client: use io.LimitedReader for reading HTTP error

client.checkResponseErr() was hanging and consuming infinite memory
when the serverResp.Body io.Reader returns infinite stream.

This commit prohibits reading more than 1MiB.

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

client/request.go

@@ -195,10 +195,18 @@ func (cli *Client) checkResponseErr(serverResp serverResponse) error {
 		return nil
 	}
 
-	body, err := ioutil.ReadAll(serverResp.body)
+	bodyMax := 1 * 1024 * 1024 // 1 MiB
+	bodyR := &io.LimitedReader{
+		R: serverResp.body,
+		N: int64(bodyMax),
+	}
+	body, err := ioutil.ReadAll(bodyR)
 	if err != nil {
 		return err
 	}
+	if bodyR.N == 0 {
+		return fmt.Errorf("request returned %s with a message (> %d bytes) for API route and version %s, check if the server supports the requested API version", http.StatusText(serverResp.statusCode), bodyMax, serverResp.reqURL)
+	}
 	if len(body) == 0 {
 		return fmt.Errorf("request returned %s for API route and version %s, check if the server supports the requested API version", http.StatusText(serverResp.statusCode), serverResp.reqURL)
 	}

client/request_test.go

@@ -5,12 +5,14 @@ import (
 	"context"
 	"fmt"
 	"io/ioutil"
+	"math/rand"
 	"net/http"
 	"strings"
 	"testing"
 
 	"github.com/docker/docker/api/types"
 	"gotest.tools/assert"
+	is "gotest.tools/assert/cmp"
 )
 
 // TestSetHostHeader should set fake host for local communications, set real host
@@ -87,3 +89,18 @@ func TestPlainTextError(t *testing.T) {
 		t.Fatalf("expected a Server Error, got %v", err)
 	}
 }
+
+func TestInfiniteError(t *testing.T) {
+	infinitR := rand.New(rand.NewSource(42))
+	client := &Client{
+		client: newMockClient(func(req *http.Request) (*http.Response, error) {
+			resp := &http.Response{StatusCode: http.StatusInternalServerError}
+			resp.Header = http.Header{}
+			resp.Body = ioutil.NopCloser(infinitR)
+			return resp, nil
+		}),
+	}
+
+	_, err := client.Ping(context.Background())
+	assert.Check(t, is.ErrorContains(err, "request returned Internal Server Error"))
+}