I am hitting a REST API and getting some data back. I came across an interesting behaviour yesterday. I haven't understood the exact reasoning behind the it yet. Which is what I'm trying to seek here. For a payload that looks like -
{
"id": 2091967,
"first_name": "",
"last_name": "",
"email": "",
"telephone": "",
"timezone": "",
"weekly_capacity": "",
"has_access_to_all_future_projects": false,
"is_contractor": false,
"is_admin": false,
"is_project_manager": false,
"can_see_rates": false,
"can_create_projects": false,
"can_create_invoices": false,
"is_active": false,
"created_at": "2018-04-16T00:48:30Z",
"updated_at": "2018-11-07T22:47:43Z",
"default_hourly_rate": null,
"cost_rate": null,
"roles": [
"blah"
],
"avatar_url": ""
}
I used a function like below to get the email -
func GetUserEmail(userID int) string {
resp := getFromSomething("https://something/users/" + strconv.Itoa(userID))
var result map[string]string
json.NewDecoder(resp.Body).Decode(&result)
log.Printf("userEmail: %s", result["email"])
return result["email"]
}
The code worked perfectly on my mac where I was building it like - env GOOS=linux go build -ldflags="-s -w" -o bin/something cmd/main.go But, it failed to deserialize, and didn't print anything on an EC2 instance when using the same build command.
But then, I changed the var result map[string]string to var result map[string]interface{} and it worked on both my EC2 instance and mac.
I also had to typecast the interface{} object at the end before returning it.
func GetUserEmail(userID int) string {
resp := getFromSomething("https://something/users/" + strconv.Itoa(userID))
var result map[string]interface{}
json.NewDecoder(resp.Body).Decode(&result)
log.Printf("userEmail: %s", result["email"])
return result["email"].(string)
}
Has anyone seen things like this before? Or, does anyone know why this happened?
I understand that the payload can always be represented better by var result map[string]interface{}, but my question is - why did that earlier representation of var result map[string]string work on the Mac and not on EC2?
Go version on Mac - go version go1.11.2 darwin/amd64 and that on EC2 is go version go1.10.3 linux/amd64
Always check for and handle errors.
The error returned from Decode explains the problem. The application is attempting to decode numbers, booleans and arrays to string values.
var v map[string]string
err := json.NewDecoder(data).Decode(&v) // data is the JSON document from the question
fmt.Println(err) // prints json: cannot unmarshal number into Go value of type string
This issue is not platform specific. I have a couple of guesses why you saw different results:
env GOOS=linux go build -ldflags="-s -w" -o bin/something cmd/main.go was used to build the Mac version, but this command does not build a binary that's executable on the Mac. Perhaps you were not running the code you thought you were running.Either decode to map[string]interface{} as you discovered or decode to a struct with the one field you want:
var v struct{ Email string }
if err := json.NewDecoder(data).Decode(&v); err != nil {
// handle error
}
fmt.Println(v.Email) // prints the decoded email value.