CODEWITHSUNDEEP
cfilesocketsbuffer
Sergey Potekhin
Sergey Potekhin

Reputation: 701

Is it possible to write directly from file to the socket?

I'm interested in the basic principles of Web-servers, like Apache or Nginx, so now I'm developing my own server.

When my server gets a request, it's searching for a file (e.g index.html), if it exists - read all the content to the buffer (content) and write it to the socket after. Here's a simplified code:

int return_file(char* content, char* fullPath) {
    file = open(fullPath, O_RDONLY);
    if (file > 0) { // File was found, OK
      while ((nread = read(file, content, 2048)) > 0) {}
      close(file);
      return 200;
    }
}

The question is pretty simple: is it possible to avoid using buffer and write file content directly to the socket?

Thanks for any tips :)

Upvotes: 1

Views: 2687

Answers (3)

rici
rici

Reputation: 241671

There is no standardized system call which can write directly from a file to a socket.

However, some operating systems do provide such a call. For example, both FreeBSD and Linux implement a system call called sendfile, but the precise details differ between the two systems. (In both cases, you need the underlying file descriptor for the file, not the FILE* pointer, although on both these platforms you can use fileno() to extract the fd from the FILE*.)

For more information:

Upvotes: 4

Iharob Al Asimi
Iharob Al Asimi

Reputation: 53006

What you can do is write the "chunk" you read immediately to the client.

In order to write the content, you MUST read it, so you can't avoid that, but you can use a smaller buffer, and write the contents as you read them eliminating the need to read the whole file into memory.

For instance, you could

unsigned char byte;
// FIXME: store the return value to allow
//        choosing the right action on error.
//
//        Note that `0' is not really an error.
while (read(file, &byte, 1) > 0) {
    if (write(client, &byte, 1) <= 0) {
        // Handle error.
    }
}

but then, unsigned char byte; could be unsigned char byte[A_REASONABLE_BUFFER_SIZE]; which would be better, and you don't need to store ALL the content in memory. }

Upvotes: 3

Valeri Atamaniouk
Valeri Atamaniouk

Reputation: 5163

No, it is not. There must be an intermediate storage that you use for reading/writing the data.

There is one edge case: when you use memory mapped files, the mapped file's region can be used for writing into socket. But internally, the system would anyway perform a read into memory buffer operation.

Upvotes: 0

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