#include #include #define __USE_GNU #include #include #include #include #include #include #include #define WWW_PORT 80 //-------------------------------------------------------------------------- // Print an error message to stderr and terminate the program immediately void printerror(char *pcErrStr) { fprintf(stderr, "ERROR: %s\n\n", pcErrStr); exit(1); } //-------------------------------------------------------------------------- // Input parameters are the name of the server to query and a pointer to a // sockaddr_in structure to fill. The function performs a lookup of the // specified Internet name and stores the address along with the web port // number (WWW_PORT) in the provided sockaddr_in structure void FillAddress(char *pcURL, struct sockaddr_in *psAddress) { struct hostent *psHostDetails; if ((psHostDetails = gethostbyname(pcURL)) == NULL) printerror("Can't determine address of website"); memcpy(&(psAddress->sin_addr), psHostDetails->h_addr_list[0], 4); psAddress->sin_family = AF_INET; psAddress->sin_port = htons(WWW_PORT); printf("Server details:\n"); printf(" Server:\t%s\n", pcURL); printf(" IP Address:\t%s\n", inet_ntoa(psAddress->sin_addr)); //Convert to human readable string } //-------------------------------------------------------------------------- int main(int iArgC, char **ppcArgV) { struct sockaddr_in sAddress; char *pcWWWServer, *pcPage, *pcPos; if (iArgC != 2) printerror("Command Line requires one parameter = website"); // If the provided URL begins with "http://" then set pcWWWServer to point // to the next character otherwise set it to point to the entire provided URL // // strstr() - find a string in another string. return the first position if (pcWWWServer = strstr(ppcArgV[1], "http://")) pcWWWServer+= 7; //skip our pointer pcWWWServer forward 7 characters. Past the "http://" else pcWWWServer = ppcArgV[1]; //It doesnt have http://, just grab the pointer to the string //Work out what the page part of the path is // If there is a "/" in the URL (after the http:// has been stripped) then // replace it with a 0 so the string terminates as just the name. Create // a new string pointer (pcPage) to be a copy of the remaining string OR // just "/" if no page details have been provided // // strstr() - find a string in another string. return the first position // strdup() - duplicate a string, return a pointer to a new string that's a copy. New memory! if (pcPos = strstr(pcWWWServer, "/")) { pcPage = strdup(pcPos); pcPos[0] = 0; //We're splitting the original string by doing this. But entering a null } else pcPage = strdup("/"); // Call FillAddress() to fill sAddress with the IP address details (and port // number 80) of the requested URL // // INPUT OUTPUT FillAddress(pcWWWServer, &sAddress); /* Download The Webpage */ //Get some memory ready to store the entire page //What if our page was bigger than this?! //This is a bad design and we wouldn't use it in production code. char bufferAllOfPage[1000000]; bzero(bufferAllOfPage, sizeof(bufferAllOfPage)); //Get the variables we need to open a network socket to the webserver //and get data back int sockfd; //This will the be the var we communicate with the server through char buffer[1024]; //We'll use this for recieving data int bytes_read; //This is to know how much data we've got //Try to create a new network socket if( (sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) printerror("Socket error"); //Try to connect that socket to the webserver //See we use sAddress that we got earlier if( connect(sockfd, (struct sockaddr*)&sAddress, sizeof(sAddress)) != 0) printerror("Couldn't connect"); //Ok, we're connected //Tell the webserver what page we want to retrieve //Don't forget to tell them which site we're asking for (The host bit) // and which page we want sprintf(buffer, "GET %s HTTP/1.0\nHost: %s\n\n", pcPage, pcWWWServer); send(sockfd, buffer, strlen(buffer), 0); //Start recieving data from the server //Grab a chunk at a time and put it into the temporary buffer //we made before called....buffer do { //Blank out our buffer of retreived data //Then ask the network stack to give us some more bzero(buffer, sizeof(buffer)); bytes_read = recv(sockfd, buffer, sizeof(buffer), 0); if( bytes_read > 0) //Did we get any? { //Copy the text we just got from the server into the //buffer we're storing the whole page in strncat(bufferAllOfPage, buffer, bytes_read); //strncat stuffs one string on to the end of another string. It's smart //enough to find the right place by itself. We still pass along bytes_read //so that it only copies as many characters as we want it to. } } while ( bytes_read > 0); //keep going through this loop until we have all the page //Clean up our network socket close(sockfd); /* Now lets try and parse out the links and images */ //We're doing to do some very nieve searching, so first thigns first, make //the whole string lower case. (Uses the ctype.h library) int i = 0; while(bufferAllOfPage[i]) { bufferAllOfPage[i] = tolower(bufferAllOfPage[i]); i++; } printf("\nLooking for Links:\n"); //Step through the string looking for things like this // href=' ...... ' //These are links to other pages and documents //Work out where it starts and ends, then print this URL out to the user char *posStartLink; char *posEndLink; char *placeToStartLooking; placeToStartLooking = bufferAllOfPage; do { //Find the first text saying ' href="' posStartLink = strstr(placeToStartLooking, " href=\""); if(posStartLink) { //If we found the start of a link, then try to find the end of it posStartLink += 7; //+7 to get us past the href=" characters posEndLink = strstr(posStartLink, "\""); } //Did we find anything (start AND end)? if(posStartLink && posEndLink) { //Ok we found a link //Extract the text of that link into a new string int linkLength; char linkBuf[1000]; linkLength = posEndLink - posStartLink; strncpy(linkBuf, posStartLink, linkLength); linkBuf[linkLength] = 0; //Print out the link we found printf("%s\n", linkBuf); //Move up the position of where to look placeToStartLooking = posEndLink; } else break; //We didnt find anything, so stop looking. } while(posEndLink <= (bufferAllOfPage + strlen(bufferAllOfPage)) ); //Keep going until the end of the HTML we got return 0; }