NGINX HTTP协议解析分析

小二刀山羊2024-04-09 13:23

简介

现在web应用无处不在，nginx 作为流行的反代服务器，自然需要对HTTP协议 进行解析，其中主要用到了状态机 的机制分别对请求行 、标头 、状态行进行字段解析。

环境搭建

HTTP服务

  • 编译 go build -o httpserver main.go
  • 运行 ./httpserver
  • 请求 curl http://127.0.0.1:8888/api/hello
main.go 复制代码 
package main

import (
        "io"
        "log"
        "net/http"
)

func main() {
        // Hello world, the web server

        helloHandler := func(w http.ResponseWriter, req *http.Request) {
                io.WriteString(w, "Hello, world!\n")
        }

        http.HandleFunc("/api/hello", helloHandler)
        log.Fatal(http.ListenAndServe(":8888", nil))
}

NGINX服务

安装

进入官网nginx.org/en/download... 选择相应的版本点击下载。

此处以最新稳定版1.24.0为例

  1. 下载 wget https://nginx.org/download/nginx-1.24.0.tar.gz
  2. 解压 tar -xzvf nginx-1.24.0.tar.gz
  3. 配置 cd nginx-1.24.0/; ./configure --prefix=/home/xiaofeng/workspace/C/nginx/install/
  4. 编译 make
  5. 安装 make install

配置

  • 文件位置 install/conf/nginx.conf
  • 设置用户 user root;
  • 设置端口 listen 88;
  • 反向代理，将api开头的请求反代到监听8888端口的HTTP服务程序
javascript 复制代码 
    location ~ ^/api/ {
        proxy_pass http://127.0.0.1:8888;
    }
nginx.conf 复制代码 
user  root;
worker_processes  1;

#error_log  logs/error.log;
#error_log  logs/error.log  notice;
#error_log  logs/error.log  info;

#pid        logs/nginx.pid;


events {
    worker_connections  1024;
}


http {
    include       mime.types;
    default_type  application/octet-stream;

    #log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';

    #access_log  logs/access.log  main;

    sendfile        on;
    #tcp_nopush     on;

    #keepalive_timeout  0;
    keepalive_timeout  65;

    #gzip  on;

    server {
        listen       88;
        server_name  localhost;

        #charset koi8-r;

        #access_log  logs/host.access.log main;

        location / {
            root   html;
            index  index.html index.htm;
        }

        #error_page  404              /404.html;

        # redirect server error pages to the static page /50x.html
        #
        error_page   500 502 503 504  /50x.html;
        location = /50x.html {
            root   html;
        }

        # api server
        location ~ ^/api/ {
                proxy_pass http://127.0.0.1:8888;
        }

        # proxy the PHP scripts to Apache listening on 127.0.0.1:80
        #
        #location ~ \.php$ {
        #    proxy_pass   http://127.0.0.1;
        #}

        # pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
        #
        #location ~ \.php$ {
        #    root           html;
        #    fastcgi_pass   127.0.0.1:9000;
        #    fastcgi_index  index.php;
        #    fastcgi_param  SCRIPT_FILENAME  /scripts$fastcgi_script_name;
        #    include        fastcgi_params;
        #}

        # deny access to .htaccess files, if Apache's document root
        # concurs with nginx's one
        #
        #location ~ /\.ht {
        #    deny  all;
        #}
    }


    # another virtual host using mix of IP-, name-, and port-based configuration
    #
    #server {
    #    listen       8000;
    #    listen       somename:8080;
    #    server_name  somename  alias  another.alias;

    #    location / {
    #        root   html;
    #        index  index.html index.htm;
    #    }
    #}


    # HTTPS server
    #
    #server {
    #    listen       443 ssl;
    #    server_name  localhost;

    #    ssl_certificate      cert.pem;
    #    ssl_certificate_key  cert.key;

    #    ssl_session_cache    shared:SSL:1m;
    #    ssl_session_timeout  5m;

    #    ssl_ciphers  HIGH:!aNULL:!MD5;
    #    ssl_prefer_server_ciphers  on;

    #    location / {
    #        root   html;
    #        index  index.html index.htm;
    #    }
    #}

}

启动

  • 直接运行nginx命令，使用默认配置文件
  • nginx -h可以查看命令参数
  • nginx -v可以查看版本信息
  • nginx -c filename可以指定配置文件路径
  • nginx -s reload可以重新加载配置
shell 复制代码 
[xiaofeng@localhost nginx]$ sudo ./install/sbin/nginx

[xiaofeng@localhost nginx]$ ps aux|grep nginx
root     1288003  0.0  0.0  36576   412 ?        Ss   17:42   0:00 nginx: master process ./install/sbin/nginx
root     1288004  0.0  0.0  66624  3948 ?        S    17:42   0:00 nginx: worker process
xiaofeng 1288023  0.0  0.0   9212  1196 pts/11   S+   17:42   0:00 grep --color=auto nginx

[xiaofeng@localhost nginx]$ sudo netstat -antup|grep nginx
tcp        0      0 0.0.0.0:88              0.0.0.0:*               LISTEN      1288003/nginx: mast

测试

shell 复制代码 
[xiaofeng@localhost workspace]$ curl -v  http://127.0.0.1:88/api/hello
*   Trying 127.0.0.1...
* TCP_NODELAY set
* Connected to 127.0.0.1 (127.0.0.1) port 88 (#0)
> GET /api/hello HTTP/1.1
> Host: 127.0.0.1:88
> User-Agent: curl/7.61.1
> Accept: */*
>
< HTTP/1.1 200 OK
< Server: nginx/1.24.0
< Date: Mon, 08 Apr 2024 10:56:41 GMT
< Content-Type: text/plain; charset=utf-8
< Content-Length: 14
< Connection: keep-alive
<
Hello, world!
* Connection #0 to host 127.0.0.1 left intact

HTTP解析

HTTP requests, and responses, share similar structure and are composed of:

  1. A start-line describing the requests to be implemented, or its status of whether successful or a failure. This is always a single line.（第一行是请求行或者状态行）
  2. An optional set of HTTP headers specifying the request, or describing the body included in the message.（HTTP表头行，用于说明请求或描述body消息体）
  3. A blank line indicating all meta-information for the request has been sent.（空行）
  4. An optional body containing data associated with the request (like content of an HTML form), or the document associated with a response. The presence of the body and its size is specified by the start-line and HTTP headers.（body部分）

示例如下：

请求行解析

  • usual数组配合usual[ch >> 5] & (1U << (ch & 0x1f))用于判断是否为常规字符，如?对应位为0则条件表达式为假，>对应位为1则条件表达式为真，其他同理
  • 定义好请求行中可能的状态
  • 每次往后偏移一个字符
  • 根据当前字符信息更新当前状态，并保存解析结果
  • 空格作为每部分的分隔符
  • 解析第一部分方法
  • 解析第二部分URI（http_URL = "http:" "//" host [ ":" port ] [ abs_path [ "?" query ]]）
  • 解析第三部分版本
  • 回车\r换行符\n作为结束标识
c 复制代码 
static uint32_t  usual[] = {
    0x00000000, /* 0000 0000 0000 0000  0000 0000 0000 0000 */

                /* ?>=< ;:98 7654 3210  /.-, +*)( '&%$ #"!  */
    0x7fff37d6, /* 0111 1111 1111 1111  0011 0111 1101 0110 */

                /* _^]\ [ZYX WVUT SRQP  ONML KJIH GFED CBA@ */
#if (NGX_WIN32)
    0xefffffff, /* 1110 1111 1111 1111  1111 1111 1111 1111 */
#else
    0xffffffff, /* 1111 1111 1111 1111  1111 1111 1111 1111 */
#endif

                /*  ~}| {zyx wvut srqp  onml kjih gfed cba` */
    0x7fffffff, /* 0111 1111 1111 1111  1111 1111 1111 1111 */

    0xffffffff, /* 1111 1111 1111 1111  1111 1111 1111 1111 */
    0xffffffff, /* 1111 1111 1111 1111  1111 1111 1111 1111 */
    0xffffffff, /* 1111 1111 1111 1111  1111 1111 1111 1111 */
    0xffffffff  /* 1111 1111 1111 1111  1111 1111 1111 1111 */
};

ngx_int_t
ngx_http_parse_request_line(ngx_http_request_t *r, ngx_buf_t *b)
{
    u_char  c, ch, *p, *m;
    enum {
        sw_start = 0,
        sw_method,
        sw_spaces_before_uri,
        sw_schema,
        sw_schema_slash,
        sw_schema_slash_slash,
        sw_host_start,
        sw_host,
        sw_host_end,
        sw_host_ip_literal,
        sw_port,
        sw_after_slash_in_uri,
        sw_check_uri,
        sw_uri,
        sw_http_09,
        sw_http_H,
        sw_http_HT,
        sw_http_HTT,
        sw_http_HTTP,
        sw_first_major_digit,
        sw_major_digit,
        sw_first_minor_digit,
        sw_minor_digit,
        sw_spaces_after_digit,
        sw_almost_done
    } state;

    state = r->state;

    for (p = b->pos; p < b->last; p++) {
        ch = *p;

        switch (state) {

        /* HTTP methods: GET, HEAD, POST */
        case sw_start:
            r->request_start = p;

            if (ch == CR || ch == LF) {
                break;
            }

            if ((ch < 'A' || ch > 'Z') && ch != '_' && ch != '-') {
                return NGX_HTTP_PARSE_INVALID_METHOD;
            }

            state = sw_method;
            break;

        case sw_method:
            if (ch == ' ') {
                r->method_end = p - 1;
                m = r->request_start;

                switch (p - m) {

                case 3:
                    if (ngx_str3_cmp(m, 'G', 'E', 'T', ' ')) {
                        r->method = NGX_HTTP_GET;
                        break;
                    }

                    if (ngx_str3_cmp(m, 'P', 'U', 'T', ' ')) {
                        r->method = NGX_HTTP_PUT;
                        break;
                    }

                    break;

                case 4:
                    if (m[1] == 'O') {

                        if (ngx_str3Ocmp(m, 'P', 'O', 'S', 'T')) {
                            r->method = NGX_HTTP_POST;
                            break;
                        }

                        if (ngx_str3Ocmp(m, 'C', 'O', 'P', 'Y')) {
                            r->method = NGX_HTTP_COPY;
                            break;
                        }

                        if (ngx_str3Ocmp(m, 'M', 'O', 'V', 'E')) {
                            r->method = NGX_HTTP_MOVE;
                            break;
                        }

                        if (ngx_str3Ocmp(m, 'L', 'O', 'C', 'K')) {
                            r->method = NGX_HTTP_LOCK;
                            break;
                        }

                    } else {

                        if (ngx_str4cmp(m, 'H', 'E', 'A', 'D')) {
                            r->method = NGX_HTTP_HEAD;
                            break;
                        }
                    }

                    break;

                case 5:
                    if (ngx_str5cmp(m, 'M', 'K', 'C', 'O', 'L')) {
                        r->method = NGX_HTTP_MKCOL;
                        break;
                    }

                    if (ngx_str5cmp(m, 'P', 'A', 'T', 'C', 'H')) {
                        r->method = NGX_HTTP_PATCH;
                        break;
                    }

                    if (ngx_str5cmp(m, 'T', 'R', 'A', 'C', 'E')) {
                        r->method = NGX_HTTP_TRACE;
                        break;
                    }

                    break;

                case 6:
                    if (ngx_str6cmp(m, 'D', 'E', 'L', 'E', 'T', 'E')) {
                        r->method = NGX_HTTP_DELETE;
                        break;
                    }

                    if (ngx_str6cmp(m, 'U', 'N', 'L', 'O', 'C', 'K')) {
                        r->method = NGX_HTTP_UNLOCK;
                        break;
                    }

                    break;

                case 7:
                    if (ngx_str7_cmp(m, 'O', 'P', 'T', 'I', 'O', 'N', 'S', ' '))
                    {
                        r->method = NGX_HTTP_OPTIONS;
                    }

                    if (ngx_str7_cmp(m, 'C', 'O', 'N', 'N', 'E', 'C', 'T', ' '))
                    {
                        r->method = NGX_HTTP_CONNECT;
                    }

                    break;

                case 8:
                    if (ngx_str8cmp(m, 'P', 'R', 'O', 'P', 'F', 'I', 'N', 'D'))
                    {
                        r->method = NGX_HTTP_PROPFIND;
                    }

                    break;

                case 9:
                    if (ngx_str9cmp(m,
                            'P', 'R', 'O', 'P', 'P', 'A', 'T', 'C', 'H'))
                    {
                        r->method = NGX_HTTP_PROPPATCH;
                    }

                    break;
                }

                state = sw_spaces_before_uri;
                break;
            }

            if ((ch < 'A' || ch > 'Z') && ch != '_' && ch != '-') {
                return NGX_HTTP_PARSE_INVALID_METHOD;
            }

            break;

        /* space* before URI */
        case sw_spaces_before_uri:

            if (ch == '/') {
                r->uri_start = p;
                state = sw_after_slash_in_uri;
                break;
            }

            c = (u_char) (ch | 0x20);
            if (c >= 'a' && c <= 'z') {
                r->schema_start = p;
                state = sw_schema;
                break;
            }

            switch (ch) {
            case ' ':
                break;
            default:
                return NGX_HTTP_PARSE_INVALID_REQUEST;
            }
            break;

        case sw_schema:

            c = (u_char) (ch | 0x20);
            if (c >= 'a' && c <= 'z') {
                break;
            }

            if ((ch >= '0' && ch <= '9') || ch == '+' || ch == '-' || ch == '.')
            {
                break;
            }

            switch (ch) {
            case ':':
                r->schema_end = p;
                state = sw_schema_slash;
                break;
            default:
                return NGX_HTTP_PARSE_INVALID_REQUEST;
            }
            break;

        case sw_schema_slash:
            switch (ch) {
            case '/':
                state = sw_schema_slash_slash;
                break;
            default:
                return NGX_HTTP_PARSE_INVALID_REQUEST;
            }
            break;

        case sw_schema_slash_slash:
            switch (ch) {
            case '/':
                state = sw_host_start;
                break;
            default:
                return NGX_HTTP_PARSE_INVALID_REQUEST;
            }
            break;

        case sw_host_start:

            r->host_start = p;

            if (ch == '[') {
                state = sw_host_ip_literal;
                break;
            }

            state = sw_host;

            /* fall through */

        case sw_host:

            c = (u_char) (ch | 0x20);
            if (c >= 'a' && c <= 'z') {
                break;
            }

            if ((ch >= '0' && ch <= '9') || ch == '.' || ch == '-') {
                break;
            }

            /* fall through */

        case sw_host_end:

            r->host_end = p;

            switch (ch) {
            case ':':
                state = sw_port;
                break;
            case '/':
                r->uri_start = p;
                state = sw_after_slash_in_uri;
                break;
            case '?':
                r->uri_start = p;
                r->args_start = p + 1;
                r->empty_path_in_uri = 1;
                state = sw_uri;
                break;
            case ' ':
                /*
                 * use single "/" from request line to preserve pointers,
                 * if request line will be copied to large client buffer
                 */
                r->uri_start = r->schema_end + 1;
                r->uri_end = r->schema_end + 2;
                state = sw_http_09;
                break;
            default:
                return NGX_HTTP_PARSE_INVALID_REQUEST;
            }
            break;

        case sw_host_ip_literal:

            if (ch >= '0' && ch <= '9') {
                break;
            }

            c = (u_char) (ch | 0x20);
            if (c >= 'a' && c <= 'z') {
                break;
            }

            switch (ch) {
            case ':':
                break;
            case ']':
                state = sw_host_end;
                break;
            case '-':
            case '.':
            case '_':
            case '~':
                /* unreserved */
                break;
            case '!':
            case '$':
            case '&':
            case '\'':
            case '(':
            case ')':
            case '*':
            case '+':
            case ',':
            case ';':
            case '=':
                /* sub-delims */
                break;
            default:
                return NGX_HTTP_PARSE_INVALID_REQUEST;
            }
            break;

        case sw_port:
            if (ch >= '0' && ch <= '9') {
                break;
            }

            switch (ch) {
            case '/':
                r->uri_start = p;
                state = sw_after_slash_in_uri;
                break;
            case '?':
                r->uri_start = p;
                r->args_start = p + 1;
                r->empty_path_in_uri = 1;
                state = sw_uri;
                break;
            case ' ':
                /*
                 * use single "/" from request line to preserve pointers,
                 * if request line will be copied to large client buffer
                 */
                r->uri_start = r->schema_end + 1;
                r->uri_end = r->schema_end + 2;
                state = sw_http_09;
                break;
            default:
                return NGX_HTTP_PARSE_INVALID_REQUEST;
            }
            break;

        /* check "/.", "//", "%", and "\" (Win32) in URI */
        case sw_after_slash_in_uri:

            if (usual[ch >> 5] & (1U << (ch & 0x1f))) {
                state = sw_check_uri;
                break;
            }

            switch (ch) {
            case ' ':
                r->uri_end = p;
                state = sw_http_09;
                break;
            case CR:
                r->uri_end = p;
                r->http_minor = 9;
                state = sw_almost_done;
                break;
            case LF:
                r->uri_end = p;
                r->http_minor = 9;
                goto done;
            case '.':
                r->complex_uri = 1;
                state = sw_uri;
                break;
            case '%':
                r->quoted_uri = 1;
                state = sw_uri;
                break;
            case '/':
                r->complex_uri = 1;
                state = sw_uri;
                break;
#if (NGX_WIN32)
            case '\\':
                r->complex_uri = 1;
                state = sw_uri;
                break;
#endif
            case '?':
                r->args_start = p + 1;
                state = sw_uri;
                break;
            case '#':
                r->complex_uri = 1;
                state = sw_uri;
                break;
            case '+':
                r->plus_in_uri = 1;
                break;
            default:
                if (ch < 0x20 || ch == 0x7f) {
                    return NGX_HTTP_PARSE_INVALID_REQUEST;
                }
                state = sw_check_uri;
                break;
            }
            break;

        /* check "/", "%" and "\" (Win32) in URI */
        case sw_check_uri:

            if (usual[ch >> 5] & (1U << (ch & 0x1f))) {
                break;
            }

            switch (ch) {
            case '/':
#if (NGX_WIN32)
                if (r->uri_ext == p) {
                    r->complex_uri = 1;
                    state = sw_uri;
                    break;
                }
#endif
                r->uri_ext = NULL;
                state = sw_after_slash_in_uri;
                break;
            case '.':
                r->uri_ext = p + 1;
                break;
            case ' ':
                r->uri_end = p;
                state = sw_http_09;
                break;
            case CR:
                r->uri_end = p;
                r->http_minor = 9;
                state = sw_almost_done;
                break;
            case LF:
                r->uri_end = p;
                r->http_minor = 9;
                goto done;
#if (NGX_WIN32)
            case '\\':
                r->complex_uri = 1;
                state = sw_after_slash_in_uri;
                break;
#endif
            case '%':
                r->quoted_uri = 1;
                state = sw_uri;
                break;
            case '?':
                r->args_start = p + 1;
                state = sw_uri;
                break;
            case '#':
                r->complex_uri = 1;
                state = sw_uri;
                break;
            case '+':
                r->plus_in_uri = 1;
                break;
            default:
                if (ch < 0x20 || ch == 0x7f) {
                    return NGX_HTTP_PARSE_INVALID_REQUEST;
                }
                break;
            }
            break;

        /* URI */
        case sw_uri:

            if (usual[ch >> 5] & (1U << (ch & 0x1f))) {
                break;
            }

            switch (ch) {
            case ' ':
                r->uri_end = p;
                state = sw_http_09;
                break;
            case CR:
                r->uri_end = p;
                r->http_minor = 9;
                state = sw_almost_done;
                break;
            case LF:
                r->uri_end = p;
                r->http_minor = 9;
                goto done;
            case '#':
                r->complex_uri = 1;
                break;
            default:
                if (ch < 0x20 || ch == 0x7f) {
                    return NGX_HTTP_PARSE_INVALID_REQUEST;
                }
                break;
            }
            break;

        /* space+ after URI */
        case sw_http_09:
            switch (ch) {
            case ' ':
                break;
            case CR:
                r->http_minor = 9;
                state = sw_almost_done;
                break;
            case LF:
                r->http_minor = 9;
                goto done;
            case 'H':
                r->http_protocol.data = p;
                state = sw_http_H;
                break;
            default:
                return NGX_HTTP_PARSE_INVALID_REQUEST;
            }
            break;

        case sw_http_H:
            switch (ch) {
            case 'T':
                state = sw_http_HT;
                break;
            default:
                return NGX_HTTP_PARSE_INVALID_REQUEST;
            }
            break;

        case sw_http_HT:
            switch (ch) {
            case 'T':
                state = sw_http_HTT;
                break;
            default:
                return NGX_HTTP_PARSE_INVALID_REQUEST;
            }
            break;

        case sw_http_HTT:
            switch (ch) {
            case 'P':
                state = sw_http_HTTP;
                break;
            default:
                return NGX_HTTP_PARSE_INVALID_REQUEST;
            }
            break;

        case sw_http_HTTP:
            switch (ch) {
            case '/':
                state = sw_first_major_digit;
                break;
            default:
                return NGX_HTTP_PARSE_INVALID_REQUEST;
            }
            break;

        /* first digit of major HTTP version */
        case sw_first_major_digit:
            if (ch < '1' || ch > '9') {
                return NGX_HTTP_PARSE_INVALID_REQUEST;
            }

            r->http_major = ch - '0';

            if (r->http_major > 1) {
                return NGX_HTTP_PARSE_INVALID_VERSION;
            }

            state = sw_major_digit;
            break;

        /* major HTTP version or dot */
        case sw_major_digit:
            if (ch == '.') {
                state = sw_first_minor_digit;
                break;
            }

            if (ch < '0' || ch > '9') {
                return NGX_HTTP_PARSE_INVALID_REQUEST;
            }

            r->http_major = r->http_major * 10 + (ch - '0');

            if (r->http_major > 1) {
                return NGX_HTTP_PARSE_INVALID_VERSION;
            }

            break;

        /* first digit of minor HTTP version */
        case sw_first_minor_digit:
            if (ch < '0' || ch > '9') {
                return NGX_HTTP_PARSE_INVALID_REQUEST;
            }

            r->http_minor = ch - '0';
            state = sw_minor_digit;
            break;

        /* minor HTTP version or end of request line */
        case sw_minor_digit:
            if (ch == CR) {
                state = sw_almost_done;
                break;
            }

            if (ch == LF) {
                goto done;
            }

            if (ch == ' ') {
                state = sw_spaces_after_digit;
                break;
            }

            if (ch < '0' || ch > '9') {
                return NGX_HTTP_PARSE_INVALID_REQUEST;
            }

            if (r->http_minor > 99) {
                return NGX_HTTP_PARSE_INVALID_REQUEST;
            }

            r->http_minor = r->http_minor * 10 + (ch - '0');
            break;

        case sw_spaces_after_digit:
            switch (ch) {
            case ' ':
                break;
            case CR:
                state = sw_almost_done;
                break;
            case LF:
                goto done;
            default:
                return NGX_HTTP_PARSE_INVALID_REQUEST;
            }
            break;

        /* end of request line */
        case sw_almost_done:
            r->request_end = p - 1;
            switch (ch) {
            case LF:
                goto done;
            default:
                return NGX_HTTP_PARSE_INVALID_REQUEST;
            }
        }
    }

    b->pos = p;
    r->state = state;

    return NGX_AGAIN;

done:

    b->pos = p + 1;

    if (r->request_end == NULL) {
        r->request_end = p;
    }

    r->http_version = r->http_major * 1000 + r->http_minor;
    r->state = sw_start;

    if (r->http_version == 9 && r->method != NGX_HTTP_GET) {
        return NGX_HTTP_PARSE_INVALID_09_METHOD;
    }

    return NGX_OK;
}

标头解析

  • lowcase数组用于字符转为小写，且非字母和数字值为0
  • 解析第一部分标头名称
  • 冒号:作为分隔符
  • 解析第二部分标头值
  • 标头值前后空格进行跳过即可
  • 回车\r换行符\n作为结束标识
c 复制代码 
ngx_int_t
ngx_http_parse_header_line(ngx_http_request_t *r, ngx_buf_t *b,
    ngx_uint_t allow_underscores)
{
    u_char      c, ch, *p;
    ngx_uint_t  hash, i;
    enum {
        sw_start = 0,
        sw_name,
        sw_space_before_value,
        sw_value,
        sw_space_after_value,
        sw_ignore_line,
        sw_almost_done,
        sw_header_almost_done
    } state;

    /* the last '\0' is not needed because string is zero terminated */

    static u_char  lowcase[] =
        "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
        "\0\0\0\0\0\0\0\0\0\0\0\0\0-\0\0" "0123456789\0\0\0\0\0\0"
        "\0abcdefghijklmnopqrstuvwxyz\0\0\0\0\0"
        "\0abcdefghijklmnopqrstuvwxyz\0\0\0\0\0"
        "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
        "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
        "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
        "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";

    state = r->state;
    hash = r->header_hash;
    i = r->lowcase_index;

    for (p = b->pos; p < b->last; p++) {
        ch = *p;

        switch (state) {

        /* first char */
        case sw_start:
            r->header_name_start = p;
            r->invalid_header = 0;

            switch (ch) {
            case CR:
                r->header_end = p;
                state = sw_header_almost_done;
                break;
            case LF:
                r->header_end = p;
                goto header_done;
            default:
                state = sw_name;

                c = lowcase[ch];

                if (c) {
                    hash = ngx_hash(0, c);
                    r->lowcase_header[0] = c;
                    i = 1;
                    break;
                }

                if (ch == '_') {
                    if (allow_underscores) {
                        hash = ngx_hash(0, ch);
                        r->lowcase_header[0] = ch;
                        i = 1;

                    } else {
                        hash = 0;
                        i = 0;
                        r->invalid_header = 1;
                    }

                    break;
                }

                if (ch <= 0x20 || ch == 0x7f || ch == ':') {
                    r->header_end = p;
                    return NGX_HTTP_PARSE_INVALID_HEADER;
                }

                hash = 0;
                i = 0;
                r->invalid_header = 1;

                break;

            }
            break;

        /* header name */
        case sw_name:
            c = lowcase[ch];

            if (c) {
                hash = ngx_hash(hash, c);
                r->lowcase_header[i++] = c;
                i &= (NGX_HTTP_LC_HEADER_LEN - 1);
                break;
            }

            if (ch == '_') {
                if (allow_underscores) {
                    hash = ngx_hash(hash, ch);
                    r->lowcase_header[i++] = ch;
                    i &= (NGX_HTTP_LC_HEADER_LEN - 1);

                } else {
                    r->invalid_header = 1;
                }

                break;
            }

            if (ch == ':') {
                r->header_name_end = p;
                state = sw_space_before_value;
                break;
            }

            if (ch == CR) {
                r->header_name_end = p;
                r->header_start = p;
                r->header_end = p;
                state = sw_almost_done;
                break;
            }

            if (ch == LF) {
                r->header_name_end = p;
                r->header_start = p;
                r->header_end = p;
                goto done;
            }

            /* IIS may send the duplicate "HTTP/1.1 ..." lines */
            if (ch == '/'
                && r->upstream
                && p - r->header_name_start == 4
                && ngx_strncmp(r->header_name_start, "HTTP", 4) == 0)
            {
                state = sw_ignore_line;
                break;
            }

            if (ch <= 0x20 || ch == 0x7f) {
                r->header_end = p;
                return NGX_HTTP_PARSE_INVALID_HEADER;
            }

            r->invalid_header = 1;

            break;

        /* space* before header value */
        case sw_space_before_value:
            switch (ch) {
            case ' ':
                break;
            case CR:
                r->header_start = p;
                r->header_end = p;
                state = sw_almost_done;
                break;
            case LF:
                r->header_start = p;
                r->header_end = p;
                goto done;
            case '\0':
                r->header_end = p;
                return NGX_HTTP_PARSE_INVALID_HEADER;
            default:
                r->header_start = p;
                state = sw_value;
                break;
            }
            break;

        /* header value */
        case sw_value:
            switch (ch) {
            case ' ':
                r->header_end = p;
                state = sw_space_after_value;
                break;
            case CR:
                r->header_end = p;
                state = sw_almost_done;
                break;
            case LF:
                r->header_end = p;
                goto done;
            case '\0':
                r->header_end = p;
                return NGX_HTTP_PARSE_INVALID_HEADER;
            }
            break;

        /* space* before end of header line */
        case sw_space_after_value:
            switch (ch) {
            case ' ':
                break;
            case CR:
                state = sw_almost_done;
                break;
            case LF:
                goto done;
            case '\0':
                r->header_end = p;
                return NGX_HTTP_PARSE_INVALID_HEADER;
            default:
                state = sw_value;
                break;
            }
            break;

        /* ignore header line */
        case sw_ignore_line:
            switch (ch) {
            case LF:
                state = sw_start;
                break;
            default:
                break;
            }
            break;

        /* end of header line */
        case sw_almost_done:
            switch (ch) {
            case LF:
                goto done;
            case CR:
                break;
            default:
                return NGX_HTTP_PARSE_INVALID_HEADER;
            }
            break;

        /* end of header */
        case sw_header_almost_done:
            switch (ch) {
            case LF:
                goto header_done;
            default:
                return NGX_HTTP_PARSE_INVALID_HEADER;
            }
        }
    }

    b->pos = p;
    r->state = state;
    r->header_hash = hash;
    r->lowcase_index = i;

    return NGX_AGAIN;

done:

    b->pos = p + 1;
    r->state = sw_start;
    r->header_hash = hash;
    r->lowcase_index = i;

    return NGX_OK;

header_done:

    b->pos = p + 1;
    r->state = sw_start;

    return NGX_HTTP_PARSE_HEADER_DONE;
}

状态行解析

  • 解析第一部分版本信息
  • 解析第二部分状态码
  • status->code = status->code * 10 + (ch - '0');可将字符串200解析为整数200
  • 解析第三部分描述信息
c 复制代码 
ngx_int_t
ngx_http_parse_status_line(ngx_http_request_t *r, ngx_buf_t *b,
    ngx_http_status_t *status)
{
    u_char   ch;
    u_char  *p;
    enum {
        sw_start = 0,
        sw_H,
        sw_HT,
        sw_HTT,
        sw_HTTP,
        sw_first_major_digit,
        sw_major_digit,
        sw_first_minor_digit,
        sw_minor_digit,
        sw_status,
        sw_space_after_status,
        sw_status_text,
        sw_almost_done
    } state;

    state = r->state;

    for (p = b->pos; p < b->last; p++) {
        ch = *p;

        switch (state) {

        /* "HTTP/" */
        case sw_start:
            switch (ch) {
            case 'H':
                state = sw_H;
                break;
            default:
                return NGX_ERROR;
            }
            break;

        case sw_H:
            switch (ch) {
            case 'T':
                state = sw_HT;
                break;
            default:
                return NGX_ERROR;
            }
            break;

        case sw_HT:
            switch (ch) {
            case 'T':
                state = sw_HTT;
                break;
            default:
                return NGX_ERROR;
            }
            break;

        case sw_HTT:
            switch (ch) {
            case 'P':
                state = sw_HTTP;
                break;
            default:
                return NGX_ERROR;
            }
            break;

        case sw_HTTP:
            switch (ch) {
            case '/':
                state = sw_first_major_digit;
                break;
            default:
                return NGX_ERROR;
            }
            break;

        /* the first digit of major HTTP version */
        case sw_first_major_digit:
            if (ch < '1' || ch > '9') {
                return NGX_ERROR;
            }

            r->http_major = ch - '0';
            state = sw_major_digit;
            break;

        /* the major HTTP version or dot */
        case sw_major_digit:
            if (ch == '.') {
                state = sw_first_minor_digit;
                break;
            }

            if (ch < '0' || ch > '9') {
                return NGX_ERROR;
            }

            if (r->http_major > 99) {
                return NGX_ERROR;
            }

            r->http_major = r->http_major * 10 + (ch - '0');
            break;

        /* the first digit of minor HTTP version */
        case sw_first_minor_digit:
            if (ch < '0' || ch > '9') {
                return NGX_ERROR;
            }

            r->http_minor = ch - '0';
            state = sw_minor_digit;
            break;

        /* the minor HTTP version or the end of the request line */
        case sw_minor_digit:
            if (ch == ' ') {
                state = sw_status;
                break;
            }

            if (ch < '0' || ch > '9') {
                return NGX_ERROR;
            }

            if (r->http_minor > 99) {
                return NGX_ERROR;
            }

            r->http_minor = r->http_minor * 10 + (ch - '0');
            break;

        /* HTTP status code */
        case sw_status:
            if (ch == ' ') {
                break;
            }

            if (ch < '0' || ch > '9') {
                return NGX_ERROR;
            }

            status->code = status->code * 10 + (ch - '0');

            if (++status->count == 3) {
                state = sw_space_after_status;
                status->start = p - 2;
            }

            break;

        /* space or end of line */
        case sw_space_after_status:
            switch (ch) {
            case ' ':
                state = sw_status_text;
                break;
            case '.':                    /* IIS may send 403.1, 403.2, etc */
                state = sw_status_text;
                break;
            case CR:
                state = sw_almost_done;
                break;
            case LF:
                goto done;
            default:
                return NGX_ERROR;
            }
            break;

        /* any text until end of line */
        case sw_status_text:
            switch (ch) {
            case CR:
                state = sw_almost_done;

                break;
            case LF:
                goto done;
            }
            break;

        /* end of status line */
        case sw_almost_done:
            status->end = p - 1;
            switch (ch) {
            case LF:
                goto done;
            default:
                return NGX_ERROR;
            }
        }
    }

    b->pos = p;
    r->state = state;

    return NGX_AGAIN;

done:

    b->pos = p + 1;

    if (status->end == NULL) {
        status->end = p;
    }

    status->http_version = r->http_major * 1000 + r->http_minor;
    r->state = sw_start;

    return NGX_OK;
}

总结

  • 可以通过gdb断点解析函数进行解析流程跟踪
  • 支持应用层HTTP业务流量的网络安全设备研发可参考HTTP解析代码
  • 一些详细的特性需要参考对应的RFC进行确认
  • 核心思路在于利用状态机循环偏移分段解析

参考

MDN HTTP文档

HTTP1.1 RFC2616 双语

HTTP1.1 RFC2616 英文

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