OnSymbolTick HOW

Example from file: examples/demos/lowlevel/03_streaming_methods.go

The OnSymbolTick() method is used to subscribe to a real-time tick data stream (Bid/Ask). It opens a continuous gRPC stream between the client and the MetaTrader server, sending updates on every price change.

This is analogous to the OnTick() function in MQL5, but implemented as a persistent asynchronous stream.

---

🧩 Code example

tickReq := &pb.OnSymbolTickRequest{
    Symbol: cfg.TestSymbol, // Single symbol to stream
}

tickChan, tickErrChan := account.OnSymbolTick(ctx, tickReq)

fmt.Printf("Streaming %s tick data (max %d events or %d seconds)...\n", cfg.TestSymbol, MAX_EVENTS, MAX_SECONDS)

eventCount := 0
timeout := time.After(MAX_SECONDS * time.Second)

streamTick:
for {
    select {
    case tickData, ok := <-tickChan:
        if !ok {
            fmt.Println("  Stream closed by server")
            break streamTick
        }
        eventCount++
        fmt.Printf("  Event #%d: Bid=%.5f Ask=%.5f Spread=%.5f\n",
            eventCount,
            tickData.Bid,
            tickData.Ask,
            tickData.Ask-tickData.Bid)

        if eventCount >= MAX_EVENTS {
            fmt.Printf("  ✓ Received %d events, stopping stream\n", MAX_EVENTS)
            break streamTick
        }

    case err := <-tickErrChan:
        if err != nil {
            helpers.PrintShortError(err, "Stream error")
            break streamTick
        }

    case <-timeout:
        fmt.Printf("  ⏱ Timeout after %d seconds, stopping stream\n", MAX_SECONDS)
        break streamTick
    }
}

---

🟢 Detailed Code Explanation

1️. Subscribe to Tick Data Stream

tickReq := &pb.OnSymbolTickRequest{
    Symbol: cfg.TestSymbol,
}

Create a request to stream ticks for the symbol cfg.TestSymbol (e.g., EURUSD).

🔸 Note: To stream multiple symbols, create separate streams for each symbol.

---

2️. Start the Stream

tickChan, tickErrChan := account.OnSymbolTick(ctx, tickReq)

The method returns two channels:

• tickChan — data channel for tick updates;
• tickErrChan — error channel if the stream is interrupted.

The stream works asynchronously — new ticks arrive continuously until timeout or event limit is reached.

---

3️. Set Up Limits

eventCount := 0
timeout := time.After(MAX_SECONDS * time.Second)

• MAX_EVENTS — how many ticks to receive (e.g., 10);
• MAX_SECONDS — time limit (e.g., 5 seconds).

This is a safeguard to prevent the example from running indefinitely.

---

4️. Main Data Reception Loop

for {
    select {
    case tickData, ok := <-tickChan:
        ...
    case err := <-tickErrChan:
        ...
    case <-timeout:
        ...
    }
}

Uses the select construct to listen to three sources simultaneously:

1. tickChan — new tick arrived;
2. tickErrChan — stream error;
3. timeout — time expired.

---

5️. Process Incoming Tick

fmt.Printf("  Event #%d: Bid=%.5f Ask=%.5f Spread=%.5f\n",
    eventCount,
    tickData.Bid,
    tickData.Ask,
    tickData.Ask-tickData.Bid)

Each tick contains:

• Bid — buy price;
• Ask — sell price;
• Spread — difference between Ask and Bid;
• Time — tick timestamp;
• Volume — tick volume;
• Last — last deal price.

This data is needed for strategy calculations, scalping, spread analysis, and market visualization.

---

6️. Stream Termination by Limit or Timeout

if eventCount >= MAX_EVENTS {
    fmt.Printf("  ✓ Received %d events, stopping stream\n", MAX_EVENTS)
    break streamTick
}

The stream stops either by event count (MAX_EVENTS) or when timeout expires.

---

📦 What the Server Returns

message OnSymbolTickData {
  double Bid = 1;     // Current bid price
  double Ask = 2;     // Current ask price
  double Last = 3;    // Last deal price
  uint64 Volume = 4;  // Volume
  google.protobuf.Timestamp Time = 5; // Tick timestamp
  uint32 Flags = 6;   // Tick flags
}

---

💡 Example Output

Streaming EURUSD tick data (max 5 events or 10 seconds)...
  Event #1: Bid=1.08542 Ask=1.08558 Spread=0.00016
  Event #2: Bid=1.08540 Ask=1.08555 Spread=0.00015
  Event #3: Bid=1.08539 Ask=1.08554 Spread=0.00015
  ✓ Received 3 events, stopping stream

---

🧠 What It's Used For

The OnSymbolTick() method is used for:

• receiving real-time quotes;
• building streaming strategies (scalping, market making);
• monitoring broker latency and market activity;
• updating visualization or statistics in real-time.

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💬 In Simple Terms

OnSymbolTick() is a live price subscription. The gateway server sends you every Bid/Ask change, and you can process it instantly. For example, calculate spread, build charts, or react to market changes — all in real-time.