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stdlib/socket: tcp_bytes_to_str O(N²) → O(N) via list-then-join #6

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stdlib/socket: tcp_bytes_to_str O(N²) → O(N) via list-then-join #6

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10 changes: 7 additions & 3 deletions stdlib/socket.rail
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Original file line number Diff line number Diff line change
Expand Up @@ -193,12 +193,16 @@ accept_tcp listen_fd =
cfd

-- Copy `n` bytes from buf[off..off+n) into a Rail string.
-- Uses char_from_int + join; O(N²) alloc, fine for small reads.
-- Builds a list of single-char strings then joins once: O(N) allocation
-- instead of O(N²) from repeated prefix-copying concat.
tcp_bytes_to_str buf off n acc =
if n <= 0 then acc
join "" (tcp_bytes_to_list buf off n)

tcp_bytes_to_list buf off n =
if n <= 0 then []
else
let c = byte_at buf off
tcp_bytes_to_str buf (off + 1) (n - 1) (join "" [acc, char_from_int c])
(char_from_int c) : (tcp_bytes_to_list buf (off + 1) (n - 1))

-- Receive bytes until the HTTP header terminator \r\n\r\n appears, then
-- continue reading Content-Length bytes of body if present. Returns the
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