I am trying to extract a file path from an HTTP request in x86-64 assembly. However, the extracted path appears to be an empty string when I try to use it with the open syscall. The HTTP request is correctly read into a buffer, but the parsing logic might be failing. What might be the problem? Thanks.

lea rsi, [read_buffer] # <- HTTP request
xor rcx, rcx

find_first_space:
    mov al, byte [rsi + rcx]
    test al, al
    jz done_copy
    cmp al, ' '
    je start_copy
    inc rcx
    jmp find_first_space

start_copy:
    inc rcx
    lea rdi, [path_buffer]
    xor rdx, rdx

copy_path:
    mov al, byte [rsi + rcx]
    test al, al
    jz done_copy
    cmp al, ' '
    je done_copy
    mov byte [rdi + rdx], al
    inc rdx
    inc rcx
    jmp copy_path

done_copy:
    mov byte ptr [rdi + rdx], 0

I tried extracting the file path from the HTTP request by searching for the first space after GET, then copying characters until the next space. I expected path_buffer to contain the extracted file path (e.g., /path/to/file), but instead, it ends up empty (""). This causes the open syscall to fail since it's receiving an invalid file path."