Implement a specific error type for API responses

cmd/public-api-demo/main.go

@@ -141,7 +141,7 @@ func main() {
 	err := runDemo(os.Args[1], os.Args[2], os.Args[3], regcode)
 
 	if err != nil {
-		fmt.Printf("ERROR: %s\n", err)
+		fmt.Printf("%s\n", err)
 		os.Exit(1)
 	}
 }

pkg/connection/api_error.go

@@ -0,0 +1,36 @@
+package connection
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+)
+
+// ApiError contains all the information for any given API error response. Don't
+// build it directly, but use `ErrorFromResponse` instead.
+type ApiError struct {
+	Code             int
+	Message          string `json:"error"`
+	LocalizedMessage string `json:"localized_error"`
+}
+
+func (ae *ApiError) Error() string {
+	if ae.LocalizedMessage != "" {
+		return fmt.Sprintf("API error: %v (code: %v)", ae.LocalizedMessage, ae.Code)
+	}
+	return fmt.Sprintf("API error: %v (code: %v)", ae.Message, ae.Code)
+}
+
+// Returns a new ApiError from the given response if it contained an API error
+// response. Otherwise it just returns nil.
+func ErrorFromResponse(resp *http.Response) *ApiError {
+	if resp.StatusCode >= 200 && resp.StatusCode < 300 {
+		return nil
+	}
+
+	ae := &ApiError{Code: resp.StatusCode}
+	if err := json.NewDecoder(resp.Body).Decode(ae); err != nil {
+		return nil
+	}
+	return ae
+}

pkg/connection/connection.go

@@ -78,9 +78,9 @@ func (conn ApiConnection) Do(request *http.Request) ([]byte, error) {
 		return nil, err
 	}
 
-	if !successCode(response.StatusCode) {
-		msg := parseError(response.Body)
-		return nil, fmt.Errorf("API error: %v (code: %v)", msg, response.StatusCode)
+	// Check if there was an error from the given API response.
+	if apiError := ErrorFromResponse(response); apiError != nil {
+		return nil, apiError
 	}
 
 	data, readErr := io.ReadAll(response.Body)
@@ -116,21 +116,3 @@ func (conn ApiConnection) setupHTTPClient() *http.Client {
 
 	return &http.Client{Transport: transport, Timeout: conn.Options.Timeout}
 }
-
-func successCode(code int) bool {
-	return code >= 200 && code < 300
-}
-
-func parseError(body io.Reader) string {
-	var errResp struct {
-		Error          string `json:"error"`
-		LocalizedError string `json:"localized_error"`
-	}
-	if err := json.NewDecoder(body).Decode(&errResp); err != nil {
-		return ""
-	}
-	if errResp.LocalizedError != "" {
-		return errResp.LocalizedError
-	}
-	return errResp.Error
-}