feat(file-logger): use io.stdout/io.stderr for /dev/stdout and /dev/stderr paths

apisix/plugins/file-logger.lua

@@ -21,6 +21,8 @@ local plugin       =   require("apisix.plugin")
 local expr         =   require("resty.expr.v1")
 local ngx          =   ngx
 local io_open      =   io.open
+local io_stdout    =   io.stdout
+local io_stderr    =   io.stderr
 local is_apisix_or, process = pcall(require, "resty.apisix.process")
 
 
@@ -89,6 +91,14 @@ local _M = {
 }
 
 
+local std_files = {
+    ["/dev/stdout"] = io_stdout,
+    ["/dev/stderr"] = io_stderr,
+}
+io_stdout:setvbuf("no")
+io_stderr:setvbuf("no")
+
+
 local function get_configured_path(conf)
     if conf.path then
         return conf.path
@@ -185,7 +195,10 @@ local function write_file_data(conf, log_message)
 
     local file, err
     local file_conf = conf.path and conf or {path = path}
-    if open_file_cache then
+    local std_file = std_files[path]
+    if std_file then
+        file = std_file
+    elseif open_file_cache then
         file, err = open_file_cache(file_conf)
     else
         file, err = io_open(path, 'a+')
@@ -204,8 +217,9 @@ local function write_file_data(conf, log_message)
             core.log.error("failed to write file: ", path, ", error info: ", err)
         end
 
+        -- stdout/stderr should not be closed
         -- file will be closed by gc, if open_file_cache exists
-        if not open_file_cache then
+        if not open_file_cache and not std_file then
             file:close()
         end
     end

docs/en/latest/plugins/file-logger.md

@@ -45,7 +45,7 @@ The `file-logger` Plugin is used to push log streams to a specific location.
 
 | Name | Type   | Required | Description   |
 | ---- | ------ | -------- | ------------- |
-| path | string | True     | Log file path. |
+| path | string | True     | Log file path. You can use `/dev/stdout` to write logs to the standard output and `/dev/stderr` to write to the standard error output. |
 | log_format | object | False    | Log format declared as key-value pairs in JSON. Values support strings and nested objects (up to five levels deep; deeper fields are truncated). Within strings, [APISIX](../apisix-variable.md) or [NGINX](http://nginx.org/en/docs/varindex.html) variables can be referenced by prefixing with `$`. |
 | include_req_body       | boolean | False    | When set to `true` includes the request body in the log. If the request body is too big to be kept in the memory, it can't be logged due to Nginx's limitations. |
 | include_req_body_expr  | array   | False    | Filter for when the `include_req_body` attribute is set to `true`. Request body is only logged when the expression set here evaluates to `true`. See [lua-resty-expr](https://github.com/api7/lua-resty-expr) for more. |

docs/zh/latest/plugins/file-logger.md

@@ -47,7 +47,7 @@ description: API 网关 Apache APISIX file-logger 插件可用于将日志数据
 
 | 名称             | 类型     | 必选项 | 描述                                             |
 | ---------------- | ------- |-----| ------------------------------------------------ |
-| path             | string  | 是   | 自定义输出文件路径。例如：`logs/file.log`。        |
+| path             | string  | 是   | 自定义输出文件路径。例如：`logs/file.log`。可以使用 `/dev/stdout` 将日志写入标准输出，使用 `/dev/stderr` 将日志写入标准错误输出。 |
 | log_format       | object  | 否   | 日志格式以 JSON 的键值对声明。值支持字符串和嵌套对象（最多五层，超出部分将被截断）。字符串中可通过在前面加上 `$` 来引用 [APISIX 变量](../apisix-variable.md) 或 [NGINX 内置变量](http://nginx.org/en/docs/varindex.html)。 |
 | include_req_body   | boolean | 否   | 当设置为 `true` 时，日志中将包含请求体。如果请求体太大而无法在内存中保存，则由于 Nginx 的限制，无法记录请求体。|
 | include_req_body_expr | array   | 否   | 当 `include_req_body` 属性设置为 `true` 时的过滤器。只有当此处设置的表达式求值为 `true` 时，才会记录请求体。有关更多信息，请参阅 [lua-resty-expr](https://github.com/api7/lua-resty-expr) 。 |

t/cli/test_file_logger_stdout.sh

@@ -0,0 +1,77 @@
+#!/usr/bin/env bash
+
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+. ./t/cli/common.sh
+
+# file-logger: verify logs are written to stdout via "/dev/stdout".
+# Uses openresty directly (like docker-entrypoint.sh) because `apisix start`
+# consumes stdout via io.popen, making /dev/stdout output unobservable.
+
+echo '
+apisix:
+  node_listen: 9080
+deployment:
+  role: data_plane
+  role_data_plane:
+    config_provider: yaml
+' > conf/config.yaml
+
+echo '
+routes:
+  - uri: /hello
+    upstream:
+      nodes:
+        "127.0.0.1:1980": 1
+      type: roundrobin
+    plugins:
+      file-logger:
+        path: /dev/stdout
+#END
+' > conf/apisix.yaml
+
+make init
+# `apisix start` would create the logs directory; since we launch openresty
+# directly, create it ourselves so nginx can open its error log.
+mkdir -p logs
+
+# run openresty directly in the foreground and capture its stdout
+openresty -p "$PWD" -g 'daemon off;' > stdout.log 2> stderr.log &
+apisix_pid=$!
+
+# wait until APISIX is ready to serve
+for _ in $(seq 1 20); do
+    if curl -s -o /dev/null http://127.0.0.1:9080/hello; then
+        break
+    fi
+    sleep 0.5
+done
+
+curl -s http://127.0.0.1:9080/hello > /dev/null
+sleep 1
+
+kill "$apisix_pid" 2>/dev/null || true
+wait "$apisix_pid" 2>/dev/null || true
+
+if ! grep -q '"uri":"/hello"' stdout.log; then
+    echo "failed: file-logger did not write to stdout"
+    cat stdout.log
+    exit 1
+fi
+
+echo "passed: file-logger writes to stdout"