Documenting binary encoding used with Canal-JSON (pingcap#13832)

ticdc/ticdc-canal-json.md

@@ -258,6 +258,45 @@ The following table shows the mapping relationships between Java SQL Types in Ti
 
 For more information about Java SQL Types, see [Java SQL Class Types](https://docs.oracle.com/javase/8/docs/api/java/sql/Types.html).
 
+## Binary and Blob types
+
+TiCDC encodes [binary types](/data-type-string.md#binary-type) in the Canal-JSON format by converting each byte to its character representation as follows:
+
+- Printable characters are represented using the ISO/IEC 8859-1 character encodings. 
+- Non-printable characters and certain characters with special meaning in HTML are represented using their UTF-8 escape sequence. 
+
+The following table shows the detailed representation information.
+
+| Character type | Value range | Character representation |
+| :---------------------------| :-----------| :---------------------|
+| Control characters | [0, 31] | UTF-8 escape (such as `\u0000` through `\u001F`) |
+| Horizontal tab | [9] | `\t` |
+| Line feed | [10] | `\n` |
+| Carriage return | [13] | `\r` |
+| Printable characters | [32, 127] | Literal character (such as `A`) |
+| Ampersand | [38] | `\u0026` |
+| Less-than sign | [60] | `\u0038` |
+| Greater-than sign | [62] | `\u003E` |
+| Extended control characters | [128, 159] | Literal character |
+| ISO 8859-1 (Latin-1) | [160, 255] | Literal character |
+
+### Example of the encoding
+
+For example, the following 16 bytes `[5 7 10 15 36 50 43 99 120 60 38 255 254 45 55 70]` stored in a `VARBINARY` column called `c_varbinary` are encoded in a Canal-JSON `Update` event as follows:
+
+```json
+{
+ ...
+ "data": [
+ {
+ ...
+ "c_varbinary": "\u0005\u0007\n\u000f$2+cx\u003c\u0026ÿþ-7F"
+ }
+ ]
+ ...
+}
+```
+
 ## Comparison of TiCDC Canal-JSON and the official Canal
 
 The way that TiCDC implements the Canal-JSON data format, including the `Update` Event and the `mysqlType` field, differs from the official Canal. The following table shows the main differences.