fix(price): widen gRPC rate fields to double (#283)

src/services/price/protos/price.proto

@@ -1,28 +1,28 @@
-syntax = "proto3";
-
-service PriceFeed {
-  rpc GetPrice(PriceQuery) returns (PriceResponse) {}
-  rpc ListCurrencies(ListCurrenciesQuery) returns (ListCurrenciesResponse) {}
-}
-
-message PriceResponse {
-  float price = 1;
-}
-
-message PriceQuery {
-  string currency = 1;
-}
-
-message ListCurrenciesQuery { }
-
-message ListCurrenciesResponse {
-  repeated Currency currencies = 1;
-}
-
-message Currency {
-  string code = 1;
-  string symbol = 2;
-  string name = 3;
-  string flag = 4;
-  int32 fractionDigits = 5;
-}
+syntax = "proto3";
+
+service PriceFeed {
+  rpc GetPrice(PriceQuery) returns (PriceResponse) {}
+  rpc ListCurrencies(ListCurrenciesQuery) returns (ListCurrenciesResponse) {}
+}
+
+message PriceResponse {
+  double price = 1;
+}
+
+message PriceQuery {
+  string currency = 1;
+}
+
+message ListCurrenciesQuery { }
+
+message ListCurrenciesResponse {
+  repeated Currency currencies = 1;
+}
+
+message Currency {
+  string code = 1;
+  string symbol = 2;
+  string name = 3;
+  string flag = 4;
+  int32 fractionDigits = 5;
+}

src/services/price/protos/price_history.proto

@@ -1,26 +1,26 @@
-syntax = "proto3";
-
-service PriceHistory {
-  rpc ListPrices(PriceHistoryQuery) returns (PriceHistoryResponse) {}
-}
-
-message PriceHistoryQuery {
-  string currency = 1;
-  enum PriceRange {
-    OneDay = 0;
-    OneWeek = 1;
-    OneMonth = 2;
-    OneYear = 3;
-    FiveYears = 4;
-  }
-  PriceRange range = 2;
-}
-
-message PriceHistoryResponse {
-  repeated Tick priceHistory = 1;
-}
-
-message Tick {
-  uint64 timestamp = 1;
-  float price = 2;
-}
+syntax = "proto3";
+
+service PriceHistory {
+  rpc ListPrices(PriceHistoryQuery) returns (PriceHistoryResponse) {}
+}
+
+message PriceHistoryQuery {
+  string currency = 1;
+  enum PriceRange {
+    OneDay = 0;
+    OneWeek = 1;
+    OneMonth = 2;
+    OneYear = 3;
+    FiveYears = 4;
+  }
+  PriceRange range = 2;
+}
+
+message PriceHistoryResponse {
+  repeated Tick priceHistory = 1;
+}
+
+message Tick {
+  uint64 timestamp = 1;
+  double price = 2;
+}

test/flash/unit/services/price/price-proto-double.spec.ts

@@ -0,0 +1,68 @@
+import path from "path"
+
+const protobuf = require("protobufjs")
+
+// Both price streams cross the gRPC boundary as a single scalar: `PriceResponse.price`
+// (src/services/price/protos/price.proto) and `Tick.price`
+// (src/services/price/protos/price_history.proto). `float` in protobuf is 32-bit
+// IEEE 754 — about 7 significant digits — so a rate such as 157.1234567 (JMD) or
+// 392.9876543 (NGN), multiplied onward through the 8-decimal sat math in
+// `getRealTimePrice`, is silently rounded inside the wire layer where no caller can
+// see it. `double` keeps the value the JS number already holds.
+//
+// The stubs are loaded at runtime straight from these .proto files (see
+// src/services/price/grpc.ts), so the schema *is* the contract: encoding and decoding
+// through the loaded type is the same round trip a gRPC call performs, without needing
+// a price-server on the other end.
+
+const PROTO_DIR = path.join(__dirname, "../../../../../src/services/price/protos")
+
+const loadRoot = (file: string) => protobuf.loadSync(path.join(PROTO_DIR, file))
+
+const roundTrip = (root: any, typeName: string, value: number) => {
+  const type = root.lookupType(typeName)
+  const bytes = type.encode(type.create({ price: value })).finish()
+
+  return type.decode(bytes).price as number
+}
+
+describe("price protos keep full rate precision", () => {
+  const priceRoot = loadRoot("price.proto")
+  const historyRoot = loadRoot("price_history.proto")
+
+  it("declares PriceResponse.price as double", () => {
+    expect(priceRoot.lookupType("PriceResponse").fields.price.type).toBe("double")
+  })
+
+  it("declares Tick.price as double", () => {
+    expect(historyRoot.lookupType("Tick").fields.price.type).toBe("double")
+  })
+
+  it.each([
+    [157.123456789], // JMD-style rate carried through sat-scale precision
+    [392.987654321], // NGN-style rate
+    [0.0000000123456], // sub-cent sats-per-unit ratio
+  ])("round-trips %p through PriceResponse bit-for-bit", (rate) => {
+    expect(roundTrip(priceRoot, "PriceResponse", rate)).toBe(rate)
+  })
+
+  it("round-trips a history tick alongside its timestamp", () => {
+    const type = historyRoot.lookupType("Tick")
+    const rate = 157.123456789
+    const bytes = type
+      .encode(type.create({ timestamp: "1700000000", price: rate }))
+      .finish()
+    const decoded = type.decode(bytes)
+
+    expect(decoded.price).toBe(rate)
+    expect(decoded.timestamp.toString()).toBe("1700000000")
+  })
+
+  it("shows what a 32-bit field would have done to the same rate", () => {
+    const rate = 157.123456789
+    const view = new DataView(new ArrayBuffer(8))
+    view.setFloat32(0, rate)
+
+    expect(view.getFloat32(0)).not.toBe(rate)
+  })
+})