mirror of https://github.com/grpc/grpc.git
The C based gRPC (C++, Python, Ruby, Objective-C, PHP, C#)
https://grpc.io/
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771 lines
34 KiB
771 lines
34 KiB
8 years ago
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=====================
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Nanopb: API reference
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=====================
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.. include :: menu.rst
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.. contents ::
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Compilation options
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===================
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The following options can be specified in one of two ways:
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1. Using the -D switch on the C compiler command line.
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2. By #defining them at the top of pb.h.
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You must have the same settings for the nanopb library and all code that
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includes pb.h.
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============================ ================================================
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PB_NO_PACKED_STRUCTS Disable packed structs. Increases RAM usage but
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is necessary on some platforms that do not
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support unaligned memory access.
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PB_ENABLE_MALLOC Set this to enable dynamic allocation support
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in the decoder.
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PB_MAX_REQUIRED_FIELDS Maximum number of required fields to check for
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presence. Default value is 64. Increases stack
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usage 1 byte per every 8 fields. Compiler
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warning will tell if you need this.
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PB_FIELD_16BIT Add support for tag numbers > 255 and fields
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larger than 255 bytes or 255 array entries.
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Increases code size 3 bytes per each field.
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Compiler error will tell if you need this.
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PB_FIELD_32BIT Add support for tag numbers > 65535 and fields
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larger than 65535 bytes or 65535 array entries.
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Increases code size 9 bytes per each field.
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Compiler error will tell if you need this.
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PB_NO_ERRMSG Disables the support for error messages; only
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error information is the true/false return
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value. Decreases the code size by a few hundred
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bytes.
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PB_BUFFER_ONLY Disables the support for custom streams. Only
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supports encoding and decoding with memory
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buffers. Speeds up execution and decreases code
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size slightly.
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PB_OLD_CALLBACK_STYLE Use the old function signature (void\* instead
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of void\*\*) for callback fields. This was the
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default until nanopb-0.2.1.
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PB_SYSTEM_HEADER Replace the standard header files with a single
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header file. It should define all the required
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functions and typedefs listed on the
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`overview page`_. Value must include quotes,
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for example *#define PB_SYSTEM_HEADER "foo.h"*.
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============================ ================================================
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The PB_MAX_REQUIRED_FIELDS, PB_FIELD_16BIT and PB_FIELD_32BIT settings allow
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raising some datatype limits to suit larger messages. Their need is recognized
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automatically by C-preprocessor #if-directives in the generated .pb.h files.
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The default setting is to use the smallest datatypes (least resources used).
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.. _`overview page`: index.html#compiler-requirements
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Proto file options
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==================
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The generator behaviour can be adjusted using these options, defined in the
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'nanopb.proto' file in the generator folder:
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============================ ================================================
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max_size Allocated size for *bytes* and *string* fields.
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max_count Allocated number of entries in arrays
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(*repeated* fields).
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int_size Override the integer type of a field.
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(To use e.g. uint8_t to save RAM.)
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type Type of the generated field. Default value
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is *FT_DEFAULT*, which selects automatically.
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You can use *FT_CALLBACK*, *FT_POINTER*,
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*FT_STATIC*, *FT_IGNORE*, or *FT_INLINE* to
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force a callback field, a dynamically
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allocated field, a static field, to
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completely ignore the field or to
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generate an inline bytes field.
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long_names Prefix the enum name to the enum value in
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definitions, i.e. *EnumName_EnumValue*. Enabled
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by default.
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packed_struct Make the generated structures packed.
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NOTE: This cannot be used on CPUs that break
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on unaligned accesses to variables.
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skip_message Skip the whole message from generation.
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no_unions Generate 'oneof' fields as optional fields
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instead of C unions.
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msgid Specifies a unique id for this message type.
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Can be used by user code as an identifier.
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anonymous_oneof Generate 'oneof' fields as anonymous unions.
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============================ ================================================
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These options can be defined for the .proto files before they are converted
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using the nanopb-generatory.py. There are three ways to define the options:
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1. Using a separate .options file.
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This is the preferred way as of nanopb-0.2.1, because it has the best
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compatibility with other protobuf libraries.
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2. Defining the options on the command line of nanopb_generator.py.
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This only makes sense for settings that apply to a whole file.
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3. Defining the options in the .proto file using the nanopb extensions.
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This is the way used in nanopb-0.1, and will remain supported in the
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future. It however sometimes causes trouble when using the .proto file
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with other protobuf libraries.
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The effect of the options is the same no matter how they are given. The most
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common purpose is to define maximum size for string fields in order to
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statically allocate them.
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Defining the options in a .options file
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---------------------------------------
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The preferred way to define options is to have a separate file
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'myproto.options' in the same directory as the 'myproto.proto'. ::
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# myproto.proto
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message MyMessage {
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required string name = 1;
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repeated int32 ids = 4;
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}
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::
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# myproto.options
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MyMessage.name max_size:40
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MyMessage.ids max_count:5
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The generator will automatically search for this file and read the
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options from it. The file format is as follows:
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* Lines starting with '#' or '//' are regarded as comments.
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* Blank lines are ignored.
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* All other lines should start with a field name pattern, followed by one or
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more options. For example: *"MyMessage.myfield max_size:5 max_count:10"*.
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* The field name pattern is matched against a string of form *'Message.field'*.
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For nested messages, the string is *'Message.SubMessage.field'*.
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* The field name pattern may use the notation recognized by Python fnmatch():
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- *\** matches any part of string, like 'Message.\*' for all fields
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- *\?* matches any single character
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- *[seq]* matches any of characters 's', 'e' and 'q'
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- *[!seq]* matches any other character
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* The options are written as *'option_name:option_value'* and several options
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can be defined on same line, separated by whitespace.
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* Options defined later in the file override the ones specified earlier, so
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it makes sense to define wildcard options first in the file and more specific
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ones later.
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If preferred, the name of the options file can be set using the command line
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switch *-f* to nanopb_generator.py.
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Defining the options on command line
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------------------------------------
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The nanopb_generator.py has a simple command line option *-s OPTION:VALUE*.
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The setting applies to the whole file that is being processed.
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Defining the options in the .proto file
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---------------------------------------
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The .proto file format allows defining custom options for the fields.
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The nanopb library comes with *nanopb.proto* which does exactly that, allowing
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you do define the options directly in the .proto file::
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import "nanopb.proto";
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message MyMessage {
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required string name = 1 [(nanopb).max_size = 40];
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repeated int32 ids = 4 [(nanopb).max_count = 5];
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}
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A small complication is that you have to set the include path of protoc so that
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nanopb.proto can be found. This file, in turn, requires the file
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*google/protobuf/descriptor.proto*. This is usually installed under
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*/usr/include*. Therefore, to compile a .proto file which uses options, use a
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protoc command similar to::
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protoc -I/usr/include -Inanopb/generator -I. -omessage.pb message.proto
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The options can be defined in file, message and field scopes::
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option (nanopb_fileopt).max_size = 20; // File scope
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message Message
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{
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option (nanopb_msgopt).max_size = 30; // Message scope
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required string fieldsize = 1 [(nanopb).max_size = 40]; // Field scope
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}
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pb.h
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====
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pb_byte_t
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---------
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Type used for storing byte-sized data, such as raw binary input and bytes-type fields. ::
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typedef uint_least8_t pb_byte_t;
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For most platforms this is equivalent to `uint8_t`. Some platforms however do not support
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8-bit variables, and on those platforms 16 or 32 bits need to be used for each byte.
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pb_type_t
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---------
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Type used to store the type of each field, to control the encoder/decoder behaviour. ::
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typedef uint_least8_t pb_type_t;
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The low-order nibble of the enumeration values defines the function that can be used for encoding and decoding the field data:
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=========================== ===== ================================================
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LTYPE identifier Value Storage format
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=========================== ===== ================================================
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PB_LTYPE_VARINT 0x00 Integer.
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PB_LTYPE_UVARINT 0x01 Unsigned integer.
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PB_LTYPE_SVARINT 0x02 Integer, zigzag encoded.
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PB_LTYPE_FIXED32 0x03 32-bit integer or floating point.
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PB_LTYPE_FIXED64 0x04 64-bit integer or floating point.
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PB_LTYPE_BYTES 0x05 Structure with *size_t* field and byte array.
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PB_LTYPE_STRING 0x06 Null-terminated string.
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PB_LTYPE_SUBMESSAGE 0x07 Submessage structure.
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PB_LTYPE_EXTENSION 0x08 Point to *pb_extension_t*.
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PB_LTYPE_FIXED_LENGTH_BYTES 0x09 Inline *pb_byte_t* array of fixed size.
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=========================== ===== ================================================
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The bits 4-5 define whether the field is required, optional or repeated:
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==================== ===== ================================================
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HTYPE identifier Value Field handling
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==================== ===== ================================================
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PB_HTYPE_REQUIRED 0x00 Verify that field exists in decoded message.
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PB_HTYPE_OPTIONAL 0x10 Use separate *has_<field>* boolean to specify
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whether the field is present.
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(Unless it is a callback)
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PB_HTYPE_REPEATED 0x20 A repeated field with preallocated array.
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Separate *<field>_count* for number of items.
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(Unless it is a callback)
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==================== ===== ================================================
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The bits 6-7 define the how the storage for the field is allocated:
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==================== ===== ================================================
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ATYPE identifier Value Allocation method
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==================== ===== ================================================
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PB_ATYPE_STATIC 0x00 Statically allocated storage in the structure.
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PB_ATYPE_CALLBACK 0x40 A field with dynamic storage size. Struct field
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actually contains a pointer to a callback
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function.
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==================== ===== ================================================
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pb_field_t
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----------
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Describes a single structure field with memory position in relation to others. The descriptions are usually autogenerated. ::
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typedef struct pb_field_s pb_field_t;
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struct pb_field_s {
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pb_size_t tag;
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pb_type_t type;
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pb_size_t data_offset;
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pb_ssize_t size_offset;
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pb_size_t data_size;
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pb_size_t array_size;
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8 years ago
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const void *ptr;
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} pb_packed;
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:tag: Tag number of the field or 0 to terminate a list of fields.
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:type: LTYPE, HTYPE and ATYPE of the field.
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:data_offset: Offset of field data, relative to the end of the previous field.
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:size_offset: Offset of *bool* flag for optional fields or *size_t* count for arrays, relative to field data.
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: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.
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:array_size: Maximum number of entries in an array, if it is an array type.
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:ptr: Pointer to default value for optional fields, or to submessage description for PB_LTYPE_SUBMESSAGE.
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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*.
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pb_bytes_array_t
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----------------
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An byte array with a field for storing the length::
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typedef struct {
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pb_size_t size;
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pb_byte_t bytes[1];
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} pb_bytes_array_t;
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In an actual array, the length of *bytes* may be different.
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pb_callback_t
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-------------
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Part of a message structure, for fields with type PB_HTYPE_CALLBACK::
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typedef struct _pb_callback_t pb_callback_t;
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struct _pb_callback_t {
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union {
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bool (*decode)(pb_istream_t *stream, const pb_field_t *field, void **arg);
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bool (*encode)(pb_ostream_t *stream, const pb_field_t *field, void * const *arg);
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} funcs;
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void *arg;
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};
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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.
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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*.
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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.
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pb_wire_type_t
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--------------
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Protocol Buffers wire types. These are used with `pb_encode_tag`_. ::
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typedef enum {
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PB_WT_VARINT = 0,
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PB_WT_64BIT = 1,
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PB_WT_STRING = 2,
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PB_WT_32BIT = 5
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} pb_wire_type_t;
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pb_extension_type_t
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-------------------
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Defines the handler functions and auxiliary data for a field that extends
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another message. Usually autogenerated by *nanopb_generator.py*::
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typedef struct {
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bool (*decode)(pb_istream_t *stream, pb_extension_t *extension,
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uint32_t tag, pb_wire_type_t wire_type);
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bool (*encode)(pb_ostream_t *stream, const pb_extension_t *extension);
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const void *arg;
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} pb_extension_type_t;
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In the normal case, the function pointers are *NULL* and the decoder and
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encoder use their internal implementations. The internal implementations
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assume that *arg* points to a *pb_field_t* that describes the field in question.
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To implement custom processing of unknown fields, you can provide pointers
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to your own functions. Their functionality is mostly the same as for normal
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callback fields, except that they get called for any unknown field when decoding.
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pb_extension_t
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--------------
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Ties together the extension field type and the storage for the field value::
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typedef struct {
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const pb_extension_type_t *type;
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void *dest;
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pb_extension_t *next;
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8 years ago
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bool found;
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} pb_extension_t;
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:type: Pointer to the structure that defines the callback functions.
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:dest: Pointer to the variable that stores the field value
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(as used by the default extension callback functions.)
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:next: Pointer to the next extension handler, or *NULL*.
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8 years ago
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:found: Decoder sets this to true if the extension was found.
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8 years ago
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PB_GET_ERROR
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------------
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Get the current error message from a stream, or a placeholder string if
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there is no error message::
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#define PB_GET_ERROR(stream) (string expression)
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This should be used for printing errors, for example::
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if (!pb_decode(...))
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{
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printf("Decode failed: %s\n", PB_GET_ERROR(stream));
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}
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The macro only returns pointers to constant strings (in code memory),
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so that there is no need to release the returned pointer.
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PB_RETURN_ERROR
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---------------
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Set the error message and return false::
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#define PB_RETURN_ERROR(stream,msg) (sets error and returns false)
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This should be used to handle error conditions inside nanopb functions
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and user callback functions::
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if (error_condition)
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{
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PB_RETURN_ERROR(stream, "something went wrong");
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}
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The *msg* parameter must be a constant string.
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pb_encode.h
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===========
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pb_ostream_from_buffer
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----------------------
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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. ::
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8 years ago
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pb_ostream_t pb_ostream_from_buffer(pb_byte_t *buf, size_t bufsize);
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8 years ago
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||
|
:buf: Memory buffer to write into.
|
||
|
:bufsize: Maximum number of bytes to write.
|
||
|
:returns: An output stream.
|
||
|
|
||
|
After writing, you can check *stream.bytes_written* to find out how much valid data there is in the buffer.
|
||
|
|
||
|
pb_write
|
||
|
--------
|
||
|
Writes data to an output stream. Always use this function, instead of trying to call stream callback manually. ::
|
||
|
|
||
8 years ago
|
bool pb_write(pb_ostream_t *stream, const pb_byte_t *buf, size_t count);
|
||
8 years ago
|
|
||
|
:stream: Output stream to write to.
|
||
|
:buf: Pointer to buffer with the data to be written.
|
||
|
:count: Number of bytes to write.
|
||
|
:returns: True on success, false if maximum length is exceeded or an IO error happens.
|
||
|
|
||
|
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.
|
||
|
|
||
|
pb_encode
|
||
|
---------
|
||
|
Encodes the contents of a structure as a protocol buffers message and writes it to output stream. ::
|
||
|
|
||
|
bool pb_encode(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct);
|
||
|
|
||
|
:stream: Output stream to write to.
|
||
|
:fields: A field description array, usually autogenerated.
|
||
|
:src_struct: Pointer to the data that will be serialized.
|
||
|
:returns: True on success, false on IO error, on detectable errors in field description, or if a field encoder returns false.
|
||
|
|
||
|
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.
|
||
|
|
||
|
pb_encode_delimited
|
||
|
-------------------
|
||
|
Calculates the length of the message, encodes it as varint and then encodes the message. ::
|
||
|
|
||
|
bool pb_encode_delimited(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct);
|
||
|
|
||
|
(parameters are the same as for `pb_encode`_.)
|
||
|
|
||
|
A common way to indicate the message length in Protocol Buffers is to prefix it with a varint.
|
||
|
This function does this, and it is compatible with *parseDelimitedFrom* in Google's protobuf library.
|
||
|
|
||
|
.. sidebar:: Encoding fields manually
|
||
|
|
||
|
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.
|
||
|
|
||
|
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.
|
||
|
|
||
|
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.
|
||
|
|
||
8 years ago
|
pb_get_encoded_size
|
||
|
-------------------
|
||
|
Calculates the length of the encoded message. ::
|
||
|
|
||
|
bool pb_get_encoded_size(size_t *size, const pb_field_t fields[], const void *src_struct);
|
||
|
|
||
|
:size: Calculated size of the encoded message.
|
||
|
:fields: A field description array, usually autogenerated.
|
||
|
:src_struct: Pointer to the data that will be serialized.
|
||
|
:returns: True on success, false on detectable errors in field description or if a field encoder returns false.
|
||
|
|
||
8 years ago
|
pb_encode_tag
|
||
|
-------------
|
||
|
Starts a field in the Protocol Buffers binary format: encodes the field number and the wire type of the data. ::
|
||
|
|
||
8 years ago
|
bool pb_encode_tag(pb_ostream_t *stream, pb_wire_type_t wiretype, uint32_t field_number);
|
||
8 years ago
|
|
||
|
:stream: Output stream to write to. 1-5 bytes will be written.
|
||
|
:wiretype: PB_WT_VARINT, PB_WT_64BIT, PB_WT_STRING or PB_WT_32BIT
|
||
|
:field_number: Identifier for the field, defined in the .proto file. You can get it from field->tag.
|
||
|
:returns: True on success, false on IO error.
|
||
|
|
||
|
pb_encode_tag_for_field
|
||
|
-----------------------
|
||
|
Same as `pb_encode_tag`_, except takes the parameters from a *pb_field_t* structure. ::
|
||
|
|
||
|
bool pb_encode_tag_for_field(pb_ostream_t *stream, const pb_field_t *field);
|
||
|
|
||
|
:stream: Output stream to write to. 1-5 bytes will be written.
|
||
|
:field: Field description structure. Usually autogenerated.
|
||
|
:returns: True on success, false on IO error or unknown field type.
|
||
|
|
||
|
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.
|
||
|
|
||
|
Wire type mapping is as follows:
|
||
|
|
||
8 years ago
|
============================================= ============
|
||
|
LTYPEs Wire type
|
||
|
============================================= ============
|
||
|
VARINT, UVARINT, SVARINT PB_WT_VARINT
|
||
|
FIXED64 PB_WT_64BIT
|
||
|
STRING, BYTES, SUBMESSAGE, FIXED_LENGTH_BYTES PB_WT_STRING
|
||
|
FIXED32 PB_WT_32BIT
|
||
|
============================================= ============
|
||
8 years ago
|
|
||
|
pb_encode_varint
|
||
|
----------------
|
||
|
Encodes a signed or unsigned integer in the varint_ format. Works for fields of type `bool`, `enum`, `int32`, `int64`, `uint32` and `uint64`::
|
||
|
|
||
|
bool pb_encode_varint(pb_ostream_t *stream, uint64_t value);
|
||
|
|
||
|
:stream: Output stream to write to. 1-10 bytes will be written.
|
||
|
:value: Value to encode. Just cast e.g. int32_t directly to uint64_t.
|
||
|
:returns: True on success, false on IO error.
|
||
|
|
||
|
.. _varint: http://code.google.com/apis/protocolbuffers/docs/encoding.html#varints
|
||
|
|
||
|
pb_encode_svarint
|
||
|
-----------------
|
||
|
Encodes a signed integer in the 'zig-zagged' format. Works for fields of type `sint32` and `sint64`::
|
||
|
|
||
|
bool pb_encode_svarint(pb_ostream_t *stream, int64_t value);
|
||
|
|
||
|
(parameters are the same as for `pb_encode_varint`_
|
||
|
|
||
|
pb_encode_string
|
||
|
----------------
|
||
|
Writes the length of a string as varint and then contents of the string. Works for fields of type `bytes` and `string`::
|
||
|
|
||
8 years ago
|
bool pb_encode_string(pb_ostream_t *stream, const pb_byte_t *buffer, size_t size);
|
||
8 years ago
|
|
||
|
:stream: Output stream to write to.
|
||
|
:buffer: Pointer to string data.
|
||
|
:size: Number of bytes in the string. Pass `strlen(s)` for strings.
|
||
|
:returns: True on success, false on IO error.
|
||
|
|
||
|
pb_encode_fixed32
|
||
|
-----------------
|
||
|
Writes 4 bytes to stream and swaps bytes on big-endian architectures. Works for fields of type `fixed32`, `sfixed32` and `float`::
|
||
|
|
||
|
bool pb_encode_fixed32(pb_ostream_t *stream, const void *value);
|
||
|
|
||
|
:stream: Output stream to write to.
|
||
|
:value: Pointer to a 4-bytes large C variable, for example `uint32_t foo;`.
|
||
|
:returns: True on success, false on IO error.
|
||
|
|
||
|
pb_encode_fixed64
|
||
|
-----------------
|
||
|
Writes 8 bytes to stream and swaps bytes on big-endian architecture. Works for fields of type `fixed64`, `sfixed64` and `double`::
|
||
|
|
||
|
bool pb_encode_fixed64(pb_ostream_t *stream, const void *value);
|
||
|
|
||
|
:stream: Output stream to write to.
|
||
|
:value: Pointer to a 8-bytes large C variable, for example `uint64_t foo;`.
|
||
|
:returns: True on success, false on IO error.
|
||
|
|
||
|
pb_encode_submessage
|
||
|
--------------------
|
||
|
Encodes a submessage field, including the size header for it. Works for fields of any message type::
|
||
|
|
||
|
bool pb_encode_submessage(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct);
|
||
|
|
||
|
:stream: Output stream to write to.
|
||
|
:fields: Pointer to the autogenerated field description array for the submessage type, e.g. `MyMessage_fields`.
|
||
|
:src: Pointer to the structure where submessage data is.
|
||
|
:returns: True on success, false on IO errors, pb_encode errors or if submessage size changes between calls.
|
||
|
|
||
|
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.
|
||
|
|
||
|
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.
|
||
|
|
||
|
|
||
|
|
||
|
|
||
|
|
||
|
|
||
|
|
||
|
|
||
|
|
||
|
|
||
|
|
||
|
|
||
|
pb_decode.h
|
||
|
===========
|
||
|
|
||
|
pb_istream_from_buffer
|
||
|
----------------------
|
||
|
Helper function for creating an input stream that reads data from a memory buffer. ::
|
||
|
|
||
8 years ago
|
pb_istream_t pb_istream_from_buffer(const pb_byte_t *buf, size_t bufsize);
|
||
8 years ago
|
|
||
|
:buf: Pointer to byte array to read from.
|
||
|
:bufsize: Size of the byte array.
|
||
|
:returns: An input stream ready to use.
|
||
|
|
||
|
pb_read
|
||
|
-------
|
||
|
Read data from input stream. Always use this function, don't try to call the stream callback directly. ::
|
||
|
|
||
8 years ago
|
bool pb_read(pb_istream_t *stream, pb_byte_t *buf, size_t count);
|
||
8 years ago
|
|
||
|
:stream: Input stream to read from.
|
||
|
:buf: Buffer to store the data to, or NULL to just read data without storing it anywhere.
|
||
|
:count: Number of bytes to read.
|
||
|
:returns: True on success, false if *stream->bytes_left* is less than *count* or if an IO error occurs.
|
||
|
|
||
|
End of file is signalled by *stream->bytes_left* being zero after pb_read returns false.
|
||
|
|
||
|
pb_decode
|
||
|
---------
|
||
|
Read and decode all fields of a structure. Reads until EOF on input stream. ::
|
||
|
|
||
|
bool pb_decode(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct);
|
||
|
|
||
|
:stream: Input stream to read from.
|
||
|
:fields: A field description array. Usually autogenerated.
|
||
|
:dest_struct: Pointer to structure where data will be stored.
|
||
|
: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.
|
||
|
|
||
|
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.
|
||
|
|
||
|
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.
|
||
|
|
||
|
For optional fields, this function applies the default value and sets *has_<field>* to false if the field is not present.
|
||
|
|
||
|
If *PB_ENABLE_MALLOC* is defined, this function may allocate storage for any pointer type fields.
|
||
|
In this case, you have to call `pb_release`_ to release the memory after you are done with the message.
|
||
|
On error return `pb_decode` will release the memory itself.
|
||
|
|
||
|
pb_decode_noinit
|
||
|
----------------
|
||
|
Same as `pb_decode`_, except does not apply the default values to fields. ::
|
||
|
|
||
|
bool pb_decode_noinit(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct);
|
||
|
|
||
|
(parameters are the same as for `pb_decode`_.)
|
||
|
|
||
|
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.
|
||
|
|
||
|
In addition to decoding a single message, this function can be used to merge two messages, so that
|
||
|
values from previous message will remain if the new message does not contain a field.
|
||
|
|
||
|
This function *will not* release the message even on error return. If you use *PB_ENABLE_MALLOC*,
|
||
|
you will need to call `pb_release`_ yourself.
|
||
|
|
||
|
pb_decode_delimited
|
||
|
-------------------
|
||
|
Same as `pb_decode`_, except that it first reads a varint with the length of the message. ::
|
||
|
|
||
|
bool pb_decode_delimited(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct);
|
||
|
|
||
|
(parameters are the same as for `pb_decode`_.)
|
||
|
|
||
|
A common method to indicate message size in Protocol Buffers is to prefix it with a varint.
|
||
|
This function is compatible with *writeDelimitedTo* in the Google's Protocol Buffers library.
|
||
|
|
||
|
pb_release
|
||
|
----------
|
||
8 years ago
|
Releases any dynamically allocated fields::
|
||
8 years ago
|
|
||
|
void pb_release(const pb_field_t fields[], void *dest_struct);
|
||
|
|
||
|
:fields: A field description array. Usually autogenerated.
|
||
8 years ago
|
:dest_struct: Pointer to structure where data is stored. If NULL, function does nothing.
|
||
8 years ago
|
|
||
|
This function is only available if *PB_ENABLE_MALLOC* is defined. It will release any
|
||
|
pointer type fields in the structure and set the pointers to NULL.
|
||
|
|
||
|
pb_decode_tag
|
||
|
-------------
|
||
|
Decode the tag that comes before field in the protobuf encoding::
|
||
|
|
||
8 years ago
|
bool pb_decode_tag(pb_istream_t *stream, pb_wire_type_t *wire_type, uint32_t *tag, bool *eof);
|
||
8 years ago
|
|
||
|
:stream: Input stream to read from.
|
||
|
:wire_type: Pointer to variable where to store the wire type of the field.
|
||
|
:tag: Pointer to variable where to store the tag of the field.
|
||
|
:eof: Pointer to variable where to store end-of-file status.
|
||
|
:returns: True on success, false on error or EOF.
|
||
|
|
||
|
When the message (stream) ends, this function will return false and set *eof* to true. On other
|
||
|
errors, *eof* will be set to false.
|
||
|
|
||
|
pb_skip_field
|
||
|
-------------
|
||
|
Remove the data for a field from the stream, without actually decoding it::
|
||
|
|
||
|
bool pb_skip_field(pb_istream_t *stream, pb_wire_type_t wire_type);
|
||
|
|
||
|
:stream: Input stream to read from.
|
||
|
:wire_type: Type of field to skip.
|
||
|
:returns: True on success, false on IO error.
|
||
|
|
||
|
.. sidebar:: Decoding fields manually
|
||
|
|
||
|
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.
|
||
|
|
||
|
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.
|
||
|
|
||
|
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`_.
|
||
|
|
||
|
Finally, for decoding submessages in a callback, simply use `pb_decode`_ and pass it the *SubMessage_fields* descriptor array.
|
||
|
|
||
|
pb_decode_varint
|
||
|
----------------
|
||
|
Read and decode a varint_ encoded integer. ::
|
||
|
|
||
|
bool pb_decode_varint(pb_istream_t *stream, uint64_t *dest);
|
||
|
|
||
|
:stream: Input stream to read from. 1-10 bytes will be read.
|
||
|
:dest: Storage for the decoded integer. Value is undefined on error.
|
||
|
:returns: True on success, false if value exceeds uint64_t range or an IO error happens.
|
||
|
|
||
|
pb_decode_svarint
|
||
|
-----------------
|
||
|
Similar to `pb_decode_varint`_, except that it performs zigzag-decoding on the value. This corresponds to the Protocol Buffers *sint32* and *sint64* datatypes. ::
|
||
|
|
||
|
bool pb_decode_svarint(pb_istream_t *stream, int64_t *dest);
|
||
|
|
||
|
(parameters are the same as `pb_decode_varint`_)
|
||
|
|
||
|
pb_decode_fixed32
|
||
|
-----------------
|
||
|
Decode a *fixed32*, *sfixed32* or *float* value. ::
|
||
|
|
||
|
bool pb_decode_fixed32(pb_istream_t *stream, void *dest);
|
||
|
|
||
|
:stream: Input stream to read from. 4 bytes will be read.
|
||
|
:dest: Pointer to destination *int32_t*, *uint32_t* or *float*.
|
||
|
:returns: True on success, false on IO errors.
|
||
|
|
||
|
This function reads 4 bytes from the input stream.
|
||
|
On big endian architectures, it then reverses the order of the bytes.
|
||
|
Finally, it writes the bytes to *dest*.
|
||
|
|
||
|
pb_decode_fixed64
|
||
|
-----------------
|
||
|
Decode a *fixed64*, *sfixed64* or *double* value. ::
|
||
|
|
||
8 years ago
|
bool pb_decode_fixed64(pb_istream_t *stream, void *dest);
|
||
8 years ago
|
|
||
|
:stream: Input stream to read from. 8 bytes will be read.
|
||
|
:dest: Pointer to destination *int64_t*, *uint64_t* or *double*.
|
||
|
:returns: True on success, false on IO errors.
|
||
|
|
||
|
Same as `pb_decode_fixed32`_, except this reads 8 bytes.
|
||
|
|
||
|
pb_make_string_substream
|
||
|
------------------------
|
||
|
Decode the length for a field with wire type *PB_WT_STRING* and create a substream for reading the data. ::
|
||
|
|
||
|
bool pb_make_string_substream(pb_istream_t *stream, pb_istream_t *substream);
|
||
|
|
||
|
:stream: Original input stream to read the length and data from.
|
||
|
:substream: New substream that has limited length. Filled in by the function.
|
||
|
:returns: True on success, false if reading the length fails.
|
||
|
|
||
|
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.
|
||
|
|
||
|
pb_close_string_substream
|
||
|
-------------------------
|
||
|
Close the substream created with `pb_make_string_substream`_. ::
|
||
|
|
||
|
void pb_close_string_substream(pb_istream_t *stream, pb_istream_t *substream);
|
||
|
|
||
|
:stream: Original input stream to read the length and data from.
|
||
|
:substream: Substream to close
|
||
|
|
||
|
This function copies back the state from the substream to the parent stream.
|
||
|
It must be called after done with the substream.
|