change: we now avoid generating the Content-Type response header when getting all response headers.

The previous behavior assumed that nginx will always generate the
Content-Type header if it is missing. However in some cases (such as the
upstream response not having a Content-Type header), nginx will not
generate the Content-Type header itself.

Thus, generating the Content-Type when getting response headers
may create an unexpected Content-Type header in the response.

Signed-off-by: Thibault Charbonnier <thibaultcha@me.com>

Author: spacewander

README.markdown

@@ -4147,25 +4147,6 @@ to be returned when reading `ngx.header.Foo`.
 
 Note that `ngx.header` is not a normal Lua table and as such, it is not possible to iterate through it using the Lua `ipairs` function.
 
-Note: if the current response does not have a Content-Type header, but you use
-`ngx.header` to attempt retrieving it, a side effect will be that a
-Content-Type header will be created and returned according to your nginx
-configuration.
-
-For example:
-
-```nginx
-
- location = /t {
-     default_type text/html;
-     content_by_lua_block {
-         -- even if the response had no Content-Type header,
-         -- it will now have: Content-Type: text/html
-         ngx.say(ngx.header['Content-Type'])
-     }
- }
-```
-
 For reading *request* headers, use the [ngx.req.get_headers](#ngxreqget_headers) function instead.
 
 [Back to TOC](#nginx-api-for-lua)
@@ -4191,24 +4172,6 @@ Returns a Lua table holding all the current response headers for the current req
  end
 ```
 
-Note: if the current response does not have a Content-Type header, but you use
-`ngx.resp.get_headers` to attempt retrieving it, a side effect will
-be that a Content-Type header will be created and returned according to your
-nginx configuration.
-
-For example:
-
-```nginx
-
- location = /t {
-     default_type text/html;
-     content_by_lua_block {
-         -- the Content-Type header will be text/html
-         ngx.say(ngx.resp.get_headers()['Content-Type'])
-     }
- }
-```
-
 This function has the same signature as [ngx.req.get_headers](#ngxreqget_headers) except getting response headers instead of request headers.
 
 Note that a maximum of 100 response headers are parsed by default (including those with the same name) and that additional response headers are silently discarded to guard against potential denial of service attacks. Since `v0.10.13`, when the limit is exceeded, it will return a second value which is the string `"truncated"`.

doc/HttpLuaModule.wiki

@@ -3433,24 +3433,6 @@ to be returned when reading <code>ngx.header.Foo</code>.
 
 Note that <code>ngx.header</code> is not a normal Lua table and as such, it is not possible to iterate through it using the Lua <code>ipairs</code> function.
 
-Note: if the current response does not have a Content-Type header, but you use
-<code>ngx.header</code> to attempt retrieving it, a side effect will be that a
-Content-Type header will be created and returned according to your nginx
-configuration.
-
-For example:
-
-<geshi lang="nginx">
-    location = /t {
-        default_type text/html;
-        content_by_lua_block {
-            -- even if the response had no Content-Type header,
-            -- it will now have: Content-Type: text/html
-            ngx.say(ngx.header['Content-Type'])
-        }
-    }
-</geshi>
-
 For reading ''request'' headers, use the [[#ngx.req.get_headers|ngx.req.get_headers]] function instead.
 
 == ngx.resp.get_headers ==
@@ -3472,23 +3454,6 @@ for k, v in pairs(h) do
 end
 </geshi>
 
-Note: if the current response does not have a Content-Type header, but you use
-<code>ngx.resp.get_headers</code>, a side effect will be that a Content-Type
-header will be created and returned according to your nginx configuration.
-
-For example:
-
-<geshi lang="nginx">
-    location = /t {
-        default_type text/html;
-        content_by_lua_block {
-            -- even if the response had no Content-Type header,
-            -- it will now have: Content-Type: text/html
-            ngx.say(ngx.resp.get_headers()['Content-Type'])
-        }
-    }
-</geshi>
-
 This function has the same signature as [[#ngx.req.get_headers|ngx.req.get_headers]] except getting response headers instead of request headers.
 
 Note that a maximum of 100 response headers are parsed by default (including those with the same name) and that additional response headers are silently discarded to guard against potential denial of service attacks. Since <code>v0.10.13</code>, when the limit is exceeded, it will return a second value which is the string `"truncated"`.

src/ngx_http_lua_headers.c

@@ -505,7 +505,6 @@ ngx_http_lua_ngx_resp_get_headers(lua_State *L)
     ngx_table_elt_t    *header;
     ngx_http_request_t *r;
     ngx_http_lua_ctx_t *ctx;
-    ngx_int_t           rc;
     u_char             *lowcase_key = NULL;
     size_t              lowcase_key_sz = 0;
     ngx_uint_t          i;
@@ -562,17 +561,6 @@ ngx_http_lua_ngx_resp_get_headers(lua_State *L)
         lua_setmetatable(L, -2);
     }
 
-    if (!r->headers_out.content_type.len) {
-        rc = ngx_http_lua_set_content_type(r, ctx);
-        if (rc != NGX_OK) {
-            return luaL_error(L,
-                              "failed to set default content type: %d",
-                              (int) rc);
-        }
-
-        ctx->headers_set = 1;
-    }
-
 #if 1
     if (r->headers_out.content_type.len) {
         extra++;
@@ -1405,21 +1393,12 @@ ngx_http_lua_ffi_get_resp_header(ngx_http_request_t *r,
         break;
 
     case 12:
-        if (ngx_strncasecmp(key_buf, (u_char *) "Content-Type", 12) == 0) {
-            if (!r->headers_out.content_type.len) {
-                if (ngx_http_lua_set_content_type(r, ctx) != NGX_OK) {
-                    *errmsg = "failed to set default content type";
-                    return NGX_ERROR;
-                }
-
-                ctx->headers_set = 1;
-            }
-
-            if (r->headers_out.content_type.len) {
-                values[0].data = r->headers_out.content_type.data;
-                values[0].len = r->headers_out.content_type.len;
-                return 1;
-            }
+        if (ngx_strncasecmp(key_buf, (u_char *) "Content-Type", 12) == 0
+            && r->headers_out.content_type.len)
+        {
+            values[0].data = r->headers_out.content_type.data;
+            values[0].len = r->headers_out.content_type.len;
+            return 1;
         }
 
         break;

src/ngx_http_lua_headers_out.c

@@ -536,7 +536,6 @@ ngx_http_lua_get_output_header(lua_State *L, ngx_http_request_t *r,
 {
     ngx_table_elt_t            *h;
     ngx_list_part_t            *part;
-    ngx_int_t                   rc;
     ngx_uint_t                  i;
     unsigned                    found;
 
@@ -555,23 +554,12 @@ ngx_http_lua_get_output_header(lua_State *L, ngx_http_request_t *r,
         break;
 
     case 12:
-        if (ngx_strncasecmp(key->data, (u_char *) "Content-Type", 12) == 0) {
-            if (r->headers_out.content_type.len == 0) {
-                rc = ngx_http_lua_set_content_type(r, ctx);
-                if (rc != NGX_OK) {
-                    return luaL_error(L,
-                                      "failed to set default content type: %d",
-                                      (int) rc);
-                }
-
-                ctx->headers_set = 1;
-            }
-
-            if (r->headers_out.content_type.len) {
-                lua_pushlstring(L, (char *) r->headers_out.content_type.data,
-                                r->headers_out.content_type.len);
-                return 1;
-            }
+        if (ngx_strncasecmp(key->data, (u_char *) "Content-Type", 12) == 0
+            && r->headers_out.content_type.len)
+        {
+            lua_pushlstring(L, (char *) r->headers_out.content_type.data,
+                            r->headers_out.content_type.len);
+            return 1;
         }
 
         break;