Fix to parse API error

apps.go

@@ -3,7 +3,6 @@ package mastodon
 import (
 	"context"
 	"encoding/json"
-	"fmt"
 	"net/http"
 	"net/url"
 	"path"
@@ -64,7 +63,7 @@ func RegisterApp(ctx context.Context, appConfig *AppConfig) (*Application, error
 	defer resp.Body.Close()
 
 	if resp.StatusCode != http.StatusOK {
-		return nil, fmt.Errorf("bad request: %v", resp.Status)
+		return nil, parseAPIError("bad request", resp)
 	}
 
 	var app Application

helper.go

@@ -2,6 +2,9 @@ package mastodon
 
 import (
 	"encoding/base64"
+	"encoding/json"
+	"errors"
+	"fmt"
 	"net/http"
 	"os"
 )
@@ -36,3 +39,17 @@ func Base64Encode(file *os.File) (string, error) {
 
 // String is a helper function to get the pointer value of a string.
 func String(v string) *string { return &v }
+
+func parseAPIError(prefix string, resp *http.Response) error {
+	errMsg := fmt.Sprintf("%s: %s", prefix, resp.Status)
+	var e struct {
+		Error string `json:"error"`
+	}
+
+	json.NewDecoder(resp.Body).Decode(&e)
+	if e.Error != "" {
+		errMsg = fmt.Sprintf("%s: %s", errMsg, e.Error)
+	}
+
+	return errors.New(errMsg)
+}

mastodon.go

@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
-	"fmt"
 	"io"
 	"mime/multipart"
 	"net/http"
@@ -131,7 +130,7 @@ func (c *Client) doAPI(ctx context.Context, method string, uri string, params in
 		}
 	}
 	if resp.StatusCode != http.StatusOK {
-		return fmt.Errorf("bad request: %v", resp.Status)
+		return parseAPIError("bad request", resp)
 	} else if res == nil {
 		return nil
 	}
@@ -175,7 +174,7 @@ func (c *Client) Authenticate(ctx context.Context, username, password string) er
 	defer resp.Body.Close()
 
 	if resp.StatusCode != http.StatusOK {
-		return fmt.Errorf("bad authorization: %v", resp.Status)
+		return parseAPIError("bad authorization", resp)
 	}
 
 	res := struct {

streaming.go

@@ -4,7 +4,6 @@ import (
 	"bufio"
 	"context"
 	"encoding/json"
-	"fmt"
 	"io"
 	"net/http"
 	"net/url"
@@ -95,7 +94,7 @@ func (c *Client) streaming(ctx context.Context, p string, tag string) (chan Even
 				req.Header.Set("Authorization", "Bearer "+c.config.AccessToken)
 				resp, err = c.Do(req)
 				if resp != nil && resp.StatusCode != 200 {
-					err = fmt.Errorf("bad request: %v", resp.Status)
+					err = parseAPIError("bad request", resp)
 				}
 			}
 			if err == nil {