JSONL in Go: bufio, json.Decoder & Nebenläufigkeit

package main

import (
	"bufio"
	"encoding/json"
	"fmt"
	"log"
	"os"
)

func main() {
	file, err := os.Open("data.jsonl")
	if err != nil {
		log.Fatal(err)
	}
	defer file.Close()

	var records []map[string]any
	scanner := bufio.NewScanner(file)

	// Puffer für Zeilen länger als 64KB vergrößern
	scanner.Buffer(make([]byte, 0, 1024*1024), 1024*1024)

	for scanner.Scan() {
		var record map[string]any
		if err := json.Unmarshal(scanner.Bytes(), &record); err != nil {
			log.Printf("skipping invalid JSON: %v", err)
			continue
		}
		records = append(records, record)
	}

	if err := scanner.Err(); err != nil {
		log.Fatal(err)
	}

	fmt.Printf("Loaded %d records\n", len(records))
}

package main

import (
	"bufio"
	"encoding/json"
	"fmt"
	"log"
	"os"
)

type User struct {
	ID    int    `json:"id"`
	Name  string `json:"name"`
	Email string `json:"email"`
	Age   int    `json:"age,omitempty"`
}

func readUsers(path string) ([]User, error) {
	file, err := os.Open(path)
	if err != nil {
		return nil, fmt.Errorf("open file: %w", err)
	}
	defer file.Close()

	var users []User
	scanner := bufio.NewScanner(file)
	lineNum := 0

	for scanner.Scan() {
		lineNum++
		var u User
		if err := json.Unmarshal(scanner.Bytes(), &u); err != nil {
			return nil, fmt.Errorf("line %d: %w", lineNum, err)
		}
		users = append(users, u)
	}

	if err := scanner.Err(); err != nil {
		return nil, fmt.Errorf("scanner error: %w", err)
	}
	return users, nil
}

func main() {
	users, err := readUsers("users.jsonl")
	if err != nil {
		log.Fatal(err)
	}
	for _, u := range users {
		fmt.Printf("%s (%s)\n", u.Name, u.Email)
	}
}

package main

import (
	"encoding/json"
	"fmt"
	"log"
	"os"
)

type Product struct {
	ID    int     `json:"id"`
	Name  string  `json:"name"`
	Price float64 `json:"price"`
}

func main() {
	products := []Product{
		{ID: 1, Name: "Laptop", Price: 999.99},
		{ID: 2, Name: "Mouse", Price: 29.99},
		{ID: 3, Name: "Keyboard", Price: 79.99},
	}

	file, err := os.Create("products.jsonl")
	if err != nil {
		log.Fatal(err)
	}
	defer file.Close()

	for _, p := range products {
		data, err := json.Marshal(p)
		if err != nil {
			log.Printf("skip marshal error: %v", err)
			continue
		}
		data = append(data, '\n')
		if _, err := file.Write(data); err != nil {
			log.Fatal(err)
		}
	}

	fmt.Printf("Wrote %d records to products.jsonl\n", len(products))
}

package main

import (
	"bufio"
	"encoding/json"
	"fmt"
	"log"
	"os"
)

type Event struct {
	Type      string         `json:"type"`
	Timestamp int64          `json:"timestamp"`
	Payload   map[string]any `json:"payload"`
}

func writeEvents(path string, events []Event) error {
	file, err := os.Create(path)
	if err != nil {
		return fmt.Errorf("create file: %w", err)
	}
	defer file.Close()

	writer := bufio.NewWriter(file)
	encoder := json.NewEncoder(writer)

	// HTML-Escaping für sauberere Ausgabe deaktivieren
	encoder.SetEscapeHTML(false)

	for i, event := range events {
		if err := encoder.Encode(event); err != nil {
			return fmt.Errorf("encode event %d: %w", i, err)
		}
	}

	// Gepufferte Daten in die Datei schreiben
	if err := writer.Flush(); err != nil {
		return fmt.Errorf("flush: %w", err)
	}

	fmt.Printf("Wrote %d events to %s\n", len(events), path)
	return nil
}

func main() {
	events := []Event{
		{Type: "click", Timestamp: 1700000001, Payload: map[string]any{"x": 120, "y": 450}},
		{Type: "view", Timestamp: 1700000002, Payload: map[string]any{"page": "/home"}},
	}
	if err := writeEvents("events.jsonl", events); err != nil {
		log.Fatal(err)
	}
}