Identity Headers

Every drain request sent by evlog is tagged with two identity headers so receivers can identify the traffic:

The browser-side evlog/http drain (used by the client transport) sets X-Evlog-Source: client instead, since browsers cannot override User-Agent.

Why

• Triage at the receiver. Quickly distinguish evlog traffic from other clients in the receiving system's logs.
• Track adapter usage and version drift. Roll out a new evlog version and watch the User-Agent distribution change centrally.
• Debug a specific drain. Filter by X-Evlog-Source to isolate one adapter's behavior in a sea of incoming requests.

Reading the version

Both constants are exported from evlog/toolkit so your drain (or your receiver) can reference the canonical values:

import { EVLOG_USER_AGENT, EVLOG_VERSION } from 'evlog/toolkit'

console.log(EVLOG_VERSION)    // → "2.16.0"
console.log(EVLOG_USER_AGENT) // → "evlog/2.16.0"

Overriding from a custom drain

Adapters built with defineHttpDrain() automatically pass the drain name as source and the canonical evlog/<version> as userAgent. You don't need to think about it.

When you build a drain on top of httpPost from evlog/toolkit directly (e.g. for a fork with a different identity, or for a vendor that wants its own UA), pass source and/or userAgent to override:

import { httpPost } from 'evlog/toolkit'

await httpPost({
  url: 'https://my-platform.example.com/ingest',
  headers: { 'Content-Type': 'application/json' },
  body: '[]',
  timeout: 5000,
  label: 'my-platform',
  source: 'my-platform',           // sent as X-Evlog-Source
  userAgent: 'my-fork/1.0',        // overrides the default User-Agent
  // userAgent: false,             // suppress the header entirely
})

Next steps

• Custom Drains — defineHttpDrain injects identity headers automatically
• Drain Pipeline — wrap any drain in batch + retry while keeping identity headers