mbedtls: configurable options for controlling dynamic memory allocations

Modifies https://github.com/espressif/esp-idf/pull/2237

components/mbedtls/port/include/mbedtls/esp_config.h

@@ -114,8 +114,13 @@
  *
  * Enable this layer to allow use of alternative memory allocators.
  */
-#ifdef CONFIG_MBEDTLS_PLATFORM_MEMORY
 #define MBEDTLS_PLATFORM_MEMORY
+
+/** Override calloc(), free() except for case where memory allocation scheme is not set to custom */
+#ifndef CONFIG_MBEDTLS_CUSTOM_MEM_ALLOC
+#include "esp_mem.h"
+#define MBEDTLS_PLATFORM_STD_CALLOC		esp_mbedtls_mem_calloc
+#define MBEDTLS_PLATFORM_STD_FREE		esp_mbedtls_mem_free
 #endif
 
 /**
@@ -2611,8 +2616,46 @@
 //#define MBEDTLS_SSL_CACHE_DEFAULT_MAX_ENTRIES      50 /**< Maximum entries in cache */
 
 /* SSL options */
+#ifndef CONFIG_MBEDTLS_ASYMMETRIC_CONTENT_LEN
 
 #define MBEDTLS_SSL_MAX_CONTENT_LEN             CONFIG_MBEDTLS_SSL_MAX_CONTENT_LEN /**< Maxium fragment length in bytes, determines the size of each of the two internal I/O buffers */
+
+#else
+
+/** \def MBEDTLS_SSL_IN_CONTENT_LEN
+ *
+ * Maximum incoming fragment length in bytes.
+ *
+ * Uncomment to set the size of the inward TLS buffer independently of the
+ * outward buffer.
+ */
+#define MBEDTLS_SSL_IN_CONTENT_LEN              CONFIG_MBEDTLS_SSL_IN_CONTENT_LEN
+
+/** \def MBEDTLS_SSL_OUT_CONTENT_LEN
+ *
+ * Maximum outgoing fragment length in bytes.
+ *
+ * Uncomment to set the size of the outward TLS buffer independently of the
+ * inward buffer.
+ *
+ * It is possible to save RAM by setting a smaller outward buffer, while keeping
+ * the default inward 16384 byte buffer to conform to the TLS specification.
+ *
+ * The minimum required outward buffer size is determined by the handshake
+ * protocol's usage. Handshaking will fail if the outward buffer is too small.
+ * The specific size requirement depends on the configured ciphers and any
+ * certificate data which is sent during the handshake.
+ *
+ * For absolute minimum RAM usage, it's best to enable
+ * MBEDTLS_SSL_MAX_FRAGMENT_LENGTH and reduce MBEDTLS_SSL_MAX_CONTENT_LEN. This
+ * reduces both incoming and outgoing buffer sizes. However this is only
+ * guaranteed if the other end of the connection also supports the TLS
+ * max_fragment_len extension. Otherwise the connection may fail.
+ */
+#define MBEDTLS_SSL_OUT_CONTENT_LEN             CONFIG_MBEDTLS_SSL_OUT_CONTENT_LEN
+
+#endif /* !CONFIG_MBEDTLS_ASYMMETRIC_CONTENT_LEN */
+
 //#define MBEDTLS_SSL_DEFAULT_TICKET_LIFETIME     86400 /**< Lifetime of session tickets (if enabled) */
 //#define MBEDTLS_PSK_MAX_LEN               32 /**< Max size of TLS pre-shared keys, in bytes (default 256 bits) */
 //#define MBEDTLS_SSL_COOKIE_TIMEOUT        60 /**< Default expiration delay of DTLS cookies, in seconds if HAVE_TIME, or in number of cookies issued */