Firebase Cloud Function对favicon.ico/robots.txt路径不执行问题

我配置了Firebase Hosting与Cloud Function，在firebase.json里通过重写规则把所有路径指向SSR函数，仅sitemap_index.xml指向serveSitemap函数。SSR函数基于Express构建，本地模拟器和部署环境中，访问sitemap.xml等路径时函数正常执行，但访问favicon.ico和robots.txt时，请求虽被正确重写到SSR函数，却没执行函数直接返回404，求原因。

相关配置代码 #

firebase.json配置 #

{
  "functions": {
    "predeploy": [
      "yarn --cwd \"$RESOURCE_DIR\" lint",
      "yarn --cwd \"$RESOURCE_DIR\" build"
    ],
    "source": "functions"
  },
  "hosting": [
    {
      "target": "dev",
      "public": "public",
      "ignore": ["firebase.json", "**/.*", "**/node_modules/**"],
      "rewrites": [
        {
          "source": "/sitemap_index.xml",
          "function": "serveSitemap",
          "region": "europe-west1"
        },
        {
          "source": "**",
          "function": "ssr",
          "region": "europe-west1"
        }
      ]
    }
  ]
}

SSR函数代码 #

const universalApp = require(`${process.cwd()}/dist/server/main.js`).app;

const app = universalApp(); // Express实例

export const ssr = functions.region(FUNCTIONS_REGION).https.onRequest(app);

模拟器日志示例 #

访问sitemap.xml时的日志 #

[hosting] Rewriting /sitemap.xml to http://127.0.0.1:5001/intergun-dev/europe-west1/ssr for local Function europe-west1/ssr
 i  functions: Beginning execution of "ssr"
 i  functions: Finished "ssr" in 17.807421ms
 i  hosting: 127.0.0.1 - - [30/Dec/2022:22:35:05 +0000] "GET /sitemap.xml HTTP/1.1" 200 339 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:108.0) Gecko/20100101 Firefox/108.0"

访问favicon.ico时的日志 #

[hosting] Rewriting /favicon.ico to http://127.0.0.1:5001/intergun-dev/europe-west1/ssr for local Function europe-west1/ssr
 i  hosting: 127.0.0.1 - - [30/Dec/2022:22:38:35 +0000] "GET /favicon.ico HTTP/1.1" 404 0 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:108.0) Gecko/20100101 Firefox/108.0"

问题原因及解决方法 #

这是Firebase Hosting的默认文件优先级规则导致的：Firebase Hosting会优先检查public目录下是否存在请求的特殊文件（比如favicon.ico、robots.txt），即使目录里没有这些文件，Hosting内部机制也会直接返回404，跳过重写规则触发Cloud Function的步骤。

解决方法有两种：

• 显式添加重写规则：在rewrites数组最顶部添加针对favicon.ico和robots.txt的规则，覆盖默认行为：

"rewrites": [
  {
    "source": "/sitemap_index.xml",
    "function": "serveSitemap",
    "region": "europe-west1"
  },
  {
    "source": "/favicon.ico",
    "function": "ssr",
    "region": "europe-west1"
  },
  {
    "source": "/robots.txt",
    "function": "ssr",
    "region": "europe-west1"
  },
  {
    "source": "**",
    "function": "ssr",
    "region": "europe-west1"
  }
]

• 禁用静态文件托管：如果不需要Hosting托管任何静态文件，将public字段设为空字符串""，这样Hosting会直接跳过静态文件检查，所有请求都走重写规则。但注意如果public目录下有其他需托管的资源，这种方法不适用。

内容的提问来源于stack exchange，提问作者Jesper