[Tarantool-patches] [PATCH v7 08/11] lua/log: allow to configure logging without a box

[Cyrill Gorcunov]

We bring in an ability to configure logger early without
calling box.cfg{}. For this sake log.cfg({}) becomes a
callable table. One can provide arguments of the looger
which later will be propagated back to box.cfg table on
demand.

Another notable change is that the settings in log module
become defaults value, thus if one configured log before
the box then new settings get propagated to box's default
logging settings (previously they are silently reset to
defaults).

Fixes #689

@TarantoolBot documnent
Title: Module log

To configure log module eary without initializing box module
at all call the `log.cfg({})` method, where the following
arguments are acceptable:

 - `log` to specify file, pipe or syslog (same as
   `box.cfg{log}` option); the default value is nil
   and stderr is used;

 - `level` to specify logging level (1-7); the default
   value is 5;

 - `format` to specify output encoding ('plain' or 'json');
   the default value is 'plain';

 - `nonblock` to open logging output in nonblocking mode
   (`true` or `false`); the default value is `false`.

Signed-off-by: Cyrill Gorcunov <gorcunov at gmail.com>
---
 src/lua/log.lua | 105 +++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 104 insertions(+), 1 deletion(-)

diff --git a/src/lua/log.lua b/src/lua/log.lua
index 33e98fd84..dfdc326fe 100644
--- a/src/lua/log.lua
+++ b/src/lua/log.lua
@@ -119,6 +119,27 @@ local log2box_keys = {
     ['format']      = 'log_format',
 }
 
+local box_module_cfg = nil
+
+-- Reflect changes in box.cfg (if
+-- box.cfg been initialized).
+local function update_box_cfg(k)
+    if box_module_cfg ~= nil then
+        local update = function(k, v)
+            if box_module_cfg[v] ~= log_cfg[k] then
+                box_module_cfg[v] = log_cfg[k]
+            end
+        end
+        if k ~= nil then
+            update(k, log2box_keys[k])
+        else
+            for k, v in pairs(log2box_keys) do
+                update(k, v)
+            end
+        end
+    end
+end
+
 local function say(level, fmt, ...)
     if ffi.C.log_level < level then
         -- don't waste cycles on debug.getinfo()
@@ -170,6 +191,7 @@ end
 local function log_level(level)
     ffi.C.say_set_log_level(level)
     rawset(log_cfg, 'level', level)
+    update_box_cfg('level')
 end
 
 local function log_format(name)
@@ -190,6 +212,7 @@ local function log_format(name)
         ffi.C.say_set_log_format(ffi.C.SF_PLAIN)
     end
     rawset(log_cfg, 'format', name)
+    update_box_cfg('format')
 end
 
 local function log_pid()
@@ -208,10 +231,87 @@ end
 -- Update own values from box interface.
 local function box_on_load_cfg(box_cfg)
     for k, v in pairs(log2box_keys) do
-        if box_cfg[v] ~= log_cfg[k] then
+        if box_cfg[v] ~= nil and box_cfg[v] ~= log_cfg[k] then
             log_cfg[k] = box_cfg[v]
         end
     end
+    -- Remember the backreference to box
+    -- module config table.
+    box_module_cfg = box_cfg
+end
+
+local params_once = {
+    'log',
+    'log_nonblock',
+}
+
+-- Setup dynamic parameters.
+local function dynamic_cfg(cfg)
+    for _, k in pairs(params_once) do
+        if cfg[k] ~= nil and cfg[k] ~= log_cfg[k] then
+            local m = "log: '%s' can't be set dynamically"
+            error(m:format(k))
+        end
+    end
+
+    if cfg.level ~= nil then
+        log_level(cfg.level)
+    end
+
+    if cfg.format ~= nil then
+        log_format(cfg.format)
+    end
+
+    -- The log_x helpers above update box
+    -- settings on their own, so no need
+    -- for more update_box_cfg calls.
+end
+
+-- Load or reload configuration via log.cfg({}) call.
+local function load_cfg(oldcfg, cfg)
+    cfg = cfg or {}
+
+    if cfg.format ~= nil then
+        if fmt_str2num[cfg.format] == nil then
+            local m = "log: 'format' must be %s"
+            error(m:format(fmt_list()))
+        end
+    end
+
+    if cfg.level ~= nil then
+        if type(cfg.level) ~= 'number' then
+            error("log: 'level' option must be a number")
+        end
+    end
+
+    if cfg.nonblock ~= nil then
+        if type(cfg.nonblock) ~= 'boolean' then
+            error("log: 'nonblock' option must be 'true' or 'false'")
+        end
+    end
+
+    if ffi.C.say_logger_initialized() == true then
+        return dynamic_cfg(cfg)
+    end
+
+    cfg.level = cfg.level or log_cfg.level
+    cfg.format = cfg.format or log_cfg.format
+    cfg.nonblock = cfg.nonblock or (log_cfg.nonblock or false)
+
+    -- We never allow confgure the logger in background
+    -- mode since we don't know how the box will be configured
+    -- later.
+    ffi.C.say_logger_init(cfg.log, cfg.level,
+                          cfg.nonblock, cfg.format, 0)
+
+    -- Update log_cfg vars to show them in module
+    -- configuration output.
+    rawset(log_cfg, 'log', cfg.log)
+    rawset(log_cfg, 'level', cfg.level)
+    rawset(log_cfg, 'nonblock', cfg.nonblock)
+    rawset(log_cfg, 'format', cfg.format)
+
+    update_box_cfg()
 end
 
 local compat_warning_said = false
@@ -235,6 +335,9 @@ local log = {
     pid = log_pid,
     level = log_level,
     log_format = log_format,
+    cfg = setmetatable(log_cfg, {
+        __call = load_cfg,
+    }),
 
     -- Internal API to box module, not for users,
     -- names can be changed.
-- 
2.26.2