cli/command/image: remove uses of JSON field

The JSON field was added in [moby@9fd2c0f], to address [moby#19177], which
reported an incompatibility with Classic (V1) Swarm, which produced a non-
standard response;

> Make docker load to output json when the response content type is json
> Swarm hijacks the response from docker load and returns JSON rather
> than plain text like the Engine does. This makes the API library to return
> information to figure that out.

A later change in [moby@96d7db6] added additional logic to make sure the
correct content-type was returned, depending on whether the `quiet` option
was set (which produced a non-JSON response). This caused inconsistency in
the API response, and [moby@2f27632] changed the endpoint to always produce
JSON (only skipping the "progress" output if `quiet` was set).

This means that the "load" endpoint ([`imageRouter.postImagesLoad`]) now
unconditionally returns JSON, making the `JSON` field fully redundant.

This patch removes the use of the JSON field, as it's redundant, and the way it handles
the content-type is incorrect because it would not handle correct, but different
formatted response-headers (`application/json; charset=utf-8`), which could
result in malformed output on the client.

[moby@9fd2c0f]: moby/moby@9fd2c0f
[moby#19177]: moby/moby#19177
[moby@96d7db6]: moby/moby@96d7db6
[moby@2f27632]: moby/moby@2f27632
[`imageRouter.postImagesLoad`]: https://github.com/moby/moby/blob/7b9d2ef6e5518a3d3f3cc418459f8df786cfbbd1/api/server/router/image/image_routes.go#L248-L255

Signed-off-by: Sebastiaan van Stijn <[email protected]>

Author: thaJeztah

cli/command/image/load.go

@@ -70,7 +70,7 @@ func runLoad(ctx context.Context, dockerCli command.Cli, opts loadOptions) error
 		if err != nil {
 			return err
 		}
-		defer file.Close()
+		defer func() { _ = file.Close() }()
 		input = file
 	}
 
@@ -95,12 +95,7 @@ func runLoad(ctx context.Context, dockerCli command.Cli, opts loadOptions) error
 	if err != nil {
 		return err
 	}
-	defer res.Close()
+	defer func() { _ = res.Close() }()
 
-	if res.JSON {
-		return jsonstream.Display(ctx, res, dockerCli.Out())
-	}
-
-	_, err = io.Copy(dockerCli.Out(), res)
-	return err
+	return jsonstream.Display(ctx, res, dockerCli.Out())
 }