goLogic errorMedium

JSON Unmarshal silent failure with lowercase fields

Time: 0:00

BugFind the bug and fix the code

What it should do

Parse JSON into a struct and return the user name. Example: parseUserConfig("{\"name\":\"Alice\"}") -> "Alice"

What happens instead

Struct field remains empty string "" after json.Unmarshal

package main

import (
	"encoding/json"
	"fmt"
)

type Config struct {
	name string
}

func parseUserConfig(jsonStr string) string {
	var c Config
	json.Unmarshal([]byte(jsonStr), &c)
	return c.name
}

func main() {
	fmt.Println(parseUserConfig("{"name":"Alice"}"))
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

⏱️0:00

Hints

🏆 0 hints = Flawless Solve

Think & Test Cooldown

2:00 remaining

Take a moment to read the bug symptom and trace the code with Run & Check before unlocking Hint 1.

Hint 2

Unlocks after Hint 1

Hint 3

Unlocks after Hint 2

This bug belongs to the logic errors pattern

The wrong operator, an inverted condition, a formula the right way round but backwards.

Learn the logic errors pattern Step through your own code

<iframe src="https://trybughunt.com/embed/75240fe4-e45a-4c52-abe9-cf3503eea825" title="Debugging challenge: JSON Unmarshal silent failure with lowercase fields" width="100%" height="580" loading="lazy" style="border:1px solid #d4d4d8;border-radius:12px;max-width:760px"></iframe> <p style="font-size:14px">Debugging challenge from <a href="https://trybughunt.com/challenges/75240fe4-e45a-4c52-abe9-cf3503eea825">TryBugHunt</a></p>

package main import ( "encoding/json" "fmt" ) type Config struct { name string } func parseUserConfig(jsonStr string) string { var c Config json.Unmarshal([]byte(jsonStr), &c) return c.name } func main() { fmt.Println(parseUserConfig("{"name":"Alice"}")) }

JSON Unmarshal silent failure with lowercase fields

What it should do

What happens instead

More logic errors to practise

JSON Unmarshal silent failure with lowercase fields

What it should do

What happens instead

More logic errors to practise