=================
For the runtime program, you always need *pb.h* for type declarations.
-Depending on whether you want to encode, decode or both, you also need *pb_encode.h/c* or *pb_decode.h/c*.
+Depending on whether you want to encode, decode, or both, you also need *pb_encode.h/c* or *pb_decode.h/c*.
-The high-level encoding and decoding functions take an array of *pb_field_t* structures, which describes the fields of a message structure. Usually you want these autogenerated from a *.proto* file. The tool string *nanopb_generator.py* accomplishes this.
+The high-level encoding and decoding functions take an array of *pb_field_t* structures, which describes the fields of a message structure. Usually you want these autogenerated from a *.proto* file. The tool script *nanopb_generator.py* accomplishes this.
+
+.. image:: generator_flow.png
So a typical project might include these files:
1) Nanopb runtime library:
- pb.h
- - pb_decode.h and pb_decode.c
- - pb_encode.h and pb_encode.c
+ - pb_decode.h and pb_decode.c (needed for decoding messages)
+ - pb_encode.h and pb_encode.c (needed for encoding messages)
2) Protocol description (you can have many):
- - person.proto
- - person.c (autogenerated, contains initializers for const arrays)
- - person.h (autogenerated, contains type declarations)
+ - person.proto (just an example)
+ - person.pb.c (autogenerated, contains initializers for const arrays)
+ - person.pb.h (autogenerated, contains type declarations)
Features and limitations
========================
#) Small code size (2–10 kB depending on processor)
#) Small ram usage (typically 200 bytes)
#) Allows specifying maximum size for strings and arrays, so that they can be allocated statically.
-#) No malloc needed: everything is stored on the stack.
+#) No malloc needed: everything can be allocated statically or on the stack.
#) You can use either encoder or decoder alone to cut the code size in half.
**Limitations**
-#) User must provide callbacks when decoding arrays or strings without maximum size.
+#) User must provide callbacks when decoding arrays or strings without maximum size. Malloc support could be added as a separate module.
#) Some speed has been sacrificed for code size. For example varint calculations are always done in 64 bits.
#) Encoding is focused on writing to streams. For memory buffers only it could be made more efficient.
#) The deprecated Protocol Buffers feature called "groups" is not supported.
#) Fields in the generated structs are ordered by the tag number, instead of the natural ordering in .proto file.
+#) Unknown fields are not preserved when decoding and re-encoding a message.
+#) Reflection (runtime introspection) is not supported. E.g. you can't request a field by giving its name in a string.
+#) Numeric arrays are always encoded as packed, even if not marked as packed in .proto. This causes incompatibility with decoders that do not support packed format.
+#) Cyclic references between messages are not supported. They could be supported in callback-mode if there was an option in the generator to set the mode.
Getting started
===============
required int32 value = 1;
}
-Save this in *example.proto* and compile it::
+Save this in *message.proto* and compile it::
user@host:~$ protoc -omessage.pb message.proto
- user@host:~$ python ../generator/nanopb_generator.py message.pb
+ user@host:~$ python nanopb/generator/nanopb_generator.py message.pb
-You should now have in *example.h*::
+You should now have in *message.pb.h*::
typedef struct {
int32_t value;
After that, buffer will contain the encoded message.
The number of bytes in the message is stored in *stream.bytes_written*.
-You can feed the message to *protoc --decode=Example example.proto* to verify its validity.
+You can feed the message to *protoc --decode=Example message.proto* to verify its validity.
+
+For complete examples of the simple cases, see *tests/test_decode1.c* and *tests/test_encode1.c*. For an example with network interface, see the *example* subdirectory.
+
+Compiler requirements
+=====================
+Nanopb should compile with most ansi-C compatible compilers. It however requires a few header files to be available:
+
+#) *string.h*, with these functions: *strlen*, *memcpy*, *memset*
+#) *stdint.h*, for definitions of *int32_t* etc.
+#) *stddef.h*, for definition of *size_t*
+#) *stdbool.h*, for definition of *bool*
+
+If these header files do not come with your compiler, you should be able to find suitable replacements online. Mostly the requirements are very simple, just a few basic functions and typedefs.
+
+Debugging and testing
+=====================
+Extensive unittests are included under the *tests* folder. Just type *make* there to run the tests.
+
+This also generates a file called *breakpoints* which includes all lines returning *false* in nanopb. You can use this in gdb by typing *source breakpoints*, after which gdb will break on first nanopb error.
Wishlist
========
Code Review / apps / agl-service-can-low-level.git / blobdiff