New flags: '-wrap' and '-unwrap'.

Refactored the func 'remashal' to implement the new flags.

Author: dbohdan

README.md

@@ -9,33 +9,76 @@ commands `toml2yaml`, `toml2json`, `yaml2toml`, `yaml2json`. `json2toml` and
 
 ```
 remarshal -if inputformat -of outputformat [-indent-json=(true|false)]
-          [-i inputfile] [-o outputfile]
+          [-i inputfile] [-o outputfile] [-wrap wrapper] [-unwrap wrapper]
 
 ```
 
 where `inputformat` and `outputformat` can each be `toml`, `yaml` or
 `json`.
 
 ```
-toml2toml [-o outputfile] [[-i] inputfile]
-yaml2toml [-o outputfile] [[-i] inputfile]
-json2toml [-o outputfile] [[-i] inputfile]
-toml2yaml [-o outputfile] [[-i] inputfile]
-yaml2yaml [-o outputfile] [[-i] inputfile]
-json2yaml [-o outputfile] [[-i] inputfile]
-toml2json [-indent-json=(true|false)] [-o outputfile] [[-i] inputfile]
-yaml2json [-indent-json=(true|false)] [-o outputfile] [[-i] inputfile]
-json2json [-indent-json=(true|false)] [-o outputfile] [[-i] inputfile]
+toml2toml [-wrap wrapper] [-unwrap wrapper] [-o outputfile] [[-i] inputfile]
+yaml2toml [-wrap wrapper] [-unwrap wrapper] [-o outputfile] [[-i] inputfile]
+json2toml [-wrap wrapper] [-unwrap wrapper] [-o outputfile] [[-i] inputfile]
+toml2yaml [-wrap wrapper] [-unwrap wrapper] [-o outputfile] [[-i] inputfile]
+yaml2yaml [-wrap wrapper] [-unwrap wrapper] [-o outputfile] [[-i] inputfile]
+json2yaml [-wrap wrapper] [-unwrap wrapper] [-o outputfile] [[-i] inputfile]
+toml2json [-indent-json=(true|false)] [-wrap wrapper] [-unwrap wrapper]
+          [-o outputfile] [[-i] inputfile]
+yaml2json [-indent-json=(true|false)] [-wrap wrapper] [-unwrap wrapper]
+          [-o outputfile] [[-i] inputfile]
+json2json [-indent-json=(true|false)] [-wrap wrapper] [-unwrap wrapper]
+          [-o outputfile] [[-i] inputfile]
 ```
 
-The all of the commands above exit with status 0 on success and 1 on failure.
+All of the commands above exit with status 0 on success and 1 on failure.
 
 If no `inputfile` is given or it is `-` or a blank string the data to convert is
 read from standard input. If no `outputfile` is given or it is `-` or a blank
 string the result of the conversion is written to standard output.
 
-For short commands (`x2y`) the flag `-i` before `inputfile` can be omitted if
-`inputfile` is the last argument.
+For the short commands (`x2y`) the flag `-i` before `inputfile` can be omitted
+if `inputfile` is the last argument.
+
+## Wrappers
+
+The flags `-wrap` and `-unwrap` are there to solve the problem of converting
+JSON and YAML data to TOML if the topmost element of that data is not of a map
+type (i.e., not an object in JSON or an associative array in YAML) but a list, a
+string or a number. Such data can not be represented as TOML directly; it needs
+to wrapped in a map type first. Passing the flag `-wrap someKey` to `remarshal`
+or one of its short commands wraps the input data in a "wrapper" map with one
+key, "someKey", with the input data as its value. The flag `-unwrap someKey`
+does the opposite: if it is specified only the value stored under the key
+"someKey" in the top-level map element of the input data is converted to the
+target format and output; all other data is skipped. If the top-level element is
+not a map or does not have the key `someKey` then `-unwrap someKey` returns an
+error.
+
+The following shell transcript demonstrates the problem and how `-wrap` and
+`-unwrap` solve it:
+
+```
+$ echo '[{"a":"b"},{"c":[1,2,3]}]' | ./remarshal -if json -of toml
+cannot convert data: top-level values must be a Go map or struct
+
+$ echo '[{"a":"b"},{"c":[1,2,3]}]' | \
+./remarshal -if json -of toml -wrap main
+[[main]]
+  a = "b"
+
+[[main]]
+  c = [1, 2, 3]
+
+$ echo '[{"a":"b"},{"c":[1,2,3]}]' | \
+./remarshal -if json -of toml -wrap main > test.toml
+
+$ ./remarshal -if toml -of json -indent-json=0 < test.toml
+{"main":[{"a":"b"},{"c":[1,2,3]}]}
+
+$ ./remarshal -if toml -of json -indent-json=0 -unwrap main < test.toml
+[{"a":"b"},{"c":[1,2,3]}]
+```
 
 # Building and installation
 
@@ -139,7 +182,7 @@ name = "Kiev"
 
 # Known bugs
 
-* Converting data with floating point values to YAML may cause the loss of
+* Converting data with floating point values to YAML may cause a loss of
 precision.
 
 # License

VERSION

@@ -1 +1 @@
-0.2.3
+0.3.0

remarshal.go

@@ -27,6 +27,11 @@ const (
 	fUnknown
 )
 
+const (
+	defaultFormatFlagValue = "unspecified"
+	defaultWrapFlagValue = "key"
+)
+
 // convertMapsToStringMaps recursively converts values of type
 // map[interface{}]interface{} contained in item to map[string]interface{}. This
 // is needed before the encoders for TOML and JSON can accept data returned by
@@ -58,7 +63,7 @@ func convertMapsToStringMaps(item interface{}) (res interface{}, err error) {
 
 // convertNumberToInt64 recursively walks the structures contained in item
 // converting values of the type json.Number to int64 or, failing that, float64.
-// This approach is meant to prevent encoders putting numbers stored as
+// This approach is meant to prevent encoders from putting numbers stored as
 // json.Number in quotes or encoding large intergers in scientific notation.
 func convertNumberToInt64(item interface{}) (res interface{}, err error) {
 	switch item.(type) {
@@ -104,7 +109,7 @@ func stringToFormat(s string) (f format, err error) {
 		return fYAML, nil
 	case "json":
 		return fJSON, nil
-	case "unknown":
+	case defaultFormatFlagValue:
 		return fPlaceholder, errors.New("placeholder format")
 	default:
 		return fUnknown, errors.New("cannot convert string to format: '" +
@@ -131,13 +136,10 @@ func filenameToFormat(s string) (inputf format, outputf format, err error) {
 	return prefix, suffix, nil
 }
 
-// remarshal converts input data of format inputFormat to outputFormat and
-// returns the result.
-func remarshal(input []byte, inputFormat format, outputFormat format,
-	indentJSON bool) (result []byte, err error) {
-	var data interface{}
-
-	// Decode the serialized data.
+// unmarshal decodes serialized data in the format inputFormat into a structure
+// of nested maps and slices.
+func unmarshal(input []byte, inputFormat format) (data interface{},
+	err error) {
 	switch inputFormat {
 	case fTOML:
 		_, err = toml.Decode(string(input), &data)
@@ -157,8 +159,13 @@ func remarshal(input []byte, inputFormat format, outputFormat format,
 	if err != nil {
 		return nil, err
 	}
+	return
+}
 
-	// Reencode the data in the output format.
+// marshal encodes data stored in nested maps and slices in the format
+// outputFormat.
+func marshal(data interface{}, outputFormat format,
+	indentJSON bool) (result []byte, err error) {
 	switch outputFormat {
 	case fTOML:
 		buf := new(bytes.Buffer)
@@ -177,31 +184,36 @@ func remarshal(input []byte, inputFormat format, outputFormat format,
 	if err != nil {
 		return nil, err
 	}
-
 	return
 }
 
-func main() {
-	var inputFile, outputFile, inputFormatStr, outputFormatStr string
-	var inputFormat, outputFormat format
-	indentJSON := true
+// processCommandLine parses the command line arguments (including os.Args[0],
+// the program name) and sets the input and the output file names as well as
+// other conversion options based on them.
+func processCommandLine() (inputFile string, outputFile string,
+	inputFormat format, outputFormat format,
+	indentJSON bool, wrap string, unwrap string) {
+	var inputFormatStr, outputFormatStr string
 
-	// Parse the command line arguments and choose the input and the output
-	// format.
 	flag.StringVar(&inputFile, "i", "-", "input file")
 	flag.StringVar(&outputFile, "o", "-", "output file")
+	flag.StringVar(&wrap, "wrap", defaultWrapFlagValue,
+		"wrap the data in a map type with the given key")
+	flag.StringVar(&unwrap, "unwrap", defaultWrapFlagValue,
+		"only output the data stored under the given key")
 
-	// See if our executable is named, e.g., "json2yaml".
+	// See if our program is named, e.g., "json2yaml" (normally due to having
+	// been started through a symlink).
 	inputFormat, outputFormat, err := filenameToFormat(os.Args[0])
 	formatFromProgramName := err == nil
 	if !formatFromProgramName {
 		// Only give the user an option to specify the input and the output
 		// format with flags when it is mandatory, i.e., when we are *not* being
 		// run as "json2yaml" or similar. This makes the usage messages for the
 		// "x2y" commands more accurate as well.
-		flag.StringVar(&inputFormatStr, "if", "unknown",
+		flag.StringVar(&inputFormatStr, "if", defaultFormatFlagValue,
 			"input format ('toml', 'yaml' or 'json')")
-		flag.StringVar(&outputFormatStr, "of", "unknown",
+		flag.StringVar(&outputFormatStr, "of", defaultFormatFlagValue,
 			"input format ('toml', 'yaml' or 'json')")
 	}
 	if !formatFromProgramName || outputFormat == fJSON {
@@ -252,9 +264,16 @@ func main() {
 			os.Exit(1)
 		}
 	}
+	return
+}
+
+func main() {
+	inputFile, outputFile, inputFormat, outputFormat,
+	indentJSON, wrap, unwrap := processCommandLine()
 
 	// Read the input data from either standard input or a file.
 	var input []byte
+	var err error
 	if inputFile == "" || inputFile == "-" {
 		input, err = ioutil.ReadAll(os.Stdin)
 	} else {
@@ -270,11 +289,33 @@ func main() {
 
 	}
 
-	output, err := remarshal(input, inputFormat, outputFormat, indentJSON)
+	// Convert the input data from inputFormat to outputFormat.
+	data, err := unmarshal(input, inputFormat)
 	if err != nil {
 		fmt.Println(err)
 		os.Exit(1)
 	}
+	// Unwrap and/or wrap the data in a map if we were told to.
+	if unwrap != defaultWrapFlagValue {
+		temp, ok := data.(map[string]interface{})
+		if !ok {
+			fmt.Printf("cannot unwrap data: top-level value not a map\n")
+			os.Exit(1)
+		}
+		data, ok = temp[unwrap]
+		if !ok {
+			fmt.Printf("cannot unwrap data: no key '%s'\n", unwrap)
+			os.Exit(1)
+		}
+	}
+	if wrap != defaultWrapFlagValue {
+		data = map[string]interface{}{wrap: data}
+	}
+	output, err := marshal(data, outputFormat, indentJSON)
+	if err != nil {
+		fmt.Printf("cannot convert data: %v\n", err)
+		os.Exit(1)
+	}
 
 	// Print the result to either standard output or a file.
 	if outputFile == "" || outputFile == "-" {