YAML to JsonObject

[tobozo]

hey @bblanchon and thanks for your awesome library !

Ref.

given the differences/similarities between JSON and YAML, how far is serializeJsonPretty from producing yml output, and how hard would it be to produce an ArduinoYAML library based on your awesome work ?

your answer:

serializeYaml() would be easy, but deserializeYaml() would require a lot of work!

deserializeYaml() is now implemented: https://github.com/tobozo/esp32-yaml

I wish I could produce the serializeYaml() and serializeYmlPretty() for ArduinoJson too but the level of C++ in this library is way beyond my skills.

[bblanchon]

Hi @tobozo,

For serializeYaml(), you need to walk the JsonDocument recursively, as shown in the "Recursive Analyzer" case study in Mastering ArduinoJson.
In summary, you must first test the type of the variant; if it's an object, enumerate the key-value pairs and do a recursive call; if it's an array, enumerate the elements, etc.

Best regards,
Benoit

[tobozo]

thanks for your helpful feedback and marvelous documentation 👍

I came up with this recursive function and got a satisfying result, did I miss anything?

[edit] pasted the non-leaky version + yaml multiline helper

enum JNestingType_t { NONE, SEQ_KEY, MAP_KEY };

#define indent(x) std::string(x*2, ' ').c_str()

// multiline helper
void yaml_multiline_escape_string( Stream* stream, const char* str, size_t length, size_t *bytes_out, size_t depth )
{
  size_t i;
  char c;
  char l = '\0';

  String _str = String(str);
  bool has_multiline = _str.indexOf('\n') > -1;
  if( has_multiline ) *bytes_out += stream->printf("|\n%s",  indent(depth) );

  for (i = 0; i < length; i++) {
    c = *(str + i);
    if( c== '\r' || c=='\n' ) {
      if( l != '\\' && has_multiline ) { // unescaped \r or \n
        if(c == '\r') *bytes_out += 1;  // ignore \r
        else          *bytes_out += stream->printf("\n%s",  indent(depth) ); // print CRLF
      } else {
        if(c == '\n') *bytes_out += stream->printf("\\n");
        else          *bytes_out += stream->printf("\\r");
      }
    } else {
      if( has_multiline ) {
        *bytes_out += stream->printf("%c", c);
      } else {
        if      (c == '\\') *bytes_out += stream->printf("\\\\");
        else if (c == '\0') *bytes_out += stream->printf("\\0");
        else if (c == '\b') *bytes_out += stream->printf("\\b");
        else if (c == '\t') *bytes_out += stream->printf("\\t");
        else                *bytes_out += stream->printf("%c", c);
      }
    }
    l = c; // memoize last char to spot escaped entities
  }
}

// JsonVariant deconstructor => YAML stream
size_t serializeYml_JsonVariant( JsonVariant root, Stream &out, int depth=0, JNestingType_t nt=NONE )
{
  int parent_level = depth>0?depth-1:0;
  size_t out_size = 0;
  if (root.is<JsonArray>()) {
    JsonArray array = root;
    for( size_t i=0; i<array.size(); i++ ) {
      size_t child_depth = array[i].is<JsonObject>() ? depth+1 : depth-1;
      out_size += serializeYml_JsonVariant(array[i], out, child_depth, SEQ_KEY);
    }
  } else if (root.is<JsonObject>()) {
    JsonObject object = root;
    int i = 0;
    for (JsonPair pair : object) {
      bool is_seqfirst = (i++==0 && nt==SEQ_KEY);
      out_size += out.printf("\n%s%s%s: ", is_seqfirst ? indent(parent_level) : indent(depth), is_seqfirst ? "- " : "", pair.key().c_str() );
      out_size += serializeYml_JsonVariant( pair.value(), out, depth+1, MAP_KEY );
    }
  } else if( !root.isNull() ) {
    if( nt == SEQ_KEY ) out_size += out.printf("\n%s%s",  indent(depth), "- " );
    yaml_multiline_escape_string(&out, root.as<String>().c_str(), root.as<String>().length(), &out_size, depth);
  } else {
    // Error, root is null
  }
  return out_size;
}

[bblanchon]

Yep, that's the idea.

[tobozo]

Since most data processing softwares bundle their own codecs when exporting to other formats I mostly wrote this function for ArduinoJson (e.g. as an extra example), but just noticed the label change so I guess it's too much out of scope?

Please let me know if you want a PR for this, I'll add the function to my esp32-yaml library anyway.

thanks again for your support!