Function prepareClientToWrite

src/networking.cpp:295–333

This function is called every time we are going to transmit new data * to the client. The behavior is the following: * * If the client should receive new data (normal clients will) the function * returns C_OK, and make sure to install the write handler in our event * loop so that when the socket is writable new data gets written. * * If the client should not receive new data, because it is

 * data to the clients output buffers. If the function returns C_ERR no
 * data should be appended to the output buffers. */
int prepareClientToWrite(client *c) {
    bool fAsync = !FCorrectThread(c);  // Not async if we're on the right thread

	if (!fAsync) {
		serverAssert(c->conn == nullptr || c->lock.fOwnLock());
	} else {
		serverAssert(GlobalLocksAcquired());
	}

    auto flags = c->flags.load(std::memory_order_relaxed);

    if (flags & CLIENT_FORCE_REPLY) return C_OK; // FORCE REPLY means we're doing something else with the buffer.
                                                // do not install a write handler

    /* If it's the Lua client we always return ok without installing any
     * handler since there is no socket at all. */
    if (flags & (CLIENT_LUA|CLIENT_MODULE)) return C_OK;

    /* If CLIENT_CLOSE_ASAP flag is set, we need not write anything. */
    if (c->flags & CLIENT_CLOSE_ASAP) return C_ERR;

    /* CLIENT REPLY OFF / SKIP handling: don't send replies. */
    if (flags & (CLIENT_REPLY_OFF|CLIENT_REPLY_SKIP)) return C_ERR;

    /* Masters don't receive replies, unless CLIENT_MASTER_FORCE_REPLY flag
     * is set. */
    if ((flags & CLIENT_MASTER) &&
        !(flags & CLIENT_MASTER_FORCE_REPLY)) return C_ERR;

    if (!c->conn) return C_ERR; /* Fake client for AOF loading. */

    /* Schedule the client to write the output buffers to the socket, unless
     * it should already be setup to do so (it has already pending data). */
    if (!fAsync && (c->flags & CLIENT_SLAVE || !clientHasPendingReplies(c))) clientInstallWriteHandler(c);
    if (fAsync && !(c->fPendingAsyncWrite)) clientInstallAsyncWriteHandler(c);

    /* Authorize the caller to queue in the output buffer of this client. */
    return C_OK;
}

/* -----------------------------------------------------------------------------
 * Low level functions to add more data to output buffers.