extension-to-functions-codebase

Extension to Functions Codebase & npm Package Migration

Overview

This skill guides the agent in migrating a Firebase Extension repository or instance into either:

1. A standalone Cloud Functions for Firebase codebase (firebase-functions, for end-user app integration), or
2. A publishable npm package / shareable open source package (for extension publishers distributing reusable V2 functions).

It leverages native Cloud Functions for Firebase GA capabilities to handle permissions, dependencies, and lifecycle hooks natively in code, and provides instructions for modernizing legacy V1 triggers to V2 using the Destructuring Compatibility Shim.

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Triggers

Activate this skill when a user asks to:

• Migrate or convert an installed Firebase Extension into a standalone functions codebase.
• Convert an extension repository into a publishable npm package (shareable open source package).
• Upgrade extension triggers from V1 to V2.

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Target Migration Workflows

Before starting, determine the target destination with the developer:

• Target A: Local Functions Codebase (End-User App Integration)

  • Output: Source code placed in the project's functions/src/ folder.
  • Configuration: Parameters defined via defineString, defineSecret, etc. in .env.
  • Deployment: Deployed directly via firebase deploy --only functions.

• Target B: Publishable npm Package / Shareable Open Source Package

  • Output: Reusable npm package containing exported V2 functions.
  • Configuration: package.json with exports map and firebase-functions declared in dependencies (or peerDependencies).
  • Usage: End users install the package (npm i <package-name>) and re-export functions in their index.ts.

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Getting Started & Git Safety

1. Git Status: Verify the workspace has a clean git status before starting.
2. In-Place Copying: If copying code to a new subdirectory within the same repository:
   • Use git cp (or copy files and commit) to copy the extension's source directory to the target directory.
   • Commit immediately: "Copying [extension-name] extension to [directory] in preparation for rewrite"

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Rules and Constraints

1. Zero-Local-Overhead (Cloud Functions Integration)

Assume Cloud Functions for Firebase Workload Identities, Declarative Security, and SDK Lifecycle Hooks are fully GA.

• Do NOT output instructions or scripts telling users to run manual gcloud IAM commands or create service accounts.
• Do NOT write code comments instructing users to manually enable Google APIs in the cloud console.
• Instead, use declarative requiresAPI and requiresRole imports from the SDK.

2. Global Parameter Access Restriction

• Never call .value() on any parameter at global scope.
• If a global variable or class instance is initialized using a parameter value, declare the variable globally and initialize it inside the onInit() callback:

  import { defineString } from "firebase-functions/params";
  import { onInit } from "firebase-functions/v2";
  
  const bqDataset = defineString("DATASET_ID");
  let bqClient: BigQuery;
  
  onInit(() => {
    bqClient = new BigQuery({ datasetId: bqDataset.value() });
  });
  

3. Concurrency & Cost Parity for V2

When upgrading triggers to V2:

• By default, V2 functions enable concurrency (up to 80 requests per instance).
• If you want to maintain V1 fractional CPU pricing (and disable concurrency), set cpu: "gcf_gen1" in the function's options object.

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Step-by-Step Migration Execution

Step 1: Inventory the Extension

Conduct a complete inventory of everything the extension declares, ships, and documents so that nothing is lost during migration:

1. Inventory extension.yaml:
   • params: Convert to Functions params (defineString, defineSecret, etc.).
   • apis: Convert to requiresAPI(...) declarations.
   • roles: Convert to requiresRole(...) declarations.
   • lifecycleEvents (onInstall, onUpdate, onConfigure): Convert to afterFirstDeploy and afterRedeploy hooks.
   • resources: Note all function triggers to convert from 1st gen (firebase-functions/v1) to 2nd gen (firebase-functions/v2), including standard event triggers, HTTP handlers, and task queues (onTaskDispatched).
2. Inventory Files & Tooling:
   • functions/: Source code, triggers, helpers, and task queue handlers.
   • Documentation: README.md, PREINSTALL.md, and POSTINSTALL.md.
   • scripts/: Note any backfill, import, or helper scripts shipped with the extension.

Step 2: Create / Update package.json

Create an npm package for the migrated extension code (either at project root or in a dedicated workspace directory):

• Set a publishable package name (name: "<package-name>").
• Preserve Dev & Test Dependencies: Preserve all existing devDependencies, test runners (jest, ts-jest, @types/jest, mocha, @types/mocha), and test scripts ("test": "...") from the legacy extension (functions/package.json or root package.json). Do not drop test frameworks or type definitions.
• Declare firebase-functions (e.g. ^7.0.0) in dependencies (or peerDependencies if creating a lightweight middleware package where the root consumer manages the runtime version):

  {
    "name": "<package-name>",
    "version": "1.0.0",
    "main": "lib/index.js",
    "types": "lib/index.d.ts",
    "exports": {
      ".": {
        "types": "./lib/index.d.ts",
        "default": "./lib/index.js"
      }
    },
    "engines": {
      "node": ">=22"
    },
    "dependencies": {
      "firebase-admin": "^12.0.0",
      "firebase-functions": "^7.0.0"
    }
  }
  

Step 3: Move Function Code & Expose Deployable Functions

Move the extension's function source into the package's src/ folder:

1. Keep normal Firebase trigger exports. The package must expose deployable functions that end users can re-export from their entrypoint (index.ts).
2. Document that consumers must deploy packaged functions by re-exporting them:

   export * from "<package-name>";
   // Or named exports:
   // export { syncV2, initBigQuerySync } from "<package-name>";
   

   Note: A bare import (import "<package-name>") is not enough. The Firebase CLI only deploys functions exported from the user's root entry file.

Step 4: Upgrade Functions from 1st Gen to 2nd Gen

Convert each exported 1st gen function trigger (onWrite, onRequest, tasks.taskQueue().onDispatch) to its 2nd gen equivalent (onDocumentWritten, onRequest, onTaskDispatched from firebase-functions/v2/...):

1. Signatures & Destructuring Shim: Use the Destructuring Compatibility Shim ({ shimmedKey, context }) to preserve V1 business logic without rewriting function bodies. See signature-mapping.md and destructuring-shim.md.
2. Authentication Triggers Exception: If your extension uses v1 Authentication Triggers (auth.user().onCreate(), auth.user().onDelete()), instruct the agent to check live whether a 2nd gen alternative exists in the installed firebase-functions package or live documentation. If 2nd gen Auth triggers are not yet supported for those events, warn the user clearly and halt or refuse the migration for those specific triggers until a V2 alternative becomes available.

Step 5: Replace Extension Params with Functions Params

Each parameter in extension.yaml becomes a Parameterized Configuration call:

1. Map parameter primitives and attributes:
   • Type string -> defineString("PARAM_NAME", { label: "...", description: "...", default: "..." })
   • Type secret -> defineSecret("PARAM_NAME")
   • Type int -> defineInt("PARAM_NAME", { label: "...", default: 123 })
   • Type boolean -> defineBoolean("PARAM_NAME", { default: true })
   • Type select / multiSelect -> map options into input: defineString("PARAM_NAME", { input: { select: { options: [{ value: "val", label: "Val" }] } } })
   • validationRegex -> map into text input options: defineString("PARAM_NAME", { input: { text: { validationRegex: "^[a-z]+$" } } })
   • required: true / Non-empty validation -> map nonEmpty: true into input options: defineString("PARAM_NAME", { input: { text: { nonEmpty: true } } })
2. Read parameter values inside handlers using paramName.value().
3. Keep Exact Parameter Names: Never change parameter names (COLLECTION_PATH, DATASET_ID, etc.) so that existing values carry over seamlessly in .env.

Step 6: Migrate Internal Task Queue Calls (queue.enqueue(...))

If your extension code enqueues tasks onto its own queue using the Admin SDK (getFunctions().taskQueue(...)):

• Under the Extensions runtime, the Admin SDK resolved queues by function name plus process.env.EXT_INSTANCE_ID.
• In an npm package / regular codebase: Remove the second argument (EXT_INSTANCE_ID) entirely. The Admin SDK automatically targets the current codebase:

  // Before (extension runtime):
  // const queue = getFunctions().taskQueue(`locations/${region}/functions/syncBigQuery`, process.env.EXT_INSTANCE_ID);
  
  // After (npm package):
  const queue = getFunctions().taskQueue(`locations/${region}/functions/syncBigQuery`);
  await queue.enqueue(taskData);
  

Step 7: Migrate Secrets

For parameters declared with type: secret:

1. Declare the secret explicitly:

   import { defineSecret } from "firebase-functions/params";
   const apiKey = defineSecret("API_KEY");
   

2. Bind the secret in the trigger options:

   export const fn = onRequest({ secrets: [apiKey] }, handler);
   

3. Keep exact secret names unchanged so existing Secret Manager bindings work.

Step 8: Declare Required APIs and IAM Roles

Replace apis and roles from extension.yaml with declarative code in your entry file:

import { requiresAPI, requiresRole } from "firebase-functions";

requiresAPI("bigquery.googleapis.com", "Needed to write changelog rows");
requiresRole("roles/bigquery.dataEditor");
requiresRole("roles/bigquery.user");

At deploy time, the Firebase CLI automatically grants these roles to the managed runtime service account and enables the required APIs.

Step 9: Convert Lifecycle Hooks (afterFirstDeploy & afterRedeploy)

Replace lifecycleEvents (onInstall, onUpdate, onConfigure) with SDK lifecycle hooks:

1. Convert task queue handlers (initBigQuerySync, setupBigQuerySync) to V2 onTaskDispatched from firebase-functions/v2/tasks (removing legacy getExtensions().runtime().setProcessingState(...) calls).
2. Register lifecycle hooks in code:

   import { afterFirstDeploy, afterRedeploy } from "firebase-functions/v2";
   
   // Replaces onInstall:
   afterFirstDeploy({
     task: {
       function: "runInitialSetup",
       body: {}
     }
   });
   
   // Replaces onUpdate & onConfigure:
   afterRedeploy({
     task: {
       function: "runInitialSetup",
       body: { reconcile: true }
     }
   });
   

3. Ensure handlers are idempotent and document manual rerun commands:

   firebase functions:lifecycle:run afterFirstDeploy CODEBASE_NAME
   firebase functions:lifecycle:run afterRedeploy CODEBASE_NAME
   

Step 10: Document Setup for Your Users (README.md)

Preserve whatever documentation, secrets, and setup instructions the original extension already documented in README.md (and PREINSTALL.md / POSTINSTALL.md), updating them as needed:

1. Update Configuration References: Replace instructions referencing legacy extension.yaml installation prompts or ext-*.env files with standard .env Parameterized Configuration setup matching the defineString parameters.
2. Include Re-export Snippet: Ensure the basic root re-export snippet is shown (export * from "<package-name>";) so users know how to expose the functions in their root index.ts.
3. Avoid Unnecessary Boilerplate: Do not generate redundant comparison tables or generic installation steps if the setup is self-evident in the code or already covered by existing README sections.

Step 11: Build & Test Verification

1. Verify Source Compilation: Run npm run build (tsc) to ensure no TypeScript compilation errors in src/.
2. Verify Unit Test Suite & Type Definitions:
   • If existing unit tests (__tests__/, test/) are present in the extension:
     • Ensure @types/jest (or the original test framework types) are present in devDependencies so test files type-check cleanly.
     • Update test invocations for upgraded V2 triggers to pass a single destructured event object (({ change: mockChange, context: mockContext }) instead of positional arguments (mockChange, mockContext)).
     • Run npm test or type-check test files (npx tsc --noEmit) to verify zero regressions.

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References & Official Resources

• Official Google Migration Guide: Prepare Firebase Extensions for migration to Cloud Functions
• Publisher Support Contacts:
  • Support Email: firebase-extensions-migrator-support-external@google.com
  • Support Group Subscription: firebase-extensions-migrator-support-external+subscribe@google.com
• Destructuring Shim: See destructuring-shim.md for details on event property translation.
• Trigger Mapping: See signature-mapping.md for V1 vs V2 trigger definitions and shim keys.
• Configuration & Parameters: See configuration-migration.md for runWith options, params, and secret bindings.