从koa-static中间件学习搭建静态文件服务器
原文地址
koa-send
Static file serving middleware
koa-static中有说明它只是koa-send的一个包装
const send = require(‘koa-send‘);
app.use(async (ctx) => {
await send(ctx, ctx.path, { root: __dirname + ‘/public‘ });
})
查看koa-send的源码可以发现,它做的工作是根据传入的path查找文件是否存在,如果存在就创建一个流,不存在就抛出错误。
send函数可以传入第三个参数
-
maxage
Browser cache max-age in milliseconds. (defaults to0
) -
immutable
Tell the browser the resource is immutable and can be cached indefinitely. (defaults tofalse
) -
hidden
Allow transfer of hidden files. (defaults tofalse
) -
root
Root directory to restrict file access. -
index
Name of the index file to serve automatically when visiting the root location. (defaults to none) -
gzip
Try to serve the gzipped version of a file automatically whengzip
is supported by a client and if the requested file with.gz
extension exists. (defaults totrue
). -
brotli
Try to serve the brotli version of a file automatically whenbrotli
is supported by a client and if the requested file with.br
extension exists. (defaults totrue
). -
format
If notfalse
(defaults totrue
), format the path to serve static file servers and not require a trailing slash for directories, so that you can do both/directory
and/directory/
. -
setHeaders
Function to set custom headers on response. -
extensions
Try to match extensions from passed array to search for file when no extension is sufficed in URL. First found is served. (defaults tofalse
)
可以看一下index的作用,事实上当我们在地址栏输入
http://www.aaa.com/
或者
http://www.aaa.com/index.html
可以发现效果是一样的,原因就是配置了index选项,服务端首先检查你的path是否以 ‘/‘ 结尾,假如你配置了index选项且以 ‘/‘ 结尾,那么服务端会自动将你的path和index选项拼接,如下:
const trailingSlash = path[path.length - 1] === ‘/‘
...
if (index && trailingSlash) path += index
再看一下format的作用,其实我们经常在地址栏输入的是
http://www.aaa.com
而不是
http://www.aaa.com/
但他们的效果也是一样的,原因就是配置了format,经过resolve之后的path返回的是一个绝对路径,它是其中一种状态(文件或者文件夹),如果是文件夹,且设置了format(默认为true)和index,那么就自动添加index
stats = await fs.stat(path)
// Format the path to serve static file servers
// and not require a trailing slash for directories,
// so that you can do both `/directory` and `/directory/`
if (stats.isDirectory()) {
if (format && index) {
path += ‘/‘ + index
stats = await fs.stat(path)
} else {
return
}
}
extensions的作用好像不多见,比如你的a文件夹
| - a
| - demo.txt
| - demo.json
| - demo.html
假如你设置了extensions(假设为[‘json‘, ‘txt‘]),那么你在地址栏输入
http://www.aaa.com/a/demo
事实上等同于
http://www.aaa.com/a/demo.json
服务端会首先判断你是否设置了extensions且path不以 ‘.**‘ 结尾
if (extensions && !/..*$/.exec(path)) {
const list = [].concat(extensions)
for (let i = 0; i < list.length; i++) {
let ext = list[i]
if (typeof ext !== ‘string‘) {
throw new TypeError(‘option extensions must be array of strings or false‘)
}
// [‘.js‘] 或者 [‘js‘] 均可以
if (!/^./.exec(ext)) ext = ‘.‘ + ext
if (await fs.exists(path + ext)) {
path = path + ext
break
}
}
}
然后按照extensions的顺序依次查找拼接的path是否存在,存在即停止查找
koa-static
koa-static的只是给koa-send包了一层,koa-send的第二个参数path是ctx.path
koa-static有个defer选项
-
defer
If true, serves after return next(), allowing any downstream middleware to respond first.
if (!opts.defer) {
return async function serve (ctx, next) {
let done = false
if (ctx.method === ‘HEAD‘ || ctx.method === ‘GET‘) {
try {
// koa-send 输入的path不存在时抛错(404或者500)
done = await send(ctx, ctx.path, opts)
} catch (err) {
// 如果错误码是404说明请求的不是静态文件
if (err.status !== 404) {
throw err
}
}
}
// 请求不是静态文件 继续执行下面的逻辑
if (!done) {
await next()
}
}
}
return async function serve (ctx, next) {
await next()
// 假如请求方法不是get 必然不是访问静态资源
if (ctx.method !== ‘HEAD‘ && ctx.method !== ‘GET‘) return
// 说明对请求已经做了响应
if (ctx.body != null || ctx.status !== 404) return // eslint-disable-line
try {
await send(ctx, ctx.path, opts)
} catch (err) {
if (err.status !== 404) {
throw err
}
}
}