14 The following options can be specified in one of two ways:
16 1. Using the -D switch on the C compiler command line.
17 2. By #defining them at the top of pb.h.
19 You must have the same settings for the nanopb library and all code that
22 ============================ ================================================
23 PB_NO_PACKED_STRUCTS Disable packed structs. Increases RAM usage but
24 is necessary on some platforms that do not
25 support unaligned memory access.
26 PB_ENABLE_MALLOC Set this to enable dynamic allocation support
28 PB_MAX_REQUIRED_FIELDS Maximum number of required fields to check for
29 presence. Default value is 64. Increases stack
30 usage 1 byte per every 8 fields. Compiler
31 warning will tell if you need this.
32 PB_FIELD_16BIT Add support for tag numbers > 255 and fields
33 larger than 255 bytes or 255 array entries.
34 Increases code size 3 bytes per each field.
35 Compiler error will tell if you need this.
36 PB_FIELD_32BIT Add support for tag numbers > 65535 and fields
37 larger than 65535 bytes or 65535 array entries.
38 Increases code size 9 bytes per each field.
39 Compiler error will tell if you need this.
40 PB_NO_ERRMSG Disables the support for error messages; only
41 error information is the true/false return
42 value. Decreases the code size by a few hundred
44 PB_BUFFER_ONLY Disables the support for custom streams. Only
45 supports encoding and decoding with memory
46 buffers. Speeds up execution and decreases code
48 PB_OLD_CALLBACK_STYLE Use the old function signature (void\* instead
49 of void\*\*) for callback fields. This was the
50 default until nanopb-0.2.1.
51 PB_SYSTEM_HEADER Replace the standard header files with a single
52 header file. It should define all the required
53 functions and typedefs listed on the
54 `overview page`_. Value must include quotes,
55 for example *#define PB_SYSTEM_HEADER "foo.h"*.
56 ============================ ================================================
58 The PB_MAX_REQUIRED_FIELDS, PB_FIELD_16BIT and PB_FIELD_32BIT settings allow
59 raising some datatype limits to suit larger messages. Their need is recognized
60 automatically by C-preprocessor #if-directives in the generated .pb.h files.
61 The default setting is to use the smallest datatypes (least resources used).
63 .. _`overview page`: index.html#compiler-requirements
68 The generator behaviour can be adjusted using these options, defined in the
69 'nanopb.proto' file in the generator folder:
71 ============================ ================================================
72 max_size Allocated size for *bytes* and *string* fields.
73 max_count Allocated number of entries in arrays
75 int_size Override the integer type of a field.
76 (To use e.g. uint8_t to save RAM.)
77 type Type of the generated field. Default value
78 is *FT_DEFAULT*, which selects automatically.
79 You can use *FT_CALLBACK*, *FT_POINTER*,
80 *FT_STATIC* or *FT_IGNORE* to force a callback
81 field, a dynamically allocated field, a static
82 field or to completely ignore the field.
83 long_names Prefix the enum name to the enum value in
84 definitions, i.e. *EnumName_EnumValue*. Enabled
86 packed_struct Make the generated structures packed.
87 NOTE: This cannot be used on CPUs that break
88 on unaligned accesses to variables.
89 skip_message Skip the whole message from generation.
90 no_unions Generate 'oneof' fields as optional fields
92 msgid Specifies a unique id for this message type.
93 Can be used by user code as an identifier.
94 anonymous_oneof Generate 'oneof' fields as anonymous unions.
95 ============================ ================================================
97 These options can be defined for the .proto files before they are converted
98 using the nanopb-generatory.py. There are three ways to define the options:
100 1. Using a separate .options file.
101 This is the preferred way as of nanopb-0.2.1, because it has the best
102 compatibility with other protobuf libraries.
103 2. Defining the options on the command line of nanopb_generator.py.
104 This only makes sense for settings that apply to a whole file.
105 3. Defining the options in the .proto file using the nanopb extensions.
106 This is the way used in nanopb-0.1, and will remain supported in the
107 future. It however sometimes causes trouble when using the .proto file
108 with other protobuf libraries.
110 The effect of the options is the same no matter how they are given. The most
111 common purpose is to define maximum size for string fields in order to
112 statically allocate them.
114 Defining the options in a .options file
115 ---------------------------------------
116 The preferred way to define options is to have a separate file
117 'myproto.options' in the same directory as the 'myproto.proto'. ::
121 required string name = 1;
122 repeated int32 ids = 4;
128 MyMessage.name max_size:40
129 MyMessage.ids max_count:5
131 The generator will automatically search for this file and read the
132 options from it. The file format is as follows:
134 * Lines starting with '#' or '//' are regarded as comments.
135 * Blank lines are ignored.
136 * All other lines should start with a field name pattern, followed by one or
137 more options. For example: *"MyMessage.myfield max_size:5 max_count:10"*.
138 * The field name pattern is matched against a string of form *'Message.field'*.
139 For nested messages, the string is *'Message.SubMessage.field'*.
140 * The field name pattern may use the notation recognized by Python fnmatch():
142 - *\** matches any part of string, like 'Message.\*' for all fields
143 - *\?* matches any single character
144 - *[seq]* matches any of characters 's', 'e' and 'q'
145 - *[!seq]* matches any other character
147 * The options are written as *'option_name:option_value'* and several options
148 can be defined on same line, separated by whitespace.
149 * Options defined later in the file override the ones specified earlier, so
150 it makes sense to define wildcard options first in the file and more specific
153 If preferred, the name of the options file can be set using the command line
154 switch *-f* to nanopb_generator.py.
156 Defining the options on command line
157 ------------------------------------
158 The nanopb_generator.py has a simple command line option *-s OPTION:VALUE*.
159 The setting applies to the whole file that is being processed.
161 Defining the options in the .proto file
162 ---------------------------------------
163 The .proto file format allows defining custom options for the fields.
164 The nanopb library comes with *nanopb.proto* which does exactly that, allowing
165 you do define the options directly in the .proto file::
167 import "nanopb.proto";
170 required string name = 1 [(nanopb).max_size = 40];
171 repeated int32 ids = 4 [(nanopb).max_count = 5];
174 A small complication is that you have to set the include path of protoc so that
175 nanopb.proto can be found. This file, in turn, requires the file
176 *google/protobuf/descriptor.proto*. This is usually installed under
177 */usr/include*. Therefore, to compile a .proto file which uses options, use a
178 protoc command similar to::
180 protoc -I/usr/include -Inanopb/generator -I. -omessage.pb message.proto
182 The options can be defined in file, message and field scopes::
184 option (nanopb_fileopt).max_size = 20; // File scope
187 option (nanopb_msgopt).max_size = 30; // Message scope
188 required string fieldsize = 1 [(nanopb).max_size = 40]; // Field scope
204 Type used for storing byte-sized data, such as raw binary input and bytes-type fields. ::
206 typedef uint_least8_t pb_byte_t;
208 For most platforms this is equivalent to `uint8_t`. Some platforms however do not support
209 8-bit variables, and on those platforms 16 or 32 bits need to be used for each byte.
213 Type used to store the type of each field, to control the encoder/decoder behaviour. ::
215 typedef uint_least8_t pb_type_t;
217 The low-order nibble of the enumeration values defines the function that can be used for encoding and decoding the field data:
219 ==================== ===== ================================================
220 LTYPE identifier Value Storage format
221 ==================== ===== ================================================
222 PB_LTYPE_VARINT 0x00 Integer.
223 PB_LTYPE_SVARINT 0x01 Integer, zigzag encoded.
224 PB_LTYPE_FIXED32 0x02 32-bit integer or floating point.
225 PB_LTYPE_FIXED64 0x03 64-bit integer or floating point.
226 PB_LTYPE_BYTES 0x04 Structure with *size_t* field and byte array.
227 PB_LTYPE_STRING 0x05 Null-terminated string.
228 PB_LTYPE_SUBMESSAGE 0x06 Submessage structure.
229 ==================== ===== ================================================
231 The bits 4-5 define whether the field is required, optional or repeated:
233 ==================== ===== ================================================
234 HTYPE identifier Value Field handling
235 ==================== ===== ================================================
236 PB_HTYPE_REQUIRED 0x00 Verify that field exists in decoded message.
237 PB_HTYPE_OPTIONAL 0x10 Use separate *has_<field>* boolean to specify
238 whether the field is present.
239 (Unless it is a callback)
240 PB_HTYPE_REPEATED 0x20 A repeated field with preallocated array.
241 Separate *<field>_count* for number of items.
242 (Unless it is a callback)
243 ==================== ===== ================================================
245 The bits 6-7 define the how the storage for the field is allocated:
247 ==================== ===== ================================================
248 ATYPE identifier Value Allocation method
249 ==================== ===== ================================================
250 PB_ATYPE_STATIC 0x00 Statically allocated storage in the structure.
251 PB_ATYPE_CALLBACK 0x40 A field with dynamic storage size. Struct field
252 actually contains a pointer to a callback
254 ==================== ===== ================================================
259 Describes a single structure field with memory position in relation to others. The descriptions are usually autogenerated. ::
261 typedef struct pb_field_s pb_field_t;
265 pb_size_t data_offset;
266 pb_ssize_t size_offset;
268 pb_size_t array_size;
272 :tag: Tag number of the field or 0 to terminate a list of fields.
273 :type: LTYPE, HTYPE and ATYPE of the field.
274 :data_offset: Offset of field data, relative to the end of the previous field.
275 :size_offset: Offset of *bool* flag for optional fields or *size_t* count for arrays, relative to field data.
276 :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.
277 :array_size: Maximum number of entries in an array, if it is an array type.
278 :ptr: Pointer to default value for optional fields, or to submessage description for PB_LTYPE_SUBMESSAGE.
280 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*.
284 An byte array with a field for storing the length::
291 In an actual array, the length of *bytes* may be different.
295 Part of a message structure, for fields with type PB_HTYPE_CALLBACK::
297 typedef struct _pb_callback_t pb_callback_t;
298 struct _pb_callback_t {
300 bool (*decode)(pb_istream_t *stream, const pb_field_t *field, void **arg);
301 bool (*encode)(pb_ostream_t *stream, const pb_field_t *field, void * const *arg);
307 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.
309 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*.
311 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.
315 Protocol Buffers wire types. These are used with `pb_encode_tag`_. ::
326 Defines the handler functions and auxiliary data for a field that extends
327 another message. Usually autogenerated by *nanopb_generator.py*::
330 bool (*decode)(pb_istream_t *stream, pb_extension_t *extension,
331 uint32_t tag, pb_wire_type_t wire_type);
332 bool (*encode)(pb_ostream_t *stream, const pb_extension_t *extension);
334 } pb_extension_type_t;
336 In the normal case, the function pointers are *NULL* and the decoder and
337 encoder use their internal implementations. The internal implementations
338 assume that *arg* points to a *pb_field_t* that describes the field in question.
340 To implement custom processing of unknown fields, you can provide pointers
341 to your own functions. Their functionality is mostly the same as for normal
342 callback fields, except that they get called for any unknown field when decoding.
346 Ties together the extension field type and the storage for the field value::
349 const pb_extension_type_t *type;
351 pb_extension_t *next;
355 :type: Pointer to the structure that defines the callback functions.
356 :dest: Pointer to the variable that stores the field value
357 (as used by the default extension callback functions.)
358 :next: Pointer to the next extension handler, or *NULL*.
359 :found: Decoder sets this to true if the extension was found.
363 Get the current error message from a stream, or a placeholder string if
364 there is no error message::
366 #define PB_GET_ERROR(stream) (string expression)
368 This should be used for printing errors, for example::
372 printf("Decode failed: %s\n", PB_GET_ERROR(stream));
375 The macro only returns pointers to constant strings (in code memory),
376 so that there is no need to release the returned pointer.
380 Set the error message and return false::
382 #define PB_RETURN_ERROR(stream,msg) (sets error and returns false)
384 This should be used to handle error conditions inside nanopb functions
385 and user callback functions::
389 PB_RETURN_ERROR(stream, "something went wrong");
392 The *msg* parameter must be a constant string.
399 pb_ostream_from_buffer
400 ----------------------
401 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. ::
403 pb_ostream_t pb_ostream_from_buffer(pb_byte_t *buf, size_t bufsize);
405 :buf: Memory buffer to write into.
406 :bufsize: Maximum number of bytes to write.
407 :returns: An output stream.
409 After writing, you can check *stream.bytes_written* to find out how much valid data there is in the buffer.
413 Writes data to an output stream. Always use this function, instead of trying to call stream callback manually. ::
415 bool pb_write(pb_ostream_t *stream, const pb_byte_t *buf, size_t count);
417 :stream: Output stream to write to.
418 :buf: Pointer to buffer with the data to be written.
419 :count: Number of bytes to write.
420 :returns: True on success, false if maximum length is exceeded or an IO error happens.
422 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.
426 Encodes the contents of a structure as a protocol buffers message and writes it to output stream. ::
428 bool pb_encode(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct);
430 :stream: Output stream to write to.
431 :fields: A field description array, usually autogenerated.
432 :src_struct: Pointer to the data that will be serialized.
433 :returns: True on success, false on IO error, on detectable errors in field description, or if a field encoder returns false.
435 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.
439 Calculates the length of the message, encodes it as varint and then encodes the message. ::
441 bool pb_encode_delimited(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct);
443 (parameters are the same as for `pb_encode`_.)
445 A common way to indicate the message length in Protocol Buffers is to prefix it with a varint.
446 This function does this, and it is compatible with *parseDelimitedFrom* in Google's protobuf library.
448 .. sidebar:: Encoding fields manually
450 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.
452 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.
454 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.
458 Calculates the length of the encoded message. ::
460 bool pb_get_encoded_size(size_t *size, const pb_field_t fields[], const void *src_struct);
462 :size: Calculated size of the encoded message.
463 :fields: A field description array, usually autogenerated.
464 :src_struct: Pointer to the data that will be serialized.
465 :returns: True on success, false on detectable errors in field description or if a field encoder returns false.
469 Starts a field in the Protocol Buffers binary format: encodes the field number and the wire type of the data. ::
471 bool pb_encode_tag(pb_ostream_t *stream, pb_wire_type_t wiretype, uint32_t field_number);
473 :stream: Output stream to write to. 1-5 bytes will be written.
474 :wiretype: PB_WT_VARINT, PB_WT_64BIT, PB_WT_STRING or PB_WT_32BIT
475 :field_number: Identifier for the field, defined in the .proto file. You can get it from field->tag.
476 :returns: True on success, false on IO error.
478 pb_encode_tag_for_field
479 -----------------------
480 Same as `pb_encode_tag`_, except takes the parameters from a *pb_field_t* structure. ::
482 bool pb_encode_tag_for_field(pb_ostream_t *stream, const pb_field_t *field);
484 :stream: Output stream to write to. 1-5 bytes will be written.
485 :field: Field description structure. Usually autogenerated.
486 :returns: True on success, false on IO error or unknown field type.
488 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.
490 Wire type mapping is as follows:
492 ========================= ============
494 ========================= ============
495 VARINT, SVARINT PB_WT_VARINT
497 STRING, BYTES, SUBMESSAGE PB_WT_STRING
499 ========================= ============
503 Encodes a signed or unsigned integer in the varint_ format. Works for fields of type `bool`, `enum`, `int32`, `int64`, `uint32` and `uint64`::
505 bool pb_encode_varint(pb_ostream_t *stream, uint64_t value);
507 :stream: Output stream to write to. 1-10 bytes will be written.
508 :value: Value to encode. Just cast e.g. int32_t directly to uint64_t.
509 :returns: True on success, false on IO error.
511 .. _varint: http://code.google.com/apis/protocolbuffers/docs/encoding.html#varints
515 Encodes a signed integer in the 'zig-zagged' format. Works for fields of type `sint32` and `sint64`::
517 bool pb_encode_svarint(pb_ostream_t *stream, int64_t value);
519 (parameters are the same as for `pb_encode_varint`_
523 Writes the length of a string as varint and then contents of the string. Works for fields of type `bytes` and `string`::
525 bool pb_encode_string(pb_ostream_t *stream, const pb_byte_t *buffer, size_t size);
527 :stream: Output stream to write to.
528 :buffer: Pointer to string data.
529 :size: Number of bytes in the string. Pass `strlen(s)` for strings.
530 :returns: True on success, false on IO error.
534 Writes 4 bytes to stream and swaps bytes on big-endian architectures. Works for fields of type `fixed32`, `sfixed32` and `float`::
536 bool pb_encode_fixed32(pb_ostream_t *stream, const void *value);
538 :stream: Output stream to write to.
539 :value: Pointer to a 4-bytes large C variable, for example `uint32_t foo;`.
540 :returns: True on success, false on IO error.
544 Writes 8 bytes to stream and swaps bytes on big-endian architecture. Works for fields of type `fixed64`, `sfixed64` and `double`::
546 bool pb_encode_fixed64(pb_ostream_t *stream, const void *value);
548 :stream: Output stream to write to.
549 :value: Pointer to a 8-bytes large C variable, for example `uint64_t foo;`.
550 :returns: True on success, false on IO error.
554 Encodes a submessage field, including the size header for it. Works for fields of any message type::
556 bool pb_encode_submessage(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct);
558 :stream: Output stream to write to.
559 :fields: Pointer to the autogenerated field description array for the submessage type, e.g. `MyMessage_fields`.
560 :src: Pointer to the structure where submessage data is.
561 :returns: True on success, false on IO errors, pb_encode errors or if submessage size changes between calls.
563 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.
565 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.
581 pb_istream_from_buffer
582 ----------------------
583 Helper function for creating an input stream that reads data from a memory buffer. ::
585 pb_istream_t pb_istream_from_buffer(const pb_byte_t *buf, size_t bufsize);
587 :buf: Pointer to byte array to read from.
588 :bufsize: Size of the byte array.
589 :returns: An input stream ready to use.
593 Read data from input stream. Always use this function, don't try to call the stream callback directly. ::
595 bool pb_read(pb_istream_t *stream, pb_byte_t *buf, size_t count);
597 :stream: Input stream to read from.
598 :buf: Buffer to store the data to, or NULL to just read data without storing it anywhere.
599 :count: Number of bytes to read.
600 :returns: True on success, false if *stream->bytes_left* is less than *count* or if an IO error occurs.
602 End of file is signalled by *stream->bytes_left* being zero after pb_read returns false.
606 Read and decode all fields of a structure. Reads until EOF on input stream. ::
608 bool pb_decode(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct);
610 :stream: Input stream to read from.
611 :fields: A field description array. Usually autogenerated.
612 :dest_struct: Pointer to structure where data will be stored.
613 :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.
615 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.
617 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.
619 For optional fields, this function applies the default value and sets *has_<field>* to false if the field is not present.
621 If *PB_ENABLE_MALLOC* is defined, this function may allocate storage for any pointer type fields.
622 In this case, you have to call `pb_release`_ to release the memory after you are done with the message.
623 On error return `pb_decode` will release the memory itself.
627 Same as `pb_decode`_, except does not apply the default values to fields. ::
629 bool pb_decode_noinit(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct);
631 (parameters are the same as for `pb_decode`_.)
633 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.
635 In addition to decoding a single message, this function can be used to merge two messages, so that
636 values from previous message will remain if the new message does not contain a field.
638 This function *will not* release the message even on error return. If you use *PB_ENABLE_MALLOC*,
639 you will need to call `pb_release`_ yourself.
643 Same as `pb_decode`_, except that it first reads a varint with the length of the message. ::
645 bool pb_decode_delimited(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct);
647 (parameters are the same as for `pb_decode`_.)
649 A common method to indicate message size in Protocol Buffers is to prefix it with a varint.
650 This function is compatible with *writeDelimitedTo* in the Google's Protocol Buffers library.
654 Releases any dynamically allocated fields::
656 void pb_release(const pb_field_t fields[], void *dest_struct);
658 :fields: A field description array. Usually autogenerated.
659 :dest_struct: Pointer to structure where data is stored. If NULL, function does nothing.
661 This function is only available if *PB_ENABLE_MALLOC* is defined. It will release any
662 pointer type fields in the structure and set the pointers to NULL.
666 Decode the tag that comes before field in the protobuf encoding::
668 bool pb_decode_tag(pb_istream_t *stream, pb_wire_type_t *wire_type, uint32_t *tag, bool *eof);
670 :stream: Input stream to read from.
671 :wire_type: Pointer to variable where to store the wire type of the field.
672 :tag: Pointer to variable where to store the tag of the field.
673 :eof: Pointer to variable where to store end-of-file status.
674 :returns: True on success, false on error or EOF.
676 When the message (stream) ends, this function will return false and set *eof* to true. On other
677 errors, *eof* will be set to false.
681 Remove the data for a field from the stream, without actually decoding it::
683 bool pb_skip_field(pb_istream_t *stream, pb_wire_type_t wire_type);
685 :stream: Input stream to read from.
686 :wire_type: Type of field to skip.
687 :returns: True on success, false on IO error.
689 .. sidebar:: Decoding fields manually
691 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.
693 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.
695 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`_.
697 Finally, for decoding submessages in a callback, simply use `pb_decode`_ and pass it the *SubMessage_fields* descriptor array.
701 Read and decode a varint_ encoded integer. ::
703 bool pb_decode_varint(pb_istream_t *stream, uint64_t *dest);
705 :stream: Input stream to read from. 1-10 bytes will be read.
706 :dest: Storage for the decoded integer. Value is undefined on error.
707 :returns: True on success, false if value exceeds uint64_t range or an IO error happens.
711 Similar to `pb_decode_varint`_, except that it performs zigzag-decoding on the value. This corresponds to the Protocol Buffers *sint32* and *sint64* datatypes. ::
713 bool pb_decode_svarint(pb_istream_t *stream, int64_t *dest);
715 (parameters are the same as `pb_decode_varint`_)
719 Decode a *fixed32*, *sfixed32* or *float* value. ::
721 bool pb_decode_fixed32(pb_istream_t *stream, void *dest);
723 :stream: Input stream to read from. 4 bytes will be read.
724 :dest: Pointer to destination *int32_t*, *uint32_t* or *float*.
725 :returns: True on success, false on IO errors.
727 This function reads 4 bytes from the input stream.
728 On big endian architectures, it then reverses the order of the bytes.
729 Finally, it writes the bytes to *dest*.
733 Decode a *fixed64*, *sfixed64* or *double* value. ::
735 bool pb_decode_fixed64(pb_istream_t *stream, void *dest);
737 :stream: Input stream to read from. 8 bytes will be read.
738 :dest: Pointer to destination *int64_t*, *uint64_t* or *double*.
739 :returns: True on success, false on IO errors.
741 Same as `pb_decode_fixed32`_, except this reads 8 bytes.
743 pb_make_string_substream
744 ------------------------
745 Decode the length for a field with wire type *PB_WT_STRING* and create a substream for reading the data. ::
747 bool pb_make_string_substream(pb_istream_t *stream, pb_istream_t *substream);
749 :stream: Original input stream to read the length and data from.
750 :substream: New substream that has limited length. Filled in by the function.
751 :returns: True on success, false if reading the length fails.
753 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.
755 pb_close_string_substream
756 -------------------------
757 Close the substream created with `pb_make_string_substream`_. ::
759 void pb_close_string_substream(pb_istream_t *stream, pb_istream_t *substream);
761 :stream: Original input stream to read the length and data from.
762 :substream: Substream to close
764 This function copies back the state from the substream to the parent stream.
765 It must be called after done with the substream.