How to specify and handle specific errors in Go?

Question

I wrote this very basic parser that goes through Reddit JSON and am curious how I can specifically manage an error in Go.

For example I have this "Get" method for a link:

func Get(reddit string) ([]Item, error) {
    url := fmt.Sprintf("http://reddit.com/r/%s.json", reddit)
    resp, err := http.Get(url)
    if err != nil {
        return nil, err
    }
    defer resp.Body.Close()
    if resp.StatusCode != http.StatusOK {
        return nil, err
    }
    /*
     * Other code here
    */
}

How can I handle, say, a 404 error from the StatusCode? I know I can test for the 404 error itself:

if resp.StatusCode == http.StatusNotfound {
    //do stuff here
}

But is there a way I can directly manage the resp.StatusCode != http.StatusOK without having to write a bunch of if statements? Is there a way I can use err in a switch statement?

Nick Craig-Wood · Accepted Answer · 2015-01-03 22:04:34Z

1

Firstly note that http.Get doesn't return an error for an HTTP return which isn't 200. The Get did its job successfully even when the server gave it a 404 error. From the docs

A non-2xx response doesn't cause an error.

Therfore in your code, err will be nil when you call this which means it will return err=nil which probably isn't what you want.

if resp.StatusCode != http.StatusOK {
    return nil, err
}

This should do what you want

if resp.StatusCode != http.StatusOK {
    return nil, fmt.Errorf("HTTP Error %d: %s", resp.StatusCode, resp.Status)
}

Which will return an error for any kind of HTTP error, with a message as to what it was.

answered Jan 3, 2015 at 22:04

Nick Craig-Wood

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RoboTamer · Accepted Answer · 2015-01-03 22:05:03Z

0

Sure you can:

package main

import "fmt"

func main() {
    var err error
    switch err {
    case nil:
        fmt.Println("Is nil")
    }
}

https://play.golang.org/p/4VdHW87wCr

answered Jan 3, 2015 at 22:05

RoboTamer

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