1 files changed, 89 insertions, 0 deletions
diff --git a/SmartDeviceLink/SDLProtocolMessageDisassembler.m b/SmartDeviceLink/SDLProtocolMessageDisassembler.m
new file mode 100644
index 000000000..76d722956
--- /dev/null
+++ b/SmartDeviceLink/SDLProtocolMessageDisassembler.m
@@ -0,0 +1,89 @@
+//  SDLProtocolMessageDisassembler.m
+//
+
+#import "SDLProtocolMessageDisassembler.h"
+#import "SDLProtocolHeader.h"
+#import "SDLProtocolMessage.h"
+
+
+@implementation SDLProtocolMessageDisassembler
+
+
+// Use to break up a large message into a sequence of smaller messages,
+// each of which is less than 'mtu' number of bytes total size.
++ (NSArray *)disassemble:(SDLProtocolMessage *)incomingMessage withLimit:(NSUInteger)mtu {
+    // Questions:
+    // What message IDs does the current system use? Same messageIDs? Same CorrelationIDs?
+    // What gets simply copied from incoming header to created headers; and what needs adjustment?
+
+    // How big is the message header?
+    NSUInteger headerSize = incomingMessage.header.size;
+
+    // The size of the message is too big to send in one chunk.
+    // So lets break it up.
+    // Just how big IS this message?
+    NSUInteger incomingPayloadSize = (incomingMessage.data.length - headerSize);
+
+    // How many messages do we need to create to hold that many bytes?
+    // Note: this does NOT count the special first message which acts as a descriptor.
+    NSUInteger numberOfMessagesRequired = ceil((float)incomingPayloadSize / (float)(mtu - headerSize));
+
+    // And how many data bytes go in each message?
+    NSUInteger numberOfDataBytesPerMessage = mtu - headerSize;
+
+    // Create the outgoing array to hold the messages we will create.
+    NSMutableArray *outgoingMessages = [NSMutableArray arrayWithCapacity:numberOfMessagesRequired + 1];
+
+
+    // Create the first message
+    SDLProtocolHeader *firstFrameHeader = [incomingMessage.header copy];
+    firstFrameHeader.frameType = SDLFrameType_First;
+
+    UInt32 payloadData[2];
+    payloadData[0] = CFSwapInt32HostToBig((UInt32)incomingMessage.payload.length);
+    payloadData[1] = CFSwapInt32HostToBig((UInt32)numberOfMessagesRequired);
+    NSMutableData *firstFramePayload = [NSMutableData dataWithBytes:payloadData length:sizeof(payloadData)];
+    firstFrameHeader.bytesInPayload = (UInt32)firstFramePayload.length;
+
+    SDLProtocolMessage *firstMessage = [SDLProtocolMessage messageWithHeader:firstFrameHeader andPayload:firstFramePayload];
+    outgoingMessages[0] = firstMessage;
+
+
+    // Create the middle messages (the ones carrying the actual data).
+    for (int n = 0; n < numberOfMessagesRequired - 1; n++) {
+        // Frame # after 255 must cycle back to 1, not 0.
+        // A 0 signals last frame.
+        UInt8 frameNumber = (n % 255) + 1;
+
+        SDLProtocolHeader *nextFrameHeader = [incomingMessage.header copy];
+        nextFrameHeader.frameType = SDLFrameType_Consecutive;
+        nextFrameHeader.frameData = frameNumber;
+
+        NSUInteger offsetOfDataForThisFrame = headerSize + (n * numberOfDataBytesPerMessage);
+        NSData *nextFramePayload = [incomingMessage.data subdataWithRange:NSMakeRange(offsetOfDataForThisFrame, numberOfDataBytesPerMessage)];
+        nextFrameHeader.bytesInPayload = (UInt32)nextFramePayload.length;
+
+        SDLProtocolMessage *nextMessage = [SDLProtocolMessage messageWithHeader:nextFrameHeader andPayload:nextFramePayload];
+        outgoingMessages[n + 1] = nextMessage;
+    }
+
+
+    // Create the last message
+    SDLProtocolHeader *lastFrameHeader = [incomingMessage.header copy];
+    lastFrameHeader.frameType = SDLFrameType_Consecutive;
+    lastFrameHeader.frameData = SDLFrameData_ConsecutiveLastFrame;
+
+    NSUInteger numberOfMessagesCreatedSoFar = numberOfMessagesRequired - 1;
+    NSUInteger numberOfDataBytesSentSoFar = numberOfMessagesCreatedSoFar * numberOfDataBytesPerMessage;
+    NSUInteger numberOfDataBytesInLastMessage = incomingPayloadSize - numberOfDataBytesSentSoFar;
+    NSUInteger offsetOfDataForLastFrame = headerSize + numberOfDataBytesSentSoFar;
+    NSData *lastFramePayload = [incomingMessage.data subdataWithRange:NSMakeRange(offsetOfDataForLastFrame, numberOfDataBytesInLastMessage)];
+    lastFrameHeader.bytesInPayload = (UInt32)lastFramePayload.length;
+
+    SDLProtocolMessage *lastMessage = [SDLProtocolMessage messageWithHeader:lastFrameHeader andPayload:lastFramePayload];
+    outgoingMessages[numberOfMessagesRequired] = lastMessage;
+
+    return outgoingMessages;
+}
+
+@end