chore(llmobs): add url origin env var (#6286)

* implementation

* test

Author: sabrenner

packages/dd-trace/src/llmobs/writers/base.js

@@ -120,7 +120,11 @@ class BaseLLMObsWriter {
     }
 
     const { hostname, port } = this._config
-    const base = this._config.url || new URL(format({
+
+    const overrideOriginEnv = getEnvironmentVariable('_DD_LLMOBS_OVERRIDE_ORIGIN')
+    const overrideOriginUrl = overrideOriginEnv && new URL(overrideOriginEnv)
+
+    const base = overrideOriginUrl ?? this._config.url ?? new URL(format({
       protocol: 'http:',
       hostname,
       port

packages/dd-trace/test/llmobs/writers/base.spec.js

@@ -1,6 +1,7 @@
 'use strict'
 const { expect } = require('chai')
 const proxyquire = require('proxyquire')
+const { useEnv } = require('../../../../../integration-tests/helpers')
 
 describe('BaseLLMObsWriter', () => {
   let BaseLLMObsWriter
@@ -60,6 +61,19 @@ describe('BaseLLMObsWriter', () => {
     expect(writer.url).to.equal('http://localhost:8126/evp_proxy/v2/endpoint')
   })
 
+  describe('with override origin', () => {
+    useEnv({
+      _DD_LLMOBS_OVERRIDE_ORIGIN: 'http://override-origin:12345'
+    })
+
+    it('constructs a writer with the correct url', () => {
+      writer = new BaseLLMObsWriter(options)
+      writer.setAgentless(false)
+
+      expect(writer.url).to.equal('http://override-origin:12345/evp_proxy/v2/endpoint')
+    })
+  })
+
   describe('with config url', () => {
     beforeEach(() => {
       options.config.url = new URL('http://test-agent:12345')