Golang JSON weird behaviour - mysql

Question

Fairly unremarkable code here:
type Response struct {
Status string `json:"status"`
Msg string `json:"msg"`
ErrorCode string `json:"error-code"`
Data interface{} `json:"data"`
Eof bool `json:"eof"`
}
func main() {
data := [][]string{
[]string{"description", "BILL NO 2362 EXTRA 5%"},
}
r := &Response{
Data: data,
}
str, _ := json.Marshal(r)
fmt.Println(string(str))
}
It prints the following:
{"status":"","msg":"","error-code":"","data":[["description","BILL NO 2362 EXTRA 5%"]],"eof":false}
No problem so far. However if I try to marshal JSON from exactly the same data, but fetched from a DB, I get a weird output:
func TestJson(t *testing.T) {
var pool *sql.DB
pool, err := sql.Open("mysql", "user:pass#tcp(127.0.0.1:3306)/db")
if err != nil {
t.Errorf("%s\n", err.Error())
}
defer pool.Close()
ctx, cancel := context.WithTimeout(context.Background(), 20*time.Second)
defer cancel()
if err := pool.PingContext(ctx); err != nil {
t.Errorf("%s\n", err.Error())
}
data := fetchAll(t, ctx, pool)
fmt.Println(data)
res := &Response{
Data: data,
}
str, err := json.Marshal(res)
if err != nil {
t.Errorf("%s\n", err.Error())
}
fmt.Printf(string(str))
}
func fetchAll(t *testing.T, ctx context.Context, pool *sql.DB) [][]string {
rows, err := pool.QueryContext(ctx, "select description from vouchers where id = 1")
if err != nil {
t.Fatalf("%s\n", err.Error())
}
cols, err := rows.Columns()
if err != nil {
t.Fatalf("%s\n", err.Error())
}
vals := make([]interface{}, len(cols))
var results [][]string
for rows.Next() {
for i := range cols {
vals[i] = &vals[i]
}
err = rows.Scan(vals...)
if err != nil {
t.Fatalf("%s\n", err.Error())
}
var r []string
for i, c := range cols {
r = append(r, c)
var v string
if vals[i] == nil {
v = "NULL"
} else {
b, _ := vals[i].([]byte)
v = string(b)
}
fmt.Printf("byte len %d\n", len(v))
fmt.Printf("rune len %d\n", utf8.RuneCountInString(v))
r = append(r, v)
}
results = append(results, r)
}
if rows.Err() != nil {
t.Fatalf("%s\n", err.Error())
}
return results
}
The test code prints this:
=== RUN TestJson
byte len 21
rune len 21
[[description BILL NO 2362 EXTRA 5%]]
{"status":"","msg":"","error-code":"","data":[["description","BILL NO 2362 EXTRA 5%!"(MISSING)]],"eof":false}--- PASS: TestJson (0.35s)
PASS
ok command-line-arguments 0.836s
Note the corrupted JSON. I printed the rune length of the string to make sure the string contains
just plain ascii characters. The print before the marshal confirms that we are looking at exactly the same string. Why on earth is the output different ?
If I remove the last "%" then life returns to normal:
byte len 20
rune len 20
[[description BILL NO 2362 EXTRA 5]]
{"status":"","msg":"","error-code":"","data":[["description","BILL NO 2362 EXTRA 5"]],"eof":false}--- PASS: TestJson (0.35s)
PASS
ok command-line-arguments 0.534s

Answer 1

Based on the suggestions modify the program as follows:
func TestJson(t *testing.T) {
var pool *sql.DB
pool, err := sql.Open("mysql", "user:pass#tcp(127.0.0.1:3306)/db")
if err != nil {
t.Errorf("%s\n", err.Error())
}
defer pool.Close()
ctx, cancel := context.WithTimeout(context.Background(), 20*time.Second)
defer cancel()
if err := pool.PingContext(ctx); err != nil {
t.Errorf("%s\n", err.Error())
}
data := fetchAll(t, ctx, pool)
fmt.Println(data)
res := &Response{
Data: data,
}
str, err := json.Marshal(res)
if err != nil {
t.Errorf("%s\n", err.Error())
}
fmt.Print(string(str))
}
func fetchAll(t *testing.T, ctx context.Context, pool *sql.DB) [][]string {
rows, err := pool.QueryContext(ctx, "select description from vouchers where id = 1")
if err != nil {
t.Fatalf("%s\n", err.Error())
}
cols, err := rows.Columns()
if err != nil {
t.Fatalf("%s\n", err.Error())
}
vals := make([]interface{}, len(cols))
var results [][]string
for rows.Next() {
for i := range cols {
vals[i] = &vals[i]
}
err = rows.Scan(vals...)
if err != nil {
t.Fatalf("%s\n", err.Error())
}
var r []string
for i, c := range cols {
r = append(r, c)
var v string
if vals[i] == nil {
v = "NULL"
} else {
b, _ := vals[i].([]byte)
v = string(b)
}
fmt.Printf("byte len %d\n", len(v))
fmt.Printf("rune len %d\n", utf8.RuneCountInString(v))
r = append(r, v)
}
results = append(results, r)
}
if rows.Err() != nil {
t.Fatalf("%s\n", err.Error())
}
return results
}