panic: sync: negative WaitGroup counter with multiple requests to the same Endpoint

Issue

Im doing a hashed password generator, i have an endpoint at the server that generates a goroutine to create the hashed password, and then send it as a response when the goroutine ends.

this is the function that is called to generate the hashed password

func SetHash(c echo.Context) error {
    hashedhPassword := make(chan string)
    var wg sync.WaitGroup
    wg.Add(2)
    go utils.GenerateSaltedHashAsync("demoprueba", wg, hashedhPassword)
    return response.Success(c, map[string]string{
        "salt": <-hashedhPassword,
    })
}

and this is the hashing class

package utils

import (
    "encoding/base64"
    "fmt"
    "golang.org/x/crypto/argon2"
    "sync"
    "tigoApi/config"
)

const (
    Time         = 4
    Memory       = 64 * 1024
    KeyLen       = 80
    Threads      = 10
)

var environment = config.Instance()

func GenerateSaltedHashAsync(password string,wg sync.WaitGroup, hashedPassword chan string) {
    cryptoKey := argon2.IDKey([]byte(password), []byte(environment.SaltedPassword), Time, Memory, uint8(Threads), KeyLen)
    encodedPassword := base64.StdEncoding.EncodeToString(cryptoKey)
    consoleHash := fmt.Sprintf("%s$%d$%d$%d$%d$%s$%s", environment.PepperPassword, Time, Memory, Threads, KeyLen, environment.SaltedPassword, encodedPassword)
    defer wg.Done()
    hashedPassword <- consoleHash
    wg.Wait()
}

everything works fine when i do a single request, however when i send multiple requests at once(stress test) the app send this error.

panic: sync: negative WaitGroup counter

goroutine 1566 [running]: sync.(*WaitGroup).Add(0xc0001320a0,
0xffffffffffffffff)
/usr/local/go/src/sync/waitgroup.go:74 +0x139 sync.(*WaitGroup).Done(0xc0001320a0)
/usr/local/go/src/sync/waitgroup.go:99 +0x34 tigoApi/utils.GenerateSaltedHashAsync(0x8e5324, 0xa, 0x0, 0x2,
0xc000226240)
/home/crdzbird/goApps/src/tigoApi/utils/hashing.go:46 +0x3cc created by tigoApi/controller.SetHash
/home/crdzbird/goApps/src/tigoApi/controller/user_controller.go:23
+0xcd

Process finished with exit code 2

please anyone can tell me what is wrong with the code.

UPDATE.

Thanks to the suggestions the code working should be like this…

func SetHash(c echo.Context) error {
    hashedhPassword := make(chan string)
    go utils.GenerateSaltedHashAsync("lacb2208", hashedhPassword)
    return response.Success(c, map[string]string{
        "salt": <-hashedhPassword,
    })
}


func GenerateSaltedHashAsync(password string, hashedPassword chan string) {
    cryptoKey := argon2.IDKey([]byte(password), []byte(environment.SaltedPassword), Time, Memory, uint8(Threads), KeyLen)
    encodedPassword := base64.StdEncoding.EncodeToString(cryptoKey)
    consoleHash := fmt.Sprintf("%s$%d$%d$%d$%d$%s$%s", environment.PepperPassword, Time, Memory, Threads, KeyLen, environment.SaltedPassword, encodedPassword)
    hashedPassword <- consoleHash
    close(hashedPassword)
}

Solution

From the sync package docs:

Values containing the types defined in this (sync) package should not
be copied.

So if something needs a reference use a pointer.

Change your function signature so wg is a pointer reference:

func GenerateSaltedHashAsync(password string,wg *sync.WaitGroup, hashedPassword chan string)

and then call with that reference:

go utils.GenerateSaltedHashAsync("demoprueba", &wg, hashedhPassword)

Answered By – colm.anseo

Answer Checked By – Gilberto Lyons (GoLangFix Admin)

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