JSON Parser CLI

A command-line JSON parser built in Go to learn fundamental programming concepts through practical implementation.

What You'll Learn

This project teaches key Go concepts through building a real-world tool:

• Basic Types: strings, numbers, booleans, slices, maps
• Structs: custom data structures for JSON representation
• Interfaces: Parser, Validator, JSONValue interfaces
• Methods: functions attached to types
• Error Handling: custom error types with wrapping
• Pointers: efficient memory usage with pointer receivers
• Recursion: processing nested JSON structures
• File I/O: reading and writing files with proper cleanup
• Type Switches: handling different JSON value types
• Package Organization: clean separation of concerns

Features

• Parse: Read and display JSON files with pretty formatting
• Validate: Check JSON syntax and report errors
• Format: Pretty-print JSON with proper indentation
• Stats: Display statistics about JSON structure (object count, depth, etc.)

Installation

# Clone the repository
cd json-parser

# Build the application
go build -o json-parser

# Run it
./json-parser help

Usage

Parse a JSON file

./json-parser parse data.json

Validate JSON syntax

./json-parser validate config.json

Format JSON with indentation

./json-parser format data.json

Display JSON statistics

./json-parser stats data.json

Project Structure

json-parser/
├── main.go                    # CLI entry point
├── go.mod                     # Go module definition
├── cmd/
│   ├── commands.go            # Command implementations
│   └── commands_test.go       # Tests for commands
├── internal/
│   ├── parser/
│   │   ├── types.go           # JSON data structures
│   │   ├── parser.go          # Parser interface & implementation
│   │   ├── validator.go       # Validation logic
│   │   └── errors.go          # Custom error types
│   └── output/
│       └── formatter.go       # JSON output formatting
└── testdata/                  # Sample JSON files
    ├── simple.json
    ├── nested.json
    ├── types.json
    └── invalid.json

Example Output

Parse Command

$ ./json-parser parse testdata/simple.json
Successfully parsed: testdata/simple.json

{
  "name": "John Doe",
  "age": 30,
  "email": "john@example.com",
  "active": true
}

Stats Command

$ ./json-parser stats testdata/nested.json
JSON Statistics for: testdata/nested.json
---------------------------
Total Objects: 7
Total Arrays:  4
Total Strings: 13
Total Numbers: 3
Total Booleans: 5
Total Nulls:   0
Max Depth:     4

Validate Command

$ ./json-parser validate testdata/simple.json
✓ testdata/simple.json is valid JSON

$ ./json-parser validate testdata/invalid.json
Error: validation failed: parse error: invalid JSON syntax

Testing

Run all tests:

go test ./...

Run tests with coverage:

go test ./... -cover

Run tests verbosely:

go test ./... -v

Key Concepts Demonstrated

1. Interfaces

type JSONValue interface {
    Type() string
}

Different types (JSONObject, JSONArray, etc.) all implement this interface.

2. Custom Error Types

type ParseError struct {
    Line    int
    Column  int
    Message string
    Err     error
}

Rich error information with error wrapping support.

3. Recursion

The parser handles nested structures by recursively calling itself:

func convertToJSONValue(raw interface{}) (JSONValue, error) {
    // ... handles nested objects and arrays recursively
}

4. Type Switches

switch typedValue := value.(type) {
case *JSONObject:
    // handle object
case *JSONArray:
    // handle array
}

5. Method Receivers

func (p *StandardParser) Parse(reader io.Reader) (*ParseResult, error) {
    // p is the receiver
}

Learning Path

1. Start with types.go - Understand the data structures
2. Read parser.go - See how JSON is converted to Go types
3. Study formatter.go - Learn about recursion and formatting
4. Explore errors.go - Understand custom error handling
5. Check validator.go - See validation in action
6. Review commands.go - Tie everything together

Contributing

This is a learning project. Feel free to:

• Add new commands
• Implement additional formatters
• Enhance error messages
• Add more test cases

License

MIT License - Feel free to use this for learning!