exponent-io / jsonpath Goto Github PK

import "github.com/exponent-io/jsonpath"

var j = []byte(`[
  {"Space": "YCbCr", "Point": {"Y": 255, "Cb": 0, "Cr": -10}},
  {"Space": "RGB",   "Point": {"R": 98, "G": 218, "B": 255}}
]`)

w := json.NewDecoder(bytes.NewReader(j))
var v interface{}

w.SeekTo(1, "Point", "G")
w.Decode(&v) // v is 218

[
  {"Space": "YCbCr", "Point": {"Y": 255, "Cb": 0, "Cr": -10}},
  {"Space": "RGB",   "Point": {"R": 98, "G": 218, "B": 255}}
]
[
  {"Space": "YCbCr", "Point": {"Y": 255, "Cb": 0, "Cr": -10}},
  {"Space": "RGB",   "Point": {"R": 98, "G": 218, "B": 255}}
]

func ExtractJSONArrayIter(filePath, arrayKey string) error {
    fmt.Printf("Extracting items from array key %s\n", arrayKey)

    // Open the input file for streaming
    file, err := os.Open(filePath)
    if err != nil {
        return fmt.Errorf("opening input file: %w", err)
    }
    defer file.Close()

    // Create a new JSONPath Decoder
    decoder := jsonpath.NewDecoder(bufio.NewReader(file))

    // Open the output file for writing NDJSON
    outputFile, err := os.Create("output.ndjson")
    if err != nil {
        return fmt.Errorf("opening output file: %w", err)
    }
    defer outputFile.Close()
    writer := bufio.NewWriter(outputFile)

    // Define PathActions to extract each item in the array
    var actions jsonpath.PathActions
    actions.Add(func(d *jsonpath.Decoder) error {
        // Decode the current item
        var item interface{}
        if err := d.Decode(&item); err != nil {
            return err
        }
        
        // Marshal the item to JSON and write to the output file
        if itemBytes, err := json.Marshal(item); err == nil {
            if _, err := writer.Write(itemBytes); err != nil {
                return err
            }
            if _, err := writer.WriteString("\n"); err != nil {
                return err
            }
        }
        return nil
    }, arrayKey)

    // Seek to the start of the specified array
    decoder.SeekTo(arrayKey)

    // Scan the JSON stream and process each item
    var ok = true
    for ok {
        ok, err = decoder.Scan(&actions)
        if err != nil && err != io.EOF {
            return fmt.Errorf("error during JSON scan: %w", err)
        }
    }

    // Flush the writer to ensure all data is written to the file
    if err := writer.Flush(); err != nil {
        return fmt.Errorf("error flushing output file: %w", err)
    }

    fmt.Println("Extraction completed")
    return nil
}