don't add padding for optimal packet size

libi2pd/ECIESX25519AEADRatchetSession.cpp

@@ -713,9 +713,13 @@ namespace garlic
 		uint8_t paddingSize = 0;
 		if (payloadLen)
 		{	
-		    RAND_bytes (&paddingSize, 1);
+			// don't create padding if we are close to optimal size
-		    paddingSize &= 0x0F; paddingSize++; // 1 - 16
+			if (first || payloadLen + 19 <= ECIESX25519_OPTIMAL_PAYLOAD_SIZE || payloadLen > ECIESX25519_OPTIMAL_PAYLOAD_SIZE)
-		    payloadLen += paddingSize + 3;   
+			{	
+				RAND_bytes (&paddingSize, 1);
+				paddingSize &= 0x0F; paddingSize++; // 1 - 16
+				payloadLen += paddingSize + 3;   
+			}	
 		}	
         std::vector<uint8_t> v(payloadLen);
         size_t offset = 0;

libi2pd/ECIESX25519AEADRatchetSession.h

@@ -26,6 +26,9 @@ namespace garlic
 	const int ECIESX25519_MAX_NUM_GENERATED_TAGS = 160;
 	const int ECIESX25519_NSR_NUM_GENERATED_TAGS = 12;
 	
+	const size_t ECIESX25519_OPTIMAL_PAYLOAD_SIZE = 1912;  // 1912 = 1956 /* to fit 2 tunnel messages */ 
+	// - 16 /* I2NP header */ - 16 /* poly hash */ - 8 /* tag */ - 4 /* garlic length */
+	
 	class ECIESX25519AEADRatchetSession;
     class RatchetTagSet
     {