This removes a bunch of checks for cases where we _read_ less bytes than
asked for.

There are several reasons why we may _read_ less bytes including reading
data from a network file system.

This has proven to be an issue.

Closes: https://github.com/nginx/nginx/issues/265
Signed-off-by: Andrew Clayton <ac@sigsegv.uk>

Passwords were not preserved in optimized SSL contexts, the bug had
appeared in d791b4aab (1.23.1), as in the following configuration:

    server {
        proxy_ssl_password_file password;
        proxy_ssl_certificate $ssl_server_name.crt;
        proxy_ssl_certificate_key $ssl_server_name.key;

        location /original/ {
            proxy_pass https://u1/;
        }

        location /optimized/ {
            proxy_pass https://u2/;
        }
    }

The fix is to always preserve passwords, by copying to the configuration
pool, if dynamic certificates are used.  This is done as part of merging
"ssl_passwords" configuration.

To minimize the number of copies, a preserved version is then used for
inheritance.  A notable exception is inheritance of preserved empty
passwords to the context with statically configured certificates:

    server {
        proxy_ssl_certificate $ssl_server_name.crt;
        proxy_ssl_certificate_key $ssl_server_name.key;

        location / {
            proxy_pass ...;

            proxy_ssl_certificate example.com.crt;
            proxy_ssl_certificate_key example.com.key;
        }
    }

In this case, an unmodified version (NULL) of empty passwords is set,
to allow reading them from the password prompt on nginx startup.

As an additional optimization, a preserved instance of inherited
configured passwords is set to the previous level, to inherit it
to other contexts:

    server {
        proxy_ssl_password_file password;

        location /1/ {
            proxy_pass https://u1/;
            proxy_ssl_certificate $ssl_server_name.crt;
            proxy_ssl_certificate_key $ssl_server_name.key;
        }

        location /2/ {
            proxy_pass https://u2/;
            proxy_ssl_certificate $ssl_server_name.crt;
            proxy_ssl_certificate_key $ssl_server_name.key;
        }
    }

It appears to be a relic from prototype locking removed in b0b7b5a35.

This makes it easier to understand why sessions may not be saved
in shared memory due to size.

All such transient buffers are converted to the single storage in BSS.

In preparation to raise the limit.

In OpenSSL, session resumption always happens in the default SSL context,
prior to invoking the SNI callback.  Further, unlike in TLSv1.2 and older
protocols, SSL_get_servername() returns values received in the resumption
handshake, which may be different from the value in the initial handshake.
Notably, this makes the restriction added in b720f650b insufficient for
sessions resumed with different SNI server name.

Considering the example from b720f650b, previously, a client was able to
request example.org by presenting a certificate for example.org, then to
resume and request example.com.

The fix is to reject handshakes resumed with a different server name, if
verification of client certificates is enabled in a corresponding server
configuration.

Caching is enabled with proxy_ssl_certificate_cache and friends.

Co-authored-by: Aleksei Bavshin <a.bavshin@nginx.com>

A new directive "ssl_certificate_cache max=N [valid=time] [inactive=time]"
enables caching of SSL certificate chain and secret key objects specified
by "ssl_certificate" and "ssl_certificate_key" directives with variables.

Co-authored-by: Aleksei Bavshin <a.bavshin@nginx.com>

This simplifies merging protocol values after ea15896 and ebd18ec.

Further, as outlined in ebd18ec18, for libraries preceeding TLSv1.2+
support, only meaningful versions TLSv1 and TLSv1.1 are set by default.

While here, fixed indentation.

MSVC generates a compilation error in case #if/#endif is used in a macro
parameter.