Golang'http.NewRequest（method，url，body）'无法创建正确格式的请求

Question

I'm trying to send a GET request to the following api:

https://poloniex.com/public?command=returnOrderBook

w/ URL parameters:

currencyPair=BTC_ETH
depth=20
--> &currencyPair=BTC_ETH&depth=20

I try to setup and execute my request as so: (note I've removed error checking for brevity)

pair := "BTC_ETH"
depth := 20
reqURL := "https://poloniex.com/public?command=returnOrderBook"
values := url.Values { "currencyPair": []string{pair}, "depth": []string{depth}}
fmt.Printf("
 Values = %s
", values.Encode())        //DEBUG
req, err := http.NewRequest("GET", reqURL, strings.NewReader(values.Encode()))
fmt.Printf("
REQUEST = %+v
", req)                   //DEBUG
resp, err := api.client.Do(req)
defer resp.Body.Close()
body, err := ioutil.ReadAll(resp.Body)
fmt.Printf("
REST CALL RETURNED: %X
",body)          //DEBUG

My DEBUG print statements print out the following:

Values = currencyPair=BTC_ETH&depth=20

REQUEST = &{Method:GET URL:https://poloniex.com/public?command=returnOrderBook Proto:HTTP/1.1 ProtoMajor:1 ProtoMinor:1 Header:map[User-Agent:[Poloniex GO API Agent]] Body:{Reader:0xc82028e840} ContentLength:29 TransferEncoding:[] Close:false Host:poloniex.com Form:map[] PostForm:map[] MultipartForm:<nil> Trailer:map[] RemoteAddr: RequestURI: TLS:<nil> Cancel:<nil>}

REST CALL RETURNED: {"error":"Please specify a currency pair."}

Playing around with Postman I figured out the API only returns this error when the currencyPair parameter is not specified (including miscapitalized). I can't figure out why the request doesn't include the URL parameters I specified as it's obvious from my debug print statements that the values.Encode() is correct. The content length in the request corresponds to the right amount of chars (bytes) needed for URL parameters.

Now after playing around a bit I found a solution. If I replace the http.NewRequest() line with the following it works:

req, err := http.NewRequest(HTTPType, reqURL + "&" + values.Encode(), nil)

However, it's really bothering me why the original statement doesn't work.

The new DEBUG output is:

Values = currencyPair=BTC_ETH&depth=20

REQUEST = &{Method:GET URL:https://poloniex.com/public?command=returnOrderBook&currencyPair=BTC_ETH&depth=5 Proto:HTTP/1.1 ProtoMajor:1 ProtoMinor:1 Header:map[User-Agent:[Poloniex GO API Agent]] Body:<nil> ContentLength:0 TransferEncoding:[] Close:false Host:poloniex.com Form:map[] PostForm:map[] MultipartForm:<nil> Trailer:map[] RemoteAddr: RequestURI: TLS:<nil> Cancel:<nil>}

REST CALL RETURNED: *way too long, just assume it's the correct financial data*

Would love some input on what I did wrong in the original statement. I used the same method (original) for a different api endpoint w/ URL parameters and it worked fine. Confused on why it didn't work in this case.

Answer 1

GET requests should not contain a body. Instead, you need to put the form into the query string.

Here's the proper way to do that, without hacky string concatenation:

reqURL := "https://poloniex.com/public"
values := url.Values { "currencyPair": []string{pair}, "depth": []string{depth}}
values.Set("command", "returnOrderBook")
uri, _ := url.Parse(reqURL)
uri.Query = values.Encode()
reqURL = uri.String()
fmt.Println(reqURL)

req, err := http.NewRequest("GET", reqURL, nil)
if err != nil {
    panic(err) // NewRequest only errors on bad methods or un-parsable urls
}

https://play.golang.org/p/ZCLUu7UgZL