feat: POST /user/contacts — save a contact to the device addressbook

[FlavioPulli]

WhatsApp syncs the contact list across devices via app state (the same channel as mute/pin/archive), and whatsmeow already applies incoming contact mutations back into Store.Contacts. The API exposes only the read side (GET /user/contacts); this adds the write side.

POST /user/contacts {phone, fullName, firstName?} builds a contact-index mutation on the critical_unblock_low patch carrying a ContactAction (FullName/FirstName + SaveOnPrimaryAddressbook: true, which asks the primary phone to also store the contact in the system addressbook) and sends it through the official Client.SendAppState primitive. After the resync SendAppState triggers, the saved contact shows up in GET /user/contacts like any contact saved on the phone itself.

Verified end to end on a paired Android device (contact appears in the phone's WhatsApp list and system addressbook); in our production since 2026-07-22.

Summary by Sourcery

Add write-side support for user contacts by wiring a new SaveContact flow from HTTP handler through the user service to WhatsApp app state mutations so contacts saved via the API appear in the synced contact list and device address book.

New Features:

• Add POST /user/contacts endpoint to save or update a contact in the WhatsApp contact list and device address book.

Enhancements:

• Introduce UserService.SaveContact and corresponding handler to encapsulate contact creation logic and app state mutation handling.

[sourcery-ai]

Reviewer's Guide

Adds a POST /user/contacts endpoint and corresponding handler/service logic that builds and sends a WhatsApp app state contact mutation via whatsmeow to save a contact to the device and primary address book.

Sequence diagram for POST /user/contacts saving a contact via app state

sequenceDiagram
  actor ApiClient
  participant GinRouter
  participant UserHandler
  participant UserService
  participant WhatsmeowClient

  ApiClient->>GinRouter: POST /user/contacts
  GinRouter->>UserHandler: SaveContact(ctx)
  UserHandler->>UserHandler: ctx.MustGet(instance)
  UserHandler->>UserHandler: ctx.ShouldBindBodyWithJSON(SaveContactStruct)
  UserHandler->>UserHandler: [validate phone and fullName]
  UserHandler->>UserService: SaveContact(data, instance)
  UserService->>UserService: ensureClientConnected(instance.Id)
  UserService->>WhatsmeowClient: SendAppState(patch)
  WhatsmeowClient-->>UserService: result
  UserService->>UserService: LogInfo(Contact saved)
  UserService-->>UserHandler: nil / error
  UserHandler-->>ApiClient: 200 {"message":"success"} / 500 {"error":...}

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File-Level Changes

Change	Details	Files
Introduce service-layer operation to construct and send WhatsApp app-state contact mutations to save contacts.	Define SaveContactStruct request model with phone and name fields mapped to JSON. Implement userService.SaveContact to validate inputs, derive firstName when missing, build contact-index mutation on the critical_unblock_low patch using waSyncAction.ContactAction, and send via Client.SendAppState. Use a fixed contactMutationVersion constant and log both success and error cases using the instance-scoped logger.	pkg/user/service/user_service.go pkg/user/service/save_contact.go
Expose the save-contact capability via a new HTTP handler and route.	Extend the UserService and UserHandler interfaces with SaveContact methods. Add POST /user/contacts route wired to userHandler.SaveContact. Implement userHandler.SaveContact to fetch the instance from context, bind and validate JSON body, call the service SaveContact method, and return appropriate HTTP status codes and messages.	pkg/routes/routes.go pkg/user/handler/user_handler.go pkg/user/handler/save_contact.go

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[sourcery-ai]

Hey - I've left some high level feedback:

• The handler duplicates validation that already exists in SaveContact (checking Number and FullName non-empty); consider consolidating this validation in one place to avoid drift and inconsistent error messages.
• In SaveContact handler, ctx.ShouldBindBodyWithJSON is not a standard gin method; replacing it with ctx.ShouldBindJSON(&data) (and using a non-pointer SaveContactStruct for binding) will be more idiomatic and avoid potential runtime issues.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- The handler duplicates validation that already exists in `SaveContact` (checking `Number` and `FullName` non-empty); consider consolidating this validation in one place to avoid drift and inconsistent error messages.
- In `SaveContact` handler, `ctx.ShouldBindBodyWithJSON` is not a standard gin method; replacing it with `ctx.ShouldBindJSON(&data)` (and using a non-pointer `SaveContactStruct` for binding) will be more idiomatic and avoid potential runtime issues.

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