Question

I’m doing client/server interaction with sockets in C. What I’m trying to do is have the client request a file to be read on the server, the server return a buffer of the file contents, and the client print out the file.

Though I was able to accomplish the server sending a buffer of a file to the client & the client printing it out successfully, I can’t seem to get the server to successfully read a filename sent by the client.

Here is what I mean:

///This is the structure of the message that gets sent back and forth
struct message { 
int code; //Just indicates 1 or 2 for readfile or writefile
int size;
char buffer[256]; //This will hold the filename when client sends readfile request
 };

Works:

char *filename = "test.c";
infile = open(filename, O_RDONLY);
//Send the file and everything back to the client

Doesn’t Work:

while( read(sockfd, &msg, sizeof(int) * 2) > 0) {
        if(msg.code == 1) { //Perform a read operation
            int infile, filesize, rr;
            int length;
            char output[256];
            size_t rb = 0;

            while(rb < msg.size) { 
                ssize_t r = read(sockfd, msg.buffer, msg.size - rb);
                if(r < 0) { 
                    error(sockfd, r, msg.buffer);
                    break;
                }
                rb += r;
            }

            msg.buffer[rb] = '\0';  
         //This has been printing out the correct amount
            printf("\nBytes read: %i", rb); 
         //This has also been printing out properly
            printf("\nmsg.buffer: %s", msg.buffer); 

            infile = open(msg.buffer, O_RDONLY);

I’ve edited to show the current state my program is in, and is still not working. Before, I had a strcpy that was improperly placed.

Answer 1

Well I’ve about found out the answer, or at least something close to it. First off, a line break character was getting sent. On the client side, I used fgets(msg.buffer, 256, stdin); to get the message. When I checked the value using printf("File |%s|", msg.buffer), I saw that the second bar was on the next line. I took that line break and overwrote it with a null character at the end.

I also changed to fopen and freads/writes. I added ./ to the beginning of the file statement but I doubt that’s needed.. it was just one of my earlier attempts. It now looks something like this:

            size_t rb = 0;
            FILE* file;
            char filename[256];
            while(rb < msg.size) { 
                ssize_t r = read(sockfd, filename, msg.size - rb);
                if(r < 0) { 
                    error(sockfd, r, msg.buffer);
                    goto end;
                }
                rb += r;
            }
            if(strlen(filename) > 253) { 
                error(sockfd, rb, msg.buffer);
                goto end;
            }
            strcpy(msg.buffer, "./");
            strcat(msg.buffer, filename);
            msg.buffer[rb + 1] = '\0';

            file = fopen(msg.buffer, "r");
            if(file == NULL) {
                error(sockfd, rb, msg.buffer);
                printf("Error opening file %s: %s\n", msg.buffer,strerror(errno));
                fflush(stdout);
                goto end;
            }

Thanks to all who helped. I learned a lot (gdb was especially useful — I never used it before)