JSON as a message is not escaped/formatted correctly?

[persona94]

I set up my formatter with a custom pattern

formatter->add_flag<ThreadIdFlags>('j').set_pattern("{\"@timestamp\":\"%Y-%m-%dT%H:%M:%S.%fZ\",\"message\":\"%v\",\"level\":\"%l\",%j,\"source\":\"%s\",\"function\":\"%!\",\"line\":\"%#\"}");
spdlog::set_formatter(std::move(formatter));

My flag "j" adds a certain uid that has relevance to my code

While calling the log, I use nlohmann::json to generate a json

nlohmann::json j;
  
j["k1"] = "v1";
  
j["k2"] = 2;
 
LOG_ERROR(j.dump()); //LOG_ERROR is SPDLOG_ERROR

The output json is invalid in the "message" field:

{"@timestamp":"2023-12-27T15:46:41.636829Z","message":"{"k1":"v1","k2":2}","level":"error","uid":25,"source":"main.cpp","function":"testPost","line":"23"}

It would work if the string supplied to message were escaped but nlohmann::json doesn't have that capability because .dump() prints the object per json spec. Any suggestions on what can be done here? Should I write a custom print for my json obj that returns the json as a string that has the key-value pairs without dquotes?

[tt4g]

Do you want to output escaped JSON for the message?
If you want the entire log message to be in JSON format, wouldn't it be odd to output escaped JSON only for the message?

If you wanted to output a JSON object in the message property, just replace "%v" with %v.

See also: #1797, #2592, #2861

[persona94]

The message could be anything - string, integer, pointers, or a json blob/object. We would like to see all messages enclosed by dquotes so I have to go with "%v". If I do that, and don't escape a json object (i.e. the message field then the entire json (i.e. the full log) will be an invalid json.

Note: Neither LOG_INFO(json.dump()) nor LOG_INFO("{}", json.dump()) escape the message

[tt4g]

spdlog does not support the JSON format and does not have a JSON escaping API.
If you want to print escaped JSON, it is your responsibility to implement the escaping process.

[persona94]

Fair enough. Thanks