Add vk bridge (#1372)

* Add vk bridge

* Vk bridge attachments

* Vk bridge forwarded messages

* Vk bridge sample config and code cleanup

* Vk bridge add vendor

* Vk bridge message edit

* Vk bridge: fix fetching names of other bots

* Vk bridge: code cleanup

* Vk bridge: fix shadows declaration

* Vk bridge: remove UseFileURL

vendor/github.com/SevereCloud/vksdk/v2/internal/transport.go

@@ -0,0 +1,74 @@
+/*
+Package internal unimportable
+*/
+package internal // import "github.com/SevereCloud/vksdk/v2/internal"
+
+import (
+	"context"
+	"net/http"
+
+	"github.com/SevereCloud/vksdk/v2"
+)
+
+// UserAgent module.
+const UserAgent = "vksdk/" + vksdk.Version + " (+https://github.com/SevereCloud/vksdk)"
+
+// ContextKey is just an empty struct. It exists so HTTPClient can be
+// an immutable public variable with a unique type. It's immutable
+// because nobody else can create a ContextKey, being unexported.
+type ContextKey int
+
+// ContextKey list.
+const (
+	HTTPClientKey ContextKey = iota
+	UserAgentKey
+	GroupIDKey
+	EventIDKey
+	LongPollTsKey
+	CallbackRetryCounterKey
+	CallbackRetryAfterKey
+)
+
+// ContextClient return *http.Client.
+func ContextClient(ctx context.Context) *http.Client {
+	if ctx != nil {
+		if hc, ok := ctx.Value(HTTPClientKey).(*http.Client); ok {
+			return hc
+		}
+	}
+
+	return http.DefaultClient
+}
+
+// ContextUserAgent return User-Agent from context.
+func ContextUserAgent(ctx context.Context) string {
+	if ctx != nil {
+		if hc, ok := ctx.Value(UserAgentKey).(string); ok {
+			return hc
+		}
+	}
+
+	return UserAgent
+}
+
+// DoRequest sends an HTTP request and returns an HTTP response.
+//
+// The provided ctx must be non-nil. If it is canceled or times out,
+// ctx.Err() will be returned.
+func DoRequest(ctx context.Context, req *http.Request) (*http.Response, error) {
+	client := ContextClient(ctx)
+
+	if req.UserAgent() == "" {
+		req.Header.Set("User-Agent", ContextUserAgent(ctx))
+	}
+
+	resp, err := client.Do(req.WithContext(ctx))
+	// If we got an error, and the context has been canceled,
+	// the context's error is probably more useful.
+	if err != nil {
+		<-ctx.Done()
+		err = ctx.Err()
+	}
+
+	return resp, err
+}