14 The following options can be specified using -D switch given to the C compiler
15 when compiling the nanopb library and applications using it. You must have the
16 same settings for the nanopb library and all code that includes pb.h.
18 ============================ ================================================
19 __BIG_ENDIAN__ Set this if your platform stores integers and
20 floats in big-endian format. Mixed-endian
21 systems (different layout for ints and floats)
22 are currently not supported.
23 NANOPB_INTERNALS Set this to expose the field encoder functions
24 that are hidden since nanopb-0.1.3.
25 PB_MAX_REQUIRED_FIELDS Maximum number of required fields to check for
26 presence. Default value is 64. Increases stack
27 usage 1 byte per every 8 fields. Compiler
28 warning will tell if you need this.
29 PB_FIELD_16BIT Add support for tag numbers > 255 and fields
30 larger than 255 bytes or 255 array entries.
31 Increases code size 3 bytes per each field.
32 Compiler error will tell if you need this.
33 PB_FIELD_32BIT Add support for tag numbers > 65535 and fields
34 larger than 65535 bytes or 65535 array entries.
35 Increases code size 9 bytes per each field.
36 Compiler error will tell if you need this.
37 PB_NO_ERRMSG Disables the support for error messages; only
38 error information is the true/false return
39 value. Decreases the code size by a few hundred
41 PB_BUFFER_ONLY Disables the support for custom streams. Only
42 supports encoding and decoding with memory
43 buffers. Speeds up execution and decreases code
45 PB_OLD_CALLBACK_STYLE Use the old function signature (void\* instead
46 of void\*\*) for callback fields. This was the
47 default until nanopb-0.2.1.
48 ============================ ================================================
50 The PB_MAX_REQUIRED_FIELDS, PB_FIELD_16BIT and PB_FIELD_32BIT settings allow
51 raising some datatype limits to suit larger messages. Their need is recognized
52 automatically by C-preprocessor #if-directives in the generated .pb.h files.
53 The default setting is to use the smallest datatypes (least resources used).
60 The generator behaviour can be adjusted using these options, defined in the
61 'nanopb.proto' file in the generator folder:
63 ============================ ================================================
64 max_size Allocated size for 'bytes' and 'string' fields.
65 max_count Allocated number of entries in arrays
67 type Type of the generated field. Default value
68 is FT_DEFAULT, which selects automatically.
69 You can use FT_CALLBACK, FT_STATIC or FT_IGNORE
70 to force a callback field, a static field or
71 to completely ignore the field.
72 long_names Prefix the enum name to the enum value in
73 definitions, i.e. 'EnumName_EnumValue'. Enabled
75 packed_struct Make the generated structures packed.
76 NOTE: This cannot be used on CPUs that break
77 on unaligned accesses to variables.
78 ============================ ================================================
80 These options can be defined for the .proto files before they are converted
81 using the nanopb-generatory.py. There are three ways to define the options:
83 1. Using a separate .options file.
84 This is the preferred way as of nanopb-0.2.1, because it has the best
85 compatibility with other protobuf libraries.
86 2. Defining the options on the command line of nanopb_generator.py.
87 This only makes sense for settings that apply to a whole file.
88 3. Defining the options in the .proto file using the nanopb extensions.
89 This is the way used in nanopb-0.1, and will remain supported in the
90 future. It however sometimes causes trouble when using the .proto file
91 with other protobuf libraries.
93 The effect of the options is the same no matter how they are given. The most
94 common purpose is to define maximum size for string fields in order to
95 statically allocate them.
97 Defining the options in a .options file
98 ---------------------------------------
99 The preferred way to define options is to have a separate file
100 'myproto.options' in the same directory as the 'myproto.proto'. The
101 generator will automatically search for this file and read the options from
102 it. The file format is as follows:
104 * Lines starting with '#' or '//' are regarded as comments.
105 * Blank lines are ignored.
106 * All other lines should start with a field name pattern, followed by one or
107 more options. For example: *"MyMessage.myfield max_size:5 max_count:10"*.
108 * The field name pattern is matched against a string of form 'Message.field'.
109 For nested messages, the string is 'Message.SubMessage.field'.
110 * The field name pattern may use the notation recognized by Python fnmatch():
111 - \* matches any part of string, like 'Message.\*' for all fields
112 - \? matches any single character
113 - [seq] matches any of characters 's', 'e' and 'q'
114 - [!seq] matches any other character
115 * The options are written as 'option_name:option_value' and several options
116 can be defined on same line, separated by whitespace.
117 * Options defined later in the file override the ones specified earlier, so
118 it makes sense to define wildcard options first in the file and more specific
121 If preferred, the name of the options file can be set using the command line
122 switch '-f' to nanopb_generator.py.
124 Defining the options on command line
125 ------------------------------------
126 The nanopb_generator.py has a simple command line option '-s OPTION:VALUE'.
127 The setting applies to the whole file that is being processed.
129 Defining the options in the .proto file
130 ---------------------------------------
131 The .proto file format allows defining custom options for the fields.
132 The nanopb library comes with 'nanopb.proto' which does exactly that, allowing
133 you do define the options directly in the .proto file:
135 import "nanopb.proto";
136 required string name = 1 [(nanopb).max_size = 40];
137 repeated PhoneNumber phone = 4 [(nanopb).max_count = 5];
139 A small complication is that you have to set the include path of protoc so that
140 nanopb.proto can be found. This file, in turn, requires the file
141 *google/protobuf/descriptor.proto*. This is usually installed under
142 */usr/include*. Therefore, to compile a .proto file which uses options, use a
143 protoc command similar to::
145 protoc -I/usr/include -Inanopb/generator -I. -omessage.pb message.proto
147 The options can be defined in file, message and field scopes::
149 option (nanopb_fileopt).max_size = 20; // File scope
152 option (nanopb_msgopt).max_size = 30; // Message scope
153 required string fieldsize = 1 [(nanopb).max_size = 40]; // Field scope
169 Defines the encoder/decoder behaviour that should be used for a field. ::
171 typedef uint8_t pb_type_t;
173 The low-order nibble of the enumeration values defines the function that can be used for encoding and decoding the field data:
175 ==================== ===== ================================================
176 LTYPE identifier Value Storage format
177 ==================== ===== ================================================
178 PB_LTYPE_VARINT 0x00 Integer.
179 PB_LTYPE_SVARINT 0x01 Integer, zigzag encoded.
180 PB_LTYPE_FIXED32 0x02 32-bit integer or floating point.
181 PB_LTYPE_FIXED64 0x03 64-bit integer or floating point.
182 PB_LTYPE_BYTES 0x04 Structure with *size_t* field and byte array.
183 PB_LTYPE_STRING 0x05 Null-terminated string.
184 PB_LTYPE_SUBMESSAGE 0x06 Submessage structure.
185 ==================== ===== ================================================
187 The bits 4-5 define whether the field is required, optional or repeated:
189 ==================== ===== ================================================
190 HTYPE identifier Value Field handling
191 ==================== ===== ================================================
192 PB_HTYPE_REQUIRED 0x00 Verify that field exists in decoded message.
193 PB_HTYPE_OPTIONAL 0x10 Use separate *has_<field>* boolean to specify
194 whether the field is present.
195 (Unless it is a callback)
196 PB_HTYPE_REPEATED 0x20 A repeated field with preallocated array.
197 Separate *<field>_count* for number of items.
198 (Unless it is a callback)
199 ==================== ===== ================================================
201 The bits 6-7 define the how the storage for the field is allocated:
203 ==================== ===== ================================================
204 ATYPE identifier Value Allocation method
205 ==================== ===== ================================================
206 PB_ATYPE_STATIC 0x00 Statically allocated storage in the structure.
207 PB_ATYPE_CALLBACK 0x40 A field with dynamic storage size. Struct field
208 actually contains a pointer to a callback
210 ==================== ===== ================================================
215 Describes a single structure field with memory position in relation to others. The descriptions are usually autogenerated. ::
217 typedef struct _pb_field_t pb_field_t;
228 :tag: Tag number of the field or 0 to terminate a list of fields.
229 :type: LTYPE, HTYPE and ATYPE of the field.
230 :data_offset: Offset of field data, relative to the end of the previous field.
231 :size_offset: Offset of *bool* flag for optional fields or *size_t* count for arrays, relative to field data.
232 :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.
233 :array_size: Maximum number of entries in an array, if it is an array type.
234 :ptr: Pointer to default value for optional fields, or to submessage description for PB_LTYPE_SUBMESSAGE.
236 The *uint8_t* datatypes limit the maximum size of a single item to 255 bytes and arrays to 255 items. Compiler will give error if the values are too large. The types can be changed to larger ones by defining *PB_FIELD_16BIT*.
240 An byte array with a field for storing the length::
247 In an actual array, the length of *bytes* may be different.
251 Part of a message structure, for fields with type PB_HTYPE_CALLBACK::
253 typedef struct _pb_callback_t pb_callback_t;
254 struct _pb_callback_t {
256 bool (*decode)(pb_istream_t *stream, const pb_field_t *field, void **arg);
257 bool (*encode)(pb_ostream_t *stream, const pb_field_t *field, void * const *arg);
263 A pointer to the *arg* is passed to the callback when calling. It can be used to store any information that the callback might need.
265 Previously the function received just the value of *arg* instead of a pointer to it. This old behaviour can be enabled by defining *PB_OLD_CALLBACK_STYLE*.
267 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.
271 Protocol Buffers wire types. These are used with `pb_encode_tag`_. ::
293 pb_ostream_from_buffer
294 ----------------------
295 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. ::
297 pb_ostream_t pb_ostream_from_buffer(uint8_t *buf, size_t bufsize);
299 :buf: Memory buffer to write into.
300 :bufsize: Maximum number of bytes to write.
301 :returns: An output stream.
303 After writing, you can check *stream.bytes_written* to find out how much valid data there is in the buffer.
307 Writes data to an output stream. Always use this function, instead of trying to call stream callback manually. ::
309 bool pb_write(pb_ostream_t *stream, const uint8_t *buf, size_t count);
311 :stream: Output stream to write to.
312 :buf: Pointer to buffer with the data to be written.
313 :count: Number of bytes to write.
314 :returns: True on success, false if maximum length is exceeded or an IO error happens.
316 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.
320 Encodes the contents of a structure as a protocol buffers message and writes it to output stream. ::
322 bool pb_encode(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct);
324 :stream: Output stream to write to.
325 :fields: A field description array, usually autogenerated.
326 :src_struct: Pointer to the data that will be serialized.
327 :returns: True on success, false on IO error, on detectable errors in field description, or if a field encoder returns false.
329 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.
331 .. sidebar:: Encoding fields manually
333 The functions with names *pb_encode_\** 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_encode`_ will call your callback function, which in turn will call *pb_encode_\** functions repeatedly to write out values.
335 The tag of a field must be encoded separately with `pb_encode_tag_for_field`_. After that, you can call exactly one of the content-writing functions to encode the payload of the field. For repeated fields, you can repeat this process multiple times.
337 Writing packed arrays is a little bit more involved: you need to use `pb_encode_tag` and specify `PB_WT_STRING` as the wire type. Then you need to know exactly how much data you are going to write, and use `pb_encode_varint`_ to write out the number of bytes before writing the actual data. Substreams can be used to determine the number of bytes beforehand; see `pb_encode_submessage`_ source code for an example.
341 Starts a field in the Protocol Buffers binary format: encodes the field number and the wire type of the data. ::
343 bool pb_encode_tag(pb_ostream_t *stream, pb_wire_type_t wiretype, int field_number);
345 :stream: Output stream to write to. 1-5 bytes will be written.
346 :wiretype: PB_WT_VARINT, PB_WT_64BIT, PB_WT_STRING or PB_WT_32BIT
347 :field_number: Identifier for the field, defined in the .proto file. You can get it from field->tag.
348 :returns: True on success, false on IO error.
350 pb_encode_tag_for_field
351 -----------------------
352 Same as `pb_encode_tag`_, except takes the parameters from a *pb_field_t* structure. ::
354 bool pb_encode_tag_for_field(pb_ostream_t *stream, const pb_field_t *field);
356 :stream: Output stream to write to. 1-5 bytes will be written.
357 :field: Field description structure. Usually autogenerated.
358 :returns: True on success, false on IO error or unknown field type.
360 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.
362 Wire type mapping is as follows:
364 ========================= ============
366 ========================= ============
367 VARINT, SVARINT PB_WT_VARINT
369 STRING, BYTES, SUBMESSAGE PB_WT_STRING
371 ========================= ============
375 Encodes a signed or unsigned integer in the varint_ format. Works for fields of type `bool`, `enum`, `int32`, `int64`, `uint32` and `uint64`::
377 bool pb_encode_varint(pb_ostream_t *stream, uint64_t value);
379 :stream: Output stream to write to. 1-10 bytes will be written.
380 :value: Value to encode. Just cast e.g. int32_t directly to uint64_t.
381 :returns: True on success, false on IO error.
383 .. _varint: http://code.google.com/apis/protocolbuffers/docs/encoding.html#varints
387 Encodes a signed integer in the 'zig-zagged' format. Works for fields of type `sint32` and `sint64`::
389 bool pb_encode_svarint(pb_ostream_t *stream, int64_t value);
391 (parameters are the same as for `pb_encode_varint`_
395 Writes the length of a string as varint and then contents of the string. Works for fields of type `bytes` and `string`::
397 bool pb_encode_string(pb_ostream_t *stream, const uint8_t *buffer, size_t size);
399 :stream: Output stream to write to.
400 :buffer: Pointer to string data.
401 :size: Number of bytes in the string. Pass `strlen(s)` for strings.
402 :returns: True on success, false on IO error.
406 Writes 4 bytes to stream and swaps bytes on big-endian architectures. Works for fields of type `fixed32`, `sfixed32` and `float`::
408 bool pb_encode_fixed32(pb_ostream_t *stream, const void *value);
410 :stream: Output stream to write to.
411 :value: Pointer to a 4-bytes large C variable, for example `uint32_t foo;`.
412 :returns: True on success, false on IO error.
416 Writes 8 bytes to stream and swaps bytes on big-endian architecture. Works for fields of type `fixed64`, `sfixed64` and `double`::
418 bool pb_encode_fixed64(pb_ostream_t *stream, const void *value);
420 :stream: Output stream to write to.
421 :value: Pointer to a 8-bytes large C variable, for example `uint64_t foo;`.
422 :returns: True on success, false on IO error.
426 Encodes a submessage field, including the size header for it. Works for fields of any message type::
428 bool pb_encode_submessage(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct);
430 :stream: Output stream to write to.
431 :fields: Pointer to the autogenerated field description array for the submessage type, e.g. `MyMessage_fields`.
432 :src: Pointer to the structure where submessage data is.
433 :returns: True on success, false on IO errors, pb_encode errors or if submessage size changes between calls.
435 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.
437 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 garbage will be written to the output before the problem is detected.
453 pb_istream_from_buffer
454 ----------------------
455 Helper function for creating an input stream that reads data from a memory buffer. ::
457 pb_istream_t pb_istream_from_buffer(uint8_t *buf, size_t bufsize);
459 :buf: Pointer to byte array to read from.
460 :bufsize: Size of the byte array.
461 :returns: An input stream ready to use.
465 Read data from input stream. Always use this function, don't try to call the stream callback directly. ::
467 bool pb_read(pb_istream_t *stream, uint8_t *buf, size_t count);
469 :stream: Input stream to read from.
470 :buf: Buffer to store the data to, or NULL to just read data without storing it anywhere.
471 :count: Number of bytes to read.
472 :returns: True on success, false if *stream->bytes_left* is less than *count* or if an IO error occurs.
474 End of file is signalled by *stream->bytes_left* being zero after pb_read returns false.
478 Read and decode all fields of a structure. Reads until EOF on input stream. ::
480 bool pb_decode(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct);
482 :stream: Input stream to read from.
483 :fields: A field description array. Usually autogenerated.
484 :dest_struct: Pointer to structure where data will be stored.
485 :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.
487 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.
489 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.
491 For optional fields, this function applies the default value and sets *has_<field>* to false if the field is not present.
495 Same as `pb_decode`_, except does not apply the default values to fields. ::
497 bool pb_decode_noinit(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct);
499 (parameters are the same as for `pb_decode`_.)
501 The destination structure should be filled with zeros before calling this function. Doing a *memset* manually can be slightly faster than using `pb_decode`_ if you don't need any default values.
505 Skip a varint_ encoded integer without decoding it. ::
507 bool pb_skip_varint(pb_istream_t *stream);
509 :stream: Input stream to read from. Will read 1 byte at a time until the MSB is clear.
510 :returns: True on success, false on IO error.
514 Skip a varint-length-prefixed string. This means skipping a value with wire type PB_WT_STRING. ::
516 bool pb_skip_string(pb_istream_t *stream);
518 :stream: Input stream to read from.
519 :returns: True on success, false on IO error or length exceeding uint32_t.
523 Decode the tag that comes before field in the protobuf encoding::
525 bool pb_decode_tag(pb_istream_t *stream, pb_wire_type_t *wire_type, int *tag, bool *eof);
527 :stream: Input stream to read from.
528 :wire_type: Pointer to variable where to store the wire type of the field.
529 :tag: Pointer to variable where to store the tag of the field.
530 :eof: Pointer to variable where to store end-of-file status.
531 :returns: True on success, false on error or EOF.
533 When the message (stream) ends, this function will return false and set *eof* to true. On other
534 errors, *eof* will be set to false.
538 Remove the data for a field from the stream, without actually decoding it::
540 bool pb_skip_field(pb_istream_t *stream, pb_wire_type_t wire_type);
542 :stream: Input stream to read from.
543 :wire_type: Type of field to skip.
544 :returns: True on success, false on IO error.
546 .. sidebar:: Decoding fields manually
548 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.
550 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.
552 For decoding strings and bytes fields, the length has already been decoded. You can therefore check the total length in *stream->bytes_left* and read the data using `pb_read`_.
554 Finally, for decoding submessages in a callback, simply use `pb_decode`_ and pass it the *SubMessage_fields* descriptor array.
558 Read and decode a varint_ encoded integer. ::
560 bool pb_decode_varint(pb_istream_t *stream, uint64_t *dest);
562 :stream: Input stream to read from. 1-10 bytes will be read.
563 :dest: Storage for the decoded integer. Value is undefined on error.
564 :returns: True on success, false if value exceeds uint64_t range or an IO error happens.
568 Similar to `pb_decode_varint`_, except that it performs zigzag-decoding on the value. This corresponds to the Protocol Buffers *sint32* and *sint64* datatypes. ::
570 bool pb_decode_svarint(pb_istream_t *stream, int64_t *dest);
572 (parameters are the same as `pb_decode_varint`_)
576 Decode a *fixed32*, *sfixed32* or *float* value. ::
578 bool pb_decode_fixed32(pb_istream_t *stream, void *dest);
580 :stream: Input stream to read from. 4 bytes will be read.
581 :dest: Pointer to destination *int32_t*, *uint32_t* or *float*.
582 :returns: True on success, false on IO errors.
584 This function reads 4 bytes from the input stream.
585 On big endian architectures, it then reverses the order of the bytes.
586 Finally, it writes the bytes to *dest*.
590 Decode a *fixed64*, *sfixed64* or *double* value. ::
592 bool pb_dec_fixed(pb_istream_t *stream, const pb_field_t *field, void *dest);
594 :stream: Input stream to read from. 8 bytes will be read.
596 :dest: Pointer to destination *int64_t*, *uint64_t* or *double*.
597 :returns: True on success, false on IO errors.
599 Same as `pb_decode_fixed32`_, except this reads 8 bytes.
601 pb_make_string_substream
602 ------------------------
603 Decode the length for a field with wire type *PB_WT_STRING* and create a substream for reading the data. ::
605 bool pb_make_string_substream(pb_istream_t *stream, pb_istream_t *substream);
607 :stream: Original input stream to read the length and data from.
608 :substream: New substream that has limited length. Filled in by the function.
609 :returns: True on success, false if reading the length fails.
611 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, and its callback function and state the same as the parent stream.
613 pb_close_string_substream
614 -------------------------
615 Close the substream created with `pb_make_string_substream`_. ::
617 void pb_close_string_substream(pb_istream_t *stream, pb_istream_t *substream);
619 :stream: Original input stream to read the length and data from.
620 :substream: Substream to close
622 This function copies back the state from the substream to the parent stream.
623 It must be called after done with the substream.