Write in existing MCAP

[jdsika]

• Use osi version in schema name in order to make sure that the schema was not already registered
• Read existing schemas
• Can schemas have the same name?

[ClemensLinnhoff]

Let's wait for merge of initial PR, then implement this on separate branch.

[jdsika]

This method must be adapted to read exisitng meta data and adapt:

mcap::Metadata MCAPTraceFileWriter::PrepareRequiredFileMetadata() {
    mcap::Metadata metadata;
    metadata.name = "net.asam.osi.trace";

    const auto osi_version = osi3::InterfaceVersion::descriptor()->file()->options().GetExtension(osi3::current_interface_version);
    const auto osi_version_string =
        std::to_string(osi_version.version_major()) + "." + std::to_string(osi_version.version_minor()) + "." + std::to_string(osi_version.version_patch());
    metadata.metadata["version"] = osi_version_string;
    metadata.metadata["min_osi_version"] = osi_version_string;
    metadata.metadata["max_osi_version"] = osi_version_string;
    metadata.metadata["min_protobuf_version"] = google::protobuf::internal::VersionString(GOOGLE_PROTOBUF_VERSION);
    metadata.metadata["max_protobuf_version"] = google::protobuf::internal::VersionString(GOOGLE_PROTOBUF_VERSION);

    return metadata;
}

[TimmRuppert]

According to my understanding it is not possible to add data to an existing MCAP file in-place

We tend to view mcap files as append-only, write once, robot log files rather than "database" files which you can go back and modify.
foxglove/mcap#1084 (reply in thread)

Nonetheless, it would be possible to create a complete new trace file, add data and replace the existing file.

In any case, I am not sure where to add it. The writer would require a lot of changes to handle something like this transparently (e.g. the user simple using the Open() function on an existing trace file). I would argue for an new MCAPTraceFileAppender class.