7

I'm starting to learn Golang and I would like to know how to get a json response by calling an url, if you could give me an example it would be great in order to guide myself.

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2 Answers 2

Reset to default
7

Here's a simple example to get you started. Instead of a map[string]interface{} you should consider making a struct to hold the result of your request.

package main

import (
   "encoding/json"
   "fmt"
   "log"
   "net/http"
)

func main() {
   resp, err := http.Get("http://api.geonames.org/citiesJSON?north=44.1&south=-9.9&east=-22.4&west=55.2&lang=de&username=demo")
   if err != nil {
      log.Fatal(err)
   }
   var generic map[string]interface{}
   err = json.NewDecoder(resp.Body).Decode(&generic)
   if err != nil {
      log.Fatal(err)
   }
   fmt.Println(generic)
}
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4 Comments

Note that this answer is wrong in a couple of significant ways, as I've pointed out in another answer here.
I was just going for a quick and dirty single request program.
@EveFreeman....I get "map[message:401 Unauthorized]"...I know this is because of the User token value that I need to pass along with URL ....May I know how to pass the info along with URL ?
@statisticalbeginner check out headers examples. See "For control over HTTP client headers, redirect policy, and other settings, create a Client" from golang.org/pkg/net/http
4

I'd write a little helper function to do it:

// getJSON fetches the contents of the given URL
// and decodes it as JSON into the given result,
// which should be a pointer to the expected data.
func getJSON(url string, result interface{}) error {
    resp, err := http.Get(url)
    if err != nil {
        return fmt.Errorf("cannot fetch URL %q: %v", url, err)
    }
    defer resp.Body.Close()
    if resp.StatusCode != http.StatusOK {
        return fmt.Errorf("unexpected http GET status: %s", resp.Status)
    }
    // We could check the resulting content type
    // here if desired.
    err := json.NewDecoder(resp.Body).Decode(result)
    if err != nil {
        return fmt.Errorf("cannot decode JSON: %v", err)
    }
    return nil
}

A full working example can be found here: http://play.golang.org/p/b1WJb7MbQV

Note that it is important to check the status code as well as the Get error, and the response body must be closed explicitly (see the documentation here: http://golang.org/pkg/net/http/#Get)

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1 Comment

I've also had trouble with responses not closing fast enough when requesting at a high rate--ended up doing ioutil.ReadAll() after Decode(). Not sure if it's supposed to be strictly necessary, but I would run out of fds without it, even with defer resp.Body.Close().