1 ===================== 2 Nanopb: API reference 3 ===================== 4 5 .. include :: menu.rst 6 7 .. contents :: 8 9 10 11 12 Compilation options 13 =================== 14 The following options can be specified in one of two ways: 15 16 1. Using the -D switch on the C compiler command line. 17 2. By #defining them at the top of pb.h. 18 19 You must have the same settings for the nanopb library and all code that 20 includes pb.h. 21 22 ============================ ================================================ 23 __BIG_ENDIAN__ Set this if your platform stores integers and 24 floats in big-endian format. Mixed-endian 25 systems (different layout for ints and floats) 26 are currently not supported. 27 PB_ENABLE_MALLOC Set this to enable dynamic allocation support 28 in the decoder. 29 PB_MAX_REQUIRED_FIELDS Maximum number of required fields to check for 30 presence. Default value is 64. Increases stack 31 usage 1 byte per every 8 fields. Compiler 32 warning will tell if you need this. 33 PB_FIELD_16BIT Add support for tag numbers > 255 and fields 34 larger than 255 bytes or 255 array entries. 35 Increases code size 3 bytes per each field. 36 Compiler error will tell if you need this. 37 PB_FIELD_32BIT Add support for tag numbers > 65535 and fields 38 larger than 65535 bytes or 65535 array entries. 39 Increases code size 9 bytes per each field. 40 Compiler error will tell if you need this. 41 PB_NO_ERRMSG Disables the support for error messages; only 42 error information is the true/false return 43 value. Decreases the code size by a few hundred 44 bytes. 45 PB_BUFFER_ONLY Disables the support for custom streams. Only 46 supports encoding and decoding with memory 47 buffers. Speeds up execution and decreases code 48 size slightly. 49 PB_OLD_CALLBACK_STYLE Use the old function signature (void\* instead 50 of void\*\*) for callback fields. This was the 51 default until nanopb-0.2.1. 52 PB_SYSTEM_HEADER Replace the standard header files with a single 53 header file. It should define all the required 54 functions and typedefs listed on the 55 `overview page`_. Value must include quotes, 56 for example *#define PB_SYSTEM_HEADER "foo.h"*. 57 ============================ ================================================ 58 59 The PB_MAX_REQUIRED_FIELDS, PB_FIELD_16BIT and PB_FIELD_32BIT settings allow 60 raising some datatype limits to suit larger messages. Their need is recognized 61 automatically by C-preprocessor #if-directives in the generated .pb.h files. 62 The default setting is to use the smallest datatypes (least resources used). 63 64 .. _`overview page`: index.html#compiler-requirements 65 66 67 Proto file options 68 ================== 69 The generator behaviour can be adjusted using these options, defined in the 70 'nanopb.proto' file in the generator folder: 71 72 ============================ ================================================ 73 max_size Allocated size for *bytes* and *string* fields. 74 max_count Allocated number of entries in arrays 75 (*repeated* fields). 76 type Type of the generated field. Default value 77 is *FT_DEFAULT*, which selects automatically. 78 You can use *FT_CALLBACK*, *FT_POINTER*, 79 *FT_STATIC* or *FT_IGNORE* to force a callback 80 field, a dynamically allocated field, a static 81 field or to completely ignore the field. 82 long_names Prefix the enum name to the enum value in 83 definitions, i.e. *EnumName_EnumValue*. Enabled 84 by default. 85 packed_struct Make the generated structures packed. 86 NOTE: This cannot be used on CPUs that break 87 on unaligned accesses to variables. 88 ============================ ================================================ 89 90 These options can be defined for the .proto files before they are converted 91 using the nanopb-generatory.py. There are three ways to define the options: 92 93 1. Using a separate .options file. 94 This is the preferred way as of nanopb-0.2.1, because it has the best 95 compatibility with other protobuf libraries. 96 2. Defining the options on the command line of nanopb_generator.py. 97 This only makes sense for settings that apply to a whole file. 98 3. Defining the options in the .proto file using the nanopb extensions. 99 This is the way used in nanopb-0.1, and will remain supported in the 100 future. It however sometimes causes trouble when using the .proto file 101 with other protobuf libraries. 102 103 The effect of the options is the same no matter how they are given. The most 104 common purpose is to define maximum size for string fields in order to 105 statically allocate them. 106 107 Defining the options in a .options file 108 --------------------------------------- 109 The preferred way to define options is to have a separate file 110 'myproto.options' in the same directory as the 'myproto.proto'. :: 111 112 # myproto.proto 113 message MyMessage { 114 required string name = 1; 115 repeated int32 ids = 4; 116 } 117 118 :: 119 120 # myproto.options 121 MyMessage.name max_size:40 122 MyMessage.ids max_count:5 123 124 The generator will automatically search for this file and read the 125 options from it. The file format is as follows: 126 127 * Lines starting with '#' or '//' are regarded as comments. 128 * Blank lines are ignored. 129 * All other lines should start with a field name pattern, followed by one or 130 more options. For example: *"MyMessage.myfield max_size:5 max_count:10"*. 131 * The field name pattern is matched against a string of form *'Message.field'*. 132 For nested messages, the string is *'Message.SubMessage.field'*. 133 * The field name pattern may use the notation recognized by Python fnmatch(): 134 135 - *\** matches any part of string, like 'Message.\*' for all fields 136 - *\?* matches any single character 137 - *[seq]* matches any of characters 's', 'e' and 'q' 138 - *[!seq]* matches any other character 139 140 * The options are written as *'option_name:option_value'* and several options 141 can be defined on same line, separated by whitespace. 142 * Options defined later in the file override the ones specified earlier, so 143 it makes sense to define wildcard options first in the file and more specific 144 ones later. 145 146 If preferred, the name of the options file can be set using the command line 147 switch *-f* to nanopb_generator.py. 148 149 Defining the options on command line 150 ------------------------------------ 151 The nanopb_generator.py has a simple command line option *-s OPTION:VALUE*. 152 The setting applies to the whole file that is being processed. 153 154 Defining the options in the .proto file 155 --------------------------------------- 156 The .proto file format allows defining custom options for the fields. 157 The nanopb library comes with *nanopb.proto* which does exactly that, allowing 158 you do define the options directly in the .proto file:: 159 160 import "nanopb.proto"; 161 162 message MyMessage { 163 required string name = 1 [(nanopb).max_size = 40]; 164 repeated int32 ids = 4 [(nanopb).max_count = 5]; 165 } 166 167 A small complication is that you have to set the include path of protoc so that 168 nanopb.proto can be found. This file, in turn, requires the file 169 *google/protobuf/descriptor.proto*. This is usually installed under 170 */usr/include*. Therefore, to compile a .proto file which uses options, use a 171 protoc command similar to:: 172 173 protoc -I/usr/include -Inanopb/generator -I. -omessage.pb message.proto 174 175 The options can be defined in file, message and field scopes:: 176 177 option (nanopb_fileopt).max_size = 20; // File scope 178 message Message 179 { 180 option (nanopb_msgopt).max_size = 30; // Message scope 181 required string fieldsize = 1 [(nanopb).max_size = 40]; // Field scope 182 } 183 184 185 186 187 188 189 190 191 192 pb.h 193 ==== 194 195 pb_type_t 196 --------- 197 Defines the encoder/decoder behaviour that should be used for a field. :: 198 199 typedef uint8_t pb_type_t; 200 201 The low-order nibble of the enumeration values defines the function that can be used for encoding and decoding the field data: 202 203 ==================== ===== ================================================ 204 LTYPE identifier Value Storage format 205 ==================== ===== ================================================ 206 PB_LTYPE_VARINT 0x00 Integer. 207 PB_LTYPE_SVARINT 0x01 Integer, zigzag encoded. 208 PB_LTYPE_FIXED32 0x02 32-bit integer or floating point. 209 PB_LTYPE_FIXED64 0x03 64-bit integer or floating point. 210 PB_LTYPE_BYTES 0x04 Structure with *size_t* field and byte array. 211 PB_LTYPE_STRING 0x05 Null-terminated string. 212 PB_LTYPE_SUBMESSAGE 0x06 Submessage structure. 213 ==================== ===== ================================================ 214 215 The bits 4-5 define whether the field is required, optional or repeated: 216 217 ==================== ===== ================================================ 218 HTYPE identifier Value Field handling 219 ==================== ===== ================================================ 220 PB_HTYPE_REQUIRED 0x00 Verify that field exists in decoded message. 221 PB_HTYPE_OPTIONAL 0x10 Use separate *has_<field>* boolean to specify 222 whether the field is present. 223 (Unless it is a callback) 224 PB_HTYPE_REPEATED 0x20 A repeated field with preallocated array. 225 Separate *<field>_count* for number of items. 226 (Unless it is a callback) 227 ==================== ===== ================================================ 228 229 The bits 6-7 define the how the storage for the field is allocated: 230 231 ==================== ===== ================================================ 232 ATYPE identifier Value Allocation method 233 ==================== ===== ================================================ 234 PB_ATYPE_STATIC 0x00 Statically allocated storage in the structure. 235 PB_ATYPE_CALLBACK 0x40 A field with dynamic storage size. Struct field 236 actually contains a pointer to a callback 237 function. 238 ==================== ===== ================================================ 239 240 241 pb_field_t 242 ---------- 243 Describes a single structure field with memory position in relation to others. The descriptions are usually autogenerated. :: 244 245 typedef struct _pb_field_t pb_field_t; 246 struct _pb_field_t { 247 uint8_t tag; 248 pb_type_t type; 249 uint8_t data_offset; 250 int8_t size_offset; 251 uint8_t data_size; 252 uint8_t array_size; 253 const void *ptr; 254 } pb_packed; 255 256 :tag: Tag number of the field or 0 to terminate a list of fields. 257 :type: LTYPE, HTYPE and ATYPE of the field. 258 :data_offset: Offset of field data, relative to the end of the previous field. 259 :size_offset: Offset of *bool* flag for optional fields or *size_t* count for arrays, relative to field data. 260 :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. 261 :array_size: Maximum number of entries in an array, if it is an array type. 262 :ptr: Pointer to default value for optional fields, or to submessage description for PB_LTYPE_SUBMESSAGE. 263 264 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*. 265 266 pb_bytes_array_t 267 ---------------- 268 An byte array with a field for storing the length:: 269 270 typedef struct { 271 size_t size; 272 uint8_t bytes[1]; 273 } pb_bytes_array_t; 274 275 In an actual array, the length of *bytes* may be different. 276 277 pb_callback_t 278 ------------- 279 Part of a message structure, for fields with type PB_HTYPE_CALLBACK:: 280 281 typedef struct _pb_callback_t pb_callback_t; 282 struct _pb_callback_t { 283 union { 284 bool (*decode)(pb_istream_t *stream, const pb_field_t *field, void **arg); 285 bool (*encode)(pb_ostream_t *stream, const pb_field_t *field, void * const *arg); 286 } funcs; 287 288 void *arg; 289 }; 290 291 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. 292 293 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*. 294 295 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. 296 297 pb_wire_type_t 298 -------------- 299 Protocol Buffers wire types. These are used with `pb_encode_tag`_. :: 300 301 typedef enum { 302 PB_WT_VARINT = 0, 303 PB_WT_64BIT = 1, 304 PB_WT_STRING = 2, 305 PB_WT_32BIT = 5 306 } pb_wire_type_t; 307 308 pb_extension_type_t 309 ------------------- 310 Defines the handler functions and auxiliary data for a field that extends 311 another message. Usually autogenerated by *nanopb_generator.py*:: 312 313 typedef struct { 314 bool (*decode)(pb_istream_t *stream, pb_extension_t *extension, 315 uint32_t tag, pb_wire_type_t wire_type); 316 bool (*encode)(pb_ostream_t *stream, const pb_extension_t *extension); 317 const void *arg; 318 } pb_extension_type_t; 319 320 In the normal case, the function pointers are *NULL* and the decoder and 321 encoder use their internal implementations. The internal implementations 322 assume that *arg* points to a *pb_field_t* that describes the field in question. 323 324 To implement custom processing of unknown fields, you can provide pointers 325 to your own functions. Their functionality is mostly the same as for normal 326 callback fields, except that they get called for any unknown field when decoding. 327 328 pb_extension_t 329 -------------- 330 Ties together the extension field type and the storage for the field value:: 331 332 typedef struct { 333 const pb_extension_type_t *type; 334 void *dest; 335 pb_extension_t *next; 336 } pb_extension_t; 337 338 :type: Pointer to the structure that defines the callback functions. 339 :dest: Pointer to the variable that stores the field value 340 (as used by the default extension callback functions.) 341 :next: Pointer to the next extension handler, or *NULL*. 342 343 PB_GET_ERROR 344 ------------ 345 Get the current error message from a stream, or a placeholder string if 346 there is no error message:: 347 348 #define PB_GET_ERROR(stream) (string expression) 349 350 This should be used for printing errors, for example:: 351 352 if (!pb_decode(...)) 353 { 354 printf("Decode failed: %s\n", PB_GET_ERROR(stream)); 355 } 356 357 The macro only returns pointers to constant strings (in code memory), 358 so that there is no need to release the returned pointer. 359 360 PB_RETURN_ERROR 361 --------------- 362 Set the error message and return false:: 363 364 #define PB_RETURN_ERROR(stream,msg) (sets error and returns false) 365 366 This should be used to handle error conditions inside nanopb functions 367 and user callback functions:: 368 369 if (error_condition) 370 { 371 PB_RETURN_ERROR(stream, "something went wrong"); 372 } 373 374 The *msg* parameter must be a constant string. 375 376 377 378 pb_encode.h 379 =========== 380 381 pb_ostream_from_buffer 382 ---------------------- 383 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. :: 384 385 pb_ostream_t pb_ostream_from_buffer(uint8_t *buf, size_t bufsize); 386 387 :buf: Memory buffer to write into. 388 :bufsize: Maximum number of bytes to write. 389 :returns: An output stream. 390 391 After writing, you can check *stream.bytes_written* to find out how much valid data there is in the buffer. 392 393 pb_write 394 -------- 395 Writes data to an output stream. Always use this function, instead of trying to call stream callback manually. :: 396 397 bool pb_write(pb_ostream_t *stream, const uint8_t *buf, size_t count); 398 399 :stream: Output stream to write to. 400 :buf: Pointer to buffer with the data to be written. 401 :count: Number of bytes to write. 402 :returns: True on success, false if maximum length is exceeded or an IO error happens. 403 404 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. 405 406 pb_encode 407 --------- 408 Encodes the contents of a structure as a protocol buffers message and writes it to output stream. :: 409 410 bool pb_encode(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct); 411 412 :stream: Output stream to write to. 413 :fields: A field description array, usually autogenerated. 414 :src_struct: Pointer to the data that will be serialized. 415 :returns: True on success, false on IO error, on detectable errors in field description, or if a field encoder returns false. 416 417 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. 418 419 pb_encode_delimited 420 ------------------- 421 Calculates the length of the message, encodes it as varint and then encodes the message. :: 422 423 bool pb_encode_delimited(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct); 424 425 (parameters are the same as for `pb_encode`_.) 426 427 A common way to indicate the message length in Protocol Buffers is to prefix it with a varint. 428 This function does this, and it is compatible with *parseDelimitedFrom* in Google's protobuf library. 429 430 .. sidebar:: Encoding fields manually 431 432 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. 433 434 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. 435 436 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. 437 438 pb_encode_tag 439 ------------- 440 Starts a field in the Protocol Buffers binary format: encodes the field number and the wire type of the data. :: 441 442 bool pb_encode_tag(pb_ostream_t *stream, pb_wire_type_t wiretype, int field_number); 443 444 :stream: Output stream to write to. 1-5 bytes will be written. 445 :wiretype: PB_WT_VARINT, PB_WT_64BIT, PB_WT_STRING or PB_WT_32BIT 446 :field_number: Identifier for the field, defined in the .proto file. You can get it from field->tag. 447 :returns: True on success, false on IO error. 448 449 pb_encode_tag_for_field 450 ----------------------- 451 Same as `pb_encode_tag`_, except takes the parameters from a *pb_field_t* structure. :: 452 453 bool pb_encode_tag_for_field(pb_ostream_t *stream, const pb_field_t *field); 454 455 :stream: Output stream to write to. 1-5 bytes will be written. 456 :field: Field description structure. Usually autogenerated. 457 :returns: True on success, false on IO error or unknown field type. 458 459 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. 460 461 Wire type mapping is as follows: 462 463 ========================= ============ 464 LTYPEs Wire type 465 ========================= ============ 466 VARINT, SVARINT PB_WT_VARINT 467 FIXED64 PB_WT_64BIT 468 STRING, BYTES, SUBMESSAGE PB_WT_STRING 469 FIXED32 PB_WT_32BIT 470 ========================= ============ 471 472 pb_encode_varint 473 ---------------- 474 Encodes a signed or unsigned integer in the varint_ format. Works for fields of type `bool`, `enum`, `int32`, `int64`, `uint32` and `uint64`:: 475 476 bool pb_encode_varint(pb_ostream_t *stream, uint64_t value); 477 478 :stream: Output stream to write to. 1-10 bytes will be written. 479 :value: Value to encode. Just cast e.g. int32_t directly to uint64_t. 480 :returns: True on success, false on IO error. 481 482 .. _varint: http://code.google.com/apis/protocolbuffers/docs/encoding.html#varints 483 484 pb_encode_svarint 485 ----------------- 486 Encodes a signed integer in the 'zig-zagged' format. Works for fields of type `sint32` and `sint64`:: 487 488 bool pb_encode_svarint(pb_ostream_t *stream, int64_t value); 489 490 (parameters are the same as for `pb_encode_varint`_ 491 492 pb_encode_string 493 ---------------- 494 Writes the length of a string as varint and then contents of the string. Works for fields of type `bytes` and `string`:: 495 496 bool pb_encode_string(pb_ostream_t *stream, const uint8_t *buffer, size_t size); 497 498 :stream: Output stream to write to. 499 :buffer: Pointer to string data. 500 :size: Number of bytes in the string. Pass `strlen(s)` for strings. 501 :returns: True on success, false on IO error. 502 503 pb_encode_fixed32 504 ----------------- 505 Writes 4 bytes to stream and swaps bytes on big-endian architectures. Works for fields of type `fixed32`, `sfixed32` and `float`:: 506 507 bool pb_encode_fixed32(pb_ostream_t *stream, const void *value); 508 509 :stream: Output stream to write to. 510 :value: Pointer to a 4-bytes large C variable, for example `uint32_t foo;`. 511 :returns: True on success, false on IO error. 512 513 pb_encode_fixed64 514 ----------------- 515 Writes 8 bytes to stream and swaps bytes on big-endian architecture. Works for fields of type `fixed64`, `sfixed64` and `double`:: 516 517 bool pb_encode_fixed64(pb_ostream_t *stream, const void *value); 518 519 :stream: Output stream to write to. 520 :value: Pointer to a 8-bytes large C variable, for example `uint64_t foo;`. 521 :returns: True on success, false on IO error. 522 523 pb_encode_submessage 524 -------------------- 525 Encodes a submessage field, including the size header for it. Works for fields of any message type:: 526 527 bool pb_encode_submessage(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct); 528 529 :stream: Output stream to write to. 530 :fields: Pointer to the autogenerated field description array for the submessage type, e.g. `MyMessage_fields`. 531 :src: Pointer to the structure where submessage data is. 532 :returns: True on success, false on IO errors, pb_encode errors or if submessage size changes between calls. 533 534 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. 535 536 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. 537 538 539 540 541 542 543 544 545 546 547 548 549 pb_decode.h 550 =========== 551 552 pb_istream_from_buffer 553 ---------------------- 554 Helper function for creating an input stream that reads data from a memory buffer. :: 555 556 pb_istream_t pb_istream_from_buffer(uint8_t *buf, size_t bufsize); 557 558 :buf: Pointer to byte array to read from. 559 :bufsize: Size of the byte array. 560 :returns: An input stream ready to use. 561 562 pb_read 563 ------- 564 Read data from input stream. Always use this function, don't try to call the stream callback directly. :: 565 566 bool pb_read(pb_istream_t *stream, uint8_t *buf, size_t count); 567 568 :stream: Input stream to read from. 569 :buf: Buffer to store the data to, or NULL to just read data without storing it anywhere. 570 :count: Number of bytes to read. 571 :returns: True on success, false if *stream->bytes_left* is less than *count* or if an IO error occurs. 572 573 End of file is signalled by *stream->bytes_left* being zero after pb_read returns false. 574 575 pb_decode 576 --------- 577 Read and decode all fields of a structure. Reads until EOF on input stream. :: 578 579 bool pb_decode(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct); 580 581 :stream: Input stream to read from. 582 :fields: A field description array. Usually autogenerated. 583 :dest_struct: Pointer to structure where data will be stored. 584 :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. 585 586 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. 587 588 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. 589 590 For optional fields, this function applies the default value and sets *has_<field>* to false if the field is not present. 591 592 If *PB_ENABLE_MALLOC* is defined, this function may allocate storage for any pointer type fields. 593 In this case, you have to call `pb_release`_ to release the memory after you are done with the message. 594 On error return `pb_decode` will release the memory itself. 595 596 pb_decode_noinit 597 ---------------- 598 Same as `pb_decode`_, except does not apply the default values to fields. :: 599 600 bool pb_decode_noinit(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct); 601 602 (parameters are the same as for `pb_decode`_.) 603 604 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. 605 606 In addition to decoding a single message, this function can be used to merge two messages, so that 607 values from previous message will remain if the new message does not contain a field. 608 609 This function *will not* release the message even on error return. If you use *PB_ENABLE_MALLOC*, 610 you will need to call `pb_release`_ yourself. 611 612 pb_decode_delimited 613 ------------------- 614 Same as `pb_decode`_, except that it first reads a varint with the length of the message. :: 615 616 bool pb_decode_delimited(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct); 617 618 (parameters are the same as for `pb_decode`_.) 619 620 A common method to indicate message size in Protocol Buffers is to prefix it with a varint. 621 This function is compatible with *writeDelimitedTo* in the Google's Protocol Buffers library. 622 623 pb_release 624 ---------- 625 Releases any dynamically allocated fields. 626 627 void pb_release(const pb_field_t fields[], void *dest_struct); 628 629 :fields: A field description array. Usually autogenerated. 630 :dest_struct: Pointer to structure where data will be stored. 631 632 This function is only available if *PB_ENABLE_MALLOC* is defined. It will release any 633 pointer type fields in the structure and set the pointers to NULL. 634 635 pb_skip_varint 636 -------------- 637 Skip a varint_ encoded integer without decoding it. :: 638 639 bool pb_skip_varint(pb_istream_t *stream); 640 641 :stream: Input stream to read from. Will read 1 byte at a time until the MSB is clear. 642 :returns: True on success, false on IO error. 643 644 pb_skip_string 645 -------------- 646 Skip a varint-length-prefixed string. This means skipping a value with wire type PB_WT_STRING. :: 647 648 bool pb_skip_string(pb_istream_t *stream); 649 650 :stream: Input stream to read from. 651 :returns: True on success, false on IO error or length exceeding uint32_t. 652 653 pb_decode_tag 654 ------------- 655 Decode the tag that comes before field in the protobuf encoding:: 656 657 bool pb_decode_tag(pb_istream_t *stream, pb_wire_type_t *wire_type, int *tag, bool *eof); 658 659 :stream: Input stream to read from. 660 :wire_type: Pointer to variable where to store the wire type of the field. 661 :tag: Pointer to variable where to store the tag of the field. 662 :eof: Pointer to variable where to store end-of-file status. 663 :returns: True on success, false on error or EOF. 664 665 When the message (stream) ends, this function will return false and set *eof* to true. On other 666 errors, *eof* will be set to false. 667 668 pb_skip_field 669 ------------- 670 Remove the data for a field from the stream, without actually decoding it:: 671 672 bool pb_skip_field(pb_istream_t *stream, pb_wire_type_t wire_type); 673 674 :stream: Input stream to read from. 675 :wire_type: Type of field to skip. 676 :returns: True on success, false on IO error. 677 678 .. sidebar:: Decoding fields manually 679 680 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. 681 682 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. 683 684 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`_. 685 686 Finally, for decoding submessages in a callback, simply use `pb_decode`_ and pass it the *SubMessage_fields* descriptor array. 687 688 pb_decode_varint 689 ---------------- 690 Read and decode a varint_ encoded integer. :: 691 692 bool pb_decode_varint(pb_istream_t *stream, uint64_t *dest); 693 694 :stream: Input stream to read from. 1-10 bytes will be read. 695 :dest: Storage for the decoded integer. Value is undefined on error. 696 :returns: True on success, false if value exceeds uint64_t range or an IO error happens. 697 698 pb_decode_svarint 699 ----------------- 700 Similar to `pb_decode_varint`_, except that it performs zigzag-decoding on the value. This corresponds to the Protocol Buffers *sint32* and *sint64* datatypes. :: 701 702 bool pb_decode_svarint(pb_istream_t *stream, int64_t *dest); 703 704 (parameters are the same as `pb_decode_varint`_) 705 706 pb_decode_fixed32 707 ----------------- 708 Decode a *fixed32*, *sfixed32* or *float* value. :: 709 710 bool pb_decode_fixed32(pb_istream_t *stream, void *dest); 711 712 :stream: Input stream to read from. 4 bytes will be read. 713 :dest: Pointer to destination *int32_t*, *uint32_t* or *float*. 714 :returns: True on success, false on IO errors. 715 716 This function reads 4 bytes from the input stream. 717 On big endian architectures, it then reverses the order of the bytes. 718 Finally, it writes the bytes to *dest*. 719 720 pb_decode_fixed64 721 ----------------- 722 Decode a *fixed64*, *sfixed64* or *double* value. :: 723 724 bool pb_dec_fixed(pb_istream_t *stream, const pb_field_t *field, void *dest); 725 726 :stream: Input stream to read from. 8 bytes will be read. 727 :field: Not used. 728 :dest: Pointer to destination *int64_t*, *uint64_t* or *double*. 729 :returns: True on success, false on IO errors. 730 731 Same as `pb_decode_fixed32`_, except this reads 8 bytes. 732 733 pb_make_string_substream 734 ------------------------ 735 Decode the length for a field with wire type *PB_WT_STRING* and create a substream for reading the data. :: 736 737 bool pb_make_string_substream(pb_istream_t *stream, pb_istream_t *substream); 738 739 :stream: Original input stream to read the length and data from. 740 :substream: New substream that has limited length. Filled in by the function. 741 :returns: True on success, false if reading the length fails. 742 743 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. 744 745 pb_close_string_substream 746 ------------------------- 747 Close the substream created with `pb_make_string_substream`_. :: 748 749 void pb_close_string_substream(pb_istream_t *stream, pb_istream_t *substream); 750 751 :stream: Original input stream to read the length and data from. 752 :substream: Substream to close 753 754 This function copies back the state from the substream to the parent stream. 755 It must be called after done with the substream. 756
