2: header already sent

[Dk Jack]

Sorry, I made a typo in my earlier email. Please read the following
sentence:

"When I send the response in the *content* phase handler, I am am seeing
'header already sent' messages in the error log."

as

"When I send the response in the *access* phase handler, I am am seeing
'header already sent' messages in the error log."

On Thu, Jul 12, 2018 at 1:29 PM Dk Jack <dnj0496 at gmail.com> wrote:

> Hi,
> Sorry for sending this again. I haven't been able to resolve my issue.
> I've read several modules for example and gone over several docs etc. but
> with no success so far.
>
> In my module, I need to either drop the request or allow the request. When
> I drop the request, I need to send custom response and status. The custom
> response and status don't come from the config file. When I send the
> response in the content phase handler, I am am seeing 'header already sent'
> messages in the error log. How can prevent further processing of the
> request after my handler is called for the terminal case?
>
> Since my module needs to examine all requests irrespective of the uri, I
> tried registering a content phase handler and send the custom response in
> that handler. However, my content phase handler is never invoked. I suspect
> some other content handler is overriding my content handler.  Is there a
> way I can prevent that i.e. for a request, can I force only my content
> handler to be called.
>
> Please let me know what I am doing wrong? I just need to send/perform
> custom response/actions when a request matches my criteria. I've include a
> skeleton of my code.
> Any inputs are greatly appreciated. Thanks.
>
> regards,
> Dk.
>
> http_mod_send_response(ngx_http_request_t *r, ngx_uint_t custom_status,
> char *body, ngx_int_t blen)
> {
>   ngx_int_t rc;
>   ngx_log_t *log = r->connection->log;
>   ngx_buf_t *buf = ngx_create_temp_buf(r->pool, (blen+16)); // pad.
>
>   if (NULL == buf) {
>     ngx_log_error(NGX_LOG_ERR, log, 0, "%s: Failed to allocate buffer",
> __FUNCTION__);
>     return NGX_ERROR;
>   }
>
>   buf->last = ngx_copy(buf->start, (unsigned char*) data, dlen);
>   rc = ngx_http_discard_request_body(r);
>   if (rc != NGX_OK) {
>     ngx_log_error(NGX_LOG_ERR, log, 0, "%s: Discard req. body failed.
> rc=%i", __FUNCTION__, rc);
>     return rc;
>   }
>
>   r->headers_out.status = custom_status;
>   r->headers_out.content_length_n = buf->last - buf->pos;
>   r->headers_out.content_type.len = sizeof("text/plain") - 1;
>   r->headers_out.content_type.data = (u_char *) "text/plain";
>
>   rc = ngx_http_send_header(r);
>   if (rc == NGX_ERROR || rc > NGX_OK || r->header_only) {
>     ngx_log_error(NGX_LOG_ERR, log, 0, "%s: Send header failed. rc=%i",
> __FUNCTION__, rc);
>     return rc;
>   }
>
>   ngx_chain_t *out_chain = ngx_alloc_chain_link(r->pool);
>   if (NULL == out_chain) {
>     ngx_log_error(NGX_LOG_ERR, log, 0, "%s: Buffer chain alloc failed",
> __FUNCTION__);
>     return NGX_ERROR;
>   }
>
>   out_chain->buf = buf;
>   out_chain->next = NULL;
>   buf->last_buf = 1;
>   buf->last_in_chain = 1;
>
>   return ngx_http_output_filter(r, out_chain);
> }
>
> typedef struct {
>   unsigned done:1;
> } ngx_http_mod_ctx_t;
>
> int
> http_module_process_request(ngx_http_request_t *r, ngx_uint_t *status,
> char *body, ngx_uint_t *blen)
> {
>   if (/* request matches criteria */) {
>     /* other boiler plate code */
>     *status = get_custom_status();
>     *body = get_custom_body();
>     *blen = ngx_strlen(body);
>     return *status;    // this can be different from custom status.
>   }
>
>   return NGX_DECLINED;
> }
>
> static ngx_int_t
> ngx_http_request_handler(ngx_http_request_t *r)
> {
>   ngx_http_mod_ctx_t *ctx = ngx_http_get_module_ctx(r, nginx_http_module);
>
>   if (ctx) {
>     ngx_log_error(NGX_LOG_DEBUG, r->connection->log, 0, "duplicate
>     invokation");
>     return NGX_DECLINED;
>   } else {
>     ctx = ngx_palloc(r->connection->pool, sizeof(ngx_http_mod_ctx_t));
>     if (ctx == NULL) {
>       ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
>       "Out of memory. Cannot allocate context");
>       return NGX_ERROR;
>     }
>
>     ctx->done = 0;
>     ngx_http_set_ctx(r, ctx, nginx_http_module);
>   }
>
>   ngx_int_t rc = 0;
>   char custom_body[512];
>   ngx_uint_t blen;
>   ngx_uint_t custom_status;
>   if (!ctx->done) {
>     rc = http_module_process_request(r, &custom_status, custom_body,
> &blen);
>   }
>
>   ctx->done = 1;
>   if ((rc != 0) && (rc != NGX_DECLINED)) {
>     return http_mod_send_response(r, custom_status, custom_body, blen);
>     /* alternate implementation, send response in content handler.
>       ngx_buf_t *buf = ngx_create_temp_buf(r->pool, blen);
>       buf->last = ngx_copy(buf->start, (unsigned char*) data, dlen);
>       ctx->custom_body = buf;
>       ctx->rcode = custom_status;
>      */
>   }
>
>   return NGX_DECLINED;
> }
>
> static ngx_int_t
> http_module_content_handler(ngx_http_request_t *r)
> {
>   ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, "%s: invoked",
> __FUNCTION__);
>   ngx_http_ss_ctx_t *ctx = ngx_http_get_module_ctx(r,
> nginx_mitigator_module);
>
>   if (ctx && ctx->content) {
>     ctx->content = 0;
>     return http_mod_send_response(r, ctx->rcode, ctx->custom_body);
>   } else {
>     ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
>                   "%s: ctx = %p, content = %d", __FUNCTION__, ctx, ctx ?
> ctx->content : -1);
>   }
>
>   return NGX_DECLINED;
> }
>
> static ngx_int_t
> ngx_http_module_init (ngx_conf_t *cf)
> {
>   ngx_http_core_main_conf_t *cmcf = ngx_http_conf_get_module_main_conf(cf,
> ngx_http_core_module);
>
>   if (!cmcf) {
>     ngx_log_error(NGX_LOG_ERR, cf->log, 0, "Failed to retrieve module main
> conf");
>     return NGX_ERROR;
>   }
>
>   ngx_http_handler_pt *hptr =
> ngx_array_push(&cmcf->phases[NGX_HTTP_ACCESS_PHASE].handlers);
>   if (hptr == NULL) {
>     ngx_log_error(NGX_LOG_ERR, cf->log, 0, "Could not retrieve access
> phase handler");
>     return NGX_ERROR;
>   }
>
>   *hptr = ngx_http_request_handler;
>   ngx_log_error(NGX_LOG_INFO, cf->log, 0, "[init] Installed request
> handler");
>
>   ngx_http_handler_pt *cptr =
> ngx_array_push(&cmcf->phases[NGX_HTTP_CONTENT_PHASE].handlers);
>   if (cptr == NULL) {
>     ngx_log_error(NGX_LOG_ERR, cf->log, 0, "Could not retrieve access
> phase handler");
>     return NGX_ERROR;
>   }
>
>   *cptr = ngx_http_request_handler;
>   ngx_log_error(NGX_LOG_INFO, cf->log, 0, "[init] Installed request
> handler");
>
>   return NGX_OK;
> }
>
>
>
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