ngx_http_slice_filter_module: print mismatching ETags to error_log

ngx_http_slice_filter_module.c.diff

--- nginx-1.11.5/src/http/modules/ngx_http_slice_filter_module.c.orig   2016-10-11 18:03:02.000000000 +0300
+++ nginx-1.11.5/src/http/modules/ngx_http_slice_filter_module.c        2016-12-02 04:22:14.000000000 +0300
@@ -131,8 +131,12 @@
             || ngx_strncmp(h->value.data, ctx->etag.data, ctx->etag.len)
                != 0)
         {
-            ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
-                          "etag mismatch in slice response");
+            char msg[1024];
+            snprintf(msg, sizeof(msg), "etag mismatch in slice response: ctx_len=%u, ctx_etag=%s, r_len=%u, r_etag=%s",
+                          (unsigned)ctx->etag.len, (const char*)ctx->etag.data, h ? (unsigned)h->value.len : 0, h ? (const char*)h->value.data : "(null)" );
+            msg[sizeof(msg)-1] = 0;
+            ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, msg);
+
             return NGX_ERROR;
         }
     }