Map: the "volatile" parameter.

By default, "map" creates cacheable variables [1].  With this
parameter it creates a non-cacheable variable.

An original idea was to deduce the cacheability of the "map"
variable by checking the cacheability of variables specified
in source and resulting values, but it turned to be too hard.
For example, a cacheable variable can be overridden with the
"set" directive or with the SSI "set" command.  Also, keeping
"map" variables cacheable by default is good for performance
reasons.  This required adding a new parameter.

[1] Before db699978a33f (1.11.0), the cacheability of the
"map" variable could vary depending on the cacheability of
variables specified in resulting values (ticket #1090).
This is believed to be a bug rather than a feature.

src/http/modules/ngx_http_map_module.c

diff --git a/src/http/modules/ngx_http_map_module.c b/src/http/modules/ngx_http_map_module.c
index 3239343..2fc9be9 100644
--- a/src/http/modules/ngx_http_map_module.c
+++ b/src/http/modules/ngx_http_map_module.c
@@ -26,7 +26,8 @@
 
     ngx_http_variable_value_t  *default_value;
     ngx_conf_t                 *cf;
-    ngx_uint_t                  hostnames;      /* unsigned  hostnames:1 */
+    unsigned                    hostnames:1;
+    unsigned                    no_cacheable:1;
 } ngx_http_map_conf_ctx_t;
 
 
@@ -265,6 +266,7 @@
     ctx.default_value = NULL;
     ctx.cf = &save;
     ctx.hostnames = 0;
+    ctx.no_cacheable = 0;
 
     save = *cf;
     cf->pool = pool;
@@ -281,6 +283,10 @@
         return rv;
     }
 
+    if (ctx.no_cacheable) {
+        var->flags |= NGX_HTTP_VAR_NOCACHEABLE;
+    }
+
     map->default_value = ctx.default_value ? ctx.default_value:
                                              &ngx_http_variable_null_value;
 
@@ -395,6 +401,13 @@
         return NGX_CONF_OK;
     }
 
+    if (cf->args->nelts == 1
+        && ngx_strcmp(value[0].data, "volatile") == 0)
+    {
+        ctx->no_cacheable = 1;
+        return NGX_CONF_OK;
+    }
+
     if (cf->args->nelts != 2) {
         ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                            "invalid number of the map parameters");

src/stream/ngx_stream_map_module.c

diff --git a/src/stream/ngx_stream_map_module.c b/src/stream/ngx_stream_map_module.c
index e65c70c..ef06b2d 100644
--- a/src/stream/ngx_stream_map_module.c
+++ b/src/stream/ngx_stream_map_module.c
@@ -26,7 +26,8 @@
 
     ngx_stream_variable_value_t  *default_value;
     ngx_conf_t                   *cf;
-    ngx_uint_t                    hostnames;      /* unsigned  hostnames:1 */
+    unsigned                      hostnames:1;
+    unsigned                      no_cacheable:1;
 } ngx_stream_map_conf_ctx_t;
 
 
@@ -264,6 +265,7 @@
     ctx.default_value = NULL;
     ctx.cf = &save;
     ctx.hostnames = 0;
+    ctx.no_cacheable = 0;
 
     save = *cf;
     cf->pool = pool;
@@ -280,6 +282,10 @@
         return rv;
     }
 
+    if (ctx.no_cacheable) {
+        var->flags |= NGX_STREAM_VAR_NOCACHEABLE;
+    }
+
     map->default_value = ctx.default_value ? ctx.default_value:
                                              &ngx_stream_variable_null_value;
 
@@ -394,6 +400,13 @@
         return NGX_CONF_OK;
     }
 
+    if (cf->args->nelts == 1
+        && ngx_strcmp(value[0].data, "volatile") == 0)
+    {
+        ctx->no_cacheable = 1;
+        return NGX_CONF_OK;
+    }
+
     if (cf->args->nelts != 2) {
         ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                            "invalid number of the map parameters");