From ddb7d61f6173c2f191f4eddc15f1f912e940e42c Mon Sep 17 00:00:00 2001
From: Alejandro Colomar <alx@nginx.com>
Date: Wed, 19 Jul 2023 13:36:59 +0200
Subject: HTTP: filter: supporting a list of filter_handlers

Filter handlers are a new handler that takes place when a buffer is
about to be sent.  It filters (modifies) the contents of the buffer
in-place, so that the new contents will be sent.  Several filters can be
applied in a loop.

Signed-off-by: Alejandro Colomar <alx@nginx.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>
---
 src/nxt_http.h         |  2 ++
 src/nxt_http_filter.h  | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++
 src/nxt_http_request.c | 13 +++++++++++++
 3 files changed, 68 insertions(+)
 create mode 100644 src/nxt_http_filter.h

diff --git a/src/nxt_http.h b/src/nxt_http.h
index d614b303..300c197d 100644
--- a/src/nxt_http.h
+++ b/src/nxt_http.h
@@ -142,6 +142,7 @@ struct nxt_http_request_s {
 
     nxt_work_handler_t              body_handler;
     void                            *body_handler_data;
+    nxt_list_t                      *response_filters;
 
     nxt_nsec_t                      start_time;
 
@@ -439,4 +440,5 @@ nxt_msec_t nxt_h1p_conn_request_timer_value(nxt_conn_t *c, uintptr_t data);
 
 extern const nxt_conn_state_t  nxt_h1p_idle_close_state;
 
+
 #endif  /* _NXT_HTTP_H_INCLUDED_ */
diff --git a/src/nxt_http_filter.h b/src/nxt_http_filter.h
new file mode 100644
index 00000000..d26ae1a9
--- /dev/null
+++ b/src/nxt_http_filter.h
@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) Alejandro Colomar
+ * Copyright (C) NGINX, Inc.
+ */
+
+#ifndef NXT_HTTP_FILTER_H_INCLUDED_
+#define NXT_HTTP_FILTER_H_INCLUDED_
+
+
+#include "nxt_router.h"
+
+#include "nxt_auto_config.h"
+
+#include <stddef.h>
+
+#include "nxt_clang.h"
+#include "nxt_errno.h"
+#include "nxt_list.h"
+#include "nxt_main.h"
+
+
+typedef struct nxt_http_filter_handler_s  nxt_http_filter_handler_t;
+
+
+struct nxt_http_filter_handler_s {
+    nxt_work_handler_t              filter_handler;
+    void                            *data;
+};
+
+
+nxt_inline nxt_int_t nxt_http_filter_handler_add(nxt_http_request_t *r,
+    nxt_work_handler_t filter_handler, void *data);
+
+
+nxt_inline nxt_int_t
+nxt_http_filter_handler_add(nxt_http_request_t *r,
+    nxt_work_handler_t filter_handler, void *data)
+{
+    nxt_http_filter_handler_t  *elem;
+
+    elem = nxt_list_add(r->response_filters);
+    if (nxt_slow_path(elem == NULL)) {
+        return NXT_ERROR;
+    }
+
+    elem->filter_handler = filter_handler;
+    elem->data = data;
+
+    return NXT_OK;
+}
+
+
+#endif  /* NXT_HTTP_FILTER_H_INCLUDED_ */
diff --git a/src/nxt_http_request.c b/src/nxt_http_request.c
index 3bcf3d94..e72a7492 100644
--- a/src/nxt_http_request.c
+++ b/src/nxt_http_request.c
@@ -7,6 +7,8 @@
 #include <nxt_router.h>
 #include <nxt_http.h>
 
+#include "nxt_http_filter.h"
+
 
 static nxt_int_t nxt_http_validate_host(nxt_str_t *host, nxt_mp_t *mp);
 static void nxt_http_request_start(nxt_task_t *task, void *obj, void *data);
@@ -262,6 +264,11 @@ nxt_http_request_create(nxt_task_t *task)
         goto fail;
     }
 
+    r->response_filters = nxt_list_create(mp, 1, sizeof(nxt_http_filter_handler_t));
+    if (nxt_slow_path(r->response_filters == NULL)) {
+        goto fail;
+    }
+
     last = nxt_mp_zget(mp, NXT_BUF_SYNC_SIZE);
     if (nxt_slow_path(last == NULL)) {
         goto fail;
@@ -723,6 +730,12 @@ nxt_http_request_ws_frame_start(nxt_task_t *task, nxt_http_request_t *r,
 void
 nxt_http_request_send(nxt_task_t *task, nxt_http_request_t *r, nxt_buf_t *out)
 {
+    nxt_http_filter_handler_t  *filter;
+
+    nxt_list_each(filter, r->response_filters) {
+        filter->filter_handler(task, &out, filter->data);
+    } nxt_list_loop;
+
     if (nxt_fast_path(r->proto.any != NULL)) {
         nxt_http_proto[r->protocol].send(task, r, out);
     }
-- 
cgit