write() undefined behavior - c

Question

I've this code in which I receive a server response, check if it's a successful one, and if it is - create the file under the requested path and then write the response body to the file:
I'm testing it with the following URL:
http://neverssl.com/index.html
So it means that I need to create a folder named neverssl.com with an index.html file inside.
I'm creating the file using the following method:
//full_path = "http://neverssl.com/index.html"
int create_file_under_path(char *full_path) {
int fd, path_len = (int) strlen(full_path);
char *curr_path = calloc(path_len + 1, 1);
char *token = strtok(full_path, "/");
strncpy(curr_path, token, path_len);
while (token) {
if (path_len == strlen(curr_path))
break;
if (access(curr_path, F_OK) != 0) {//The folder doesn't exist
if (mkdir(curr_path, S_IRWXU | S_IRWXG | S_IRWXO) == -1) {
perror("mkdir failed\n");
return -1;
}
}
token = strtok(NULL, "/");
strcat(curr_path, "/");
strncat(curr_path, token, strlen(token));
}
if ((fd = open(curr_path, O_CREAT | O_WRONLY, 0700)) == -1) {
perror("failed to open file\n");
return -1;
}
free(curr_path);
return fd;
}
And then I write to it using write system call as follows:
if ((fd = create_file_under_path(url->full_path)) == -1) {
free_URL(url);
free(buf);
exit(EXIT_FAILURE);
}
if (write(fd, buf + header_size, tot_read - header_size) != (buf_size - header_size)) {
perror("write:\n");
exit(EXIT_FAILURE);
}
9 out of 10 times everything works fine, but sometimes even though that the folder and the file are created, write fails with the following message: No such file or directory.
I printed the FD when this happens and it's 4 as it should be.
I've no idea how to procced with debugging it any further and will apricate the help!
Here's an example where you can see that the file exists, the fd is indeed 4 and even so it enters the if statement:

Answer 1

write(fd, buf + header_size, tot_read - header_size) != (buf_size - header_size)
From man 3p write:
Upon successful completion, these functions shall return the number of bytes actually written to the file associated with
fildes. This number shall never be greater than nbyte. Otherwise, -1 shall be returned and errno set to indicate the error.
Only when write() == -1 then errno is set, otherwise it is irrelevant - leftover from some other operation. The number returned by write() can be lower than the requested number of bytes.
You have to write a small loop where you loop over the bytes to be written. When by it, consider handling errno == EAGAIN.