Add --hex-blob support to mysqldump and mariadb-import for --tab/--dir mode to enable reliable export and import of BLOB and BINARY columns containing null bytes and other binary data.

Problem:

When using mysqldump with --tab or --dir to export tables to tab-separated text files (.txt), BLOB and BINARY columns containing binary data (especially null bytes 0x00) get corrupted or truncated. The tab-separated text format cannot properly represent binary data, making it impossible to reliably backup and restore tables with binary content using this method.

Current workarounds are inadequate:

• Using standard mysqldump (without --tab) creates large SQL files with INSERT statements
• Manual hex encoding/decoding is error-prone and not integrated
• Binary data is lost or corrupted during the export/import cycle

Proposed Solution:

Extend the existing --hex-blob option to work with --tab/--dir mode for both mysqldump and mariadb-import:

1. mysqldump --hex-blob --tab/--dir:

• Automatically detect BLOB and BINARY columns
• Wrap them with HEX() in the SELECT statement
• Export binary data as hexadecimal strings in .txt files

2. mariadb-import --hex-blob:

• Automatically detect BLOB and BINARY columns from table structure
• Apply UNHEX() transformation during LOAD DATA
• Convert hex strings back to binary data

Together, these changes enable a complete round-trip export/import workflow for tables containing binary data.

Implementation Details:

mysqldump changes (client/mysqldump.cc):

• Query INFORMATION_SCHEMA.COLUMNS for column metadata:
• data_type (binary, varbinary, tinyblob, blob, mediumblob, longblob)
• character_set_name (NULL or 'binary' for binary data)
• When --hex-blob and --tab/--dir are both specified:
• Wrap BLOB/BINARY columns with HEX(column_name) AS column_name
• Generate SELECT statement with hex-encoded binary columns
• Non-binary columns remain unchanged

mariadb-import changes (client/mysqlimport.cc):

• Add --hex-blob command-line option
• Query INFORMATION_SCHEMA.COLUMNS to determine table structure:
• column_name, data_type, character_set_name
• Identify BLOB/BINARY columns based on data type and charset
• Modify LOAD DATA INFILE statement:
• Load hex data into user variables: (col1, @blob_col_hex, col3)
• Add SET clause: SET blob_col=UNHEX(@blob_col_hex)
• Works with:
• --columns parameter (explicit column list)
• All columns (default)
• --dir mode and standalone .txt files

Benefits:

1. Data Integrity:

• Preserves binary data exactly, including null bytes
• Verifiable round-trip export/import
• No data loss or corruption

2. Performance:

• Tab-separated files are faster than SQL INSERT statements
• Efficient for large tables
• Suitable for parallel processing

3. Compatibility:

• Works with existing --tab/--dir infrastructure
• Compatible with other text processing tools
• Human-readable hex format for debugging

4. Flexibility:

• Works with mixed column types (BLOB + VARCHAR + INT)
• Handles NULL and empty values correctly
• Supports partial column imports with --columns

Backward Compatibility:

• Fully backward compatible
• --hex-blob is optional; existing behavior unchanged without it
• No changes to default mysqldump or mariadb-import behavior
• Only affects --tab and --dir mode when explicitly requested