How do I dynamically allocate a string such that it can contain the response header? (lemmy.ml)

submitted 1 week ago by velox_vulnus@lemmy.ml to c/c_programming@lemmy.ml

1 comments fedilink hide all child comments

I am reading data through a socket connected to a proxy, which in turn connects to a website of a choice, based on the IP and port I've assigned. After the successful connection, I am supposed to start sending headers to the server I've successfully connected to:

    ...
    char *request_header = "HEAD / HTTP/1.0\r\n";

    int response_size = 512;
    char *response_header = malloc(response_size * sizeof(char));

    write(proxy_fd, request_header, strlen(request_header));
    read(proxy_fd, response_header, response_size);

    printf("Response header:\n%s\n", response_header);
    free(response_header);
    ...

Now, creating a statically-allocated string array is problematic, because the response header can have any size. Is there a way to dynamically allocate the string response_header?

top 1 comments

sorted by: hot top controversial new old

[-] OneCardboardBox@lemmy.sdf.org 3 points 1 week ago* (last edited 1 week ago)

I think a simple approach would be:

read a chunk of the response into a char array of known size
iterate through the buffer, looking for the CRLF characters that signify the end of the header section
copy the header into a dynamically-allocated char array
if you didn't get to the CRLF characters that signify the end of the header section, read more data from the socket into the known-size char array
if it takes multiple read operations to get through the header section, then each read you can allocate a longer header string, copy your old data to it, and then append the next chunk
when you hit the CRLF, or if read indicates no more data is waiting in the socket (eg connection terminated early) then you can throw a null character at the end of your string and that's the headers

This is a somewhat naive implementation. Instead of reallocating and copying the header string array for each read, a linked-list data structure could hold the chunks of buffered data. Then at the end you combine them into a string that's exactly the right size.

this post was submitted on 08 Oct 2024

4 points (100.0% liked)

The C Programming Language

632 readers

5 users here now

Everything related to the C programming language.

founded 5 years ago

MODERATORS

Lofenyy@lemmy.ml