/******************************************************************************* #                                                                              # #      MJPG-streamer allows to stream JPG frames from an input-plugin          # #      to several output plugins                                               # #                                                                              # #      Copyright (C) 2007 busybox-project (base64 function)                    # #      Copyright (C) 2007 Tom St枚veken                                         # #                                                                              # # This program is free software; you can redistribute it and/or modify         # # it under the terms of the GNU General Public License as published by         # # the Free Software Foundation; version 2 of the License.                      # #                                                                              # # This program is distributed in the hope that it will be useful,              # # but WITHOUT ANY WARRANTY; without even the implied warranty of               # # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the                # # GNU General Public License for more details.                                 # #                                                                              # # You should have received a copy of the GNU General Public License            # # along with this program; if not, write to the Free Software                  # # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA    # #                                                                              # *******************************************************************************/ #include <string.h> #include <sys/time.h> #include <sys/types.h> #include <unistd.h> #include <stdlib.h> #include <stdio.h> #include <pthread.h> #include <sys/socket.h> #include <arpa/inet.h> #include <sys/stat.h> #include <fcntl.h> #include <syslog.h> #include "../../mjpg_streamer.h" #include "../../utils.h" #include "httpd.h" static globals *pglobal; extern context servers[MAX_OUTPUT_PLUGINS]; /****************************************************************************** Description.: initializes the iobuffer structure properly Input Value.: pointer to already allocated iobuffer Return Value: iobuf ******************************************************************************/ void init_iobuffer(iobuffer *iobuf) {     memset(iobuf->buffer, 0, sizeof(iobuf->buffer));     iobuf->level = 0; } /****************************************************************************** Description.: initializes the request structure properly Input Value.: pointer to already allocated req Return Value: req ******************************************************************************/ void init_request(request *req) {   req->type        = A_UNKNOWN;   req->parameter   = NULL;   req->client      = NULL;   req->credentials = NULL; } /****************************************************************************** Description.: If strings were assigned to the different members free them               This will fail if strings are static, so always use strdup(). Input Value.: req: pointer to request structure Return Value: - ******************************************************************************/ void free_request(request *req) {   if ( req->parameter != NULL ) free(req->parameter);   if ( req->client != NULL ) free(req->client);   if ( req->credentials != NULL ) free(req->credentials); } /****************************************************************************** Description.: read with timeout, implemented without using signals               tries to read len bytes and returns if enough bytes were read               or the timeout was triggered. In case of timeout the return               value may differ from the requested bytes "len". Input Value.: * fd.....: fildescriptor to read from               * iobuf..: iobuffer that allows to use this functions from multiple                          threads because the complete context is the iobuffer.               * buffer.: The buffer to store values at, will be set to zero                          before storing values.               * len....: the length of buffer               * timeout: seconds to wait for an answer Return Value: * buffer.: will become filled with bytes read               * iobuf..: May get altered to save the context for future calls.               * func().: bytes copied to buffer or -1 in case of error ******************************************************************************/ int _read(int fd, iobuffer *iobuf, void *buffer, size_t len, int timeout) {     int copied=0, rc, i;     fd_set fds;     struct timeval tv;     memset(buffer, 0, len);     while ( (copied < len) )     {         i = MIN(iobuf->level, len-copied);    // 第一次,i=0,以後，i=1         memcpy(buffer+copied, iobuf->buffer+IO_BUFFER-iobuf->level, i);         iobuf->level -= i;         copied += i;         if ( copied >= len )             return copied;         /* select will return in case of timeout or new data arrived */         /*             當客服端發有資料或者超時的時候，select函式就返回         */         tv.tv_sec = timeout;         tv.tv_usec = 0;         FD_ZERO(&fds);         FD_SET(fd, &fds);         if ( (rc = select(fd+1, &fds, NULL, NULL, &tv)) <= 0 )         {             if ( rc < 0)             exit(EXIT_FAILURE);             /* this must be a timeout */             return copied;         }         init_iobuffer(iobuf);    // 將 iobuf 清0         /*         * there should be at least one byte, because select signalled it.         * But: It may happen (very seldomly), that the socket gets closed remotly between         * the select() and the following read. That is the reason for not relying         * on reading at least one byte.         */         /*             呼叫read函式,從客服端讀取最多 256 位元組的資料

        */         if ( (iobuf->level = read(fd, &iobuf->buffer, IO_BUFFER)) <= 0 )         {             /* an error occured */             return -1;         }         /* align data to the end of the buffer if less than IO_BUFFER bytes were read */         /* 拷貝iobuf->buffer中的資料 */         memmove(iobuf->buffer+(IO_BUFFER-iobuf->level), iobuf->buffer, iobuf->level);

    }     return 0; } /****************************************************************************** Description.: Read a single line from the provided fildescriptor.               This funtion will return under two conditions:               * line end was reached               * timeout occured Input Value.: * fd.....: fildescriptor to read from               * iobuf..: iobuffer that allows to use this functions from multiple                          threads because the complete context is the iobuffer.               * buffer.: The buffer to store values at, will be set to zero                          before storing values.               * len....: the length of buffer               * timeout: seconds to wait for an answer Return Value: * buffer.: will become filled with bytes read               * iobuf..: May get altered to save the context for future calls.               * func().: bytes copied to buffer or -1 in case of error ******************************************************************************/ /* read just a single line or timeout */ int _readline(int fd, iobuffer *iobuf, void *buffer, size_t len, int timeout) {     char c='\0', *out=buffer;     int i;     /*         _readline:             從iobuf.buf[]中一個位元組一個位元組的將資料取出存放到buffer中,直到遇見

        換行符號'\n'或者長度達到了.     */     memset(buffer, 0, len);     for ( i=0; i<len && c != '\n'; i++ )     {         if ( _read(fd, iobuf, &c, 1, timeout) <= 0 )         {             /* timeout or error occured */             return -1;         }         *out++ = c;     }     return i; } /****************************************************************************** Description.: Decodes the data and stores the result to the same buffer.               The buffer will be large enough, because base64 requires more               space then plain text. Hints.......: taken from busybox, but it is GPL code Input Value.: base64 encoded data Return Value: plain decoded data ******************************************************************************/ void decodeBase64(char *data) {   const unsigned char *in = (const unsigned char *)data;   /* The decoded size will be at most 3/4 the size of the encoded */   unsigned ch = 0;   int i = 0;   while (*in) {     int t = *in++;     if (t >= '0' && t <= '9')       t = t - '0' + 52;     else if (t >= 'A' && t <= 'Z')       t = t - 'A';     else if (t >= 'a' && t <= 'z')       t = t - 'a' + 26;     else if (t == '+')       t = 62;     else if (t == '/')       t = 63;     else if (t == '=')       t = 0;     else       continue;     ch = (ch << 6) | t;     i++;     if (i == 4) {       *data++ = (char) (ch >> 16);       *data++ = (char) (ch >> 8);       *data++ = (char) ch;       i = 0;     }   }   *data = '\0'; } /****************************************************************************** Description.: Send a complete HTTP response and a single JPG-frame. Input Value.: fildescriptor fd to send the answer to Return Value: - ******************************************************************************/ void send_snapshot(int fd) {     unsigned char *frame=NULL;     int frame_size=0;     char buffer[BUFFER_SIZE] = {0};     /* wait for a fresh frame */     /* 等待輸入通道傳送資料更新請求 */     pthread_cond_wait(&pglobal->db_update, &pglobal->db);     /* read buffer */     frame_size = pglobal->size;        // 得到一幀資料的大小     /* allocate a buffer for this single frame */     /* 根據一幀資料的大小,分配一個 frame 緩衝區 */     if ( (frame = malloc(frame_size+1)) == NULL )     {         free(frame);         pthread_mutex_unlock( &pglobal->db );         send_error(fd, 500, "not enough memory");         return;     }     /* 從倉庫(pglobal->buf)中取出資料 */     memcpy(frame, pglobal->buf, frame_size);     DBG("got frame (size: %d kB)\n", frame_size/1024);     pthread_mutex_unlock( &pglobal->db );     /* write the response */     /* 讓buffer = "" */     sprintf(buffer, "HTTP/1.0 200 OK\r\n" \       STD_HEADER \       "Content-type: image/jpeg\r\n" \       "\r\n");     /* send header and image now */     /* 將buffer中的字串傳送給客服端 */     if( write(fd, buffer, strlen(buffer)) < 0 )     {         free(frame);         return;     }     write(fd, frame, frame_size);    // 將一幀圖片給傳送出去     free(frame);    // 釋放緩衝區 } /****************************************************************************** Description.: Send a complete HTTP response and a stream of JPG-frames. Input Value.: fildescriptor fd to send the answer to Return Value: - ******************************************************************************/ void send_stream(int fd) {     unsigned char *frame=NULL, *tmp=NULL;     int frame_size=0, max_frame_size=0;     char buffer[BUFFER_SIZE] = {0};     DBG("preparing header\n");     /* 讓buffer = "" */     sprintf(buffer, "HTTP/1.0 200 OK\r\n" \     STD_HEADER \     "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \     "\r\n" \     "--" BOUNDARY "\r\n");     /* 將 buffer 中的字串傳送出去(報文) */     if ( write(fd, buffer, strlen(buffer)) < 0 )     {         free(frame);         return;     }     DBG("Headers send, sending stream now\n");     while ( !pglobal->stop )     {         /* wait for fresh frames */         /* 等待輸入通道發出資料更新的訊號 */         pthread_cond_wait(&pglobal->db_update, &pglobal->db);         /* read buffer */         frame_size = pglobal->size;    // 得到一幀圖片的大小         /* check if framebuffer is large enough, increase it if necessary */         /* 檢查我們之前分配的快取是否夠大,如果不夠,則重新分配 */         if ( frame_size > max_frame_size )         {             DBG("increasing buffer size to %d\n", frame_size);             max_frame_size = frame_size+TEN_K;             if ( (tmp = realloc(frame, max_frame_size)) == NULL )    // 重新分配快取             {                 free(frame);                 pthread_mutex_unlock( &pglobal->db );                 send_error(fd, 500, "not enough memory");                 return;             }             frame = tmp;         }         /* 從倉庫中取出一幀資料 */         memcpy(frame, pglobal->buf, frame_size);         DBG("got frame (size: %d kB)\n", frame_size/1024);         pthread_mutex_unlock( &pglobal->db );         /*         * print the individual mimetype and the length         * sending the content-length fixes random stream disruption observed         * with firefox         */         /* 讓 buffer = ""報文，告訴客服端即將傳送的圖片的大小 */         sprintf(buffer, "Content-Type: image/jpeg\r\n" \         "Content-Length: %d\r\n" \         "\r\n", frame_size);         DBG("sending intemdiate header\n");         if ( write(fd, buffer, strlen(buffer)) < 0 ) break;         /* 將一幀圖片傳送出去 */         DBG("sending frame\n");         if( write(fd, frame, frame_size) < 0 ) break;         /* 讓 buffer = "boundarydonotcross" */         DBG("sending boundary\n");         sprintf(buffer, "\r\n--" BOUNDARY "\r\n");         if ( write(fd, buffer, strlen(buffer)) < 0 ) break;     }     free(frame);    // 釋放快取 } /****************************************************************************** Description.: Send error messages and headers. Input Value.: * fd.....: is the filedescriptor to send the message to               * which..: HTTP error code, most popular is 404               * message: append this string to the displayed response Return Value: - ******************************************************************************/ void send_error(int fd, int which, char *message) {   char buffer[BUFFER_SIZE] = {0};   if ( which == 401 ) {     sprintf(buffer, "HTTP/1.0 401 Unauthorized\r\n" \                     "Content-type: text/plain\r\n" \                     STD_HEADER \                     "WWW-Authenticate: Basic realm=\"MJPG-Streamer\"\r\n" \                     "\r\n" \                     "401: Not Authenticated!\r\n" \                     "%s", message);   } else if ( which == 404 ) {     sprintf(buffer, "HTTP/1.0 404 Not Found\r\n" \                     "Content-type: text/plain\r\n" \                     STD_HEADER \                     "\r\n" \                     "404: Not Found!\r\n" \                     "%s", message);   } else if ( which == 500 ) {     sprintf(buffer, "HTTP/1.0 500 Internal Server Error\r\n" \                     "Content-type: text/plain\r\n" \                     STD_HEADER \                     "\r\n" \                     "500: Internal Server Error!\r\n" \                     "%s", message);   } else if ( which == 400 ) {     sprintf(buffer, "HTTP/1.0 400 Bad Request\r\n" \                     "Content-type: text/plain\r\n" \                     STD_HEADER \                     "\r\n" \                     "400: Not Found!\r\n" \                     "%s", message);   } else {     sprintf(buffer, "HTTP/1.0 501 Not Implemented\r\n" \                     "Content-type: text/plain\r\n" \                     STD_HEADER \                     "\r\n" \                     "501: Not Implemented!\r\n" \                     "%s", message);   }   write(fd, buffer, strlen(buffer)); } /****************************************************************************** Description.: Send HTTP header and copy the content of a file. To keep things               simple, just a single folder gets searched for the file. Just               files with known extension and supported mimetype get served.               If no parameter was given, the file "index.html" will be copied. Input Value.: * fd.......: filedescriptor to send data to               * parameter: string that consists of the filename               * id.......: specifies which server-context is the right one Return Value: - ******************************************************************************/ void send_file(int id, int fd, char *parameter) {   char buffer[BUFFER_SIZE] = {0};   char *extension, *mimetype=NULL;   int i, lfd;   config conf = servers[id].conf;   /* in case no parameter was given */   if ( parameter == NULL || strlen(parameter) == 0 )     parameter = "index.html";   /* find file-extension */   if ( (extension = strstr(parameter, ".")) == NULL ) {     send_error(fd, 400, "No file extension found");     return;   }   /* determine mime-type */   for ( i=0; i < LENGTH_OF(mimetypes); i++ ) {     if ( strcmp(mimetypes[i].dot_extension, extension) == 0 ) {       mimetype = (char *)mimetypes[i].mimetype;       break;     }   }   /* in case of unknown mimetype or extension leave */   if ( mimetype == NULL ) {     send_error(fd, 404, "MIME-TYPE not known");     return;   }   /* now filename, mimetype and extension are known */   DBG("trying to serve file \"%s\", extension: \"%s\" mime: \"%s\"\n", parameter, extension, mimetype);   /* build the absolute path to the file */   strncat(buffer, conf.www_folder, sizeof(buffer)-1);   strncat(buffer, parameter, sizeof(buffer)-strlen(buffer)-1);   /* try to open that file */   if ( (lfd = open(buffer, O_RDONLY)) < 0 ) {     DBG("file %s not accessible\n", buffer);     send_error(fd, 404, "Could not open file");     return;   }   DBG("opened file: %s\n", buffer);   /* prepare HTTP header */   sprintf(buffer, "HTTP/1.0 200 OK\r\n" \                   "Content-type: %s\r\n" \                   STD_HEADER \                   "\r\n", mimetype);   i = strlen(buffer);   /* first transmit HTTP-header, afterwards transmit content of file */   do {     if ( write(fd, buffer, i) < 0 ) {       close(lfd);       return;     }   } while ( (i=read(lfd, buffer, sizeof(buffer))) > 0 );   /* close file, job done */   close(lfd); } /****************************************************************************** Description.: Perform a command specified by parameter. Send response to fd. Input Value.: * fd.......: filedescriptor to send HTTP response to.               * parameter: contains the command and value as string.               * id.......: specifies which server-context to choose. Return Value: - ******************************************************************************/ void command(int id, int fd, char *parameter) {   char buffer[BUFFER_SIZE] = {0}, *command=NULL, *svalue=NULL;   int i=0, res=0, ivalue=0, len=0;   DBG("parameter is: %s\n", parameter);   /* sanity check of parameter-string */   if ( parameter == NULL || strlen(parameter) >= 100 || strlen(parameter) == 0 ) {     DBG("parameter string looks bad\n");     send_error(fd, 400, "Parameter-string of command does not look valid.");     return;   }   /* search for required variable "command" */   if ( (command = strstr(parameter, "command=")) == NULL ) {     DBG("no command specified\n");     send_error(fd, 400, "no GET variable \"command=...\" found, it is required to specify which command to execute");     return;   }   /* allocate and copy command string */   command += strlen("command=");   len = strspn(command, "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_1234567890");   if ( (command = strndup(command, len)) == NULL ) {     send_error(fd, 500, "could not allocate memory");     LOG("could not allocate memory\n");     return;   }   DBG("command string: %s\n", command);   /* find and convert optional parameter "value" */   if ( (svalue = strstr(parameter, "value=")) != NULL ) {     svalue += strlen("value=");     len = strspn(svalue, "-1234567890");     if ( (svalue = strndup(svalue, len)) == NULL ) {       if (command != NULL) free(command);       send_error(fd, 500, "could not allocate memory");       LOG("could not allocate memory\n");       return;     }     ivalue = MAX(MIN(strtol(svalue, NULL, 10), 999), -999);     DBG("converted value form string %s to integer %d\n", svalue, ivalue);     free(svalue);   }   /*    * determine command, try the input command-mappings first    * this is the interface to send commands to the input plugin.    * if the input-plugin does not implement the optional command    * function, a short error is reported to the HTTP-client.    */   for ( i=0; i < LENGTH_OF(in_cmd_mapping); i++ ) {     if ( strcmp(in_cmd_mapping[i].string, command) == 0 ) {       if ( pglobal->in.cmd == NULL ) {         send_error(fd, 501, "input plugin does not implement commands");         if (command != NULL) free(command);         return;       }       res = pglobal->in.cmd(in_cmd_mapping[i].cmd, ivalue);       break;     }   }   /* check if the command is for the output plugin itself */   for ( i=0; i < LENGTH_OF(out_cmd_mapping); i++ ) {     if ( strcmp(out_cmd_mapping[i].string, command) == 0 ) {       res = output_cmd(id, out_cmd_mapping[i].cmd, ivalue);       break;     }   }   /* Send HTTP-response */   sprintf(buffer, "HTTP/1.0 200 OK\r\n" \                   "Content-type: text/plain\r\n" \                   STD_HEADER \                   "\r\n" \                   "%s: %d", command, res);   write(fd, buffer, strlen(buffer));   if (command != NULL) free(command); } /****************************************************************************** Description.: Serve a connected TCP-client. This thread function is called               for each connect of a HTTP client like a webbrowser. It determines               if it is a valid HTTP request and dispatches between the different               response options. Input Value.: arg is the filedescriptor and server-context of the connected TCP               socket. It must have been allocated so it is freeable by this               thread function. Return Value: always NULL ******************************************************************************/ /* thread for clients that connected to this server */ void *client_thread( void *arg ) {     int cnt;     char buffer[BUFFER_SIZE]={0}, *pb=buffer;     iobuffer iobuf;     request req;     cfd lcfd; /* local-connected-file-descriptor */     /* we really need the fildescriptor and it must be freeable by us */     if (arg != NULL)    // 如果我們傳入的引數不為空,則將引數的內容拷貝到 lcfd 中(引數為 pcfd ,不為空)     {         memcpy(&lcfd, arg, sizeof(cfd));         free(arg);     }     else         return NULL;     /* initializes the structures */     /* 初始化iobuf、req這兩個變數 */     init_iobuffer(&iobuf);        // 把iobuf清為0     init_request(&req);        // http協議,需要客服端給伺服器傳送一個請求,而request就是這個請求     /* What does the client want to receive? Read the request. */     /* 從客服端接收一些資料,用來表示客服端發來的請求，才知道給客服端發什麼資料 */     memset(buffer, 0, sizeof(buffer));     /* _readline:從客服端中讀取一行的資料,以換行符結束 */     /* buffer中存有"abcd\n" */     /*         客服此時必須傳送一個請求字串，以換行符作為結束!         問:可以傳送哪些字串?         答:有             "GET /?action=snapshot\n"             "GET /?action=stream\n"             "GET /?action=command\n"     */     if ( (cnt = _readline(lcfd.fd, &iobuf, buffer, sizeof(buffer)-1, 5)) == -1 )     {         close(lcfd.fd);         return NULL;     }     /* determine what to deliver */     /* 解析buf中的字串 */     if ( strstr(buffer, "GET /?action=snapshot") != NULL )     {         req.type = A_SNAPSHOT;    // 如果請求字串中含有"GET /?action=snapshot"，則請求型別為 A_SNAPSHOT     }     else if ( strstr(buffer, "GET /?action=stream") != NULL )     {         req.type = A_STREAM;    // 如果請求字串中含有"GET /?action=stream",則請求型別為 A_STREAM     }     else if ( strstr(buffer, "GET /?action=command") != NULL )     {         /* 將請求後面的引數儲存到 req.parameter*/         int len;         req.type = A_COMMAND;         /* advance by the length of known string */         if ( (pb = strstr(buffer, "GET /?action=command")) == NULL ) {         DBG("HTTP request seems to be malformed\n");         send_error(lcfd.fd, 400, "Malformed HTTP request");         close(lcfd.fd);         return NULL;         }         pb += strlen("GET /?action=command");         /* only accept certain characters */         len = MIN(MAX(strspn(pb, "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_-=&1234567890"), 0), 100);         req.parameter = malloc(len+1);         if ( req.parameter == NULL ) {         exit(EXIT_FAILURE);         }         memset(req.parameter, 0, len+1);         strncpy(req.parameter, pb, len);         DBG("command parameter (len: %d): \"%s\"\n", len, req.parameter);     }     else     {            /* 將請求後面的引數儲存到 req.parameter */         int len;         DBG("try to serve a file\n");         req.type = A_FILE;         if ( (pb = strstr(buffer, "GET /")) == NULL ) {         DBG("HTTP request seems to be malformed\n");         send_error(lcfd.fd, 400, "Malformed HTTP request");         close(lcfd.fd);         return NULL;         }         pb += strlen("GET /");         len = MIN(MAX(strspn(pb, "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ._-1234567890"), 0), 100);         req.parameter = malloc(len+1);         if ( req.parameter == NULL ) {         exit(EXIT_FAILURE);         }         memset(req.parameter, 0, len+1);         strncpy(req.parameter, pb, len);         DBG("parameter (len: %d): \"%s\"\n", len, req.parameter);     }     /*     * parse the rest of the HTTP-request     * the end of the request-header is marked by a single, empty line with "\r\n"     */     do     {         memset(buffer, 0, sizeof(buffer));        // 將buffer清0         /* 從客服端讀取一行資料 */         /*             客服端必須再發送一次字串         */         if ( (cnt = _readline(lcfd.fd, &iobuf, buffer, sizeof(buffer)-1, 5)) == -1 )         {             free_request(&req);             close(lcfd.fd);             return NULL;         }         /* 開始解析 buffer 中的資料 */         if ( strstr(buffer, "User-Agent: ") != NULL )         {             /* 如果buffer(客服端)中存有(傳送了)使用者名稱,則將使用者名稱儲存到 req.client 中 */             req.client = strdup(buffer+strlen("User-Agent: "));         }         else if ( strstr(buffer, "Authorization: Basic ") != NULL )         {             /* 如果buffer(客服端)中存有(傳送了)密碼,則將密碼儲存到 req.credentials 中 */             req.credentials = strdup(buffer+strlen("Authorization: Basic "));             decodeBase64(req.credentials);        // 對密碼進行解碼             DBG("username:password: %s\n", req.credentials);         }     } while( cnt > 2 && !(buffer[0] == '\r' && buffer[1] == '\n') );     /* check for username and password if parameter -c was given */     /* 如果支援密碼功能,則要檢查使用者名稱和密碼是否匹配 */     if ( lcfd.pc->conf.credentials != NULL )     {         if ( req.credentials == NULL || strcmp(lcfd.pc->conf.credentials, req.credentials) != 0 ) {         DBG("access denied\n");         send_error(lcfd.fd, 401, "username and password do not match to configuration");         close(lcfd.fd);         if ( req.parameter != NULL ) free(req.parameter);         if ( req.client != NULL ) free(req.client);         if ( req.credentials != NULL ) free(req.credentials);         return NULL;         }         DBG("access granted\n");     }     /* now it's time to answer */     /* 根據請求的型別，採取相應的行動 */     switch ( req.type )     {         case A_SNAPSHOT:             DBG("Request for snapshot\n");             send_snapshot(lcfd.fd);             break;         case A_STREAM:             DBG("Request for stream\n");             send_stream(lcfd.fd);             break;         case A_COMMAND:             if ( lcfd.pc->conf.nocommands ) {             send_error(lcfd.fd, 501, "this server is configured to not accept commands");             break;             }             command(lcfd.pc->id, lcfd.fd, req.parameter);             break;         case A_FILE:             if ( lcfd.pc->conf.www_folder == NULL )             send_error(lcfd.fd, 501, "no www-folder configured");             else             send_file(lcfd.pc->id, lcfd.fd, req.parameter);             break;         default:             DBG("unknown request\n");     }     close(lcfd.fd);     free_request(&req);     DBG("leaving HTTP client thread\n");     return NULL; } /****************************************************************************** Description.: This function cleans up ressources allocated by the server_thread Input Value.: arg is not used Return Value: - ******************************************************************************/ void server_cleanup(void *arg) {   context *pcontext = arg;   OPRINT("cleaning up ressources allocated by server thread #%02d\n", pcontext->id);   close(pcontext->sd); } /****************************************************************************** Description.: Open a TCP socket and wait for clients to connect. If clients               connect, start a new thread for each accepted connection. Input Value.: arg is a pointer to the globals struct Return Value: always NULL, will only return on exit ******************************************************************************/ void *server_thread( void *arg ) {     struct sockaddr_in addr, client_addr;     int on;     pthread_t client;     socklen_t addr_len = sizeof(struct sockaddr_in);     context *pcontext = arg;     pglobal = pcontext->pglobal;        // 取出globals結構體變數     /* set cleanup handler to cleanup ressources */     /* 當執行緒結束的時候，會呼叫 server_cleanup 來做些清理工作 */     pthread_cleanup_push(server_cleanup, pcontext);     /* open socket for server */     pcontext->sd = socket(PF_INET, SOCK_STREAM, 0);        // open函式     if ( pcontext->sd < 0 )     {         fprintf(stderr, "socket failed\n");         exit(EXIT_FAILURE);     }     /* ignore "socket already in use" errors */     /*         設定套接字         SO_REUSEADDR:可以重複使用同一個IP和埠號     */     on = 1;     if (setsockopt(pcontext->sd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)     {         perror("setsockopt(SO_REUSEADDR) failed");         exit(EXIT_FAILURE);     }     /* perhaps we will use this keep-alive feature oneday */     /* setsockopt(sd, SOL_SOCKET, SO_KEEPALIVE, &on, sizeof(on)); */     /* configure server address to listen to all local IPs */     memset(&addr, 0, sizeof(addr));     addr.sin_family = AF_INET;     addr.sin_port = pcontext->conf.port; /* (埠號)is already in right byteorder */     addr.sin_addr.s_addr = htonl(INADDR_ANY);    /* 可以監聽本地的所有的ip */     if ( bind(pcontext->sd, (struct sockaddr*)&addr, sizeof(addr)) != 0 )    // 繫結埠和IP     {         perror("bind");         OPRINT("%s(): bind(%d) failed", __FUNCTION__, htons(pcontext->conf.port));         closelog();         exit(EXIT_FAILURE);     }     /* start listening on socket */     /* 啟動監測資料,最多可以同時連線10個客服端 */     if ( listen(pcontext->sd, 10) != 0 )     {         fprintf(stderr, "listen failed\n");         exit(EXIT_FAILURE);     }     /* create a child for every client that connects */     while ( !pglobal->stop )     {         //int *pfd = (int *)malloc(sizeof(int));         cfd *pcfd = malloc(sizeof(cfd));        // 分配一個cfd結構體         if (pcfd == NULL)        // 判斷是否分配成功         {             fprintf(stderr, "failed to allocate (a very small amount of) memory\n");             exit(EXIT_FAILURE);         }         DBG("waiting for clients to connect\n");         /* 等待客服端的連結，如果有連結,則建立連結 */         pcfd->fd = accept(pcontext->sd, (struct sockaddr *)&client_addr, &addr_len);         pcfd->pc = pcontext;         /* start new thread that will handle this TCP connected client */         DBG("create thread to handle client that just established a connection\n");         syslog(LOG_INFO, "serving client: %s:%d\n", inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));    // 將除錯資訊寫入記錄本         /* 建立一個執行緒 */         /*             pthread_create:                 第一個引數:執行緒識別符號的指標                 第二個引數:設定執行緒的屬性                 第三個引數:執行緒函式的起始地址                 第四個引數:傳給執行緒函式的引數         */         if( pthread_create(&client, NULL, &client_thread, pcfd) != 0 )         {             DBG("could not launch another client thread\n");             close(pcfd->fd);             free(pcfd);             continue;         }         pthread_detach(client);    // 等待執行緒結束,回收資源     }     DBG("leaving server thread, calling cleanup function now\n");     pthread_cleanup_pop(1);     return NULL; }