SWI-Prolog -- protobuf_parse_from

Documentation
- Reference manual
- Packages
  - Google's Protocol Buffers Library
    - library(protobufs): Google's Protocol Buffers ("protobufs")

Availability::- use_module(library(protobufs)).(can be autoloaded)

[semidet]protobuf_parse_from_codes(+WireCodes:list(int), +MessageType:atom, -Term)

Process bytes (list of int) that is the serialized form of a message (designated by MessageType), creating a Prolog term.

Protoc must have been run (with the --swipl_out= option and the resulting top-level _pb.pl file loaded. For more details, see the "protoc" section of the overview documentation.

Fails if the message can't be parsed or if the appropriate meta-data from protoc hasn't been loaded.

All fields that are omitted from the WireCodes are set to their default values (typically the empty string or 0, depending on the type; or [] for repeated groups). There is no way of testing whether a value was specified in WireCodes or given its default value (that is, there is no equivalent of the Python implementation's =HasField`). Optional embedded messages and groups do not have any default value -- you must check their existence by using get_dict/3 or similar. If a field is part of a "oneof" set, then none of the other fields is set. You can determine which field had a value by using get_dict/3.

`WireCodes`	Wire format of the message from e.g., read_stream_to_codes/2. (The stream should have options `encoding(octet)` and `type(binary)`, either as options to read_file_to_codes/3 or by calling set_stream/2 on the stream to read_stream_to_codes/2.)
`MessageType`	Fully qualified message name (from the `.proto` file's `package` and `message`). For example, if the `package` is `google.protobuf` and the message is `FileDescriptorSet`, then you would use `'.google.protobuf.FileDescriptorSet'` or `'google.protobuf.FileDescriptorSet'`. If there's no package name, use e.g.: `'MyMessage` or `'.MyMessage'`. You can see the packages by looking at `protobufs:proto_meta_package(Pkg,File,_)` and the message names and fields by `protobufs:proto_meta_field_name('.google.protobuf.FileDescriptorSet', FieldNumber, FieldName, FqnName)` (the initial’.’is not optional for these facts, only for the top-level name given to protobuf_serialize_to_codes/3).
`Term`	The generated term, as nested dicts.

Errors: version_error(Module-Version) you need to recompile the Module with a newer version of protoc.
See also: library(protobufs): Google's Protocol Buffers (section 1.3.1)
bug: - Ignores .proto extensions.
- map fields don't get special treatment (but see protobuf_map_pairs/3).
- Generates fields in a different order from the C++, Python, Java implementations, which use the field number to determine field order whereas currently this implementation uses field name. (This isn't stricly speaking a bug, because it's allowed by the specification; but it might cause some surprise.)
To be done: - document the generated terms (see library(json) and json_read_dict/3)
- add options such as true and value_string_as (similar to json_read_dict/3)
- add option for form of the dict tags (fully qualified or not)
- add option for outputting fields in the C++/Python/Java order (by field number rather than by field name).