服务器架设笔记——使用Apache插件解析简单请求

        一般来说，对于一个请求，服务器都会对其进行解析，以确定请求的合法性以及行进的路径。于是本节将讲解如何获取请求的数据。（转载请指明出于breaksoftware的csdn博客）

        我们使用《服务器架设笔记——编译Apache及其插件》一文中的方法创建一个Handler工程——get_request。该工程中，我们可以操作的入口函数是

static int get_request_handler(request_rec *r)
{
    r->content_type = "text/html";  

        通过该入口函数，我们可以直接得到的数据就是request_rec结构体对象指针r。通过查阅源码，我们得到其定义

/**
 * @brief A structure that represents the current request
 */
struct request_rec {
    /** The pool associated with the request */
    apr_pool_t *pool;
    /** The connection to the client */
    conn_rec *connection;
    /** The virtual host for this request */
    server_rec *server;

    /** Pointer to the redirected request if this is an external redirect */
    request_rec *next;
    /** Pointer to the previous request if this is an internal redirect */
    request_rec *prev;

    /** Pointer to the main request if this is a sub-request
     * (see http_request.h) */
    request_rec *main;

    /* Info about the request itself... we begin with stuff that only
     * protocol.c should ever touch...
     */
    /** First line of request */
    char *the_request;
    /** HTTP/0.9, "simple" request (e.g. GET /foo\n w/no headers) */
    int assbackwards;
    /** A proxy request (calculated during post_read_request/translate_name)
     *  possible values PROXYREQ_NONE, PROXYREQ_PROXY, PROXYREQ_REVERSE,
     *                  PROXYREQ_RESPONSE
     */
    int proxyreq;
    /** HEAD request, as opposed to GET */
    int header_only;
    /** Protocol version number of protocol; 1.1 = 1001 */
    int proto_num;
    /** Protocol string, as given to us, or HTTP/0.9 */
    char *protocol;
    /** Host, as set by full URI or Host: */
    const char *hostname;

    /** Time when the request started */
    apr_time_t request_time;

    /** Status line, if set by script */
    const char *status_line;
    /** Status line */
    int status;

    /* Request method, two ways; also, protocol, etc..  Outside of protocol.c,
     * look, but don't touch.
     */

    /** M_GET, M_POST, etc. */
    int method_number;
    /** Request method (eg. GET, HEAD, POST, etc.) */
    const char *method;

    /**
     *  'allowed' is a bitvector of the allowed methods.
     *
     *  A handler must ensure that the request method is one that
     *  it is capable of handling.  Generally modules should DECLINE
     *  any request methods they do not handle.  Prior to aborting the
     *  handler like this the handler should set r->allowed to the list
     *  of methods that it is willing to handle.  This bitvector is used
     *  to construct the "Allow:" header required for OPTIONS requests,
     *  and HTTP_METHOD_NOT_ALLOWED and HTTP_NOT_IMPLEMENTED status codes.
     *
     *  Since the default_handler deals with OPTIONS, all modules can
     *  usually decline to deal with OPTIONS.  TRACE is always allowed,
     *  modules don't need to set it explicitly.
     *
     *  Since the default_handler will always handle a GET, a
     *  module which does *not* implement GET should probably return
     *  HTTP_METHOD_NOT_ALLOWED.  Unfortunately this means that a Script GET
     *  handler can't be installed by mod_actions.
     */
    apr_int64_t allowed;
    /** Array of extension methods */
    apr_array_header_t *allowed_xmethods;
    /** List of allowed methods */
    ap_method_list_t *allowed_methods;

    /** byte count in stream is for body */
    apr_off_t sent_bodyct;
    /** body byte count, for easy access */
    apr_off_t bytes_sent;
    /** Last modified time of the requested resource */
    apr_time_t mtime;

    /* HTTP/1.1 connection-level features */

    /** The Range: header */
    const char *range;
    /** The "real" content length */
    apr_off_t clength;
    /** sending chunked transfer-coding */
    int chunked;

    /** Method for reading the request body
     * (eg. REQUEST_CHUNKED_ERROR, REQUEST_NO_BODY,
     *  REQUEST_CHUNKED_DECHUNK, etc...) */
    int read_body;
    /** reading chunked transfer-coding */
    int read_chunked;
    /** is client waiting for a 100 response? */
    unsigned expecting_100;
    /** The optional kept body of the request. */
    apr_bucket_brigade *kept_body;
    /** For ap_body_to_table(): parsed body */
    /* XXX: ap_body_to_table has been removed. Remove body_table too or
     * XXX: keep it to reintroduce ap_body_to_table without major bump? */
    apr_table_t *body_table;
    /** Remaining bytes left to read from the request body */
    apr_off_t remaining;
    /** Number of bytes that have been read  from the request body */
    apr_off_t read_length;

    /* MIME header environments, in and out.  Also, an array containing
     * environment variables to be passed to subprocesses, so people can
     * write modules to add to that environment.
     *
     * The difference between headers_out and err_headers_out is that the
     * latter are printed even on error, and persist across internal redirects
     * (so the headers printed for ErrorDocument handlers will have them).
     *
     * The 'notes' apr_table_t is for notes from one module to another, with no
     * other set purpose in mind...
     */

    /** MIME header environment from the request */
    apr_table_t *headers_in;
    /** MIME header environment for the response */
    apr_table_t *headers_out;
    /** MIME header environment for the response, printed even on errors and
     * persist across internal redirects */
    apr_table_t *err_headers_out;
    /** Array of environment variables to be used for sub processes */
    apr_table_t *subprocess_env;
    /** Notes from one module to another */
    apr_table_t *notes;

    /* content_type, handler, content_encoding, and all content_languages
     * MUST be lowercased strings.  They may be pointers to static strings;
     * they should not be modified in place.
     */
    /** The content-type for the current request */
    const char *content_type;   /* Break these out --- we dispatch on 'em */
    /** The handler string that we use to call a handler function */
    const char *handler;        /* What we *really* dispatch on */

    /** How to encode the data */
    const char *content_encoding;
    /** Array of strings representing the content languages */
    apr_array_header_t *content_languages;

    /** variant list validator (if negotiated) */
    char *vlist_validator;

    /** If an authentication check was made, this gets set to the user name. */
    char *user;
    /** If an authentication check was made, this gets set to the auth type. */
    char *ap_auth_type;

    /* What object is being requested (either directly, or via include
     * or content-negotiation mapping).
     */

    /** The URI without any parsing performed */
    char *unparsed_uri;
    /** The path portion of the URI, or "/" if no path provided */
    char *uri;
    /** The filename on disk corresponding to this response */
    char *filename;
    /* XXX: What does this mean? Please define "canonicalize" -aaron */
    /** The true filename, we canonicalize r->filename if these don't match */
    char *canonical_filename;
    /** The PATH_INFO extracted from this request */
    char *path_info;
    /** The QUERY_ARGS extracted from this request */
    char *args;

    /**
     * Flag for the handler to accept or reject path_info on
     * the current request.  All modules should respect the
     * AP_REQ_ACCEPT_PATH_INFO and AP_REQ_REJECT_PATH_INFO
     * values, while AP_REQ_DEFAULT_PATH_INFO indicates they
     * may follow existing conventions.  This is set to the
     * user's preference upon HOOK_VERY_FIRST of the fixups.
     */
    int used_path_info;

    /** A flag to determine if the eos bucket has been sent yet */
    int eos_sent;

    /* Various other config info which may change with .htaccess files
     * These are config vectors, with one void* pointer for each module
     * (the thing pointed to being the module's business).
     */

    /** Options set in config files, etc. */
    struct ap_conf_vector_t *per_dir_config;
    /** Notes on *this* request */
    struct ap_conf_vector_t *request_config;

    /** Optional request log level configuration. Will usually point
     *  to a server or per_dir config, i.e. must be copied before
     *  modifying */
    const struct ap_logconf *log;

    /** Id to identify request in access and error log. Set when the first
     *  error log entry for this request is generated.
     */
    const char *log_id;

    /**
     * A linked list of the .htaccess configuration directives
     * accessed by this request.
     * N.B. always add to the head of the list, _never_ to the end.
     * that way, a sub request's list can (temporarily) point to a parent's list
     */
    const struct htaccess_result *htaccess;

    /** A list of output filters to be used for this request */
    struct ap_filter_t *output_filters;
    /** A list of input filters to be used for this request */
    struct ap_filter_t *input_filters;

    /** A list of protocol level output filters to be used for this
     *  request */
    struct ap_filter_t *proto_output_filters;
    /** A list of protocol level input filters to be used for this
     *  request */
    struct ap_filter_t *proto_input_filters;

    /** This response can not be cached */
    int no_cache;
    /** There is no local copy of this response */
    int no_local_copy;

    /** Mutex protect callbacks registered with ap_mpm_register_timed_callback
     * from being run before the original handler finishes running
     */
    apr_thread_mutex_t *invoke_mtx;

    /** A struct containing the components of URI */
    apr_uri_t parsed_uri;
    /**  finfo.protection (st_mode) set to zero if no such file */
    apr_finfo_t finfo;

    /** remote address information from conn_rec, can be overridden if
     * necessary by a module.
     * This is the address that originated the request.
     */
    apr_sockaddr_t *useragent_addr;
    char *useragent_ip;

    /** MIME trailer environment from the request */
    apr_table_t *trailers_in;
    /** MIME trailer environment from the response */
    apr_table_t *trailers_out;
};

        这是个非常大的结构体，可谓是包罗万象。对于初学者来说，想完全弄明白各项是什么还是比较困难的。而我们的需求很简单，我们就列出我们可能需要关心的数据

    /** First line of request */
    char *the_request;

        请求的第一行数据

    /** Protocol version number of protocol; 1.1 = 1001 */
    int proto_num;
    /** Protocol string, as given to us, or HTTP/0.9 */
    char *protocol;
    /** Host, as set by full URI or Host: */
    const char *hostname;

        协议的版本和请求的类型

    /** Time when the request started */
    apr_time_t request_time;

        请求的时间

    /** The URI without any parsing performed */
    char *unparsed_uri;
    /** The path portion of the URI, or "/" if no path provided */
    char *uri;
    /** The filename on disk corresponding to this response */
    char *filename;

        未进行urldecode的URI、经过urldecode的URI和处理该请求的文件路径

    /** The PATH_INFO extracted from this request */
    char *path_info;
    /** The QUERY_ARGS extracted from this request */
    char *args;

         请求中的路径和参数

    /** A struct containing the components of URI */
    apr_uri_t parsed_uri;

        请求解析的详细结果

    char *useragent_ip;

        请求来源的IP

/** MIME header environment from the request */
    apr_table_t *headers_in;

        以table形式保存的http头信息

        对于基础数据类型我们很容易编写出例程

	if (r->the_request) {
		ap_rprintf(r, "the request : %s\n", r->the_request);
	}
	else {
		ap_rprintf(r, "the request is NULL\n");
	}

	if (r->protocol) {
		ap_rprintf(r, "protocol : %s\n", r->protocol);
	}
	else {
		ap_rprintf(r, "protocol is NULL\n");
	}

	ap_rprintf(r, "proto_num is %d\n", r->proto_num);

        而对于请求时间apr_time_t类型，我们可以参考 《服务器架设笔记——Apache模块开发基础知识》中对模块的介绍。我们查看源码，可以编写出如下例程

static void print_time(request_rec* r) {
	if (!r) {
		ap_rprintf(r, "request_rec pointer is NULL\n");
		return;
	}
	char data_str[128] = {0};
	apr_status_t status = apr_ctime(data_str, r->request_time);
	if (APR_SUCCESS != status) {
		ap_rprintf(r, "apr_ctime error\n");	
	}
	else {
		ap_rprintf(r, "ctime\t:\t%s\n", data_str);
	}

	apr_time_exp_t exp_t;
	memset(&exp_t, 0, sizeof(exp_t));
	status = apr_time_exp_gmt(&exp_t, r->request_time);
	if (APR_SUCCESS != status) {
		ap_rprintf(r, "apr_time_exp_gmt error\n");
	}
	else {
		ap_rprintf(r, "exp time\t:\n");
		ap_rprintf(r, "\ttm_usec\t:\t%d\n", exp_t.tm_usec);
		ap_rprintf(r, "\ttm_sec\t:\t%d\n", exp_t.tm_sec);
		ap_rprintf(r, "\ttm_min\t:\t%d\n", exp_t.tm_min);
		ap_rprintf(r, "\ttm_hour\t:\t%d\n", exp_t.tm_hour);
		ap_rprintf(r, "\ttm_mday\t:\t%d\n", exp_t.tm_mday);
		ap_rprintf(r, "\ttm_mon\t:\t%d\n", exp_t.tm_mon);
		ap_rprintf(r, "\ttm_year\t:\t%d\n", exp_t.tm_year);
		ap_rprintf(r, "\ttm_wday\t:\t%d\n", exp_t.tm_wday);
		ap_rprintf(r, "\ttm_yday\t:\t%d\n", exp_t.tm_yday);
		ap_rprintf(r, "\ttm_isdst\t:\t%d\n", exp_t.tm_isdst);
		ap_rprintf(r, "\ttm_gmtoff\t:\t%d\n", exp_t.tm_gmtoff);
	}
}

        其中apr_time_exp_t的定义在《apr_time.h》中。

/**
 * a structure similar to ANSI struct tm with the following differences:
 *  - tm_usec isn't an ANSI field
 *  - tm_gmtoff isn't an ANSI field (it's a BSDism)
 */
struct apr_time_exp_t {
    /** microseconds past tm_sec */
    apr_int32_t tm_usec;
    /** (0-61) seconds past tm_min */
    apr_int32_t tm_sec;
    /** (0-59) minutes past tm_hour */
    apr_int32_t tm_min;
    /** (0-23) hours past midnight */
    apr_int32_t tm_hour;
    /** (1-31) day of the month */
    apr_int32_t tm_mday;
    /** (0-11) month of the year */
    apr_int32_t tm_mon;
    /** year since 1900 */
    apr_int32_t tm_year;
    /** (0-6) days since Sunday */
    apr_int32_t tm_wday;
    /** (0-365) days since January 1 */
    apr_int32_t tm_yday;
    /** daylight saving time */
    apr_int32_t tm_isdst;
    /** seconds east of UTC */
    apr_int32_t tm_gmtoff;
};

        对于已分析过了的请求结构体apr_uri_t的例程也非常简单，我就不再列出来，只是把其结构体定义贴一下。大家一看就明白

/**
 * A structure to encompass all of the fields in a uri
 */
struct apr_uri_t {
    /** scheme ("http"/"ftp"/...) */
    char *scheme;
    /** combined [user[:password]\@]host[:port] */
    char *hostinfo;
    /** user name, as in http://user:passwd\@host:port/ */
    char *user;
    /** password, as in http://user:passwd\@host:port/ */
    char *password;
    /** hostname from URI (or from Host: header) */
    char *hostname;
    /** port string (integer representation is in "port") */
    char *port_str;
    /** the request path (or NULL if only scheme://host was given) */
    char *path;
    /** Everything after a '?' in the path, if present */
    char *query;
    /** Trailing "#fragment" string, if present */
    char *fragment;

    /** structure returned from gethostbyname() */
    struct hostent *hostent;

    /** The port number, numeric, valid only if port_str != NULL */
    apr_port_t port;
    
    /** has the structure been initialized */
    unsigned is_initialized:1;

    /** has the DNS been looked up yet */
    unsigned dns_looked_up:1;
    /** has the dns been resolved yet */
    unsigned dns_resolved:1;
};

        这些例程中麻烦的是对apr_table_t的解析。因为网上很难找到对该table的遍历代码，于是我只能参考apr_table_clone中代码得出如下

static void print_table(request_rec *r, const apr_table_t* t) {
	const apr_array_header_t* array = apr_table_elts(t);
	apr_table_entry_t* elts = (apr_table_entry_t*)array->elts;
	for (int i = 0; i < array->nelts; i++) {
		ap_rprintf(r, "\t%s : %s\n", elts[i].key, elts[i].val);
	}
}

        我们请求一个URL： http://192.168.191.129/AP%26AC%3aHE?a=b#c

        其返回如下

headers_in start
	Host : 192.168.191.129
	Connection : keep-alive
	Cache-Control : max-age=0
	Accept : text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
	User-Agent : Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/28.0.1500.72 Safari/537.36
	Accept-Encoding : gzip,deflate,sdch
	Accept-Language : zh-CN,zh;q=0.8
headers_in end

headers_out start
headers_out end

the request : GET /AP%26AC%3aHE?a=b HTTP/1.1
protocol : HTTP/1.1
proto_num is 1001
method : GET
host name : 192.168.191.129
unparsed uri : /AP%26AC%3aHE?a=b
uri : /AP&AC:HE
filename : /usr/local/apache2/htdocs/AP&AC:HE
path info : 
args : a=b
user is NULL
log id is NULL
useragent ip : 192.168.191.1
ctime	:	Mon Feb 16 18:20:39 2015
exp time	:
	tm_usec	:	200039
	tm_sec	:	39
	tm_min	:	20
	tm_hour	:	10
	tm_mday	:	16
	tm_mon	:	1
	tm_year	:	115
	tm_wday	:	1
	tm_yday	:	46
	tm_isdst	:	0
	tm_gmtoff	:	0
scheme is NULL
hostinfo is NULL
user is NULL
password is NULL
hostname is NULL
port_str is NULL
path : /AP&AC:HE
query : a=b
fragment is NULL
The sample page from mod_get_request.c