c - 如何获取底层套接字读取缓冲区大小？

Question

有一个用于原始套接字的 api:

int sz;
ioctlsocket(sock, FIONREAD, &sz); 
::recv(sock, buff, sz, 0);

ioctlsocket 可用于获取传入缓冲区大小，但如何使用 openssl 获取它:

int sz = what?
SSL_read(pSSL, buff, sz);

Answer 1

but how to get [incoming buffer size] with openssl?

OpenSSL 使用 BIO。写缓冲区有BIO_get_write_buf_size，但读缓冲区没有相应的控制。您可以使用 BIO_set_read_buffer_size 设置读取缓冲区大小。但我相信为 BIO 设置缓冲区，而不是套接字上的 I/O 缓冲区。请参阅 crypto/bio/bss_bio.c 中的 struct bio_bio_st 和 BIO_f_buffer(3) 中的文档和 BIO_s_bio(3) .

您应该可以在BIO 上调用BIO_get_fd 来获取底层套接字，然后使用ioctl 或ioctlsocket。您可以在 SSL* 中找到 BIO。 OpenSSL 方便地具有 SSL_get_rbio 和 SSL_get_wbio。来自 ssl/ssl.h:

struct ssl_st
    {
    /* protocol version
     * (one of SSL2_VERSION, SSL3_VERSION, TLS1_VERSION, DTLS1_VERSION)
     */
    int version;
    int type; /* SSL_ST_CONNECT or SSL_ST_ACCEPT */

    const SSL_METHOD *method; /* SSLv3 */

    /* There are 2 BIO's even though they are normally both the
     * same.  This is so data can be read and written to different
     * handlers */

#ifndef OPENSSL_NO_BIO
    BIO *rbio; /* used by SSL_read */
    BIO *wbio; /* used by SSL_write */
    BIO *bbio; /* used during session-id reuse to concatenate messages */
#else
    char *rbio; /* used by SSL_read */
    char *wbio; /* used by SSL_write */
    char *bbio;
#endif
    /* This holds a variable that indicates what we were doing
     * when a 0 or -1 is returned.  This is needed for
     * non-blocking IO so we know what request needs re-doing when
     * in SSL_accept or SSL_connect */
    int rwstate;
    ...
};