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uhttpd作为一个简单的web服务器，其代码量并不多，而且组织结构比较清楚。和其它网络服务器差不多，其main函数进行一些初始化（首先parse config-file，然后parse argv），然后进入一个循环，不断地监听，每当有一个客户请求到达时，则对它进行处理。
1、uhttpd uci配置参数说明
/etc/init.d/uhttpd脚本会使用procd的方式启动uhttpd进程，该工具后面可以带很多参数，如下：
root@zihome:~# uhttpd -h
uhttpd: option requires an argument -- h
Usage: uhttpd -p [addr:]port -h docroot-f Do not fork to background-c file Configuration file, default is '/etc/httpd.conf'-p [addr:]port Bind to specified address and port, multiple allowed-s [addr:]port Like -p but provide HTTPS on this port-C file ASN.1 server certificate file-K file ASN.1 server private key file-h directory Specify the document root, default is '.'-E string Use given virtual URL as 404 error handler-I string Use given filename as index for directories, multiple allowed-S Do not follow symbolic links outside of the docroot-D Do not allow directory listings, send 403 instead-R Enable RFC1918 filter-n count Maximum allowed number of concurrent script requests-N count Maximum allowed number of concurrent connections-l string URL prefix for Lua handler, default is '/lua'-L file Lua handler script, omit to disable Lua-u string URL prefix for UBUS via JSON-RPC handler-U file Override ubus socket path-a Do not authenticate JSON-RPC requests against UBUS session api-X Enable CORS HTTP headers on JSON-RPC api-x string URL prefix for CGI handler, default is '/cgi-bin'-i .ext=path Use interpreter at path for files with the given extension-t seconds CGI, Lua and UBUS script timeout in seconds, default is 60-T seconds Network timeout in seconds, default is 30-k seconds HTTP keepalive timeout-d string URL decode given string-r string Specify basic auth realm-m string MD5 crypt given string
openwrt上面还是通过uci来配置uhttpd，配置文件如下：
config uhttpd 'main'list listen_http '0.0.0.0:80'list listen_http '[::]:80'list listen_https '0.0.0.0:443'list listen_https '[::]:443'option home '/www'option rfc1918_filter '1'option max_requests '3'option max_connections '10'option cert '/etc/uhttpd.crt'option key '/etc/uhttpd.key'option cgi_prefix '/cgi-bin'option script_timeout '120'option network_timeout '60'option http_keepalive '60'option tcp_keepalive '5'option no_ubusauth '0'option ubus_prefix '/ubus'
uHTTPd 配置项含义:
| 名 称 | 类 型 | 含 义 |
|---|---|---|
| listen_http | 字符串 | 定义服务器的 IP 和端口。指所监听的非加密的地址和端口。如果仅给出端口号，将同时服务于IPv4和IPv6请求。使用0.0.0.0:80仅绑定在 IPv4 接口，使用[::]:80 仅绑定 IPv6 |
| home | 目录路径 | 定义服务器的文档根目录 |
| max_requests | 整型数字 | 最大的并行请求数，如果大于这个值，后续的请求将进入排队队列中 |
| cert | 文件路径 | 用于 HTTPS 连接的 ASN.1/DER 证书。在提供 HTTS 连接时必须提供 |
| key | 文件路径 | 用于 HTTPS 连接的 ASN.1/DER 私钥。在提供 HTTPS 连接时必须提供 |
| cgi_prefix | 字符串 | 定义 CGI 脚本的相对于根目录的前缀。如果没有该选项，CGI功能将不支持 |
| script_timeout | 整型数字 | Lua 或CGI请求的最大等待时间秒值。如果没有输出产生，则超时后执行就结束了 |
| network_timeout | 整型数字 | 网络活动的最大等待时间，如果指定的秒数内没有网络活动发生，则程序终止，连接关闭 |
| tcp_keepalive | 整型数字 | tcp 心跳检测时间间隔，发现对端已不存在时则关闭连接。设置为 0 则关闭 tcp 心跳检测 |
| realm | 字符串 | 基本认证的域值，默认为主机名，是当客户端进行基本认证的提示内容 |
| config | 文件路径 | 用于基本认证的配置文件 |
| no_dirlists | 是否显示文件列表 | 正常情况可以直接通过浏览器查看文件，不安全可以使用该字段屏蔽浏览器查看 |
| max_requests | 最大请求数 | 同时处理的请求的最大数量。当这个数量被超过时，额外的请求将被放入队列中等待 |
| max_connections | 最大连接数 | 同时处理的最大TCP连接数量。当这个数量被超过时，额外的TCP连接尝试将被放入队列中等待 |
| ubus_prefix | ubus前缀 | 使用JSON-RPC访问，如http://192.168.18.1/ubus. |
| ubus_noauth | session认证 | 关闭后可以不用认证，直接访问http接口 |
/etc/init.d/uhttpd脚本在启动的时候会去获取/etc/config/uhttpd配置里面的信息然后进行启动，我们现在用到的参数如下：
root@zihome:/# ps | grep uhttp1395 root 1556 S /usr/sbin/uhttpd -f -h /www -r openwrt -x /cgi-bin -t 120 -T 60 -k 60 -A 5 -n 3 -N 10 -R -p 0.0.0.0:80 -p [::]:80
31572 root 1520 S grep uhttp
https://openwrt.org/docs/guide-user/services/webserver/uhttpd
2、uhttpd的登录认证超时机制
登录做为web登录最基础的功能，其背后是由rpcd提供的session模式实现的。
session模式实现了创建、更新、退出、添加acl权限等功能。
具体使用可以查看rpcd的介绍：
'session' @3602a25d"create":{"timeout":"Integer"}"list":{"ubus_rpc_session":"String"}"grant":{"ubus_rpc_session":"String","scope":"String","objects":"Array"}"revoke":{"ubus_rpc_session":"String","scope":"String","objects":"Array"}"access":{"ubus_rpc_session":"String","scope":"String","object":"String","function":"String"}"set":{"ubus_rpc_session":"String","values":"Table"}"get":{"ubus_rpc_session":"String","keys":"Array"}"unset":{"ubus_rpc_session":"String","keys":"Array"}"destroy":{"ubus_rpc_session":"String"}"login":{"username":"String","password":"String","timeout":"Integer"
3、ubus over http功能
在openwrt默认的web应用中，很主要的一共功能点，就是展示和设置信息。因为ubus -v list里面覆盖了大部分我们需要的信息，所以如果可以通过一种简单的rpc方案，通过http直接访问ubus的内容那就方便了。
这就是ubus over http功能，web发送一个http请求，这个请求的结构根据ubus命令封装之后，直接从ubus接口里面获取内容返回给web页面。
因为ubus接口里面包含了太多的信息，我们不想把所有信息都暴露给web，所以有了rpcd里面的acls权限管理。权限管理里面说明了只能执行那些命令。
使用该功能需要在uci里面把配置打开
option ubus_prefix /ubus
之后可以用postman发送post请求
登录：
{"jsonrpc":"2.0","id":1,"method":"call","params":["00000000000000000000000000000000","session","login",{"username":"root","password":"admin"}]
}
此时会返回该账号的session，还有权限之类的
{"jsonrpc": "2.0","id": 1,"result": [0,{"ubus_rpc_session": "e5333f3fe2ed4601be3b0a8da0a6998e","timeout": 300,"expires": 300,"acls": {"access-group": {"luci-access": ["read","write"],"luci-app-firewall": ["read","write"],..."uci-access": ["read","write"],"unauthenticated": ["read"]},"cgi-io": {"backup": ["read"],"download": ["read"],"exec": ["read"],"upload": ["write"]},"file": {"/": ["list"],"/*": ["list"],"/bin/dmesg -r": ["exec"],..."/usr/sbin/logread -e ^": ["exec"]},"ubus": {"file": ["list","read","stat","write","remove","exec"],"hostapd.*": ["del_client"],"iwinfo": ["assoclist","freqlist","txpowerlist","countrylist","scan"],"luci": ["getFeatures","getConntrackList","getInitList","getLocaltime","getProcessList","getRealtimeStats","getTimezones","getLEDs","getUSBDevices","getSwconfigFeatures","getSwconfigPortState","getBlockDevices","getMountPoints","setInitAction","setLocaltime","setPassword","setBlockDetect","getConntrackHelpers"],"luci-rpc": ["getBoardJSON","getDHCPLeases","getDSLStatus","getDUIDHints","getHostHints","getNetworkDevices","getWirelessDevices"],"network": ["get_proto_handlers"],"network.interface": ["dump"],"network.rrdns": ["lookup"],"session": ["access","login"],"system": ["board","info","validate_firmware_image"],"uci": ["changes","get","add","apply","confirm","delete","order","set","rename"]},"uci": {"*": ["read","write"],..."uhttpd": ["read","write"]}},"data": {"username": "root"}}]
}
之后我们就可以使用这个session进行发送ubus请求，比如系统信息
{"jsonrpc":"2.0","id":1,"method":"call","params":["2cd182b0120310db8869b43d4340a307","system","board",{}]
}
返回内容：
{"jsonrpc": "2.0","id": 1,"result": [0,{"kernel": "4.14.275","hostname": "OpenWrt","system": "Intel(R) Core(TM) i7-6700 CPU @ 3.40GHz","model": "VMware, Inc. VMware Virtual Platform","board_name": "vmware-inc-vmware-virtual-platform","release": {"distribution": "OpenWrt","version": "19.07-SNAPSHOT","revision": "r11430-ecbbb37","target": "x86/64","description": "OpenWrt 19.07-SNAPSHOT r11430-ecbbb37"}}]
}
可以看到返回的内容跟直接输入ubus call一致
root@OpenWrt:~# ubus call system board
{"kernel": "4.14.275","hostname": "OpenWrt","system": "Intel(R) Core(TM) i7-6700 CPU @ 3.40GHz","model": "VMware, Inc. VMware Virtual Platform","board_name": "vmware-inc-vmware-virtual-platform","release": {"distribution": "OpenWrt","version": "19.07-SNAPSHOT","revision": "r11430-ecbbb37","target": "x86/64","description": "OpenWrt 19.07-SNAPSHOT r11430-ecbbb37"}
}
当然如果不属于上面权限的ubus消息是无法发送的，比如
{"jsonrpc":"2.0","id":1,"method":"call","params":["2cd182b0120310db8869b43d4340a307","network.interface.lan","status",{}]
}
返回没有权限
{"jsonrpc": "2.0","id": 1,"error": {"code": -32002,"message": "Access denied"}
}
这些权限的配置都位于/usr/share/rpcd/acl.d/目录下面配置，我们可以自己按照规则增删。
上面json请求的结构体描述如下：
{ "jsonrpc": "2.0","id": <unique-id-to-identify-request>, "method": "call","params": [<ubus_rpc_session>, <ubus_object>, <ubus_method>, { <ubus_arguments> }]
}
{ "jsonrpc": "2.0", "id": 1, "method": "call", "params": [ "c1ed6c7b025d0caca723a816fa61b668", "file", "read", { "path": "/etc/board.json" } ] }
how to use ubus over http in openwrt 12.09
：https://www.cnblogs.com/nicephil/p/6768381.html#e4bdbfe794a8e696b9e6b395_2
openwrt-rpcd服务ACL配置错误风险分析：https://www.cnblogs.com/hac425/p/9416854.html
https://openwrt.org/docs/techref/ubus#access_to_ubus_over_http
4、cgi框架
要运行cgi程序，首先意味着需fork出一个子进程，并通过execl函数替换进程空间为cgi程序；其次，数据传递，子进程替换了进程空间后，怎么获得原信息，有怎么把回馈数据传输给父进程（即uhttpd），父进程又怎么接收这些数据。
https://www.cnblogs.com/zmkeil/archive/2013/05/14/3078766.html