Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Implement a ReadJSON() utility to help reduce some code-duplication,
and to make sure we handle JSON requests consistently (e.g. always
check for the content-type).

Differences compared to current handling:

- prevent possible panic if request.Body is nil ("should never happen")
- always require Content-Type to be "application/json"
- be stricter about additional content after JSON (previously ignored)
- but, allow the body to be empty (an empty body is not invalid);
  update TestContainerInvalidJSON accordingly, which was testing the
  wrong expectation.
- close body after reading (some code did this)

We should consider to add a "max body size" on this function, similar to
https://github.com/moby/moby/blob/7b9275c0da707b030e62c96b679a976f31f929d3/api/server/middleware/debug.go#L27-L40

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

```
api/server/router/build/build_routes.go:309:41: Error return value of `(*encoding/json.Decoder).Decode` is not checked (errcheck)
api/server/router/build/build_routes.go:431:11: Error return value of `io.Copy` is not checked (errcheck)
api/server/router/container/container_routes.go:582:13: Error return value of `conn.Write` is not checked (errcheck)
api/server/router/grpc/grpc_routes.go:38:12: Error return value of `conn.Write` is not checked (errcheck)
api/server/router/grpc/grpc_routes.go:39:12: Error return value of `resp.Write` is not checked (errcheck)
api/server/router/image/image_routes.go:94:15: Error return value of `output.Write` is not checked (errcheck)
api/server/router/image/image_routes.go:139:15: Error return value of `output.Write` is not checked (errcheck)
api/server/router/image/image_routes.go:164:15: Error return value of `output.Write` is not checked (errcheck)
api/server/router/image/image_routes.go:180:15: Error return value of `output.Write` is not checked (errcheck)
api/server/router/plugin/plugin_routes.go:126:15: Error return value of `output.Write` is not checked (errcheck)
api/server/router/plugin/plugin_routes.go:165:15: Error return value of `output.Write` is not checked (errcheck)
api/server/router/plugin/plugin_routes.go:273:15: Error return value of `output.Write` is not checked (errcheck)
```

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

The cancellable handler is no longer needed as the context that is
passed with the http request will be cancelled just like the close
notifier was doing.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

The API did not treat invalid JSON payloads as a 400 error, as a result
returning a 500 error;

Before this change, an invalid JSON body would return a 500 error;

```bash
curl -v \
  --unix-socket /var/run/docker.sock \
  -X POST \
  "http://localhost/v1.30/networks/create" \
  -H "Content-Type: application/json" \
  -d '{invalid json'
```

```
> POST /v1.30/networks/create HTTP/1.1
> Host: localhost
> User-Agent: curl/7.52.1
> Accept: */*
> Content-Type: application/json
> Content-Length: 13
>
* upload completely sent off: 13 out of 13 bytes
< HTTP/1.1 500 Internal Server Error
< Api-Version: 1.40
< Content-Type: application/json
< Docker-Experimental: false
< Ostype: linux
< Server: Docker/dev (linux)
< Date: Mon, 05 Nov 2018 11:55:20 GMT
< Content-Length: 79
<
{"message":"invalid character 'i' looking for beginning of object key string"}
```

Empty request:

```bash
curl -v \
  --unix-socket /var/run/docker.sock \
  -X POST \
  "http://localhost/v1.30/networks/create" \
  -H "Content-Type: application/json"
```

```
> POST /v1.30/networks/create HTTP/1.1
> Host: localhost
> User-Agent: curl/7.54.0
> Accept: */*
> Content-Type: application/json
>
< HTTP/1.1 500 Internal Server Error
< Api-Version: 1.38
< Content-Length: 18
< Content-Type: application/json
< Date: Mon, 05 Nov 2018 12:00:18 GMT
< Docker-Experimental: true
< Ostype: linux
< Server: Docker/18.06.1-ce (linux)
<
{"message":"EOF"}
```

After this change, a 400 is returned;

```bash
curl -v \
  --unix-socket /var/run/docker.sock \
  -X POST \
  "http://localhost/v1.30/networks/create" \
  -H "Content-Type: application/json" \
  -d '{invalid json'
```

```
> POST /v1.30/networks/create HTTP/1.1
> Host: localhost
> User-Agent: curl/7.52.1
> Accept: */*
> Content-Type: application/json
> Content-Length: 13
>
* upload completely sent off: 13 out of 13 bytes
< HTTP/1.1 400 Bad Request
< Api-Version: 1.40
< Content-Type: application/json
< Docker-Experimental: false
< Ostype: linux
< Server: Docker/dev (linux)
< Date: Mon, 05 Nov 2018 11:57:15 GMT
< Content-Length: 79
<
{"message":"invalid character 'i' looking for beginning of object key string"}
```

Empty request:

```bash
curl -v \
  --unix-socket /var/run/docker.sock \
  -X POST \
  "http://localhost/v1.30/networks/create" \
  -H "Content-Type: application/json"
```

```
> POST /v1.30/networks/create HTTP/1.1
> Host: localhost
> User-Agent: curl/7.52.1
> Accept: */*
> Content-Type: application/json
>
< HTTP/1.1 400 Bad Request
< Api-Version: 1.40
< Content-Type: application/json
< Docker-Experimental: false
< Ostype: linux
< Server: Docker/dev (linux)
< Date: Mon, 05 Nov 2018 11:59:22 GMT
< Content-Length: 49
<
{"message":"got EOF while reading request body"}
```

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Since Go 1.7, context is a standard package. Since Go 1.9, everything
that is provided by "x/net/context" is a couple of type aliases to
types in "context".

Many vendored packages still use x/net/context, so vendor entry remains
for now.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>