feature: shared ngx.ctx among SSL_* phases and the following phases.

[spacewander]

TODO: update documentation & support the non-FFI version of API.

I hereby granted the copyright of the changes in this pull request
to the authors of this lua-nginx-module project.

[spacewander]

This is the sister PR of openresty/lua-resty-core#243

[agentzh]

@spacewander We don't need the non-FFI version of the API. Actually we are retiring all the non-FFI variants of the existing API functions which already have an FFI version.

[dndx]

I might be missing something, but it seems that we can change the existing ngx_http_lua_ffi_get_ctx_ref function to look for ssl_ctx-> ssl_ctx as well and return int *need_clone based on the current phase and where ref was located instead? That will save one FFI call and introducing new function.

[spacewander]

Updated.

[mergify]

This pull request is now in conflict :(

[doujiang24]

style: break a new line may be better?

[spacewander]

@doujiang24
Updated.

[doujiang24]

better clarify the inherited value from ngx.ctx is read-only.

[doujiang24]

Suggested change

	Note that the inherited value from <code>ngx.ctx</code> is read-only.
	Note that overwrite values in <code>ngx.ctx</code> in the http request phases (like `rewrite_by_lua*`) will only take affect in the current http request.

[doujiang24]

and add the following case will be much clearer.

for example:

ssl_certificate_by_lua_by_block {
    ngx.ctx.foo = 1  -- it will always be 1 in all of the http requests over this SSL connection.
}

location /foo-1 {
    rewrite_by_lua_block {
        ngx.ctx.foo = 2 -- only take affects in current http request
    }
}

location /foo-2 {
    rewrite_by_lua_block {
        ngx.say(ngx.ctx.foo) -- will alway be 1
    }
}

[spacewander]

@doujiang24
Done. Test case is added in openresty/lua-resty-core#243

[agentzh]

This has indentation problem caught by ngx-releng:

src/ngx_http_lua_ctx.c:
incorrect front spaces, unclosed bracket
89:                     | NGX_HTTP_LUA_CONTEXT_SSL_SESS_FETCH

[spacewander]

Solved.