Opentelemetry metadata and attributes are lost when wasm filter is usedΒ #11302
Description
Bug Report
Describe the bug
OpenTelemetry group attributes and scopes are lost when opentelemetry input is used with wasm filter.
To Reproduce
Prerequisite: Create and build blank WASM plugin.
//export debugFn
func debugFn(tag *uint8, tagLen uint, timeSec uint32, timeNsec uint32, record *uint8, recordLen uint) *uint8 {
// some business filtering logic would be added here.
return record
}Case A) (Incorrect)
Step 1) Create configuration with opentelemetry input and wasm filter and start HTTP server.
Configuration:
service:
http_port: 2020
pipeline:
inputs:
- name: opentelemetry
filters:
- name: wasm
match: 'v1_logs'
function_name: 'debugFn'
wasm_path: /fluent-bit/lib/filter/debug.wasm
outputs:
- name: stdout
match: '*'Step 2) Send HTTP request to fluent-bit that contains group attributes and scopes.
curl --header "Content-Type: application/json" --request POST --data '{"resourceLogs":[{"resource":{"attributes":[{"key":"service.name","value":{"stringValue":"filter-service"}}]},"scopeLogs":[{"scope":{"name":"my.scope"},"logRecords":[{"timeUnixNano":"1660296023390371588","body":{"stringValue":"{\"message\":\"dummy\"}"}}]}]}]}' http://0.0.0.0:4318/v1/logsData missing: Output does not contain attributes and resource logs:
[2025/12/19 13:48:25.435367475] [ info] [output:stdout:stdout.0] worker #0 started
[0] v1_logs: [[1660296023.1698112429, {"otlp"=>{}}], {"log"=>"{"message":"dummy"}"}]
Case B) (Working)
Create configuration with dummy input processed by opentelemetry_envelope and wasm filter.
Use the same dummy's input as was sent in Case A.
service:
http_port: 2020
pipeline:
inputs:
- name: dummy
dummy: |-
{
"resourceLogs": [
{
"resource": {
"attributes": [
{
"key": "service.name",
"value": {
"stringValue": "filter-service"
}
}
]
},
"scopeLogs": [
{
"scope": {
"name": "my.scope"
},
"logRecords": [
{
"timeUnixNano": "1660296023390371588",
"body": {
"stringValue": "{\"message\":\"dummy\"}"
}
}
]
}
]
}
]
}
tag: 'v1_logs'
processors:
logs:
- name: opentelemetry_envelope
filters:
- name: wasm
match: 'v1_logs'
function_name: 'debugFn'
wasm_path: /fluent-bit/lib/filter/debug.wasm
wasm_heap_size: 256KB
wasm_stack_size: 256KB
outputs:
- name: stdout
match: '*'Output contains attributes and scopeLogs as expected:
[2025/12/19 13:45:28.787731766] [ info] [output:stdout:stdout.0] worker #0 started
[0] v1_logs: [[1766151929.431803891, {}], {"resourceLogs"=>[{"resource"=>{"attributes"=>[{"key"=>"service.name", "value"=>{"stringValue"=>"filter-service"}}]}, "scopeLogs"=>[{"scope"=>{"name"=>"my.scope"}, "logRecords"=>[{"timeUnixNano"=>"1660296023390371588", "body"=>{"stringValue"=>"{"message":"dummy"}"}}]}]}]}]
Case C) (Working)
Create configuration with opentelemetry input and no wasm filter and start HTTP server.
service:
http_port: 2020
pipeline:
inputs:
- name: opentelemetry
outputs:
- name: stdout
match: '*'Step 2) Send HTTP request to fluent-bit that contains group attributes and scopes.
curl --header "Content-Type: application/json" --request POST --data '{"resourceLogs":[{"resource":{"attributes":[{"key":"service.name","value":{"stringValue":"filter-service"}}]},"scopeLogs":[{"scope":{"name":"my.scope"},"logRecords":[{"timeUnixNano":"1660296023390371588","body":{"stringValue":"{\"message\":\"dummy\"}"}}]}]}]}' http://0.0.0.0:4318/v1/logsOutput contains group attributes and metadata as expected.
[2025/12/19 13:50:30.837814660] [ info] [output:stdout:stdout.0] worker #0 started
GROUP METADATA :
{"schema"=>"otlp", "resource_id"=>0, "scope_id"=>0}
GROUP ATTRIBUTES :
{"resource"=>{"attributes"=>{"service.name"=>"filter-service"}}, "scope"=>{"name"=>"my.scope"}}
[0] v1_logs: [[1660296023.1698112429, {"otlp"=>{}}], {"log"=>"{"message":"dummy"}"}]
Expected behavior
I expected that using opentelemetry filter together with wasm filter would not not remove group attributes and metadata.
Screenshots
Your Environment
-
Version used: v4.2.1
-
Configuration: see cases above.
-
Environment name and version (e.g. Kubernetes? What version?): Docker running on localhost
-
Server type and version: N/A
-
Operating System and version: macOS 15.7.3
-
Filters and plugins: opentelemetry, wasm, stdout
Additional context
Parts of original message are lost but could contain important information.