wasm filter unable to load module

[asimbera]

Bug Report

Describe the bug

I've been trying to run filter_rust module from the examples but fluent-bit is not able to load the wasm module.

To Reproduce

• Example log message:

Apr 10 08:45:17 devbox fluent-bit[1680]: [2025/04/10 08:45:17] [debug] [dummy:dummy.0] created event channels: read=25 write=26  
Apr 10 08:45:17 devbox fluent-bit[1680]: [2025/04/10 08:45:17] [ info] [input:storage_backlog:storage_backlog.1] initializing  
Apr 10 08:45:17 devbox fluent-bit[1680]: [2025/04/10 08:45:17] [ info] [input:storage_backlog:storage_backlog.1] storage_strategy='memory' (memory only)  
Apr 10 08:45:17 devbox fluent-bit[1680]: [2025/04/10 08:45:17] [debug] [storage_backlog:storage_backlog.1] created event channels: read=27 write=28  
Apr 10 08:45:17 devbox fluent-bit[1680]: [2025/04/10 08:45:17] [ info] [input:storage_backlog:storage_backlog.1] queue memory limit: 4.8M  
Apr 10 08:45:17 devbox fluent-bit[1680]: [2025/04/10 08:45:17] [debug] [stdout:stdout.0] created event channels: read=29 write=30  
Apr 10 08:45:17 devbox fluent-bit[1680]: [2025/04/10 08:45:17] [debug] [router] match rule dummy.0:stdout.0  
Apr 10 08:45:17 devbox fluent-bit[1680]: [2025/04/10 08:45:17] [ info] [output:stdout:stdout.0] worker #0 started  
Apr 10 08:45:17 devbox fluent-bit[1680]: [2025/04/10 08:45:17] [ info] [http_server] listen iface=0.0.0.0 tcp_port=2020  
Apr 10 08:45:17 devbox fluent-bit[1680]: [2025/04/10 08:45:17] [ info] [sp] stream processor started  
Apr 10 08:45:27 devbox fluent-bit[1680]: [2025/04/10 08:45:27] [error] Load wasm module failed. error: WASM module load failed: zero byte expected  
Apr 10 08:45:27 devbox fluent-bit[1680]: [2025/04/10 08:45:27] [debug] [filter:wasm:wasm.0] instantiate wasm [/etc/fluent-bit/wasm/flb_filter_rust.wasm] failed  
Apr 10 08:45:28 devbox fluent-bit[1680]: [2025/04/10 08:45:28] [debug] [task] created task=0x79bc8123d960 id=0 OK  
Apr 10 08:45:28 devbox fluent-bit[1680]: [2025/04/10 08:45:28] [debug] [output:stdout:stdout.0] task_id=0 assigned to thread #0  
Apr 10 08:45:28 devbox fluent-bit[1680]: [0] log.dummy: [[1744274727.544759457, {}], {"message"=>"dummy"}]  
Apr 10 08:45:28 devbox fluent-bit[1680]: [2025/04/10 08:45:28] [debug] [out flush] cb_destroy coro_id=0  
Apr 10 08:45:28 devbox fluent-bit[1680]: [2025/04/10 08:45:28] [debug] [task] destroy task=0x79bc8123d960 (task_id=0)  
Apr 10 08:45:37 devbox fluent-bit[1680]: [2025/04/10 08:45:37] [error] Load wasm module failed. error: WASM module load failed: zero byte expected  
Apr 10 08:45:37 devbox fluent-bit[1680]: [2025/04/10 08:45:37] [debug] [filter:wasm:wasm.0] instantiate wasm [/etc/fluent-bit/wasm/flb_filter_rust.wasm] failed  
Apr 10 08:45:38 devbox fluent-bit[1680]: [2025/04/10 08:45:38] [debug] [task] created task=0x79bc8123d820 id=0 OK  
Apr 10 08:45:38 devbox fluent-bit[1680]: [2025/04/10 08:45:38] [debug] [output:stdout:stdout.0] task_id=0 assigned to thread #0  
Apr 10 08:45:38 devbox fluent-bit[1680]: [0] log.dummy: [[1744274737.544253440, {}], {"message"=>"dummy"}]  
Apr 10 08:45:38 devbox fluent-bit[1680]: [2025/04/10 08:45:38] [debug] [out flush] cb_destroy coro_id=1  
Apr 10 08:45:38 devbox fluent-bit[1680]: [2025/04/10 08:45:38] [debug] [task] destroy task=0x79bc8123d820 (task_id=0)

• Steps to reproduce the problem:

Expected behavior

This should not be causing an error and output a similar message that is definded in rust source code:

{
      "message": v["message"],
      "time": format!("{}", time),
      "tag": vtag,
      "original": v.to_string(),
      "lang": "Rust",
  }

Screenshots

Your Environment

• Version used:4.0.0
• Configuration:

service:  
flush: 1  
daemon: off  
log_level: debug  
http_server: on  
parsers_file: parsers.conf  
  
storage.path: /var/lib/fluent-bit/  
storage.metrics: on  
storage.sync: normal  
storage.checksum: off  
storage.max_chunks_up: 128  
storage.backlog.mem_limit: 5M  
  
pipeline:  
inputs:  
- name: dummy  
interval_sec: 10  
tag: log.dummy  
  
filters:  
- name: wasm  
match: log.dummy  
wasm_path: /etc/fluent-bit/wasm/flb_filter_rust.wasm  
function_name: flb_filter_rust  
accessible_paths: .  
  
outputs:  
- name: stdout  
match: log.dummy

• Environment name and version (e.g. Kubernetes? What version?): VM
• Server type and version:
• Operating System and version: Ubuntu 24.04.2 LTS
• Filters and plugins: wasm

Additional context

• rustc 1.84.0 (9fc6b4312 2025-01-07)
• cargo 1.84.0 (66221abde 2024-11-19)

root@devbox:~# file /etc/fluent-bit/wasm/flb_filter_rust.wasm 
/etc/fluent-bit/wasm/flb_filter_rust.wasm: WebAssembly (wasm) binary module version 0x1 (MVP)

I've renamed the function and library name to flb_filter_rust