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      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