async triggerOutgoingHandler(buffer) {
        const bufferLength = buffer.size;
        this.executingOutgoingHandlers++;
        this.offset += bufferLength;
        try {
            await this.outgoingHandler(() => buffer.getReadableStream(), bufferLength, this.offset - bufferLength);
        }
        catch (err) {
            this.emitter.emit("error", err);
            return;
        }
        this.executingOutgoingHandlers--;
        this.reuseBuffer(buffer);
        this.emitter.emit("checkEnd");
    }
Trigger a outgoing handler for a buffer shifted from outgoing.

@param buffer -