fix(core/cbor): handle exponent notation when serializing NumericValue containers

Author: kuhe

.changeset/fuzzy-dragons-fix.md

@@ -0,0 +1,5 @@
+---
+"@smithy/core": patch
+---
+
+fix: handle exponent notation when serializing NumericValue wrappers

packages/core/src/submodules/cbor/cbor-encode.ts

@@ -179,9 +179,19 @@ export function encode(_input: any): void {
       continue;
     } else if (typeof input === "object") {
       if (input instanceof NumericValue) {
-        const decimalIndex = input.string.indexOf(".");
-        const exponent = decimalIndex === -1 ? 0 : decimalIndex - input.string.length + 1;
-        const mantissa = BigInt(input.string.replace(".", ""));
+        let str = input.string;
+        let expOffset = 0;
+
+        const eIndex = str.search(/[eE]/);
+        if (eIndex !== -1) {
+          expOffset = Number(str.slice(eIndex + 1));
+          str = str.slice(0, eIndex);
+        }
+
+        const decimalIndex = str.indexOf(".");
+        const fractionDigits = decimalIndex === -1 ? 0 : str.length - decimalIndex - 1;
+        const exponent = expOffset - fractionDigits;
+        const mantissa = BigInt(str.replace(".", ""));
 
         data[cursor++] = 0b110_00100; // major 6, tag 4.
         encodeInteger(majorList, 2);

packages/core/src/submodules/cbor/cbor.spec.ts

@@ -322,6 +322,22 @@ describe("cbor", () => {
       ]);
     });
 
+    it("should round-trip NumericValue with exponent notation", () => {
+      for (const bigDecimal of ["1.5e10", "3E-20", "-2.0e+5", "100E3", "1e2", ".5e3"]) {
+        const numericValue = new NumericValue(bigDecimal, "bigDecimal");
+        const serialized = cbor.serialize(numericValue);
+
+        const major = serialized[0] >> 5;
+        expect(major).toEqual(0b110); // 6
+
+        const tag = serialized[0] & 0b11111;
+        expect(tag).toEqual(0b0100); // 4
+
+        const deserialized = cbor.deserialize(serialized);
+        expect(deserialized).toBeInstanceOf(NumericValue);
+      }
+    });
+
     it("should round-trip sequences of big numbers", () => {
       const sequence = {
         map: {

packages/core/src/submodules/cbor/codec-v2/CborShapeSerializer2.ts

@@ -701,9 +701,19 @@ function writeTag(tagValue: number | bigint, innerValue: unknown): void {
 }
 
 function writeNumericValue(nv: NumericValue): void {
-  const decimalIndex = nv.string.indexOf(".");
-  const exponent = decimalIndex === -1 ? 0 : decimalIndex - nv.string.length + 1;
-  const mantissa = BigInt(nv.string.replace(".", ""));
+  let str = nv.string;
+  let expOffset = 0;
+
+  const eIndex = str.search(/[eE]/);
+  if (eIndex !== -1) {
+    expOffset = Number(str.slice(eIndex + 1));
+    str = str.slice(0, eIndex);
+  }
+
+  const decimalIndex = str.indexOf(".");
+  const fractionDigits = decimalIndex === -1 ? 0 : str.length - decimalIndex - 1;
+  const exponent = expOffset - fractionDigits;
+  const mantissa = BigInt(str.replace(".", ""));
 
   ensure(9);
   buf[cursor++] = 0b110_00100; // major 6, tag 4

packages/core/src/submodules/cbor/codec-v2/SinglePassCbor.spec.ts

@@ -188,6 +188,33 @@ describe("CborShapeSerializer2", () => {
       expect(cbor.deserialize(singleBytes)).toEqual(cbor.deserialize(multiBytes));
     });
 
+    it("serializes NumericValue with exponent notation", () => {
+      const schema = [
+        3,
+        "ns",
+        "Measurement",
+        0,
+        ["value"],
+        [19 satisfies BigDecimalSchema],
+      ] satisfies StaticStructureSchema;
+
+      const cases = ["1.5e10", "3E-20", "-2.0e+5", "100E3", "1e2", ".5e3"];
+      for (const str of cases) {
+        const data = { value: nv(str) };
+
+        multiPass.write(schema, data);
+        const multiBytes = multiPass.flush();
+
+        singlePass.write(schema, data);
+        const singleBytes = singlePass.flush();
+
+        const multiResult = cbor.deserialize(multiBytes);
+        const singleResult = cbor.deserialize(singleBytes);
+        expect(singleResult).toEqual(multiResult);
+        expect(singleResult.value.string).toEqual(multiResult.value.string);
+      }
+    });
+
     it("serializes unions with $unknown", () => {
       const unionSchema = [4, "ns", "Union", 0, ["a", "b"], [0, 0]] satisfies StaticUnionSchema;
       const data = { $unknown: ["c", "hello"] };