refactor(azure-metadata): parse WEBSITE_OWNER_NAME without regex (#8348)

The greedy `/.+\+(.+)-.+webspace(-Linux)?/` shape made the engine
backtrack through three open-ended `.+` quantifiers to find the right
`-` before `<region>webspace`. Plain string ops (`indexOf('+')` then
`endsWith('webspace')` then `lastIndexOf('-')`) read directly off the
documented format and stop on the first match, with no backtracking
needed.

Author: BridgeAR

packages/dd-trace/src/azure_metadata.js

@@ -19,7 +19,20 @@ function extractSubscriptionID (ownerName) {
 }
 
 function extractResourceGroup (ownerName) {
-  return /.+\+(.+)-.+webspace(-Linux)?/.exec(ownerName)?.[1]
+  // WEBSITE_OWNER_NAME format: `<sub-id>+<rg>-<region>webspace[-Linux]`. Region
+  // names have no `-`; resource groups can. Plain string ops read more directly
+  // than `/.+\+(.+)-.+webspace(-Linux)?/` and avoid the engine backtracking
+  // through three `.+` quantifiers to land on the right `-`.
+  if (typeof ownerName !== 'string') return
+  const plusIdx = ownerName.indexOf('+')
+  if (plusIdx === -1) return
+  let rest = ownerName.slice(plusIdx + 1)
+  if (rest.endsWith('-Linux')) rest = rest.slice(0, -'-Linux'.length)
+  if (!rest.endsWith('webspace')) return
+  rest = rest.slice(0, -'webspace'.length)
+  const lastDash = rest.lastIndexOf('-')
+  if (lastDash === -1) return
+  return rest.slice(0, lastDash)
 }
 
 function buildResourceID (subscriptionID, siteName, resourceGroup) {

packages/dd-trace/test/azure_metadata.spec.js

@@ -157,4 +157,39 @@ describe('Azure metadata', () => {
     const metadata = getAzureFunctionMetadata()
     assert.strictEqual(metadata.resourceGroup, 'regular_resource_group')
   })
+
+  describe('resource group extraction from WEBSITE_OWNER_NAME', () => {
+    /** @param {string} ownerName */
+    function resourceGroupFor (ownerName) {
+      process.env.WEBSITE_SITE_NAME = 'site'
+      process.env.WEBSITE_OWNER_NAME = ownerName
+      return getAzureAppMetadata().resourceGroup
+    }
+
+    it('strips the -Linux suffix before splitting on the last dash', () => {
+      assert.strictEqual(resourceGroupFor('sub+rg-regionwebspace-Linux'), 'rg')
+    })
+
+    it('preserves dashes inside the resource group', () => {
+      assert.strictEqual(resourceGroupFor('sub+with-dashes-regionwebspace'), 'with-dashes')
+    })
+
+    it('extracts from the shortest accepted form', () => {
+      assert.strictEqual(resourceGroupFor('a+b-cwebspace'), 'b')
+    })
+
+    it('returns undefined when WEBSITE_OWNER_NAME has no plus separator', () => {
+      // Suffix is otherwise valid; pins the early `plusIdx === -1` guard.
+      assert.strictEqual(resourceGroupFor('rg-regionwebspace'), undefined)
+    })
+
+    it('returns undefined when WEBSITE_OWNER_NAME does not end in webspace', () => {
+      // Length is chosen so removing the `webspace` guard would otherwise return `'rg'`.
+      assert.strictEqual(resourceGroupFor('sub+rg-something-region'), undefined)
+    })
+
+    it('returns undefined when no dash precedes the region marker', () => {
+      assert.strictEqual(resourceGroupFor('sub+regionwebspace'), undefined)
+    })
+  })
 })