gRPC API Reference

The Soul Kernel exposes its core functionality through a gRPC API, enabling language-agnostic communication between the Rust kernel and various shells (iOS, Unity, Physical AI).

Overview

The gRPC API provides three core operations:

Init: Initialize a new Soul session
Ask: Process queries with streaming responses
Remember: Store memories in the Soul’s memory graph

Service Definition

service SoulKernel {
  rpc Init(InitRequest) returns (InitResponse);
  rpc Ask(AskRequest) returns (stream AskResponse);
  rpc Remember(RememberRequest) returns (RememberResponse);
}

Endpoints

Init - Create a Soul Session

Initialize a new Soul with a name and optional metadata. Request:

message InitRequest {
  string soul_name = 1;          // Name for the Soul
  map<string, string> metadata = 2; // Optional metadata
}

Response:

message InitResponse {
  string soul_id = 1;        // Unique Soul identifier
  string session_token = 2;  // Session authentication token
  int64 created_at = 3;      // Unix timestamp
}

Example:

let request = InitRequest {
    soul_name: "Assistant".to_string(),
    metadata: HashMap::from([
        ("platform", "ios"),
        ("version", "1.0.0"),
    ]),
};

Ask - Query the Soul

Send queries to the Soul and receive streaming responses. Supports progressive text generation, thinking status, and skill execution feedback. Request:

message AskRequest {
  string soul_id = 1;           // Soul ID from Init
  string session_token = 2;     // Session token from Init
  string query = 3;             // User's query
  repeated string skill_hints = 4; // Optional skill suggestions
}

Response (Streaming):

message AskResponse {
  oneof content {
    string text_chunk = 1;        // Partial text response
    ThinkingStatus thinking = 2;  // Processing status
    SkillExecution skill = 3;     // Skill execution info
  }
  ResponseMetadata metadata = 10; // Response metadata
}

Response Types:

Text Chunks: Progressive text generation

content: TextChunk("Hello, ")
content: TextChunk("how can ")
content: TextChunk("I help?")

Thinking Status: Processing feedback

message ThinkingStatus {
  string status = 1;   // Status message
  float progress = 2;  // Progress (0.0-1.0)
}

Skill Execution: Skill activity feedback

message SkillExecution {
  string skill_name = 1;
  string status = 2;
  map<string, string> results = 3;
}

Remember - Store Memories

Store new memories in the Soul’s memory graph. Request:

message RememberRequest {
  string soul_id = 1;
  string session_token = 2;
  Memory memory = 3;
}

message Memory {
  string content = 1;              // Memory content
  repeated float embedding = 2;    // Vector embedding
  map<string, string> metadata = 3; // Memory metadata
}

Response:

message RememberResponse {
  string memory_id = 1;    // Unique memory identifier
  bool stored = 2;         // Storage success
  int64 stored_at = 3;     // Unix timestamp
}

Common Types

ResponseMetadata

All responses include metadata for observability:

message ResponseMetadata {
  string correlation_id = 1;  // Request correlation ID
  int64 timestamp = 2;        // Response timestamp
  int32 latency_ms = 3;       // Processing latency
  string kernel_version = 4;  // Kernel version
}

Client Examples

Rust Client

use soul_kernel::v1::soul_kernel_client::SoulKernelClient;

// Connect to server
let mut client = SoulKernelClient::connect("http://localhost:50051").await?;

// Initialize Soul
let init_resp = client.init(InitRequest {
    soul_name: "MyCompanion".to_string(),
    metadata: HashMap::new(),
}).await?;

// Ask a question
let mut stream = client.ask(AskRequest {
    soul_id: init_resp.soul_id.clone(),
    session_token: init_resp.session_token.clone(),
    query: "What's the weather like?".to_string(),
    skill_hints: vec!["weather".to_string()],
}).await?.into_inner();

// Process streaming response
while let Some(response) = stream.message().await? {
    match response.content {
        Some(Content::TextChunk(text)) => print!("{}", text),
        Some(Content::Thinking(status)) => println!("🤔 {}", status.status),
        Some(Content::Skill(exec)) => println!("⚡ {}: {}", exec.skill_name, exec.status),
        None => {}
    }
}

Python Client

import grpc
import soul_kernel_pb2 as sk
import soul_kernel_pb2_grpc as sk_grpc

# Connect to server
channel = grpc.insecure_channel('localhost:50051')
client = sk_grpc.SoulKernelStub(channel)

# Initialize Soul
init_resp = client.Init(sk.InitRequest(
    soul_name="PyCompanion",
    metadata={"lang": "python"}
))

# Ask a question
responses = client.Ask(sk.AskRequest(
    soul_id=init_resp.soul_id,
    session_token=init_resp.session_token,
    query="Tell me a joke"
))

# Process streaming response
for response in responses:
    if response.HasField('text_chunk'):
        print(response.text_chunk, end='')

JavaScript/TypeScript Client

const client = new SoulKernelClient('localhost:50051');

// Initialize Soul
const { soulId, sessionToken } = await client.init({
  soulName: 'JSCompanion',
  metadata: { platform: 'web' }
});

// Ask with streaming
const stream = client.ask({
  soulId,
  sessionToken,
  query: 'What can you do?'
});

for await (const response of stream) {
  if (response.textChunk) {
    process.stdout.write(response.textChunk);
  }
}

Error Handling

The gRPC API uses standard gRPC status codes:

Code	Meaning	Example
`OK`	Success	Normal response
`INVALID_ARGUMENT`	Bad request	Missing soul_id
`UNAUTHENTICATED`	Invalid session	Expired token
`NOT_FOUND`	Soul not found	Unknown soul_id
`RESOURCE_EXHAUSTED`	Rate limited	Too many requests
`INTERNAL`	Server error	Database failure

Performance

Latency: p95 < 1s (online), < 6s (offline)
Streaming: First chunk typically arrives within 100-200ms
Throughput: Supports 1000+ concurrent connections
Binary Size: Server binary < 20MB

Security

Session tokens expire after 24 hours
All responses include correlation IDs for tracing
TLS encryption recommended for production
Rate limiting per soul_id

Proto File Location

The complete protobuf definition is located at:

kernel/proto/soul_kernel.proto

To generate client code for your language:

protoc --proto_path=kernel/proto \
       --<lang>_out=. \
       --<lang>-grpc_out=. \
       kernel/proto/soul_kernel.proto

Change Log

Date	Version	Changes
2025-06-12	0.1.0	Initial gRPC API implementation with Init/Ask/Remember

API Reference

Documentation Index

​gRPC API Reference

​Overview

​Service Definition

​Endpoints

​Init - Create a Soul Session

​Ask - Query the Soul

​Remember - Store Memories

​Common Types

​ResponseMetadata

​Client Examples

​Rust Client

​Python Client

​JavaScript/TypeScript Client

​Error Handling

​Performance

​Security

​Proto File Location

​Change Log