resolves issues where failed api calls lead to obscure errors (#7051)

plugins/inputs/mailchimp/chimp_api.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"encoding/json"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"log"
 	"net/http"
@@ -143,6 +144,12 @@ func runChimp(api *ChimpAPI, params ReportsParams) ([]byte, error) {
 	}
 	defer resp.Body.Close()
 
+	if resp.StatusCode != http.StatusOK {
+		// ignore the err here; LimitReader returns io.EOF and we're not interested in read errors.
+		body, _ := ioutil.ReadAll(io.LimitReader(resp.Body, 200))
+		return nil, fmt.Errorf("%s returned HTTP status %s: %q", api.url.String(), resp.Status, body)
+	}
+
 	body, err := ioutil.ReadAll(resp.Body)
 	if err != nil {
 		return nil, err