panic when using the debug header

[hishamhm]

Originally reported by @teb510

when i add the debug header i get an output that looks like:

kong-db-less  | 2024/11/04 08:14:18 [crit] 2529#0: *6469 [proxy-wasm]["datakit" #5] panicked at src/data.rs:78:22:
kong-db-less  | index out of bounds: the len is 0 but the index is 0, client: 192.168.65.1, server: kong, request: "GET /anything HTTP/1.1", host: "localhost:8000", request_id: "00fcdc00a125be7316f1025768d4ba3a"
kong-db-less  | 2024/11/04 08:14:18 [error] 2529#0: *6469 [wasm] error while executing at wasm backtrace:
kong-db-less  |     0: 0x39ec0e - datakit.wasm!__rust_start_panic
kong-db-less  |     1: 0x39ead3 - datakit.wasm!rust_panic
kong-db-less  |     2: 0x39e889 - datakit.wasm!std::panicking::rust_panic_with_hook::h50e657195af0239c
kong-db-less  |     3: 0x39db4b - datakit.wasm!std::panicking::begin_panic_handler::{{closure}}::h0187e6969a85aab0
kong-db-less  |     4: 0x39dab2 - datakit.wasm!std::sys_common::backtrace::__rust_end_short_backtrace::h575fb82445d56667
kong-db-less  |     5: 0x39e421 - datakit.wasm!rust_begin_unwind
kong-db-less  |     6: 0x3a48d6 - datakit.wasm!core::panicking::panic_fmt::ha6764f2272b7fb95
kong-db-less  |     7: 0x3a4d83 - datakit.wasm!core::panicking::panic_bounds_check::h219d719f2d55cbcd
kong-db-less  |     8: 0x7f142 - datakit.wasm!datakit::data::Data::fill_port::hc0d5bbc5bf21e8af
kong-db-less  |     9: 0x7b520 - datakit.wasm!datakit::DataKitFilter::set_body_data::hdfb6aaa919cfd0a5
kong-db-less  |    10: 0x7cca2 - datakit.wasm!<datakit::DataKitFilter as proxy_wasm::traits::HttpContext>::on_http_response_body::h7120713bce3ee576
kong-db-less  |    11: 0x38f2a6 - datakit.wasm!proxy_wasm::dispatcher::Dispatcher::on_http_response_body::h81f271d8280e7bac
kong-db-less  |    12: 0x39594e - datakit.wasm!proxy_on_response_body
kong-db-less  | 
kong-db-less  | Caused by:
kong-db-less  |     wasm trap: wasm `unreachable` instruction executed <module: "datakit", vm: "main", runtime: "wasmtime">
kong-db-less  | 192.168.65.1 - - [04/Nov/2024:08:14:18 +0000] "GET /anything HTTP/1.1" 200 459 "-" "curl/8.7.1" kong_request_id: "00fcdc00a125be7316f1025768d4ba3a"
kong-db-less  | 2024/11/04 08:14:18 [info] 2529#0: *6469 [proxy-wasm] filter chain failed resuming: previous error (instance trapped) while logging request, client: 192.168.65.1, server: kong, request: "GET /anything HTTP/1.1", host: "localhost:8000", request_id: "00fcdc00a125be7316f1025768d4ba3a"
kong-db-less  | 2024/11/04 08:14:18 [info] 2529#0: *6469 client 192.168.65.1 closed keepalive connection
kong-db-less  | 2024/11/04 08:14:28 [info] 2533#0: *837 [lua] init.lua:155: poll_worker_data(): [counters] 11 of 10 workers reported., context: ngx.timer

interestingly when i set the header to nothing: curl -H "X-DataKit-Debug-Trace:" localhost:8000/anything the error didn't occur but i didn't get any debug output (saw the index err message)