag must be encoded separately with `pb_encode_tag_for_field`_.
217 You can use the field encoders from your callbacks. Just be aware that the pb_field_t passed to the callback is not directly compatible with most of the encoders. Instead, you must create a new pb_field_t structure and set the data_size according to the data type you pass to *src*.
221 Field encoder for PB_LTYPE_VARINT. Takes the first *field->data_size* bytes from src, casts them as *uint64_t* and calls `pb_encode_varint`_. ::
223 bool pb_enc_varint(pb_ostream_t *stream, const pb_field_t *field, const void *src);
225 :stream: Output stream to write to.
226 :field: Field description structure. Only *data_size* matters.
227 :src: Pointer to start of the field data.
228 :returns: True on success, false on IO error.
232 Field encoder for PB_LTYPE_SVARINT. Similar to `pb_enc_varint`_, except first zig-zag encodes the value for more efficient negative number encoding. ::
234 bool pb_enc_svarint(pb_ostream_t *stream, const pb_field_t *field, const void *src);
236 (parameters are the same as for `pb_enc_varint`_)
238 The number is considered negative if the high-order bit of the value is set. On big endian computers, it is the highest bit of *\*src*. On little endian computers, it is the highest bit of *\*(src + field->data_size - 1)*.
242 Field encoder for PB_LTYPE_FIXED32. Writes the data in little endian order. On big endian computers, reverses the order of bytes. ::
244 bool pb_enc_fixed32(pb_ostream_t *stream, const pb_field_t *field, const void *src);
246 :stream: Output stream to write to.
248 :src: Pointer to start of the field data.
249 :returns: True on success, false on IO error.
253 Field encoder for PB_LTYPE_FIXED64. Writes the data in little endian order. On big endian computers, reverses the order of bytes. ::
255 bool pb_enc_fixed64(pb_ostream_t *stream, const pb_field_t *field, const void *src);
257 (parameters are the same as for `pb_enc_fixed32`_)
259 The same function is used for both integers and doubles. This breaks encoding of double values on architectures where they are mixed endian (primarily some arm processors with hardware FPU).
263 Field encoder for PB_LTYPE_BYTES. Just calls `pb_encode_string`_. ::
265 bool pb_enc_bytes(pb_ostream_t *stream, const pb_field_t *field, const void *src);
267 :stream: Output stream to write to.
269 :src: Pointer to a structure similar to pb_bytes_array_t.
270 :returns: True on success, false on IO error.
272 This function expects a pointer to a structure with a *size_t* field at start, and a variable sized byte array after it. The platform-specific field offset is inferred from *pb_bytes_array_t*, which has a byte array of size 1.
276 Field encoder for PB_LTYPE_STRING. Determines size of string with strlen() and then calls `pb_encode_string`_. ::
278 bool pb_enc_string(pb_ostream_t *stream, const pb_field_t *field, const void *src);
280 :stream: Output stream to write to.
282 :src: Pointer to a null-terminated string.
283 :returns: True on success, false on IO error.
287 Field encoder for PB_LTYPE_SUBMESSAGE. Calls `pb_encode`_ to perform the actual encoding. ::
289 bool pb_enc_submessage(pb_ostream_t *stream, const pb_field_t *field, const void *src);
291 :stream: Output stream to write to.
292 :field: Field description structure. The *ptr* field must be a pointer to a field description array for the submessage.
293 :src: Pointer to the structure where submessage data is.
294 :returns: True on success, false on IO errors, pb_encode errors or if submessage size changes between calls.
296 In Protocol Buffers format, the submessage size must be written before the submessage contents. Therefore, this function has to encode the submessage twice in order to know the size beforehand.
298 If the submessage contains callback fields, the callback function might misbehave and write out a different amount of data on the second call. This situation is recognized and *false* is returned, but it is up to the caller to ensure that the receiver of the message does not interpret it as valid data.
303 pb_istream_from_buffer
304 ----------------------
305 Helper function for creating an input stream that reads data from a memory buffer. ::
307 pb_istream_t pb_istream_from_buffer(uint8_t *buf, size_t bufsize);
309 :buf: Pointer to byte array to read from.
310 :bufsize: Size of the byte array.
311 :returns: An input stream ready to use.
315 Read data from input stream. Always use this function, don't try to call the stream callback directly. ::
317 bool pb_read(pb_istream_t *stream, uint8_t *buf, size_t count);
319 :stream: Input stream to read from.
320 :buf: Buffer to store the data to, or NULL to just read data without storing it anywhere.
321 :count: Number of bytes to read.
322 :returns: True on success, false if *stream->bytes_left* is less than *count* or if an IO error occurs.
324 End of file is signalled by *stream->bytes_left* being zero after pb_read returns false.
328 Read and decode a varint_ encoded integer. ::
330 bool pb_decode_varint(pb_istream_t *stream, uint64_t *dest);
332 :stream: Input stream to read from. 1-10 bytes will be read.
333 :dest: Storage for the decoded integer. Value is undefined on error.
334 :returns: True on success, false if value exceeds uint64_t range or an IO error happens.
338 Skip a varint_ encoded integer without decoding it. ::
340 bool pb_skip_varint(pb_istream_t *stream);
342 :stream: Input stream to read from. Will read 1 byte at a time until the MSB is clear.
343 :returns: True on success, false on IO error.
347 Skip a varint-length-prefixed string. This means skipping a value with wire type PB_WT_STRING. ::
349 bool pb_skip_string(pb_istream_t *stream);
351 :stream: Input stream to read from.
352 :returns: True on success, false on IO error or length exceeding uint32_t.
356 Read and decode all fields of a structure. Reads until EOF on input stream. ::
358 bool pb_decode(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct);
360 :stream: Input stream to read from.
361 :fields: A field description array. Usually autogenerated.
362 :dest_struct: Pointer to structure where data will be stored.
363 :returns: True on success, false on IO error, on detectable errors in field description, if a field encoder returns false or if a required field is missing.
365 In Protocol Buffers binary format, EOF is only allowed between fields. If it happens anywhere else, pb_decode will return *false*. If pb_decode returns false, you cannot trust any of the data in the structure.
367 In addition to EOF, the pb_decode implementation supports terminating a message with a 0 byte. This is compatible with the official Protocol Buffers because 0 is never a valid field tag.
369 For optional fields, this function applies the default value and sets *has_<field>* to false if the field is not present.
371 Because of memory concerns, the detection of missing required fields is not perfect if the structure contains more than 32 fields.
373 .. sidebar:: Field decoders
375 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.
377 Each field decoder reads and decodes a single value. For arrays, the decoder is called repeatedly.
379 You can use the decoders from your callbacks. Just be aware that the pb_field_t passed to the callback is not directly compatible
380 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
381 you pass to *dest*, e.g. *field.data_size = sizeof(int);*. Other fields in the *pb_field_t* don't matter.
383 The field decoder interface is a bit messy as a result of the interface required inside the nanopb library.
384 Eventually they may be replaced by separate wrapper functions with a more friendly interface.
388 Field decoder for PB_LTYPE_VARINT. ::
390 bool pb_dec_varint(pb_istream_t *stream, const pb_field_t *field, void *dest)
392 :stream: Input stream to read from. 1-10 bytes will be read.
393 :field: Field description structure. Only *field->data_size* matters.
394 :dest: Pointer to destination integer. Must have size of *field->data_size* bytes.
395 :returns: True on success, false on IO errors or if `pb_decode_varint`_ fails.
397 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.
401 Field decoder for PB_LTYPE_SVARINT. Similar to `pb_dec_varint`_, except that it performs zigzag-decoding on the value. ::
403 bool pb_dec_svarint(pb_istream_t *stream, const pb_field_t *field, void *dest);
405 (parameters are the same as `pb_dec_varint`_)
409 Field decoder for PB_LTYPE_FIXED32. ::
411 bool pb_dec_fixed32(pb_istream_t *stream, const pb_field_t *field, void *dest);
413 :stream: Input stream to read from. 4 bytes will be read.
415 :dest: Pointer to destination *int32_t*, *uint32_t* or *float*.
416 :returns: True on success, false on IO errors.
418 This function reads 4 bytes from the input stream.
419 On big endian architectures, it then reverses the order of the bytes.
420 Finally, it writes the bytes to *dest*.
424 Field decoder for PB_LTYPE_FIXED64. ::
426 bool pb_dec_fixed(pb_istream_t *stream, const pb_field_t *field, void *dest);
428 :stream: Input stream to read from. 8 bytes will be read.
430 :dest: Pointer to destination *int64_t*, *uint64_t* or *double*.
431 :returns: True on success, false on IO errors.
433 Same as `pb_dec_fixed32`_, except this reads 8 bytes.
437 Field decoder for PB_LTYPE_BYTES. Reads a length-prefixed block of bytes. ::
439 bool pb_dec_bytes(pb_istream_t *stream, const pb_field_t *field, void *dest);
441 **Note:** This is an internal function that is not useful in decoder callbacks. To read bytes fields in callbacks, use
442 *stream->bytes_left* and `pb_read`_.
444 :stream: Input stream to read from.
445 :field: Field description structure. Only *field->data_size* matters.
446 :dest: Pointer to a structure similar to pb_bytes_array_t.
447 :returns: True on success, false on IO error or if length exceeds the array size.
449 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*.
453 Field decoder for PB_LTYPE_STRING. Reads a length-prefixed string. ::
455 bool pb_dec_string(pb_istream_t *stream, const pb_field_t *field, void *dest);
457 **Note:** This is an internal function that is not useful in decoder callbacks. To read string fields in callbacks, use
458 *stream->bytes_left* and `pb_read`_.
460 :stream: Input stream to read from.
461 :field: Field description structure. Only *field->data_size* matters.
462 :dest: Pointer to a character array of size *field->data_size*.
463 :returns: True on success, false on IO error or if length exceeds the array size.
465 This function null-terminates the string when successful. On error, the contents of the destination array is undefined.
469 Field decoder for PB_LTYPE_SUBMESSAGE. Calls `pb_decode`_ to perform the actual decoding. ::
471 bool pb_dec_submessage(pb_istream_t *stream, const pb_field_t *field, void *dest)
473 **Note:** This is an internal function that is not useful in decoder callbacks. To read submessage fields in callbacks, use
474 `pb_decode`_ directly.
476 :stream: Input stream to read from.
477 :field: Field description structure. Only *field->ptr* matters.
478 :dest: Pointer to the destination structure.
479 :returns: True on success, false on IO error or if `pb_decode`_ fails.
481 The *field->ptr* should be a pointer to *pb_field_t* array describing the submessage.