IPC and RPC Mechanisms

Relevant source files

The following files were used as context for generating this wiki page:

• LibDalamud/Patching/Rpc/IRpc.cs
• LibDalamud/Patching/Rpc/Implementations/InProcessRpc.cs
• LibDalamud/Patching/Rpc/Implementations/SharedMemoryRpc.cs
• LibDalamud/Patching/IndexedZiPatch/IndexedZiPatchIndexRemoteInstaller.cs
• LibDalamud/Game/Patch/PatchInstaller.cs
• LibDalamud/Patching/RemotePatchInstaller.cs
• LibDalamud/Patching/Rpc/PatcherIpcStartInstall.cs

The IPC (Inter-Process Communication) and RPC (Remote Procedure Call) mechanisms in WebLaunch provide a structured way for different application components to communicate across process boundaries. These systems primarily support patch installation, game management, and background worker coordination.

This architecture enables the main launcher to offload resource-intensive or privileged tasks—such as file patching—to separate worker processes while maintaining real-time progress tracking and control.

System Architecture

The project implements a multi-layered communication stack. At the base is the IRpc interface, which abstracts the transport layer. Implementations include SharedMemoryRpc for cross-process communication and InProcessRpc for local testing or single-process execution.

Communication Layers

• Transport Layer: Handles raw data transmission using shared memory buffers or direct object references.
• Protocol Layer: Defines the PatcherIpcEnvelope and PatcherIpcOpCode to categorize messages.
• Service Layer: High-level handlers like PatchInstaller and IndexedZiPatchIndexRemoteInstaller that execute specific business logic based on RPC calls.

Sources: LibDalamud/Patching/Rpc/IRpc.cs, LibDalamud/Game/Patch/PatchInstaller.cs:51-86

RPC Implementation Overview

The following diagram shows the relationship between the RPC interfaces and their concrete implementations.

Patching RPC Workflow

The patching system utilizes RPC to manage the lifecycle of a game update. The PatchInstaller class starts a separate XIVLauncher.PatchInstaller.exe process and establishes a connection using a unique RPC channel name.

Connection Sequence

1. The PatchInstaller generates a unique GUID-based channel name.
2. It launches the external patcher process, passing the channel name as a command-line argument.
3. The external process connects to the shared memory buffer and sends a Hello opcode.
4. The main process receives Hello and transitions its state to Ready.

Sources: LibDalamud/Game/Patch/PatchInstaller.cs:51-78, LibDalamud/Patching/RemotePatchInstaller.cs:25-39

Indexed ZiPatch Remote Installer

For complex patching operations involving indexed files, the IndexedZiPatchIndexRemoteInstaller uses a specialized RpcBuffer from the SharedMemory library. This allows for synchronous-like Task calls across processes.

Worker Opcodes and Results

The system uses specific opcodes to instruct the worker process.

Opcode	Description
Construct	Initializes a new patcher instance with a provided index.
VerifyFiles	Triggers a file integrity check in the worker process.
Install	Executes the actual patching/installation task.
CancelTask	Aborts a currently running task using a Token ID.
DisposeAndExit	Cleans up the worker and terminates the process.

Sources: LibDalamud/Patching/IndexedZiPatch/IndexedZiPatchIndexRemoteInstaller.cs:411-435

Data Serialization

The WorkerSubprocessBody inner class listens for requests on the RpcBuffer. It uses a BinaryReader to deserialize incoming byte arrays into command opcodes and parameters. Once the task is complete, it writes a WorkerResultCode back to the buffer.

Sources: LibDalamud/Patching/IndexedZiPatch/IndexedZiPatchIndexRemoteInstaller.cs:228-360

RPC Data Structures

PatcherIpcEnvelope

This is the primary container for all RPC messages.

• OpCode: A PatcherIpcOpCode enum determining the purpose of the message.
• Data: An object containing the payload (e.g., PatcherIpcStartInstall or DirectoryInfo).

Sources: LibDalamud/Game/Patch/PatchInstaller.cs:88-105

PatcherIpcStartInstall

Contains the necessary context to begin a patching operation.

Field	Type	Description
PatchFile	FileInfo	The local patch file to be applied.
Repo	Repository	The game repository (Boot, Ffxiv, etc.) being patched.
VersionId	string	The version string to be written to the .ver file.
GameDirectory	DirectoryInfo	The path to the game installation.
KeepPatch	bool	Whether to delete the patch file after successful installation.

Sources: LibDalamud/Patching/Rpc/PatcherIpcStartInstall.cs:8-14

Summary

The RPC and IPC mechanisms in WebLaunch allow the software to maintain a responsive UI while performing heavy disk operations in a separate process. By abstracting the transport layer through IRpc, the system supports both modular testing and secure, high-performance cross-process communication via shared memory. This structure ensures that patch installation is isolated, verifiable, and manageable through a standardized protocol of opcodes and envelopes.