bitchat-android/docs/file_transfer.md

Bitchat Bluetooth File Transfer: Images, Audio, and Generic Files (with Interactive Features)

This document is the exhaustive implementation guide for Bitchat’s Bluetooth file transfer protocol for voice notes (audio) and images, including interactive features like waveform seeking. It describes the on‑wire packet format (both v1 and v2), fragmentation/progress/cancellation, sender/receiver behaviors, and the complete UX we implemented in the Android client so that other implementers can interoperate and match the user experience precisely.

Protocol Versions:

• v1: Original envelope with a 2-byte payload length.
• v2: Extended envelope with a 4-byte payload length.
• Public and legacy raw file-transfer envelopes use v2. A Noise-encrypted private envelope may use v1 when its ciphertext fits, and source routing upgrades the final envelope to v2.
• The payload-length field is not the practical transfer limit. Private-media admission is limited to 256 final fragments after route, signature, encryption, and envelope overhead. Generic/public outbound fragmentation retains the UInt16 wire range; receivers may impose a lower safety bound.

Interactive Features:

• Waveform Seeking: Tap anywhere on audio waveforms to jump to that playback position
• Bounded Transfer Support: v2 removes the 16-bit envelope-length limit, while bounded fragmentation protects receivers from unbounded reassembly.
• Unified Experience: Identical UX between platforms with enhanced user control

The guide is organized into:

• Protocol overview (BitchatPacket + File Transfer payload)
• Fragmentation, progress reporting, and cancellation
• Receive path, validation, and persistence
• Sender path (audio + images)
• Interactive features (audio waveform seeking)
• UI/UX behavior (recording, sending, playback, image rendering)
• File inventory (source files and their roles)

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1) Protocol Overview

Bitchat BLE transport carries application messages inside the common BitchatPacket envelope. File transfer reuses the same envelope as public and private messages, with a distinct type and a TLV‑encoded payload.

1.1 BitchatPacket envelope

Fields (subset relevant to file transfer):

• version: UByte — protocol version (1 for v1, 2 for v2 with extended payload length).
• type: UByte — public file transfer uses MessageType.FILE_TRANSFER (0x22); private file transfer uses outer MessageType.NOISE_ENCRYPTED (0x11).
• senderID: ByteArray (8) — 8‑byte binary peer ID.
• recipientID: ByteArray (8) — 8‑byte recipient. For public: SpecialRecipients.BROADCAST (0xFF…FF); for private: the target peer’s 8‑byte ID.
• timestamp: ULong — milliseconds since epoch.
• payload: ByteArray — the public form contains the file TLV directly. The private form contains Noise ciphertext which authenticates payload type FILE_TRANSFER (0x20) followed by the same file TLV.
• signature: ByteArray? — packet signature added by the mesh send path.
• ttl: UByte — hop TTL (we use MAX_TTL for broadcast, 7 for private).

Envelope creation and broadcast paths are implemented in:

• app/src/main/java/com/bitchat/android/mesh/BluetoothMeshService.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/mesh/BluetoothMeshService.kt)
• app/src/main/java/com/bitchat/android/mesh/BluetoothConnectionManager.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/mesh/BluetoothConnectionManager.kt)
• app/src/main/java/com/bitchat/android/mesh/PacketProcessor.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/mesh/PacketProcessor.kt)

Private sends encrypt the complete file TLV as Noise payload 0x20 before outer fragmentation. See PRIVATE_MEDIA_V1.md for the capability and mixed- client interoperability contract.

1.2 Binary Protocol Extensions (v2)

v2 Header Format Changes

v1 Format (original):

Header (13 bytes):
Version: 1 byte
Type: 1 byte
TTL: 1 byte
Timestamp: 8 bytes
Flags: 1 byte
PayloadLength: 2 bytes (big-endian, max 64 KiB)

v2 Format (extended):

Header (15 bytes):
Version: 1 byte (set to 2 for v2 packets)
Type: 1 byte
TTL: 1 byte
Timestamp: 8 bytes
Flags: 1 byte
PayloadLength: 4 bytes (big-endian, max ~4 GiB)

• Header Size: Increased from 13 to 15 bytes.
• Payload Length Field: Extended from 16 bits (2 bytes) to 32 bits (4 bytes). That is the field's theoretical range, not the permitted mesh reassembly size.
• Backward Compatibility: Clients must support both v1 and v2 decoding.
• Implementation: See BinaryProtocol.kt with getHeaderSize(version) logic.

Use cases for v2

v2 carries file payloads that exceed the v1 envelope-length field and carries source-route metadata. It does not imply multi-gigabyte mesh transfer support.

Interoperability Requirements

• Clients receiving v2 packets must decode 4-byte PayloadLength fields.
• Clients sending file transfers should preferentially use v2 format.
• Fragmentation still applies. Each serialized mesh fragment fits the 512-byte transport threshold; the data portion is at most 469 bytes and becomes smaller when recipient or source-route overhead is present.

1.3 File Transfer TLV payload (BitchatFilePacket)

The file payload is a TLV structure with mixed length field sizes to support large contents efficiently.

• Defined in app/src/main/java/com/bitchat/android/model/BitchatFilePacket.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/model/BitchatFilePacket.kt)

Canonical TLVs (v2 spec):

• 0x01 FILE_NAME — UTF‑8 bytes
  • Encoding: type(1) + len(2) + value
• 0x02 FILE_SIZE — 4 bytes (UInt32, big‑endian)
  • Encoding: type(1) + len(2=4) + value(4)
  • Note: v1 used 8 bytes (UInt64). v2 standardizes to 4 bytes. See Legacy Compatibility below.
• 0x03 MIME_TYPE — UTF‑8 bytes (e.g., image/jpeg, audio/mp4, application/pdf)
  • Encoding: type(1) + len(2) + value
• 0x04 CONTENT — raw file bytes
  • Encoding: type(1) + len(4) + value(len)
  • Exactly one CONTENT TLV per file payload in v2 (no TLV‑level chunking); overall packet fragmentation happens at the transport layer.

Encoding rules:

• Standard TLVs use 1 byte type + 2 bytes big‑endian length + value.
• CONTENT uses a 4‑byte big‑endian length to allow payloads well beyond 64 KiB.
• With the v2 envelope (4-byte payload length), CONTENT can exceed 64 KiB, but sender and receiver fragmentation policies still bound practical transfers.
• Implementations should validate TLV boundaries; decoding should fail fast on malformed structures.

Decoding rules (v2):

• Accept the canonical TLVs above. Unknown TLVs should be ignored or cause failure per implementation policy (current Android rejects unknown types).
• FILE_SIZE expects len=4 and is parsed as UInt32; receivers may upcast to 64‑bit internally.
• CONTENT expects a 4‑byte length field and a single occurrence; if multiple CONTENT TLVs are present, concatenate in order (defensive tolerance).
• If FILE_SIZE is missing, receivers may fall back to content.size.
• If MIME_TYPE is missing, default to application/octet-stream.

Legacy Compatibility (optional, for mixed‑version meshes):

• FILE_SIZE (0x02): Some legacy senders used 8‑byte UInt64. Decoders MAY accept len=8 and clamp to 32‑bit if needed.
• CONTENT (0x04): Legacy payloads might have used a 2‑byte TLV length with multiple CONTENT chunks. Decoders MAY support concatenating multiple CONTENT TLVs with 2‑byte lengths if encountered.

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2) Fragmentation, Progress, and Cancellation

2.1 Fragmentation

File transfers reuse the mesh broadcaster’s fragmentation logic:

• BluetoothPacketBroadcaster checks if the serialized envelope exceeds the configured MTU and splits it into fragments via FragmentManager.
• Fragments are sent with a short inter-fragment delay (currently 20 ms).
• When only one fragment is needed, send as a single packet.
• Android receivers reject fragment sets declaring more than 256 fragments. Private senders use that same 256-fragment limit and calculate it from the exact final routed, signed, and encrypted packet before creating a local echo. Generic/public outbound planning retains its prior UInt16 count range, so this private-media migration does not silently change public sending.

2.2 Transfer ID and progress events

We derive a deterministic transfer ID to track progress:

• transferId = sha256Hex(packet.payload) (hex string of the file TLV payload).

The broadcaster emits progress events to a shared flow:

• TransferProgressManager.start(id, totalFragments)
• TransferProgressManager.progress(id, sent, totalFragments)
• TransferProgressManager.complete(id, totalFragments)

The UI maps transferId → messageId, then updates DeliveryStatus.PartiallyDelivered(sent, total) as events arrive; when complete, switches to Delivered.

2.3 Cancellation

Transfers are cancellable mid‑flight:

• The broadcaster keeps a transferId → Job map and cancels the job to stop sending remaining fragments.
• API path:
  • BluetoothPacketBroadcaster.cancelTransfer(transferId)
  • Exposed via BluetoothConnectionManager.cancelTransfer and BluetoothMeshService.cancelFileTransfer.
  • ChatViewModel.cancelMediaSend(messageId) resolves messageId → transferId and cancels.
• UX: tapping the “X” on a sending media removes the message from the timeline immediately.

Implementation files:

• app/src/main/java/com/bitchat/android/mesh/BluetoothPacketBroadcaster.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/mesh/BluetoothPacketBroadcaster.kt)
• app/src/main/java/com/bitchat/android/mesh/BluetoothConnectionManager.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/mesh/BluetoothConnectionManager.kt)
• app/src/main/java/com/bitchat/android/mesh/BluetoothMeshService.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/mesh/BluetoothMeshService.kt)
• app/src/main/java/com/bitchat/android/ui/ChatViewModel.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/ui/ChatViewModel.kt)

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3) Receive Path and Persistence

Receiver dispatch is in MessageHandler:

• For both broadcast and private paths we try BitchatFilePacket.decode(payload). If it decodes:
  • The file is persisted under app files with type‑specific subfolders:
    • Audio: files/voicenotes/incoming/
    • Image: files/images/incoming/
    • Other files: files/files/incoming/
  • Filename strategy:
    • Prefer the transmitted fileName when present; sanitize path separators.
    • Ensure uniqueness by appending " (n)" before the extension when a name exists already.
    • If fileName is absent, derive from MIME with a sensible default extension.
  • MIME determines extension hints (.m4a, .mp3, .wav, .ogg for audio; .jpg, .png, .webp for images; otherwise based on MIME or .bin).
• A synthetic chat message is created with content markers pointing to the local path:
  • Audio: "[voice] /abs/path/to/file"
  • Image: "[image] /abs/path/to/file"
  • Other: "[file] /abs/path/to/file"
  • senderPeerID is set to the origin, isPrivate set appropriately.

Files:

• app/src/main/java/com/bitchat/android/mesh/MessageHandler.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/mesh/MessageHandler.kt)

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4) Sender Path

4.1 Audio (Voice Notes)

1. Capture

   • Hold‑to‑record mic button starts MediaRecorder with AAC in MP4 (audio/mp4).
   • Sample rate: 44100 Hz, channels: mono, bitrate: ~32 kbps (to reduce payload size for BLE).
   • On release, we pad 500 ms before stopping to avoid clipping endings.
   • Files saved under files/voicenotes/outgoing/voice_YYYYMMDD_HHMMSS.m4a.

2. Local echo

   • Public/channel sends create their timeline entry before dispatch.
   • Private sends first finish capability policy and exact final-fragment admission. They create the local echo and progress mapping only for an admitted plan, then atomically commit that prepared plan.

3. Packet creation

   • Build a BitchatFilePacket:
     • fileName: basename (e.g., voice_… .m4a)
     • fileSize: file length
     • mimeType: audio/mp4
     • content: full bytes; final-packet admission determines whether it fits the 256-fragment limit.
   • Encode TLV; compute transferId = sha256Hex(payload).
   • Map transferId → messageId for UI progress.

4. Send

   • Public: BluetoothMeshService.sendFileBroadcast(filePacket).
   • Private UI: prepareFilePrivate(...), followed by one-shot commit of a ready plan. The non-interactive sendFilePrivate(...) entry point commits only encrypted-ready plans and never silently chooses a legacy downgrade.
   • Broadcaster handles fragmentation and progress emission.

5. Mixed-client private migration

   • A verified legacy recipient with no private-media capability requires a user warning and one-shot consent.
   • Approval rechecks policy. The fallback is recipient-directed raw 0x22, visible to relays, and must have a valid Ed25519 packet signature.
   • No authenticated Noise identity starts a handshake without a local echo or media send; the user retries after it completes. Signing failure or a private plan above 256 final fragments aborts without an echo or send.

6. Waveform

   • We extract a 120‑bin waveform from the recorded file (the same extractor used for the receiver) and cache by file path, so sender and receiver waveforms are identical.

Core files:

• app/src/main/java/com/bitchat/android/ui/ChatViewModel.kt (sendVoiceNote) (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/ui/ChatViewModel.kt)
• app/src/main/java/com/bitchat/android/model/BitchatFilePacket.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/model/BitchatFilePacket.kt)
• app/src/main/java/com/bitchat/android/mesh/BluetoothMeshService.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/mesh/BluetoothMeshService.kt)
• app/src/main/java/com/bitchat/android/features/voice/VoiceRecorder.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/features/voice/VoiceRecorder.kt)
• app/src/main/java/com/bitchat/android/features/voice/Waveform.kt (cache + extractor) (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/features/voice/Waveform.kt)

4.2 Images

1. Selection and processing

   • System picker (Storage Access Framework) with GetContent() (image/*). No storage permission required.
   • Selected image is downscaled so longest edge is 512 px; saved as JPEG (85% quality) under files/images/outgoing/img_<timestamp>.jpg.
   • Helper: ImageUtils.downscaleAndSaveToAppFiles(context, uri, maxDim=512).

2. Local echo

   • Insert a message with "[image] <path>" in the current context (public/channel/private).

3. Packet creation

   • Build BitchatFilePacket with mime image/jpeg and file content.
   • Encode TLV + compute transferId and map to messageId.

4. Send

   • Same paths as audio (broadcast/private), including fragmentation and progress emission.

Core files:

• app/src/main/java/com/bitchat/android/features/media/ImageUtils.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/features/media/ImageUtils.kt)
• app/src/main/java/com/bitchat/android/ui/ChatViewModel.kt (sendImageNote) (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/ui/ChatViewModel.kt)
• app/src/main/java/com/bitchat/android/mesh/BluetoothMeshService.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/mesh/BluetoothMeshService.kt)

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5) UI / UX Details

This section specifies exactly what users see and how inputs behave, so alternative clients can match the experience.

5.1 Message input area

• The input field remains mounted at all times to prevent the IME (keyboard) from collapsing during long‑press interactions (recording). We overlay recording UI atop the text field rather than replacing it.
• While recording, the text caret (cursor) is hidden by setting a transparent cursor brush.
• Mentions and slash commands are styled with a monospace look and color coding.

Files:

• app/src/main/java/com/bitchat/android/ui/InputComponents.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/ui/InputComponents.kt)

5.2 Recording UX

• Hold the mic button to start recording. Recording runs until release, then we pad 500 ms and stop.
• While recording, a dense, real‑time scrolling waveform overlays the input showing live audio; a timer is shown to the right.
  • Component: RealtimeScrollingWaveform (dense bars, ~240 columns, ~20 FPS) in app/src/main/java/com/bitchat/android/ui/media/RealtimeScrollingWaveform.kt.
  • The keyboard stays visible; the caret is hidden.
• On release, we immediately show a local echo message for the voice note and start sending.

5.3 Voice note rendering

• Displayed with a header (nickname + timestamp) then the waveform + controls row.
• Waveform
  • A 120‑bin static waveform is rendered per file, identical for sender and receiver, extracted from the actual audio file.
  • During send, the waveform fills left→right in blue based on fragment progress.
  • During playback, the waveform fills left→right in green based on player progress.
• Controls
  • Play/Pause toggle to the left of the waveform; duration text to the right.
• Cancel sending
  • While sending a voice note, a round “X” cancel button appears to the right of the controls. Tapping cancels the transfer mid‑flight.

Files:

• app/src/main/java/com/bitchat/android/ui/MessageComponents.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/ui/MessageComponents.kt)
• app/src/main/java/com/bitchat/android/ui/media/WaveformViews.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/ui/media/WaveformViews.kt)
• app/src/main/java/com/bitchat/android/features/voice/Waveform.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/features/voice/Waveform.kt)

5.4 Image sending UX

• A circular “+” button next to the mic opens the system image picker. After selection, we downscale to 512 px longest edge and show a local echo; the send begins immediately.
• Progress visualization
  • Instead of a linear progress bar, we reveal the image block‑by‑block (modem‑era homage).
  • The image is divided into a constant grid (default 24×16), and the blocks are rendered in order based on fragment progress; there are no gaps between tiles.
  • The cancel “X” button overlays the top‑right corner during sending.
• On cancel, the message is removed from the chat immediately.

Files:

• app/src/main/java/com/bitchat/android/ui/media/ImagePickerButton.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/ui/media/ImagePickerButton.kt)
• app/src/main/java/com/bitchat/android/features/media/ImageUtils.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/features/media/ImageUtils.kt)
• app/src/main/java/com/bitchat/android/ui/media/BlockRevealImage.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/ui/media/BlockRevealImage.kt)
• app/src/main/java/com/bitchat/android/ui/MessageComponents.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/ui/MessageComponents.kt)

5.5 Image receiving UX

• Received images render fully with rounded corners and are left‑aligned like text messages.
• Tapping an image opens a fullscreen viewer with an option to save to the device Downloads via MediaStore.

Files:

• app/src/main/java/com/bitchat/android/ui/media/FullScreenImageViewer.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/ui/media/FullScreenImageViewer.kt)

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5.6 Interactive Audio Features

5.6.1 Waveform Seeking

• Audio waveforms in chat messages are fully interactive: users can tap anywhere on the waveform to jump to that position in the audio playback.
• On tap, the seek position is calculated as a fraction of the waveform width (0.0 = beginning, 1.0 = end).
• This works for both playing and paused audio states.
• The MediaPlayer is seeked to the calculated position immediately, with visual feedback via progress bar update.
• Tapping provides precise control - e.g., tap 25% through waveform jumps to 25% through audio.
• No haptic feedback or visual indicator; the progress bar update serves as immediate feedback.

Waveform Canvas Implementation:

• WaveformCanvas uses pointerInput with detectTapGestures to capture tap events.
• Tap position is converted to a fraction: position.x / size.width.toFloat().
• Clamped to 0.0-1.0 range for safety.
• onSeek callback is invoked with the calculated position fraction.
• Only enabled when onSeek is provided (disabled for sending in progress).

VoiceNotePlayer Seeking:

• Accepts position fraction (0.0-1.0) and converts to milliseconds: seekMs = (position * durationMs).toInt().
• Calls MediaPlayer.seekTo(seekMs) to jump to the exact position.
• Updates progress state immediately for UI responsiveness even before playback reaches the new position.

Files:

• app/src/main/java/com/bitchat/android/ui/MessageComponents.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/ui/MessageComponents.kt) — VoiceNotePlayer with seekTo function
• app/src/main/java/com/bitchat/android/ui/media/WaveformViews.kt (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/ui/media/WaveformViews.kt) — Interactive WaveformCanvas with tap handling

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6) Edge Cases and Notes

• Filename collisions on receiver: prefer the sender‑supplied name if present; always uniquify with a (n) suffix before the extension to prevent overwrites.
• Path markers in messages
  • We use simple content markers: "[voice] <abs path>", "[image] <abs path>", "[file] <abs path>" for local rendering. These are not sent on the wire; the actual file bytes are inside the TLV payload.
• Progress math for images relies on (sent / total) from TransferProgressManager (fragment‑level granularity). The block grid density can be tuned; currently 24×16.
• Private vs public: both use the same file TLV. Private media wraps it in a Noise payload of type 0x20; public media carries it directly in a 0x22 packet.
• BLE timing: there is a 20 ms inter-fragment delay. Adjust as needed for your radio stack while maintaining compatibility.

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7) File Inventory (Added/Changed)

Core protocol and transport:

• app/src/main/java/com/bitchat/android/model/BitchatFilePacket.kt — TLV payload model + encode/decode. (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/model/BitchatFilePacket.kt)
• app/src/main/java/com/bitchat/android/mesh/BluetoothMeshService.kt — packet creation and broadcast for file messages. (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/mesh/BluetoothMeshService.kt)
• app/src/main/java/com/bitchat/android/mesh/BluetoothPacketBroadcaster.kt — fragmentation, progress, cancellation via transfer jobs. (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/mesh/BluetoothPacketBroadcaster.kt)
• app/src/main/java/com/bitchat/android/mesh/TransferProgressManager.kt — progress events bus. (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/mesh/TransferProgressManager.kt)
• app/src/main/java/com/bitchat/android/mesh/MessageHandler.kt — receive path: decode, persist to files, create chat messages. (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/mesh/MessageHandler.kt)

Audio capture and waveform:

• app/src/main/java/com/bitchat/android/features/voice/VoiceRecorder.kt — MediaRecorder wrapper. (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/features/voice/VoiceRecorder.kt)
• app/src/main/java/com/bitchat/android/features/voice/Waveform.kt — cache + extractor + resampler. (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/features/voice/Waveform.kt)
• app/src/main/java/com/bitchat/android/ui/media/WaveformViews.kt — Compose waveform preview components. (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/ui/media/WaveformViews.kt)

Image pipeline:

• app/src/main/java/com/bitchat/android/features/media/ImageUtils.kt — downscale and save to app files. (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/features/media/ImageUtils.kt)
• app/src/main/java/com/bitchat/android/ui/media/ImagePickerButton.kt — SAF picker button. (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/ui/media/ImagePickerButton.kt)
• app/src/main/java/com/bitchat/android/ui/media/BlockRevealImage.kt — block‑reveal progress renderer (no gaps, dense grid). (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/ui/media/BlockRevealImage.kt)

Recording overlay:

• app/src/main/java/com/bitchat/android/ui/media/RealtimeScrollingWaveform.kt — dense, real‑time scrolling waveform during recording. (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/ui/media/RealtimeScrollingWaveform.kt)

UI composition and view model coordination:

• app/src/main/java/com/bitchat/android/ui/InputComponents.kt — input field, overlays (recording), picker button, mic. (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/ui/InputComponents.kt)
• app/src/main/java/com/bitchat/android/ui/MessageComponents.kt — message rendering for text/audio/images including progress UIs and cancel overlays. (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/ui/MessageComponents.kt)
• app/src/main/java/com/bitchat/android/ui/ChatViewModel.kt — sendVoiceNote/sendImageNote, progress mapping, cancelMediaSend. (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/ui/ChatViewModel.kt)
• app/src/main/java/com/bitchat/android/ui/MessageManager.kt — add/remove/update messages across main, private, and channels. (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/ui/MessageManager.kt)

Fullscreen image:

• app/src/main/java/com/bitchat/android/ui/media/FullScreenImageViewer.kt — fullscreen viewer + save to Downloads. (/Users/cc/git/bitchat-android/app/src/main/java/com/bitchat/android/ui/media/FullScreenImageViewer.kt)

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8) Implementation Checklist for Other Clients

1. Implement v2 protocol support: Support both v1 (2-byte payload length) and v2 (4-byte payload length) packet decoding. Use v2 format for file transfer packets to enable large file transfers.
2. Implement BitchatFilePacket TLV exactly as specified:
   • FILE_NAME and MIME_TYPE: type(1) + len(2) + value
   • FILE_SIZE: type(1) + len(2=4) + value(4, UInt32 BE)
   • CONTENT: type(1) + len(4) + value
3. For public media, embed the TLV in FILE_TRANSFER (0x22). For private media, prefix the TLV with Noise payload type 0x20, encrypt it for the recipient, and put the ciphertext in NOISE_ENCRYPTED (0x11).
4. Fragment, send, and report progress using a transfer ID derived from sha256(payload) so the UI can map progress to a message.
5. Support cancellation at the fragment sender: stop sending remaining fragments and propagate a cancel to the UI (we remove the message).
6. On receive, decode TLV, persist to an app directory (separate audio/images/other), and create a chat message with content marker "[voice] path", "[image] path", or "[file] path" for local rendering.
7. Audio sender and receiver should use the same waveform extractor so visuals match; a 120‑bin histogram is a good balance.
8. Implement interactive waveform seeking: Tap waveforms to jump to that audio position. Calculate tap position as fraction (0.0-1.0) of waveform width.
9. For images, optionally downscale to keep TLV small; JPEG 85% at 512 px longest edge is a good baseline.
10. Mirror the UX:
    • Recording overlay that does not collapse the IME; hide the caret while recording; add 500 ms end padding.
    • Voice: waveform fill for send/playback; cancel overlay; tap-to-seek support.
    • Images: dense block‑reveal with no gaps during sending; cancel overlay; fullscreen viewer with save.
    • Generic files: render as a file pill with icon + filename; support open/save via the host OS.

Following the above should produce an interoperable and matching experience across platforms.