YAML to Argdata conversion classes

Argdata is a binary serialisation format that is structurally similar to YAML. The main difference is that Argdata allows for the embedding of POSIX file descriptors. This makes it useful for CloudABI to pass configuration and resources to programs on startup. ARPC also uses Argdata to make it possible to send RPCs to processes with file descriptors attached.

There are cases in which we want to convert YAML to Argdata, as done by the cloudabi-run utility and Scuba. To ensure that these tools process YAML in a uniform way, this package provides some wrappers around yaml-cpp to do this conversion.

These classes allow for the conversion of all YAML nodes, with the exception of ones that inject file descriptors. This is because file descriptor injection is specific to the context in which the YAML is parsed. For example, cloudabi-run allows you to open arbitrary paths on disk, whereas Scuba doesn't support this. Conversely, Scuba allows you to interact with Kubernetes' networking. This functionality will need to be added in the form of a separate adapter class.

Example usage

#include <yaml2argdata/yaml_argdata_factory.h>
#include <yaml2argdata/yaml_builder.h>
#include <yaml2argdata/yaml_canonicalizing_factory.h>
#include <yaml2argdata/yaml_error_factory.h>
#include <yaml2argdata/yaml_factory.h>

using yaml2argdata::YAMLArgdataFactory;
using yaml2argdata::YAMLBuilder;
using yaml2argdata::YAMLCanonicalizingFactory;
using yaml2argdata::YAMLErrorFactory;
using yaml2argdata::YAMLFactory;

class MyOwnFileDescriptorFactory : public YAMLFactory<const argdata_t*> {
  ...
};

... {
  YAMLErrorFactory<const argdata_t*> error_factory;
  MyOwnFileDescriptorFactory file_descriptor_factory(&error_factory);
  YAMLArgdataFactory argdata_factory(&file_descriptor_factory);
  YAMLCanonicalizingFactory<const argdata_t*> canonicalizing_factory(
      &argdata_factory);
  YAMLBuilder<const argdata_t*> builder(&canonicalizing_factory);
  std::istream* argdata_stream = ...;
  const argdata_t* argdata = builder.Build(argdata_stream);
}