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Diffstat (limited to 'docs')
| -rw-r--r-- | docs/concepts.rst | 47 | ||||
| -rw-r--r-- | docs/reference.rst | 192 |
2 files changed, 191 insertions, 48 deletions
diff --git a/docs/concepts.rst b/docs/concepts.rst index 4bc0dee8..2ae76521 100644 --- a/docs/concepts.rst +++ b/docs/concepts.rst @@ -10,47 +10,40 @@ The things outlined here are the underlying concepts of the nanopb design. Proto files =========== -All Protocol Buffers implementations use .proto files to describe the message format. -The point of these files is to be a portable interface description language. +All Protocol Buffers implementations use .proto files to describe the message +format. The point of these files is to be a portable interface description +language. Compiling .proto files for nanopb --------------------------------- -Nanopb uses the Google's protoc compiler to parse the .proto file, and then a python script to generate the C header and source code from it:: +Nanopb uses the Google's protoc compiler to parse the .proto file, and then a +python script to generate the C header and source code from it:: user@host:~$ protoc -omessage.pb message.proto user@host:~$ python ../generator/nanopb_generator.py message.pb Writing to message.h and message.c user@host:~$ -Compiling .proto files with nanopb options ------------------------------------------- -Nanopb defines two extensions for message fields described in .proto files: *max_size* and *max_count*. -These are the maximum size of a string and maximum count of items in an array:: +Modifying generator behaviour +----------------------------- +Using generator options, you can set maximum sizes for fields in order to +allocate them statically. The preferred way to do this is to create an .options +file with the same name as your .proto file:: - required string name = 1 [(nanopb).max_size = 40]; - repeated PhoneNumber phone = 4 [(nanopb).max_count = 5]; + # Foo.proto + message Foo { + required string name = 1; + } -To use these extensions, you need to place an import statement in the beginning of the file:: - - import "nanopb.proto"; - -This file, in turn, requires the file *google/protobuf/descriptor.proto*. This is usually installed under */usr/include*. Therefore, to compile a .proto file which uses options, use a protoc command similar to:: - - protoc -I/usr/include -Inanopb/generator -I. -omessage.pb message.proto - -The options can be defined in file, message and field scopes:: - - option (nanopb_fileopt).max_size = 20; // File scope - message Message - { - option (nanopb_msgopt).max_size = 30; // Message scope - required string fieldsize = 1 [(nanopb).max_size = 40]; // Field scope - } +:: -It is also possible to give the options on command line, but then they will affect the whole file. For example:: + # Foo.options + Foo.name max_size:16 - user@host:~$ python ../generator/nanopb_generator.py -s 'max_size: 20' message.pb +For more information on this, see the `Proto file options`_ section in the +reference manual. +.. _`Proto file options`: reference.html#proto-file-options Streams ======= diff --git a/docs/reference.rst b/docs/reference.rst index 0db8e43e..6094e13c 100644 --- a/docs/reference.rst +++ b/docs/reference.rst @@ -6,31 +6,160 @@ Nanopb: API reference .. contents :: + + + Compilation options =================== -The following options can be specified using -D switch given to the C compiler: - -============================ ================================================================================================ -__BIG_ENDIAN__ Set this if your platform stores integers and floats in big-endian format. - Mixed-endian systems (different layout for ints and floats) are currently not supported. -NANOPB_INTERNALS Set this to expose the field encoder functions that are hidden since nanopb-0.1.3. -PB_MAX_REQUIRED_FIELDS Maximum number of required fields to check for presence. Default value is 64. Increases stack - usage 1 byte per every 8 fields. Compiler warning will tell if you need this. -PB_FIELD_16BIT Add support for tag numbers > 255 and fields larger than 255 bytes or 255 array entries. - Increases code size 3 bytes per each field. Compiler error will tell if you need this. -PB_FIELD_32BIT Add support for tag numbers > 65535 and fields larger than 65535 bytes or 65535 array entries. - Increases code size 9 bytes per each field. Compiler error will tell if you need this. -PB_NO_ERRMSG Disables the support for error messages; only error information is the true/false return value. - Decreases the code size by a few hundred bytes. -PB_BUFFER_ONLY Disables the support for custom streams. Only supports encoding to memory buffers. - Speeds up execution and decreases code size slightly. -PB_OLD_CALLBACK_STYLE Use the old function signature (void\* instead of void\*\*) for callback fields. This was the +The following options can be specified using -D switch given to the C compiler +when compiling the nanopb library and applications using it. You must have the +same settings for the nanopb library and all code that includes pb.h. + +============================ ================================================ +__BIG_ENDIAN__ Set this if your platform stores integers and + floats in big-endian format. Mixed-endian + systems (different layout for ints and floats) + are currently not supported. +NANOPB_INTERNALS Set this to expose the field encoder functions + that are hidden since nanopb-0.1.3. +PB_MAX_REQUIRED_FIELDS Maximum number of required fields to check for + presence. Default value is 64. Increases stack + usage 1 byte per every 8 fields. Compiler + warning will tell if you need this. +PB_FIELD_16BIT Add support for tag numbers > 255 and fields + larger than 255 bytes or 255 array entries. + Increases code size 3 bytes per each field. + Compiler error will tell if you need this. +PB_FIELD_32BIT Add support for tag numbers > 65535 and fields + larger than 65535 bytes or 65535 array entries. + Increases code size 9 bytes per each field. + Compiler error will tell if you need this. +PB_NO_ERRMSG Disables the support for error messages; only + error information is the true/false return + value. Decreases the code size by a few hundred + bytes. +PB_BUFFER_ONLY Disables the support for custom streams. Only + supports encoding and decoding with memory + buffers. Speeds up execution and decreases code + size slightly. +PB_OLD_CALLBACK_STYLE Use the old function signature (void\* instead + of void\*\*) for callback fields. This was the default until nanopb-0.2.1. -============================ ================================================================================================ +============================ ================================================ + +The PB_MAX_REQUIRED_FIELDS, PB_FIELD_16BIT and PB_FIELD_32BIT settings allow +raising some datatype limits to suit larger messages. Their need is recognized +automatically by C-preprocessor #if-directives in the generated .pb.h files. +The default setting is to use the smallest datatypes (least resources used). + + + + +Proto file options +================== +The generator behaviour can be adjusted using these options, defined in the +'nanopb.proto' file in the generator folder: + +============================ ================================================ +max_size Allocated size for 'bytes' and 'string' fields. +max_count Allocated number of entries in arrays + ('repeated' fields). +type Type of the generated field. Default value + is FT_DEFAULT, which selects automatically. + You can use FT_CALLBACK, FT_STATIC or FT_IGNORE + to force a callback field, a static field or + to completely ignore the field. +long_names Prefix the enum name to the enum value in + definitions, i.e. 'EnumName_EnumValue'. Enabled + by default. +packed_struct Make the generated structures packed. + NOTE: This cannot be used on CPUs that break + on unaligned accesses to variables. +============================ ================================================ + +These options can be defined for the .proto files before they are converted +using the nanopb-generatory.py. There are three ways to define the options: + +1. Using a separate .options file. + This is the preferred way as of nanopb-0.2.1, because it has the best + compatibility with other protobuf libraries. +2. Defining the options on the command line of nanopb_generator.py. + This only makes sense for settings that apply to a whole file. +3. Defining the options in the .proto file using the nanopb extensions. + This is the way used in nanopb-0.1, and will remain supported in the + future. It however sometimes causes trouble when using the .proto file + with other protobuf libraries. + +The effect of the options is the same no matter how they are given. The most +common purpose is to define maximum size for string fields in order to +statically allocate them. + +Defining the options in a .options file +--------------------------------------- +The preferred way to define options is to have a separate file +'myproto.options' in the same directory as the 'myproto.proto'. The +generator will automatically search for this file and read the options from +it. The file format is as follows: + +* Lines starting with '#' or '//' are regarded as comments. +* Blank lines are ignored. +* All other lines should start with a field name pattern, followed by one or + more options. For example: *"MyMessage.myfield max_size:5 max_count:10"*. +* The field name pattern is matched against a string of form 'Message.field'. + For nested messages, the string is 'Message.SubMessage.field'. +* The field name pattern may use the notation recognized by Python fnmatch(): + - \* matches any part of string, like 'Message.\*' for all fields + - \? matches any single character + - [seq] matches any of characters 's', 'e' and 'q' + - [!seq] matches any other character +* The options are written as 'option_name:option_value' and several options + can be defined on same line, separated by whitespace. +* Options defined later in the file override the ones specified earlier, so + it makes sense to define wildcard options first in the file and more specific + ones later. + +If preferred, the name of the options file can be set using the command line +switch '-f' to nanopb_generator.py. + +Defining the options on command line +------------------------------------ +The nanopb_generator.py has a simple command line option '-s OPTION:VALUE'. +The setting applies to the whole file that is being processed. + +Defining the options in the .proto file +--------------------------------------- +The .proto file format allows defining custom options for the fields. +The nanopb library comes with 'nanopb.proto' which does exactly that, allowing +you do define the options directly in the .proto file: + + import "nanopb.proto"; + required string name = 1 [(nanopb).max_size = 40]; + repeated PhoneNumber phone = 4 [(nanopb).max_count = 5]; + +A small complication is that you have to set the include path of protoc so that +nanopb.proto can be found. This file, in turn, requires the file +*google/protobuf/descriptor.proto*. This is usually installed under +*/usr/include*. Therefore, to compile a .proto file which uses options, use a +protoc command similar to:: + + protoc -I/usr/include -Inanopb/generator -I. -omessage.pb message.proto + +The options can be defined in file, message and field scopes:: + + option (nanopb_fileopt).max_size = 20; // File scope + message Message + { + option (nanopb_msgopt).max_size = 30; // Message scope + required string fieldsize = 1 [(nanopb).max_size = 40]; // Field scope + } + + + + + + + -The PB_MAX_REQUIRED_FIELDS, PB_FIELD_16BIT and PB_FIELD_32BIT settings allow raising some datatype limits to suit larger messages. -Their need is recognized automatically by C-preprocessor #if-directives in the generated .pb.h files. The default setting is to use -the smallest datatypes (least resources used). pb.h ==== @@ -148,6 +277,16 @@ Protocol Buffers wire types. These are used with `pb_encode_tag`_. :: PB_WT_32BIT = 5 } pb_wire_type_t; + + + + + + + + + + pb_encode.h =========== @@ -297,6 +436,17 @@ In Protocol Buffers format, the submessage size must be written before the subme 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 =========== |