HTTP: enhanced access log with conditional filtering.

This feature allows users to specify conditions to control if access log
should be recorded. The "if" option supports a string and JavaScript code.
If its value is empty, 0, false, null, or undefined, the logs will not be
recorded. And the '!' as a prefix inverses the condition.

Example 1: Only log requests that sent a session cookie.

    {
        "access_log": {
            "if": "$cookie_session",
            "path": "..."
        }
    }

Example 2: Do not log health check requests.

    {
        "access_log": {
            "if": "`${uri == '/health' ? false : true}`",
            "path": "..."
        }
    }

Example 3: Only log requests when the time is before 22:00.

    {
        "access_log": {
            "if": "`${new Date().getHours() < 22}`",
            "path": "..."
        }
    }

or

    {
        "access_log": {
            "if": "!`${new Date().getHours() >= 22}`",
            "path": "..."
        }
    }

Closes: https://github.com/nginx/unit/issues/594

1 files changed, 2 insertions, 0 deletions

diff --git a/src/nxt_router.h b/src/nxt_router.h
index b14f8410..3e523001 100644
--- a/src/nxt_router.h
+++ b/src/nxt_router.h
@@ -54,6 +54,8 @@ typedef struct {
 
     nxt_router_access_log_t  *access_log;
     nxt_tstr_t               *log_format;
+    nxt_tstr_t               *log_expr;
+    uint8_t                  log_negate;  /* 1 bit */
 } nxt_router_conf_t;