Table of Contents

Overview

debug package of golang provides a StackTrace function that can be used print the stack trace of the panic in the recover function

Example

Let’s see a program for that

package main
import (
    "fmt"
    "runtime/debug"
)
func main() {
    a := []string{"a", "b"}
    checkAndPrint(a, 2)
    fmt.Println("Exiting normally")
}
func checkAndPrint(a []string, index int) {
    defer handleOutOfBounds()
    if index > (len(a) - 1) {
        panic("Out of bound access for slice")
    }
    fmt.Println(a[index])
}
func handleOutOfBounds() {
    if r := recover(); r != nil {
        fmt.Println("Recovering from panic:", r)
        fmt.Println("Stack Trace:")
        debug.PrintStack()
    }
}

Output

Recovering from panic: Out of bound access for slice
Stack Trace:
goroutine 1 [running]:
runtime/debug.Stack(0xd, 0x0, 0x0)
        stack.go:24 +0x9d
runtime/debug.PrintStack()
        stack.go:16 +0x22
main.handleOutOfBounds()
        main.go:27 +0x10f
panic(0x10ab8c0, 0x10e8f60)
        /Users/slohia/Documents/goversion/go1.14.1/src/runtime/panic.go:967 +0x166
main.checkAndPrint(0xc000104f58, 0x2, 0x2, 0x2)
        main.go:18 +0x111
main.main()
        main.go:11 +0x81
Exiting normally

In the above program we have a function checkAndPrint which checks and prints slice element at an index passed in the argument. If the index passed is greater than the length of the array then the program panics. We have added a defer function named handleOutIfBounds as well at the start of the function checkAndPrint. This function contains the call to recover function as below

if r := recover(); r != nil {
    fmt.Println("Recovering from panic:", r)
}

The recover function will catch the panic and we can also print the message from the panic.

Recovering from panic: Out of bound access for slice

We print the stack trace of the panic in the recover function using the StackTrace function. It prints the correct stack trace as seen from the output

golang