added parsing response body and noticing errors in exec requests

until ClickHouse/ClickHouse#18002 is fixed

conn.go

@@ -247,10 +247,15 @@ func (c *conn) exec(ctx context.Context, query string, args []driver.Value) (dri
 		return nil, err
 	}
 	body, err := c.doRequest(ctx, req)
-	if body != nil {
-		body.Close()
+	if err != nil {
+		if body != nil {
+			body.Close()
+		}
+
+		return emptyResult, err
 	}
-	return emptyResult, err
+
+	return emptyResult, noticeError(body)
 }
 
 func (c *conn) doRequest(ctx context.Context, req *http.Request) (io.ReadCloser, error) {

helpers.go

@@ -2,6 +2,7 @@ package clickhouse
 
 import (
 	"bytes"
+	"io"
 	"net/http"
 	"strings"
 	"time"
@@ -11,6 +12,8 @@ var (
 	escaper    = strings.NewReplacer(`\`, `\\`, `'`, `\'`)
 	dateFormat = "2006-01-02"
 	timeFormat = "2006-01-02 15:04:05"
+
+	exceptionMarker = "DB::Exception"
 )
 
 func escape(s string) string {
@@ -40,6 +43,22 @@ func readResponse(response *http.Response) (result []byte, err error) {
 	return
 }
 
+func noticeError(body io.ReadCloser) (err error) {
+	if body == nil {
+		return nil
+	}
+
+	buf := new(bytes.Buffer)
+	defer body.Close()
+	_, err = buf.ReadFrom(body)
+	msg := buf.String()
+	if strings.Contains(msg, exceptionMarker) {
+		return newError(msg)
+	}
+
+	return nil
+}
+
 func numOfColumns(data []byte) int {
 	var cnt int
 	for _, ch := range data {