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yaml_writer.H
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yaml_writer.H
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/*
** Copyright 2024 Double Precision, Inc.
** See COPYING for distribution information.
*/
#ifndef yaml_writer_H
#define yaml_writer_H
#include <config.h>
#include <yaml.h>
#include <fstream>
#include <string>
#include <vector>
#include <memory>
#include <type_traits>
///////////////////////////////////////////////////////////////////////////
//
// Some basic, generic scaffolding for writing out YAML. This is used to
// update the runlevel configuration file, to specify the default runlevel,
// and convert /etc/inittab to unit files.
struct yaml_writer;
extern "C" int write_yaml_data(void *data,
unsigned char *buffer,
size_t size);
// Write out a YAML node.
struct yaml_write_node {
virtual bool write(yaml_writer &w) const=0;
};
// RAII wrapper for a yaml_emitter.
struct yaml_writer {
std::ostream &o;
yaml_emitter_t emitter;
bool initialized{false};
yaml_writer(std::ostream &o) : o{o}
{
if (!yaml_emitter_initialize(&emitter))
return;
initialized=true;
yaml_emitter_set_output(&emitter, &write_yaml_data, &o);
}
~yaml_writer()
{
if (!initialized)
return;
yaml_emitter_delete(&emitter);
}
// Write out YAML documents.
template<typename iter>
bool write(iter b, iter e)
{
yaml_event_t stream_start, stream_end;
yaml_event_t doc_start, doc_end;
if (!yaml_stream_start_event_initialize(
&stream_start,
YAML_ANY_ENCODING))
return false;
if (!yaml_emitter_emit(&emitter, &stream_start))
return false;
for (; b != e; ++b)
{
if (!yaml_document_start_event_initialize(
&doc_start,
NULL, NULL, NULL, 1))
return false;
if (!yaml_emitter_emit(&emitter, &doc_start))
return false;
if (!b->write(*this))
return false;
if (!yaml_document_end_event_initialize(&doc_end, 1))
return false;
if (!yaml_emitter_emit(&emitter, &doc_end))
return false;
}
if (!yaml_stream_end_event_initialize(&stream_end))
return false;
if (!yaml_emitter_emit(&emitter, &stream_end))
return false;
return true;
}
bool write(const yaml_write_node &n)
{
return write(&n, &n+1);
}
};
// Write out a scalar.
// The object owns a std::string with the scalar's value.
struct yaml_write_scalar : yaml_write_node {
std::string s;
yaml_write_scalar(std::string s) : s{std::move(s)}
{
}
bool write(yaml_writer &w) const override
{
yaml_event_t event;
if (!yaml_scalar_event_initialize(
&event, NULL, NULL,
reinterpret_cast<const yaml_char_t *>(s.c_str()),
s.size(),
1, 1,
YAML_ANY_SCALAR_STYLE))
return false;
if (!yaml_emitter_emit(&w.emitter, &event))
return false;
return true;
}
};
// Write out a map. The map is represented as a vector of key/value tuples.
typedef std::vector<std::tuple<std::shared_ptr<yaml_write_node>,
std::shared_ptr<yaml_write_node>>> yaml_map_t;
struct yaml_write_map : yaml_write_node {
yaml_map_t map;
yaml_write_map(yaml_map_t map) : map{std::move(map)}
{
}
bool write(yaml_writer &w) const override
{
yaml_event_t start_event, end_event;
if (!yaml_mapping_start_event_initialize(
&start_event,
NULL, NULL, 1, YAML_ANY_MAPPING_STYLE
))
return false;
if (!yaml_emitter_emit(&w.emitter, &start_event))
return false;
for ( auto &[key, value] : map)
{
if (!key->write(w) || !value->write(w))
return false;
}
if (!yaml_mapping_end_event_initialize(&end_event))
return false;
if (!yaml_emitter_emit(&w.emitter, &end_event))
return false;
return true;
}
};
typedef std::vector<std::shared_ptr<yaml_write_node>> yaml_seq_t;
// Write out a YAML sequence. The sequence naturally gets defined as a vector.
struct yaml_write_seq : yaml_write_node {
yaml_seq_t seq;
template<typename iter, typename=
std::enable_if_t<std::is_same_v<typename iter::value_type,
std::string>>>
yaml_write_seq(iter b, iter e)
{
seq.reserve(std::distance(b, e));
while (b != e)
{
seq.push_back(std::make_shared<yaml_write_scalar>(*b));
++b;
}
}
yaml_write_seq(yaml_seq_t seq)
: seq{std::move(seq)}
{
}
bool write(yaml_writer &w) const override
{
yaml_event_t start_event, end_event;
if (!yaml_sequence_start_event_initialize(
&start_event,
NULL, NULL, 1, YAML_ANY_SEQUENCE_STYLE
))
return false;
if (!yaml_emitter_emit(&w.emitter, &start_event))
return false;
for ( auto &value : seq)
if (!value->write(w))
return false;
if (!yaml_sequence_end_event_initialize(&end_event))
return false;
if (!yaml_emitter_emit(&w.emitter, &end_event))
return false;
return true;
}
};
#endif