Implement CBOR date tags according to RFC 8943

src/cbor/CborDecoderBase.ts

@@ -4,6 +4,7 @@ import {JsonPackExtension} from '../JsonPackExtension';
 import {JsonPackValue} from '../JsonPackValue';
 import {Reader} from '@jsonjoy.com/util/lib/buffers/Reader';
 import sharedCachedUtf8Decoder from '@jsonjoy.com/util/lib/buffers/utf8/sharedCachedUtf8Decoder';
+import {daysSinceEpochToDate, rfc3339StringToDate} from './dates';
 import type {CachedUtf8Decoder} from '@jsonjoy.com/util/lib/buffers/utf8/CachedUtf8Decoder';
 import type {IReader, IReaderResettable} from '@jsonjoy.com/util/lib/buffers';
 import type {BinaryJsonDecoder, PackValue} from '../types';
@@ -314,7 +315,38 @@ export class CborDecoderBase<R extends IReader & IReaderResettable = IReader & I
   }
 
   public readTagRaw(tag: number): JsonPackExtension<unknown> | unknown {
-    return new JsonPackExtension<unknown>(tag, this.val());
+    const value = this.val();
+
+    // Handle CBOR date tags as defined in RFC 8943
+    switch (tag) {
+      case 100: {
+        // Tag 100: Number of days since the epoch date 1970-01-01
+        if (typeof value === 'number') {
+          try {
+            return daysSinceEpochToDate(value);
+          } catch (error) {
+            // If conversion fails, return as JsonPackExtension
+            return new JsonPackExtension<unknown>(tag, value);
+          }
+        }
+        break;
+      }
+      case 1004: {
+        // Tag 1004: RFC 3339 full-date string
+        if (typeof value === 'string') {
+          try {
+            return rfc3339StringToDate(value);
+          } catch (error) {
+            // If conversion fails, return as JsonPackExtension
+            return new JsonPackExtension<unknown>(tag, value);
+          }
+        }
+        break;
+      }
+    }
+
+    // For all other tags, return as JsonPackExtension
+    return new JsonPackExtension<unknown>(tag, value);
   }
 
   // ------------------------------------------------------------ Token reading

src/cbor/CborEncoder.ts

@@ -2,6 +2,7 @@ import {isFloat32} from '@jsonjoy.com/util/lib/buffers/isFloat32';
 import {JsonPackExtension} from '../JsonPackExtension';
 import {CborEncoderFast} from './CborEncoderFast';
 import {JsonPackValue} from '../JsonPackValue';
+import {dateToDaysSinceEpoch, dateToRfc3339String} from './dates';
 import type {IWriter, IWriterGrowable} from '@jsonjoy.com/util/lib/buffers';
 
 export class CborEncoder<W extends IWriter & IWriterGrowable = IWriter & IWriterGrowable> extends CborEncoderFast<W> {
@@ -39,6 +40,8 @@ export class CborEncoder<W extends IWriter & IWriterGrowable = IWriter & IWriter
           case JsonPackValue:
             const buf = (value as JsonPackValue).val;
             return this.writer.buf(buf, buf.length);
+          case Date:
+            return this.writeDate(value as Date);
           default:
             if (value instanceof Uint8Array) return this.writeBin(value);
             if (Array.isArray(value)) return this.writeArr(value);
@@ -68,6 +71,26 @@ export class CborEncoder<W extends IWriter & IWriterGrowable = IWriter & IWriter
     });
   }
 
+  /**
+   * Encodes a JavaScript Date object as a CBOR date tag.
+   * Uses tag 100 (days since epoch) for most dates, or tag 1004 (RFC 3339 string) 
+   * when needed for better precision or compatibility.
+   * 
+   * For now, we'll default to tag 100 (days since epoch) as it's more compact.
+   * 
+   * @param date - The Date object to encode
+   */
+  public writeDate(date: Date): void {
+    // Validate that the date is valid
+    if (isNaN(date.getTime())) {
+      throw new Error('Invalid Date object');
+    }
+
+    // Use tag 100 (days since epoch) by default for compactness
+    const daysSinceEpoch = dateToDaysSinceEpoch(date);
+    this.writeTag(100, daysSinceEpoch);
+  }
+
   public writeUndef(): void {
     this.writer.u8(0xf7);
   }

src/cbor/README.md

@@ -65,6 +65,74 @@ shallow decoding features, like skipping, one level at-a-time decoding.
 - Half-precision `f16` floats are decoded to JavaScript `number`, however,
   encoder does not support half-precision floats—floats are encoded as
   `f32` or `f64`.
+- **Date support**: JavaScript `Date` objects are automatically encoded using 
+  CBOR date tags as defined in [RFC 8943](https://tools.ietf.org/rfc/rfc8943.txt):
+  - Tag 100: Number of days since the epoch date 1970-01-01 (default encoding)
+  - Tag 1004: RFC 3339 full-date string (supported for decoding)
+  - Only the date component is preserved (time is ignored)
+  - Encoded dates are automatically decoded back to JavaScript `Date` objects
+
+## Date Support
+
+The CBOR codec includes built-in support for JavaScript `Date` objects following 
+[RFC 8943](https://tools.ietf.org/rfc/rfc8943.txt) "Tags for Date" specification.
+
+### Encoding Dates
+
+JavaScript `Date` objects are automatically encoded using tag 100 (days since epoch):
+
+```ts
+import {CborEncoder, CborDecoder} from '@jsonjoy.com/json-pack/lib/cbor';
+
+const encoder = new CborEncoder();
+const decoder = new CborDecoder();
+
+const data = {
+  event: 'Birthday',
+  date: new Date(1940, 9, 9), // October 9, 1940
+  participants: ['John', 'Paul']
+};
+
+const encoded = encoder.encode(data);
+const decoded = decoder.decode(encoded);
+
+console.log(decoded.date instanceof Date); // true
+console.log(decoded.date.toDateString()); // "Wed Oct 09 1940"
+```
+
+### Supported Date Tags
+
+- **Tag 100**: Days since 1970-01-01 (compact integer representation)
+  - Used by default when encoding `Date` objects
+  - Example: October 9, 1940 → -10676 days
+- **Tag 1004**: RFC 3339 full-date string (YYYY-MM-DD format)
+  - Supported for decoding tagged strings
+  - Example: "1940-10-09"
+
+### Date Utilities
+
+The codec also exports utility functions for manual date conversion:
+
+```ts
+import {
+  dateToDaysSinceEpoch,
+  daysSinceEpochToDate,
+  dateToRfc3339String,
+  rfc3339StringToDate
+} from '@jsonjoy.com/json-pack/lib/cbor';
+
+// Convert Date to days since epoch
+const days = dateToDaysSinceEpoch(new Date(1940, 9, 9)); // -10676
+
+// Convert days back to Date
+const date = daysSinceEpochToDate(-10676); // October 9, 1940
+
+// Convert Date to RFC 3339 string
+const dateString = dateToRfc3339String(new Date(1940, 9, 9)); // "1940-10-09"
+
+// Parse RFC 3339 string to Date
+const parsedDate = rfc3339StringToDate("1940-10-09"); // October 9, 1940
+```
 
 
 ## Benchmarks