Flushing responses in nginx modules

[Zhang Chao]

Hi!

I think you can debug your code with gdb, maybe some other modules or
filters prevent sending the data.


On 11 July 2017 at 22:57:50, Johan Andersson (ng23 at firemail.cc) wrote:

Hi Andreas and Zhang,

Thank you for your hint with the http_echo_module! I read through their
code to get a hang of how the event loop and the event handling actually
works.

If I replace the hello_world command in my config files with the
echo/echo_flush/echo_sleep commands, everything works as expected.

If I use my modified hello_world module (code below), I still get a
three second pause and then all three "hello world" at once.

So I do not think that my configuration (which is the default Debian
Stretch configuration) is at fault.

I pasted the whole debug log here: https://pastebin.com/raw/uwuK4UJB

When I look into the debug log, I see four writev lines corresponding to
the initial header and the three "helloworld" outputs.

So I think the socket gets its data, but perhaps I am missing some magic
socket options? Which would be strange, as I cannot see the
http_echo_module doing such a thing.

This is my current code (all error handling omitted -- I will take care
of that):

struct ngx_http_hello_world_ctx
{
int counter;
ngx_event_t event;
};

static int numberOfMessages = 3;

static ngx_int_t ngx_http_hello_world_handler(ngx_http_request_t *r)
{
struct ngx_http_hello_world_ctx * ctx = ngx_http_get_module_ctx(r,
ngx_http_hello_world_module);

if(ctx == NULL)
{
ctx = ngx_pcalloc(r->pool, sizeof(struct
ngx_http_hello_world_ctx));
ngx_http_set_ctx(r, ctx, ngx_http_hello_world_module);
}

ctx->counter = 0;
ctx->event.data = r;
ctx->event.handler = ngx_http_hello_world_event_handler;
ctx->event.log = r->connection->log;

r->headers_out.content_type.len = sizeof("text/html") - 1;
r->headers_out.content_type.data = (u_char *) "text/html";
r->headers_out.status = NGX_HTTP_OK;
ngx_http_send_header(r);

r->main->count++; // Increments reference count
ngx_add_timer(&ctx->event, 0);

return ngx_http_output_filter(r, NULL);
}

static void ngx_http_hello_world_event_handler(ngx_event_t *ev)
{
ngx_http_request_t * r = ev->data;
struct ngx_http_hello_world_ctx * ctx = ngx_http_get_module_ctx(r,
ngx_http_hello_world_module);

if(ctx->counter < numberOfMessages)
{
ngx_buf_t *b;
ngx_chain_t out;

b = ngx_pcalloc(r->pool, sizeof(ngx_buf_t));

out.buf = b;
out.next = NULL;

b->pos = ngx_hello_world;
b->last = ngx_hello_world + sizeof(ngx_hello_world);
b->memory = 1;
b->flush = 1;
b->last_buf = (ctx->counter == numberOfMessages);

ngx_http_output_filter(r, &out);
ngx_http_send_special(r, NGX_HTTP_FLUSH);

ctx->counter++;

if(ctx->counter == numberOfMessages)
{
ctx->counter = 0;
ngx_http_send_special(r, NGX_HTTP_LAST);
ngx_http_finalize_request(r, NGX_OK); // Decrements
reference count
}
else
{
ngx_add_timer(&ctx->event, 1000);
}
}
}

Cheers
Johan

On 2017-07-10 04:04, Zhang Chao wrote:
> Hello!
>
> You mustn’t use standard sleep function for it will block Nginx’s
> events loop, alternatively, you need to put your write event to a
> timer, set the proper handler when the timer expires.
> BTW, you should always check the return value of ngx_http_send_header
> and ngx_http_output_filter.
>
> On 10 July 2017 at 01:43:46, Johan Andersson (ng23 at firemail.cc) wrote:
>
>> Hi everyone,
>>
>> I have some issues writing my nginx modules.
>>
>> I am on Debian Stretch, installed nginx with the default
>> configuration,
>> and took the hello_world module. It works without a hitch. Then I
>> changed the handler to send three "hello world" responses, and sleep
>> for
>> one second between each response.
>>
>> However, when I look at the result in my browser, the page loads,
>> pauses
>> for three seconds, and then displays all three "hello world"
>> messages at
>> once.
>>
>> Actually I was flushing each response, so I expected each "hello
>> world"
>> message to appear one after the other, with one second pause between
>>
>> them.
>>
>> Am I doing something wrong? Is this event the correct way to achieve
>>
>> this? All functions return NGX_OK. This is my code:
>>
>> static ngx_int_t ngx_http_hello_world_handler(ngx_http_request_t *r)
>>
>> {
>> ngx_buf_t *b;
>> ngx_chain_t out;
>> ngx_int_t result;
>>
>> r->headers_out.content_type.len = sizeof("text/html") - 1;
>> r->headers_out.content_type.data = (u_char *) "text/html";
>> r->headers_out.status = NGX_HTTP_OK;
>> //r->headers_out.content_length_n = sizeof(ngx_hello_world);
>> ngx_http_send_header(r);
>>
>> for(int i = 0; i < 3; i++)
>> {
>> b = ngx_pcalloc(r->pool, sizeof(ngx_buf_t));
>>
>> out.buf = b;
>> out.next = NULL;
>>
>> b->pos = ngx_hello_world;
>> b->last = ngx_hello_world + sizeof(ngx_hello_world);
>> b->memory = 1;
>> b->flush = 1;
>> b->last_buf = (i == 2);
>>
>> result = ngx_http_output_filter(r, &out);
>> ngx_http_send_special(r, NGX_HTTP_FLUSH);
>>
>> sleep(1);
>> }
>>
>> return result;
>> }
>>
>> Cheers
>> Johann
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