Re-implement ContainerInspect call in Wings to use more performant json encoder (#119)

* First pass at re-implementing the Docker inspect call to use more efficient json parser

* Improve logic

environment/docker/api.go

@@ -0,0 +1,116 @@
+package docker
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"reflect"
+	"strings"
+	"sync"
+
+	"emperror.dev/errors"
+	"github.com/docker/docker/api/types"
+	"github.com/docker/docker/api/types/versions"
+	"github.com/docker/docker/client"
+	"github.com/docker/docker/errdefs"
+	"github.com/goccy/go-json"
+	"github.com/pterodactyl/wings/config"
+)
+
+var (
+	o           sync.Once
+	cli         cliSettings
+	fastEnabled bool
+)
+
+type cliSettings struct {
+	enabled bool
+	proto   string
+	host    string
+	scheme  string
+	version string
+}
+
+func configure(c *client.Client) {
+	o.Do(func() {
+		fastEnabled = config.Get().Docker.UsePerformantInspect
+
+		r := reflect.ValueOf(c).Elem()
+		cli.proto = r.FieldByName("proto").String()
+		cli.host = r.FieldByName("addr").String()
+		cli.scheme = r.FieldByName("scheme").String()
+		cli.version = r.FieldByName("version").String()
+	})
+}
+
+// ContainerInspect is a rough equivalent of Docker's client.ContainerInspect()
+// but re-written to use a more performant JSON decoder. This is important since
+// a large number of requests to this endpoint are spawned by Wings, and the
+// standard "encoding/json" shows its performance woes badly even with single
+// containers running.
+func (e *Environment) ContainerInspect(ctx context.Context) (types.ContainerJSON, error) {
+	configure(e.client)
+
+	// Support feature flagging of this functionality so that if something goes
+	// wrong for now it is easy enough for people to switch back to the older method
+	// of fetching stats.
+	if !fastEnabled {
+		return e.client.ContainerInspect(ctx, e.Id)
+	}
+
+	var st types.ContainerJSON
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, "/containers/"+e.Id+"/json", nil)
+	if err != nil {
+		return st, errors.WithStack(err)
+	}
+
+	if cli.proto == "unix" || cli.proto == "npipe" {
+		req.Host = "docker"
+	}
+
+	req.URL.Host = cli.host
+	req.URL.Scheme = cli.scheme
+
+	res, err := e.client.HTTPClient().Do(req)
+	if err != nil {
+		return st, errdefs.FromStatusCode(err, res.StatusCode)
+	}
+
+	body, err := io.ReadAll(res.Body)
+	if err != nil {
+		return st, errors.Wrap(err, "failed to read response body from Docker")
+	}
+	if err := parseErrorFromResponse(res, body); err != nil {
+		return st, errdefs.FromStatusCode(err, res.StatusCode)
+	}
+	if err := json.Unmarshal(body, &st); err != nil {
+		return st, errors.WithStack(err)
+	}
+	return st, nil
+}
+
+// parseErrorFromResponse is a re-implementation of Docker's
+// client.checkResponseErr() function.
+func parseErrorFromResponse(res *http.Response, body []byte) error {
+	if res.StatusCode >= 200 && res.StatusCode < 400 {
+		return nil
+	}
+
+	var ct string
+	if res.Header != nil {
+		ct = res.Header.Get("Content-Type")
+	}
+
+	var emsg string
+	if (cli.version == "" || versions.GreaterThan(cli.version, "1.23")) && ct == "application/json" {
+		var errResp types.ErrorResponse
+		if err := json.Unmarshal(body, &errResp); err != nil {
+			return errors.WithStack(err)
+		}
+		emsg = strings.TrimSpace(errResp.Message)
+	} else {
+		emsg = strings.TrimSpace(string(body))
+	}
+
+	return errors.Wrap(errors.New(emsg), "Error response from daemon")
+}