fix(sticker): send animated WebP stickers as-is (skip static re-encode)

[nicolasnovis]

SendSticker always runs convertToWebP, which decodes the image via webpDecodeRGBA and fails on animated WebP (webpDecodeRGBA: failed), so sending an animated sticker errors out.

This uploads the sticker untouched when it is already WebP (skipping the lossy re-encode), detects animation (VP8X animation flag / ANIM chunk) and sets IsAnimated accordingly, and pins the mimetype to image/webp. Static and animated WebP stickers both send correctly; non-WebP inputs still go through convertToWebP as before.

Tested in production against WhatsApp with both static and animated .webp stickers.

Summary by Sourcery

Handle sending WebP stickers by uploading existing WebP data untouched, only re-encoding non-WebP sources to WebP, and correctly marking animated stickers.

Bug Fixes:

• Prevent failures when sending animated WebP stickers by avoiding re-encoding through a decoder that cannot handle animation.

Enhancements:

• Detect WebP format and animation when fetching sticker data from a URL and set the sticker mimetype and IsAnimated flag appropriately.

[sourcery-ai]

Reviewer's Guide

Refactors sticker sending to avoid re-encoding existing WebP data, properly handle animated WebP stickers, and simplify the upload path, while explicitly setting WebP mimetype and animation flag.

Sequence diagram for updated SendSticker WebP handling

sequenceDiagram
  actor User
  participant sendService
  participant HTTPServer
  participant WhatsAppClient as whatsmeowClient
  participant waE2E as waE2EMessage

  User->>sendService: SendSticker(data, instance)
  sendService->>sendService: ensureClientConnected(instance.Id)
  sendService->>HTTPServer: http.Get(data.Sticker)
  HTTPServer-->>sendService: *resp.Body*
  sendService->>sendService: io.ReadAll(resp.Body)
  alt isWebP(raw)
    sendService->>sendService: isWebP(raw)
    sendService->>sendService: isAnimatedWebP(raw)
    note over sendService: filedata = raw
  else nonWebP
    sendService->>sendService: convertBytesToWebP(raw)
    note over sendService: filedata = converted WebP
  end
  sendService->>WhatsAppClient: Upload(context.Background(), filedata, whatsmeow.MediaImage)
  WhatsAppClient-->>sendService: UploadResponse
  sendService->>waE2E: new StickerMessage
  note over waE2E: Mimetype = image/webp
  alt isAnimated == true
    note over waE2E: IsAnimated = true
  end
  sendService->>sendService: SendMessage(instance, Message, "StickerMessage", SendDataStruct)
  sendService-->>User: MessageSendStruct

Loading

File-Level Changes

Change	Details	Files
Add in-memory image-to-WebP conversion and WebP/animated-WebP detection helpers to separate concerns and enable conditional re-encoding.	Introduce convertBytesToWebP to decode non-WebP image bytes and encode them as WebP with configured quality settings. Add isWebP helper that checks RIFF/WEBP magic bytes to identify WebP inputs. Add isAnimatedWebP helper that detects animation via VP8X animation flag and ANIM chunk presence, using isWebP as a guard.	pkg/sendMessage/service/send_service.go
Rework SendSticker to always fetch the sticker bytes, only re-encode when input is not WebP, upload the resulting WebP, and set mimetype and animation metadata explicitly.	Replace the previous URL-conditional convertToWebP path with an early URL validation check and an HTTP GET to fetch sticker bytes unconditionally for valid URLs. Use isWebP to bypass re-encoding for existing WebP stickers and isAnimatedWebP to determine if the sticker is animated, storing the result in a local isAnimated flag. Fallback to convertBytesToWebP for non-WebP inputs, propagating errors when conversion fails. Upload the prepared filedata via client.Upload and handle errors, storing the response in uploaded. Build a StickerMessage struct with fixed mimetype "image/webp" and set IsAnimated=true when appropriate before sending the message via SendMessage.	pkg/sendMessage/service/send_service.go

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[sourcery-ai]

Hey - I've left some high level feedback:

• Consider using an HTTP client with timeouts and/or the existing request context instead of bare http.Get, so sticker fetches can’t hang indefinitely and can be cancelled along with the send operation.
• The WebP detection helpers currently convert header slices to strings; you could avoid unnecessary allocations and be more explicit by using byte comparisons (e.g. bytes.Equal(data[0:4], []byte("RIFF"))) for magic and chunk IDs.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Consider using an HTTP client with timeouts and/or the existing request context instead of bare `http.Get`, so sticker fetches can’t hang indefinitely and can be cancelled along with the send operation.
- The WebP detection helpers currently convert header slices to strings; you could avoid unnecessary allocations and be more explicit by using byte comparisons (e.g. `bytes.Equal(data[0:4], []byte("RIFF"))`) for magic and chunk IDs.

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