Request body: recalculate size of a request body in scgi module.

This allows to handle requests with chunked body by scgi module, and
also simplifies handling of various request body modifications.

src/http/modules/ngx_http_scgi_module.c

@@ -533,10 +533,11 @@ ngx_http_scgi_create_key(ngx_http_request_t *r)
 static ngx_int_t
 ngx_http_scgi_create_request(ngx_http_request_t *r)
 {
+    off_t                         content_length_n;
     u_char                        ch, *key, *val, *lowcase_key;
     size_t                        len, key_len, val_len, allocated;
     ngx_buf_t                    *b;
-    ngx_str_t                    *content_length;
+    ngx_str_t                     content_length;
     ngx_uint_t                    i, n, hash, skip_empty, header_params;
     ngx_chain_t                  *cl, *body;
     ngx_list_part_t              *part;
@@ -545,12 +546,20 @@ ngx_http_scgi_create_request(ngx_http_request_t *r)
     ngx_http_script_engine_t      e, le;
     ngx_http_scgi_loc_conf_t     *scf;
     ngx_http_script_len_code_pt   lcode;
-    static ngx_str_t              zero = ngx_string("0");
+    u_char                        buffer[NGX_OFF_T_LEN];
 
-    content_length = r->headers_in.content_length ?
-                         &r->headers_in.content_length->value : &zero;
+    content_length_n = 0;
+    body = r->upstream->request_bufs;
 
-    len = sizeof("CONTENT_LENGTH") + content_length->len + 1;
+    while (body) {
+        content_length_n += ngx_buf_size(body->buf);
+        body = body->next;
+    }
+
+    content_length.data = buffer;
+    content_length.len = ngx_sprintf(buffer, "%O", content_length_n) - buffer;
+
+    len = sizeof("CONTENT_LENGTH") + content_length.len + 1;
 
     header_params = 0;
     ignored = NULL;
@@ -672,11 +681,8 @@ ngx_http_scgi_create_request(ngx_http_request_t *r)
 
     cl->buf = b;
 
-    b->last = ngx_snprintf(b->last,
-                           NGX_SIZE_T_LEN + 1 + sizeof("CONTENT_LENGTH")
-                           + NGX_OFF_T_LEN + 1,
-                           "%ui:CONTENT_LENGTH%Z%V%Z",
-                           len, content_length);
+    b->last = ngx_sprintf(b->last, "%ui:CONTENT_LENGTH%Z%V%Z",
+                          len, &content_length);
 
     if (scf->params_len) {
         ngx_memzero(&e, sizeof(ngx_http_script_engine_t));