mongoose/docs/overview/build-options/tunables.md

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Tunables

• MG_MALLOC, MG_CALLOC, MG_REALLOC, MG_FREE allow you to a use custom memory allocator, e.g. -DMG_MALLOC=my_malloc
• MG_USE_READ_WRITE when set replaces calls to recv with read and send with write, thus enabling to add any kind of file descriptor (files, serial devices) to an event manager.
• MG_SSL_CRYPTO_MODERN, MG_SSL_CRYPTO_OLD - choose either "Modern" or "Old" ciphers instead of the default "Intermediate" setting. See this article for details.
• MG_USER_FILE_FUNCTIONS allow you to use custom file operation, by defining you own mg_stat, mg_fopen, mg_open, mg_fread and mg_fwrite functions