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+=====================================
+Nanopb: Migration from older versions
+=====================================
+
+.. include :: menu.rst
+
+This document details all the breaking changes that have been made to nanopb
+since its initial release. For each change, the rationale and required
+modifications of user applications are explained. Also any error indications
+are included, in order to make it easier to find this document.
+
+.. contents ::
+
+Nanopb-0.3.5 (2016-02-13)
+=========================
+
+Add support for platforms without uint8_t
+-----------------------------------------
+**Rationale:** Some platforms cannot access 8-bit sized values directly, and
+do not define *uint8_t*. Nanopb previously didn't support these platforms.
+
+**Changes:** References to *uint8_t* were replaced with several alternatives,
+one of them being a new *pb_byte_t* typedef. This in turn uses *uint_least8_t*
+which means the smallest available type.
+
+**Required actions:** If your platform does not have a standards-compliant
+*stdint.h*, it may lack the definition for *[u]int_least8_t*. This must be
+added manually, example can be found in *extra/pb_syshdr.h*.
+
+**Error indications:** Compiler error: "unknown type name 'uint_least8_t'".
+
+Nanopb-0.3.2 (2015-01-24)
+=========================
+
+Add support for OneOfs
+----------------------
+**Rationale:** Previously nanopb did not support the *oneof* construct in
+*.proto* files. Those fields were generated as regular *optional* fields.
+
+**Changes:** OneOfs are now generated as C unions. Callback fields are not
+supported inside oneof and generator gives an error.
+
+**Required actions:** The generator option *no_unions* can be used to restore old
+behaviour and to allow callbacks to be used. To use unions, one change is
+needed: use *which_xxxx* field to detect which field is present, instead
+of *has_xxxx*. Compare the value against *MyStruct_myfield_tag*.
+
+**Error indications:** Generator error: "Callback fields inside of oneof are
+not supported". Compiler error: "Message" has no member named "has_xxxx".
+
+Nanopb-0.3.0 (2014-08-26)
+=========================
+
+Separate field iterator logic to pb_common.c
+--------------------------------------------
+**Rationale:** Originally, the field iteration logic was simple enough to be
+duplicated in *pb_decode.c* and *pb_encode.c*. New field types have made the
+logic more complex, which required the creation of a new file to contain the
+common functionality.
+
+**Changes:** There is a new file, *pb_common.c*, which must be included in
+builds.
+
+**Required actions:** Add *pb_common.c* to build rules. This file is always
+required. Either *pb_decode.c* or *pb_encode.c* can still be left out if some
+functionality is not needed.
+
+**Error indications:** Linker error: undefined reference to
+*pb_field_iter_begin*, *pb_field_iter_next* or similar.
+
+Change data type of field counts to pb_size_t
+---------------------------------------------
+**Rationale:** Often nanopb is used with small arrays, such as 255 items or
+less. Using a full *size_t* field to store the array count wastes memory if
+there are many arrays. There already exists parameters *PB_FIELD_16BIT* and
+*PB_FIELD_32BIT* which tell nanopb what is the maximum size of arrays in use.
+
+**Changes:** Generator will now use *pb_size_t* for the array *_count* fields.
+The size of the type will be controlled by the *PB_FIELD_16BIT* and
+*PB_FIELD_32BIT* compilation time options.
+
+**Required actions:** Regenerate all *.pb.h* files. In some cases casts to the
+*pb_size_t* type may need to be added in the user code when accessing the
+*_count* fields.
+
+**Error indications:** Incorrect data at runtime, crashes. But note that other
+changes in the same version already require regenerating the files and have
+better indications of errors, so this is only an issue for development
+versions.
+
+Renamed some macros and identifiers
+-----------------------------------
+**Rationale:** Some names in nanopb core were badly chosen and conflicted with
+ISO C99 reserved names or lacked a prefix. While they haven't caused trouble
+so far, it is reasonable to switch to non-conflicting names as these are rarely
+used from user code.
+
+**Changes:** The following identifier names have changed:
+
+  * Macros:
+  
+    * STATIC_ASSERT(x) -> PB_STATIC_ASSERT(x)
+    * UNUSED(x) -> PB_UNUSED(x)
+  
+  * Include guards:
+  
+    * _PB_filename_ -> PB_filename_INCLUDED
+  
+  * Structure forward declaration tags:
+  
+    * _pb_field_t -> pb_field_s
+    * _pb_bytes_array_t -> pb_bytes_array_s
+    * _pb_callback_t -> pb_callback_s
+    * _pb_extension_type_t -> pb_extension_type_s
+    * _pb_extension_t -> pb_extension_s
+    * _pb_istream_t -> pb_istream_s
+    * _pb_ostream_t -> pb_ostream_s
+
+**Required actions:** Regenerate all *.pb.c* files. If you use any of the above
+identifiers in your application code, perform search-replace to the new name.
+
+**Error indications:** Compiler errors on lines with the macro/type names.
+
+Nanopb-0.2.9 (2014-08-09)
+=========================
+
+Change semantics of generator -e option
+---------------------------------------
+**Rationale:** Some compilers do not accept filenames with two dots (like
+in default extension .pb.c). The *-e* option to the generator allowed changing
+the extension, but not skipping the extra dot.
+
+**Changes:** The *-e* option in generator will no longer add the prepending
+dot. The default value has been adjusted accordingly to *.pb.c* to keep the
+default behaviour the same as before.
+
+**Required actions:** Only if using the generator -e option. Add dot before
+the parameter value on the command line.
+
+**Error indications:** File not found when trying to compile generated files.
+
+Nanopb-0.2.7 (2014-04-07)
+=========================
+
+Changed pointer-type bytes field datatype
+-----------------------------------------
+**Rationale:** In the initial pointer encoding support since nanopb-0.2.5,
+the bytes type used a separate *pb_bytes_ptr_t* type to represent *bytes*
+fields. This made it easy to encode data from a separate, user-allocated
+buffer. However, it made the internal logic more complex and was inconsistent
+with the other types.
+
+**Changes:** Dynamically allocated bytes fields now have the *pb_bytes_array_t*
+type, just like statically allocated ones.
+
+**Required actions:** Only if using pointer-type fields with the bytes datatype.
+Change any access to *msg->field.size* to *msg->field->size*. Change any
+allocation to reserve space of amount *PB_BYTES_ARRAY_T_ALLOCSIZE(n)*. If the
+data pointer was begin assigned from external source, implement the field using
+a callback function instead.
+
+**Error indications:** Compiler error: unknown type name *pb_bytes_ptr_t*.
+
+Nanopb-0.2.4 (2013-11-07)
+=========================
+
+Remove the NANOPB_INTERNALS compilation option
+----------------------------------------------
+**Rationale:** Having the option in the headers required the functions to
+be non-static, even if the option is not used. This caused errors on some
+static analysis tools.
+
+**Changes:** The *#ifdef* and associated functions were removed from the
+header.
+
+**Required actions:** Only if the *NANOPB_INTERNALS* option was previously
+used. Actions are as listed under nanopb-0.1.3 and nanopb-0.1.6.
+
+**Error indications:** Compiler warning: implicit declaration of function
+*pb_dec_string*, *pb_enc_string*, or similar.
+
+Nanopb-0.2.1 (2013-04-14)
+=========================
+
+Callback function signature
+---------------------------
+**Rationale:** Previously the auxilary data to field callbacks was passed
+as *void\**. This allowed passing of any data, but made it unnecessarily
+complex to return a pointer from callback.
+
+**Changes:** The callback function parameter was changed to *void\*\**.
+
+**Required actions:** You can continue using the old callback style by
+defining *PB_OLD_CALLBACK_STYLE*. Recommended action is to:
+
+  * Change the callback signatures to contain *void\*\** for decoders and
+    *void \* const \** for encoders.
+  * Change the callback function body to use *\*arg* instead of *arg*.
+
+**Error indications:** Compiler warning: assignment from incompatible
+pointer type, when initializing *funcs.encode* or *funcs.decode*.
+
+Nanopb-0.2.0 (2013-03-02)
+=========================
+
+Reformatted generated .pb.c file using macros
+---------------------------------------------
+**Rationale:** Previously the generator made a list of C *pb_field_t*
+initializers in the .pb.c file. This led to a need to regenerate all .pb.c
+files after even small changes to the *pb_field_t* definition.
+
+**Changes:** Macros were added to pb.h which allow for cleaner definition
+of the .pb.c contents. By changing the macro definitions, changes to the
+field structure are possible without breaking compatibility with old .pb.c
+files.
+
+**Required actions:** Regenerate all .pb.c files from the .proto sources.
+
+**Error indications:** Compiler warning: implicit declaration of function
+*pb_delta_end*.
+
+Changed pb_type_t definitions
+-----------------------------
+**Rationale:** The *pb_type_t* was previously an enumeration type. This
+caused warnings on some compilers when using bitwise operations to set flags
+inside the values.
+
+**Changes:** The *pb_type_t* was changed to *typedef uint8_t*. The values
+were changed to *#define*. Some value names were changed for consistency.
+
+**Required actions:** Only if you directly access the `pb_field_t` contents
+in your own code, something which is not usually done. Needed changes:
+
+  * Change *PB_HTYPE_ARRAY* to *PB_HTYPE_REPEATED*.
+  * Change *PB_HTYPE_CALLBACK* to *PB_ATYPE()* and *PB_ATYPE_CALLBACK*.
+
+**Error indications:** Compiler error: *PB_HTYPE_ARRAY* or *PB_HTYPE_CALLBACK*
+undeclared.
+
+Nanopb-0.1.6 (2012-09-02)
+=========================
+
+Refactored field decoder interface
+----------------------------------
+**Rationale:** Similarly to field encoders in nanopb-0.1.3.
+
+**Changes:** New functions with names *pb_decode_\** were added.
+
+**Required actions:** By defining NANOPB_INTERNALS, you can still keep using
+the old functions. Recommended action is to replace any calls with the newer
+*pb_decode_\** equivalents.
+
+**Error indications:** Compiler warning: implicit declaration of function
+*pb_dec_string*, *pb_dec_varint*, *pb_dec_submessage* or similar.
+
+Nanopb-0.1.3 (2012-06-12)
+=========================
+
+Refactored field encoder interface
+----------------------------------
+**Rationale:** The old *pb_enc_\** functions were designed mostly for the
+internal use by the core. Because they are internally accessed through
+function pointers, their signatures had to be common. This led to a confusing
+interface for external users.
+
+**Changes:** New functions with names *pb_encode_\** were added. These have
+easier to use interfaces. The old functions are now only thin wrappers for
+the new interface.
+
+**Required actions:** By defining NANOPB_INTERNALS, you can still keep using
+the old functions. Recommended action is to replace any calls with the newer
+*pb_encode_\** equivalents.
+
+**Error indications:** Compiler warning: implicit declaration of function
+*pb_enc_string*, *pb_enc_varint, *pb_enc_submessage* or similar.
+