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 __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 NANOPB_INTERNALS Set this to expose the field encoder functions
28 that are hidden since nanopb-0.1.3.
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
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
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 ============================ ================================================
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).
64 .. _`overview page`: index.html#compiler-requirements
69 The generator behaviour can be adjusted using these options, defined in the
70 'nanopb.proto' file in the generator folder:
72 ============================ ================================================
73 max_size Allocated size for *bytes* and *string* fields.
74 max_count Allocated number of entries in arrays
76 type Type of the generated field. Default value
77 is *FT_DEFAULT*, which selects automatically.
78 You can use *FT_CALLBACK*, *FT_STATIC* or
79 *FT_IGNORE* to force a callback field, a static
80 field or to completely ignore the field.
81 long_names Prefix the enum name to the enum value in
82 definitions, i.e. *EnumName_EnumValue*. Enabled
84 packed_struct Make the generated structures packed.
85 NOTE: This cannot be used on CPUs that break
86 on unaligned accesses to variables.
87 ============================ ================================================
89 These options can be defined for the .proto files before they are converted
90 using the nanopb-generatory.py. There are three ways to define the options:
92 1. Using a separate .options file.
93 This is the preferred way as of nanopb-0.2.1, because it has the best
94 compatibility with other protobuf libraries.
95 2. Defining the options on the command line of nanopb_generator.py.
96 This only makes sense for settings that apply to a whole file.
97 3. Defining the options in the .proto file using the nanopb extensions.
98 This is the way used in nanopb-0.1, and will remain supported in the
99 future. It however sometimes causes trouble when using the .proto file
100 with other protobuf libraries.
102 The effect of the options is the same no matter how they are given. The most
103 common purpose is to define maximum size for string fields in order to
104 statically allocate them.
106 Defining the options in a .options file
107 ---------------------------------------
108 The preferred way to define options is to have a separate file
109 'myproto.options' in the same directory as the 'myproto.proto'. ::
113 required string name = 1;
114 repeated int32 ids = 4;
120 MyMessage.name max_size:40
121 MyMessage.ids max_count:5
123 The generator will automatically search for this file and read the
124 options from it. The file format is as follows:
126 * Lines starting with '#' or '//' are regarded as comments.
127 * Blank lines are ignored.
128 * All other lines should start with a field name pattern, followed by one or
129 more options. For example: *"MyMessage.myfield max_size:5 max_count:10"*.
130 * The field name pattern is matched against a string of form *'Message.field'*.
131 For nested messages, the string is *'Message.SubMessage.field'*.
132 * The field name pattern may use the notation recognized by Python fnmatch():
134 - *\** matches any part of string, like 'Message.\*' for all fields
135 - *\?* matches any single character
136 - *[seq]* matches any of characters 's', 'e' and 'q'
137 - *[!seq]* matches any other character
139 * The options are written as *'option_name:option_value'* and several options
140 can be defined on same line, separated by whitespace.
141 * Options defined later in the file override the ones specified earlier, so
142 it makes sense to define wildcard options first in the file and more specific
145 If preferred, the name of the options file can be set using the command line
146 switch *-f* to nanopb_generator.py.
148 Defining the options on command line
149 ------------------------------------
150 The nanopb_generator.py has a simple command line option *-s OPTION:VALUE*.
151 The setting applies to the whole file that is being processed.
153 Defining the options in the .proto file
154 ---------------------------------------
155 The .proto file format allows defining custom options for the fields.
156 The nanopb library comes with *nanopb.proto* which does exactly that, allowing
157 you do define the options directly in the .proto file::
159 import "nanopb.proto";
162 required string name = 1 [(nanopb).max_size = 40];
163 repeated int32 ids = 4 [(nanopb).max_count = 5];
166 A small complication is that you have to set the include path of protoc so that
167 nanopb.proto can be found. This file, in turn, requires the file
168 *google/protobuf/descriptor.proto*. This is usually installed under
169 */usr/include*. Therefore, to compile a .proto file which uses options, use a
170 protoc command similar to::
172 protoc -I/usr/include -Inanopb/generator -I. -omessage.pb message.proto
174 The options can be defined in file, message and field scopes::
176 option (nanopb_fileopt).max_size = 20; // File scope
179 option (nanopb_msgopt).max_size = 30; // Message scope
180 required string fieldsize = 1 [(nanopb).max_size = 40]; // Field scope
196 Defines the encoder/decoder behaviour that should be used for a field. ::
198 typedef uint8_t pb_type_t;
200 The low-order nibble of the enumeration values defines the function that can be used for encoding and decoding the field data:
202 ==================== ===== ================================================
203 LTYPE identifier Value Storage format
204 ==================== ===== ================================================
205 PB_LTYPE_VARINT 0x00 Integer.
206 PB_LTYPE_SVARINT 0x01 Integer, zigzag encoded.
207 PB_LTYPE_FIXED32 0x02 32-bit integer or floating point.
208 PB_LTYPE_FIXED64 0x03 64-bit integer or floating point.
209 PB_LTYPE_BYTES 0x04 Structure with *size_t* field and byte array.
210 PB_LTYPE_STRING 0x05 Null-terminated string.
211 PB_LTYPE_SUBMESSAGE 0x06 Submessage structure.
212 ==================== ===== ================================================
214 The bits 4-5 define whether the field is required, optional or repeated:
216 ==================== ===== ================================================
217 HTYPE identifier Value Field handling
218 ==================== ===== ================================================
219 PB_HTYPE_REQUIRED 0x00 Verify that field exists in decoded message.
220 PB_HTYPE_OPTIONAL 0x10 Use separate *has_<field>* boolean to specify
221 whether the field is present.
222 (Unless it is a callback)
223 PB_HTYPE_REPEATED 0x20 A repeated field with preallocated array.
224 Separate *<field>_count* for number of items.
225 (Unless it is a callback)
226 ==================== ===== ================================================
228 The bits 6-7 define the how the storage for the field is allocated:
230 ==================== ===== ================================================
231 ATYPE identifier Value Allocation method
232 ==================== ===== ================================================
233 PB_ATYPE_STATIC 0x00 Statically allocated storage in the structure.
234 PB_ATYPE_CALLBACK 0x40 A field with dynamic storage size. Struct field
235 actually contains a pointer to a callback
237 ==================== ===== ================================================
242 Describes a single structure field with memory position in relation to others. The descriptions are usually autogenerated. ::
244 typedef struct _pb_field_t pb_field_t;
255 :tag: Tag number of the field or 0 to terminate a list of fields.
256 :type: LTYPE, HTYPE and ATYPE of the field.
257 :data_offset: Offset of field data, relative to the end of the previous field.
258 :size_offset: Offset of *bool* flag for optional fields or *size_t* count for arrays, relative to field data.
259 :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.
260 :array_size: Maximum number of entries in an array, if it is an array type.
261 :ptr: Pointer to default value for optional fields, or to submessage description for PB_LTYPE_SUBMESSAGE.
263 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*.
267 An byte array with a field for storing the length::
274 In an actual array, the length of *bytes* may be different.
278 Part of a message structure, for fields with type PB_HTYPE_CALLBACK::
280 typedef struct _pb_callback_t pb_callback_t;
281 struct _pb_callback_t {
283 bool (*decode)(pb_istream_t *stream, const pb_field_t *field, void **arg);
284 bool (*encode)(pb_ostream_t *stream, const pb_field_t *field, void * const *arg);
290 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 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 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.
298 Protocol Buffers wire types. These are used with `pb_encode_tag`_. ::
309 Defines the handler functions and auxiliary data for a field that extends
310 another message. Usually autogenerated by *nanopb_generator.py*::
313 bool (*decode)(pb_istream_t *stream, pb_extension_t *extension,
314 uint32_t tag, pb_wire_type_t wire_type);
315 bool (*encode)(pb_ostream_t *stream, const pb_extension_t *extension);
317 } pb_extension_type_t;
319 In the normal case, the function pointers are *NULL* and the decoder and
320 encoder use their internal implementations. The internal implementations
321 assume that *arg* points to a *pb_field_t* that describes the field in question.
323 To implement custom processing of unknown fields, you can provide pointers
324 to your own functions. Their functionality is mostly the same as for normal
325 callback fields, except that they get called for any unknown field when decoding.
329 Ties together the extension field type and the storage for the field value::
332 const pb_extension_type_t *type;
334 pb_extension_t *next;
337 :type: Pointer to the structure that defines the callback functions.
338 :dest: Pointer to the variable that stores the field value
339 (as used by the default extension callback functions.)
340 :next: Pointer to the next extension handler, or *NULL*.
344 Get the current error message from a stream, or a placeholder string if
345 there is no error message::
347 #define PB_GET_ERROR(stream) (string expression)
349 This should be used for printing errors, for example::
353 printf("Decode failed: %s\n", PB_GET_ERROR(stream));
356 The macro only returns pointers to constant strings (in code memory),
357 so that there is no need to release the returned pointer.
361 Set the error message and return false::
363 #define PB_RETURN_ERROR(stream,msg) (sets error and returns false)
365 This should be used to handle error conditions inside nanopb functions
366 and user callback functions::
370 PB_RETURN_ERROR(stream, "something went wrong");
373 The *msg* parameter must be a constant string.
380 pb_ostream_from_buffer
381 ----------------------
382 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 pb_ostream_t pb_ostream_from_buffer(uint8_t *buf, size_t bufsize);
386 :buf: Memory buffer to write into.
387 :bufsize: Maximum number of bytes to write.
388 :returns: An output stream.
390 After writing, you can check *stream.bytes_written* to find out how much valid data there is in the buffer.
394 Writes data to an output stream. Always use this function, instead of trying to call stream callback manually. ::
396 bool pb_write(pb_ostream_t *stream, const uint8_t *buf, size_t count);
398 :stream: Output stream to write to.
399 :buf: Pointer to buffer with the data to be written.
400 :count: Number of bytes to write.
401 :returns: True on success, false if maximum length is exceeded or an IO error happens.
403 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.
407 Encodes the contents of a structure as a protocol buffers message and writes it to output stream. ::
409 bool pb_encode(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct);
411 :stream: Output stream to write to.
412 :fields: A field description array, usually autogenerated.
413 :src_struct: Pointer to the data that will be serialized.
414 :returns: True on success, false on IO error, on detectable errors in field description, or if a field encoder returns false.
416 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 .. sidebar:: Encoding fields manually
420 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.
422 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.
424 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.
428 Starts a field in the Protocol Buffers binary format: encodes the field number and the wire type of the data. ::
430 bool pb_encode_tag(pb_ostream_t *stream, pb_wire_type_t wiretype, int field_number);
432 :stream: Output stream to write to. 1-5 bytes will be written.
433 :wiretype: PB_WT_VARINT, PB_WT_64BIT, PB_WT_STRING or PB_WT_32BIT
434 :field_number: Identifier for the field, defined in the .proto file. You can get it from field->tag.
435 :returns: True on success, false on IO error.
437 pb_encode_tag_for_field
438 -----------------------
439 Same as `pb_encode_tag`_, except takes the parameters from a *pb_field_t* structure. ::
441 bool pb_encode_tag_for_field(pb_ostream_t *stream, const pb_field_t *field);
443 :stream: Output stream to write to. 1-5 bytes will be written.
444 :field: Field description structure. Usually autogenerated.
445 :returns: True on success, false on IO error or unknown field type.
447 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.
449 Wire type mapping is as follows:
451 ========================= ============
453 ========================= ============
454 VARINT, SVARINT PB_WT_VARINT
456 STRING, BYTES, SUBMESSAGE PB_WT_STRING
458 ========================= ============
462 Encodes a signed or unsigned integer in the varint_ format. Works for fields of type `bool`, `enum`, `int32`, `int64`, `uint32` and `uint64`::
464 bool pb_encode_varint(pb_ostream_t *stream, uint64_t value);
466 :stream: Output stream to write to. 1-10 bytes will be written.
467 :value: Value to encode. Just cast e.g. int32_t directly to uint64_t.
468 :returns: True on success, false on IO error.
470 .. _varint: http://code.google.com/apis/protocolbuffers/docs/encoding.html#varints
474 Encodes a signed integer in the 'zig-zagged' format. Works for fields of type `sint32` and `sint64`::
476 bool pb_encode_svarint(pb_ostream_t *stream, int64_t value);
478 (parameters are the same as for `pb_encode_varint`_
482 Writes the length of a string as varint and then contents of the string. Works for fields of type `bytes` and `string`::
484 bool pb_encode_string(pb_ostream_t *stream, const uint8_t *buffer, size_t size);
486 :stream: Output stream to write to.
487 :buffer: Pointer to string data.
488 :size: Number of bytes in the string. Pass `strlen(s)` for strings.
489 :returns: True on success, false on IO error.
493 Writes 4 bytes to stream and swaps bytes on big-endian architectures. Works for fields of type `fixed32`, `sfixed32` and `float`::
495 bool pb_encode_fixed32(pb_ostream_t *stream, const void *value);
497 :stream: Output stream to write to.
498 :value: Pointer to a 4-bytes large C variable, for example `uint32_t foo;`.
499 :returns: True on success, false on IO error.
503 Writes 8 bytes to stream and swaps bytes on big-endian architecture. Works for fields of type `fixed64`, `sfixed64` and `double`::
505 bool pb_encode_fixed64(pb_ostream_t *stream, const void *value);
507 :stream: Output stream to write to.
508 :value: Pointer to a 8-bytes large C variable, for example `uint64_t foo;`.
509 :returns: True on success, false on IO error.
513 Encodes a submessage field, including the size header for it. Works for fields of any message type::
515 bool pb_encode_submessage(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct);
517 :stream: Output stream to write to.
518 :fields: Pointer to the autogenerated field description array for the submessage type, e.g. `MyMessage_fields`.
519 :src: Pointer to the structure where submessage data is.
520 :returns: True on success, false on IO errors, pb_encode errors or if submessage size changes between calls.
522 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.
524 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.
540 pb_istream_from_buffer
541 ----------------------
542 Helper function for creating an input stream that reads data from a memory buffer. ::
544 pb_istream_t pb_istream_from_buffer(uint8_t *buf, size_t bufsize);
546 :buf: Pointer to byte array to read from.
547 :bufsize: Size of the byte array.
548 :returns: An input stream ready to use.
552 Read data from input stream. Always use this function, don't try to call the stream callback directly. ::
554 bool pb_read(pb_istream_t *stream, uint8_t *buf, size_t count);
556 :stream: Input stream to read from.
557 :buf: Buffer to store the data to, or NULL to just read data without storing it anywhere.
558 :count: Number of bytes to read.
559 :returns: True on success, false if *stream->bytes_left* is less than *count* or if an IO error occurs.
561 End of file is signalled by *stream->bytes_left* being zero after pb_read returns false.
565 Read and decode all fields of a structure. Reads until EOF on input stream. ::
567 bool pb_decode(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct);
569 :stream: Input stream to read from.
570 :fields: A field description array. Usually autogenerated.
571 :dest_struct: Pointer to structure where data will be stored.
572 :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.
574 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.
576 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.
578 For optional fields, this function applies the default value and sets *has_<field>* to false if the field is not present.
582 Same as `pb_decode`_, except does not apply the default values to fields. ::
584 bool pb_decode_noinit(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct);
586 (parameters are the same as for `pb_decode`_.)
588 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.
592 Skip a varint_ encoded integer without decoding it. ::
594 bool pb_skip_varint(pb_istream_t *stream);
596 :stream: Input stream to read from. Will read 1 byte at a time until the MSB is clear.
597 :returns: True on success, false on IO error.
601 Skip a varint-length-prefixed string. This means skipping a value with wire type PB_WT_STRING. ::
603 bool pb_skip_string(pb_istream_t *stream);
605 :stream: Input stream to read from.
606 :returns: True on success, false on IO error or length exceeding uint32_t.
610 Decode the tag that comes before field in the protobuf encoding::
612 bool pb_decode_tag(pb_istream_t *stream, pb_wire_type_t *wire_type, int *tag, bool *eof);
614 :stream: Input stream to read from.
615 :wire_type: Pointer to variable where to store the wire type of the field.
616 :tag: Pointer to variable where to store the tag of the field.
617 :eof: Pointer to variable where to store end-of-file status.
618 :returns: True on success, false on error or EOF.
620 When the message (stream) ends, this function will return false and set *eof* to true. On other
621 errors, *eof* will be set to false.
625 Remove the data for a field from the stream, without actually decoding it::
627 bool pb_skip_field(pb_istream_t *stream, pb_wire_type_t wire_type);
629 :stream: Input stream to read from.
630 :wire_type: Type of field to skip.
631 :returns: True on success, false on IO error.
633 .. sidebar:: Decoding fields manually
635 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.
637 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.
639 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`_.
641 Finally, for decoding submessages in a callback, simply use `pb_decode`_ and pass it the *SubMessage_fields* descriptor array.
645 Read and decode a varint_ encoded integer. ::
647 bool pb_decode_varint(pb_istream_t *stream, uint64_t *dest);
649 :stream: Input stream to read from. 1-10 bytes will be read.
650 :dest: Storage for the decoded integer. Value is undefined on error.
651 :returns: True on success, false if value exceeds uint64_t range or an IO error happens.
655 Similar to `pb_decode_varint`_, except that it performs zigzag-decoding on the value. This corresponds to the Protocol Buffers *sint32* and *sint64* datatypes. ::
657 bool pb_decode_svarint(pb_istream_t *stream, int64_t *dest);
659 (parameters are the same as `pb_decode_varint`_)
663 Decode a *fixed32*, *sfixed32* or *float* value. ::
665 bool pb_decode_fixed32(pb_istream_t *stream, void *dest);
667 :stream: Input stream to read from. 4 bytes will be read.
668 :dest: Pointer to destination *int32_t*, *uint32_t* or *float*.
669 :returns: True on success, false on IO errors.
671 This function reads 4 bytes from the input stream.
672 On big endian architectures, it then reverses the order of the bytes.
673 Finally, it writes the bytes to *dest*.
677 Decode a *fixed64*, *sfixed64* or *double* value. ::
679 bool pb_dec_fixed(pb_istream_t *stream, const pb_field_t *field, void *dest);
681 :stream: Input stream to read from. 8 bytes will be read.
683 :dest: Pointer to destination *int64_t*, *uint64_t* or *double*.
684 :returns: True on success, false on IO errors.
686 Same as `pb_decode_fixed32`_, except this reads 8 bytes.
688 pb_make_string_substream
689 ------------------------
690 Decode the length for a field with wire type *PB_WT_STRING* and create a substream for reading the data. ::
692 bool pb_make_string_substream(pb_istream_t *stream, pb_istream_t *substream);
694 :stream: Original input stream to read the length and data from.
695 :substream: New substream that has limited length. Filled in by the function.
696 :returns: True on success, false if reading the length fails.
698 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.
700 pb_close_string_substream
701 -------------------------
702 Close the substream created with `pb_make_string_substream`_. ::
704 void pb_close_string_substream(pb_istream_t *stream, pb_istream_t *substream);
706 :stream: Original input stream to read the length and data from.
707 :substream: Substream to close
709 This function copies back the state from the substream to the parent stream.
710 It must be called after done with the substream.