Merge of r5004, r5019-r5025: ssl fixes. *) SSL: speedup loading of configs with many ssl servers. The patch saves one EC_KEY_generate_key() call per server{} block by informing OpenSSL about SSL_OP_SINGLE_ECDH_USE we are going to use before the SSL_CTX_set_tmp_ecdh() call. For a configuration file with 10k simple server{} blocks with SSL enabled this change reduces startup time from 18s to 5s on a slow test box here. *) SSL: removed conditions that always hold true. *) SSL: resetting of flush flag after the data was written. There is no need to flush next chunk of data if it does not contain a buffer with the flush or last_buf flags set. *) SSL: preservation of flush flag for buffered data. Previously, if SSL buffer was not sent we lost information that the data must be flushed. *) SSL: calculation of buffer size moved closer to its usage. No functional changes. *) SSL: avoid calling SSL_write() with zero data size. According to documentation, calling SSL_write() with num=0 bytes to be sent results in undefined behavior. We don't currently call ngx_ssl_send_chain() with empty chain and buffer. This check handles the case of a chain with total data size that is a multiple of NGX_SSL_BUFSIZE, and with the special buffer at the end. In practice such cases resulted in premature connection close and critical error "SSL_write() failed (SSL:)" in the error log. *) SSL: take into account data in the buffer while limiting output. In some rare cases this can result in a more smooth sending rate. *) SSL: fixed ngx_ssl_handshake() with level-triggered event methods. Missing calls to ngx_handle_write_event() and ngx_handle_read_event() resulted in a CPU hog during SSL handshake if an level-triggered event method (e.g. select) was used.