Compilation options
===================
-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.
+The following options can be specified in one of two ways:
+
+1. Using the -D switch on the C compiler command line.
+2. By #defining them at the top of pb.h.
+
+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_NO_PACKED_STRUCTS Disable packed structs. Increases RAM usage but
+ is necessary on some platforms that do not
+ support unaligned memory access.
+PB_ENABLE_MALLOC Set this to enable dynamic allocation support
+ in the decoder.
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
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.
+PB_SYSTEM_HEADER Replace the standard header files with a single
+ header file. It should define all the required
+ functions and typedefs listed on the
+ `overview page`_. Value must include quotes,
+ for example *#define PB_SYSTEM_HEADER "foo.h"*.
============================ ================================================
The PB_MAX_REQUIRED_FIELDS, PB_FIELD_16BIT and PB_FIELD_32BIT settings allow
automatically by C-preprocessor #if-directives in the generated .pb.h files.
The default setting is to use the smallest datatypes (least resources used).
-
+.. _`overview page`: index.html#compiler-requirements
Proto file options
'nanopb.proto' file in the generator folder:
============================ ================================================
-max_size Allocated size for 'bytes' and 'string' fields.
+max_size Allocated size for *bytes* and *string* fields.
max_count Allocated number of entries in arrays
- ('repeated' fields).
+ (*repeated* fields).
+int_size Override the integer type of a field.
+ (To use e.g. uint8_t to save RAM.)
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.
+ is *FT_DEFAULT*, which selects automatically.
+ You can use *FT_CALLBACK*, *FT_POINTER*,
+ *FT_STATIC* or *FT_IGNORE* to force a callback
+ field, a dynamically allocated 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
+ 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.
+skip_message Skip the whole message from generation.
+no_unions Generate 'oneof' fields as optional fields
+ instead of C unions.
+msgid Specifies a unique id for this message type.
+ Can be used by user code as an identifier.
============================ ================================================
These options can be defined for the .proto files before they are converted
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:
+'myproto.options' in the same directory as the 'myproto.proto'. ::
+
+ # myproto.proto
+ message MyMessage {
+ required string name = 1;
+ repeated int32 ids = 4;
+ }
+
+::
+
+ # myproto.options
+ MyMessage.name max_size:40
+ MyMessage.ids max_count:5
+
+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 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
+
+ - *\** 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.
+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 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:
+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];
+
+ message MyMessage {
+ required string name = 1 [(nanopb).max_size = 40];
+ repeated int32 ids = 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
PB_WT_32BIT = 5
} pb_wire_type_t;
+pb_extension_type_t
+-------------------
+Defines the handler functions and auxiliary data for a field that extends
+another message. Usually autogenerated by *nanopb_generator.py*::
+ typedef struct {
+ bool (*decode)(pb_istream_t *stream, pb_extension_t *extension,
+ uint32_t tag, pb_wire_type_t wire_type);
+ bool (*encode)(pb_ostream_t *stream, const pb_extension_t *extension);
+ const void *arg;
+ } pb_extension_type_t;
+
+In the normal case, the function pointers are *NULL* and the decoder and
+encoder use their internal implementations. The internal implementations
+assume that *arg* points to a *pb_field_t* that describes the field in question.
+
+To implement custom processing of unknown fields, you can provide pointers
+to your own functions. Their functionality is mostly the same as for normal
+callback fields, except that they get called for any unknown field when decoding.
+
+pb_extension_t
+--------------
+Ties together the extension field type and the storage for the field value::
+
+ typedef struct {
+ const pb_extension_type_t *type;
+ void *dest;
+ pb_extension_t *next;
+ } pb_extension_t;
+
+:type: Pointer to the structure that defines the callback functions.
+:dest: Pointer to the variable that stores the field value
+ (as used by the default extension callback functions.)
+:next: Pointer to the next extension handler, or *NULL*.
+PB_GET_ERROR
+------------
+Get the current error message from a stream, or a placeholder string if
+there is no error message::
+ #define PB_GET_ERROR(stream) (string expression)
+This should be used for printing errors, for example::
+ if (!pb_decode(...))
+ {
+ printf("Decode failed: %s\n", PB_GET_ERROR(stream));
+ }
+The macro only returns pointers to constant strings (in code memory),
+so that there is no need to release the returned pointer.
+PB_RETURN_ERROR
+---------------
+Set the error message and return false::
+
+ #define PB_RETURN_ERROR(stream,msg) (sets error and returns false)
+
+This should be used to handle error conditions inside nanopb functions
+and user callback functions::
+
+ if (error_condition)
+ {
+ PB_RETURN_ERROR(stream, "something went wrong");
+ }
+
+The *msg* parameter must be a constant string.
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.
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. ::
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
+----------
+Releases any dynamically allocated fields.
+
+ void pb_release(const pb_field_t fields[], void *dest_struct);
+
+:fields: A field description array. Usually autogenerated.
+:dest_struct: Pointer to structure where data will be stored.
+
+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_skip_varint
--------------
Skip a varint_ encoded integer without decoding it. ::
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