Added ability to supply JSON from standard input

README.md

@@ -9,13 +9,26 @@ You will need the following packages: `build-essential` `libsdl2-dev` `libsdl2-i
 Just run `make` and an executable called `trmnl_sdl` should be produced.
 
 # How to use
-1. You will need to write a JSON config file.
-It can either be named `config.json` or you will need to pass it as the first command line parameter to the executable.
+### General use
+1. You will need to write a JSON config file named `config.json`.
 An example structure of the config file can be found in `config_example.json`.
 You can find more info on the available Widgets and their parameters at the end of this file.
 2. Run the executable
 3. Convert the image to a suitable format via an ImageMagick command from below.
 
+### Different ways to supply JSON
+1. Default
+	* Command: `./trmnl_sdl`
+	* JSON Used: `config.json`
+
+2. Specified file
+	* Command: `./trmnl_sdl path/to/json/file.json`
+	* JSON Used: `path/to/json/file.json`
+
+3. Standard input
+	* Command: `./trmnl_sdl -`
+	* JSON Used: Supplied on the standard input for the process.
+
 # ImageMagick commands to prepare image for TRMNL device
 ### Convert image without dithering
 `convert trmnl.png -monochrome -colors 2 -depth 1 -strip png:output.png`

main.cpp

@@ -60,8 +60,18 @@ int main(int argc, char **argv)
 		cfg_filename = argv[1];
 	}
 
-	// Read JSON CFG
-	ok = read_config_json(cfg, cfg_filename);
+	// Read config
+	if ("-" == cfg_filename)
+	{
+		// Read JSON from std input
+		ok = read_config_json(cfg, std::cin);
+	}
+	else
+	{
+		// Read JSON from config file
+		ok = read_config_json(cfg, cfg_filename);
+	}
+
 	if (!ok)
 	{
 		result = -1;

sdl_helpers.cpp

@@ -141,15 +141,20 @@ bool read_config_json(json& cfg, const string& filename, ostream* log)
 	{
 		if (nullptr != log)
 		{
-			*log << "Could not open config.json" << endl;
+			*log << "Could not open config file" << endl;
 		}
 		return false;
 	}
 
+	return read_config_json(cfg, cfg_file, log);
+}
+
+bool read_config_json(json& cfg, istream& in, ostream* log)
+{
 	// Parse with comments
 	try
 	{
-		cfg = json::parse(cfg_file, nullptr, true, true);
+		cfg = json::parse(in, nullptr, true, true);
 	}
 	catch (const std::exception &e)
 	{

sdl_helpers.h

@@ -90,6 +90,12 @@ SDL_Rect surface_align(const SDL_Surface* base, const SDL_Surface* applied,
 // log - output errors to this ostream, silent if NULL
 bool read_config_json(nlohmann::json& cfg, const std::string& filename, std::ostream* log = &std::cout);
 
+// Reads the stream and tries to parse JSON from it with comments
+// cfg - output json struct
+// in - input stream to read
+// log - output errors to this ostream, silent if NULL
+bool read_config_json(nlohmann::json& cfg, std::istream& in, std::ostream* log = &std::cout);
+
 // JSON Extractors - They do not override already set values if key is not present
 
 void json_extract(const nlohmann::json& j, const std::string& key, std::string& out);