Excessive memory usage / killed when compiling BitArray case

[evanlua]

When trying to compile a case expression case.zip with many BitArray matches (used for parsing HTTP headers), the compiler process gets killed by the OS.

If I remove some of the case branches, the project compiles, but it still takes 4–5 seconds for a very small file, which feels unexpectedly slow.

Version: gleam 1.12.0

[GearsDatapacks]

Yep, I can reproduce this on nightly. This must be some bug with the exhaustiveness checking for bit arrays.

[lpil]

Thank you for the report.

Here's the code shared, for those who do not want to download an potentially dangerous zip file.

const header = <<"CONTENT_LENGTH", 0, "5", 0, "QUERY_STRING", 0, "", 0, "REQUEST_URI", 0,
  "/", 0, "REDIRECT_STATUS", 0, "200", 0, "SCRIPT_NAME", 0, "/", 0,
  "SCRIPT_FILENAME", 0, "/var/www/html/", 0, "DOCUMENT_ROOT", 0, "/var/www/html",
  0, "REQUEST_METHOD", 0, "GET", 0, "SERVER_PROTOCOL", 0, "HTTP/1.1", 0,
  "SERVER_SOFTWARE", 0, "lighttpd/1.4.79", 0, "GATEWAY_INTERFACE", 0, "CGI/1.1",
  0, "REQUEST_SCHEME", 0, "http", 0, "SERVER_PORT", 0, "4000", 0, "SERVER_ADDR",
  0, "::1", 0, "SERVER_NAME", 0, "localhost", 0, "REMOTE_ADDR", 0, "::1", 0,
  "REMOTE_PORT", 0, "35194", 0, "HTTP_HOST", 0, "localhost:4000", 0,
  "HTTP_CONNECTION", 0, "keep-alive", 0, "HTTP_CACHE_CONTROL", 0, "max-age=0", 0,
  "HTTP_SEC_CH_UA", 0,
  "\"Not;A=Brand\";v=\"99\", \"Google Chrome\";v=\"139\", \"Chromium\";v=\"139\"",
  0, "HTTP_SEC_CH_UA_MOBILE", 0, "?0", 0, "HTTP_SEC_CH_UA_PLATFORM", 0,
  "\"Windows\"", 0, "HTTP_UPGRADE_INSECURE_REQUESTS", 0, "1", 0,
  "HTTP_USER_AGENT", 0,
  "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/139.0.0.0 Safari/537.36",
  0, "HTTP_ACCEPT", 0,
  "text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7",
  0, "HTTP_SEC_FETCH_SITE", 0, "none", 0, "HTTP_SEC_FETCH_MODE", 0, "navigate",
  0, "HTTP_SEC_FETCH_USER", 0, "?1", 0, "HTTP_SEC_FETCH_DEST", 0, "document", 0,
  "HTTP_ACCEPT_ENCODING", 0, "gzip, deflate, br, zstd", 0,
  "HTTP_ACCEPT_LANGUAGE", 0, "pt-BR,pt;q=0.9,en-US;q=0.8,en;q=0.7", 0, "SCGI", 0,
  "1", 0,>>

pub fn parser_headers(
  headers: BitArray,
  acc: List(#(BitArray, BitArray)),
  v_len: Int,
) -> List(#(BitArray, BitArray)) {
  case headers {
    <<>> -> acc

    <<"CONTENT_LENGTH", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"CONTENT_LENGTH">>, value), ..acc], 1)

    <<"QUERY_STRING", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"QUERY_STRING">>, value), ..acc], 1)

    <<"REQUEST_URI", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"REQUEST_URI">>, value), ..acc], 1)

    <<"REDIRECT_STATUS", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"REDIRECT_STATUS">>, value), ..acc], 1)

    <<"SCRIPT_NAME", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"SCRIPT_NAME">>, value), ..acc], 1)

    <<"SCRIPT_FILENAME", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"SCRIPT_FILENAME">>, value), ..acc], 1)

    <<"DOCUMENT_ROOT", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"DOCUMENT_ROOT">>, value), ..acc], 1)

    <<"REQUEST_METHOD", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"REQUEST_METHOD">>, value), ..acc], 1)

    <<"SERVER_PROTOCOL", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"SERVER_PROTOCOL">>, value), ..acc], 1)

    <<"SERVER_SOFTWARE", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"SERVER_SOFTWARE">>, value), ..acc], 1)

    <<"GATEWAY_INTERFACE", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"GATEWAY_INTERFACE">>, value), ..acc], 1)

    <<"REQUEST_SCHEME", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"REQUEST_SCHEME">>, value), ..acc], 1)

    <<"SERVER_PORT", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"SERVER_PORT">>, value), ..acc], 1)

    <<"SERVER_ADDR", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"SERVER_ADDR">>, value), ..acc], 1)

    <<"SERVER_NAME", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"SERVER_NAME">>, value), ..acc], 1)

    <<"REMOTE_ADDR", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"REMOTE_ADDR">>, value), ..acc], 1)

    <<"REMOTE_PORT", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"REMOTE_PORT">>, value), ..acc], 1)

    <<"HTTP_HOST", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"HTTP_HOST">>, value), ..acc], 1)

    <<"HTTP_CONNECTION", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"HTTP_CONNECTION">>, value), ..acc], 1)

    <<"HTTP_CACHE_CONTROL", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"HTTP_CACHE_CONTROL">>, value), ..acc], 1)

    <<"HTTP_UPGRADE_INSECURE_REQUESTS", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"HTTP_UPGRADE_INSECURE_REQUESTS">>, value), ..acc], 1)

    <<"HTTP_USER_AGENT", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"HTTP_USER_AGENT">>, value), ..acc], 1)

    <<"HTTP_ACCEPT", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"HTTP_ACCEPT">>, value), ..acc], 1)

    <<"HTTP_ACCEPT_LANGUAGE", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"HTTP_ACCEPT_LANGUAGE">>, value), ..acc], 1)

    <<"HTTP_ACCEPT_ENCODING", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"HTTP_ACCEPT_ENCODING">>, value), ..acc], 1)

    <<"HTTP_SEC_FETCH_SITE", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"HTTP_SEC_FETCH_SITE">>, value), ..acc], 1)

    <<"HTTP_SEC_FETCH_MODE", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"HTTP_SEC_FETCH_MODE">>, value), ..acc], 1)

    <<"HTTP_SEC_FETCH_USER", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"HTTP_SEC_FETCH_USER">>, value), ..acc], 1)

    <<"HTTP_SEC_FETCH_DEST", 0, value:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, [#(<<"HTTP_SEC_FETCH_DEST">>, value), ..acc], 1)

    <<_:bytes-size(v_len), 0, rest:bytes>> ->
      parser_headerasd(rest, acc, 0)

    _ -> parser_headerasd(headers, acc, v_len + 1)
  }
}

pub fn main() {
parser_headers(header, [], 0)
|> echo
}