Checkpointing.

include/messageFormat.h

@@ -13,9 +13,18 @@ namespace storagemanager
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wunused-variable"
 
-// all msgs to and from StorageManager begin with this magic
+// all msgs to and from StorageManager begin with this magic and a payload length
 static const uint SM_MSG_START=0xbf65a7e1;
 
+// for read/write/append, which may break a message into chunks, messages not the 
+// beginning or end of the larger message will preface a chunk with this magic 
+static const uint SM_MSG_CONT=0xfa371bd2;
+
+// for read/write/append, the last chunk of a message should begin with this magic
+static const uint SM_MSG_END=0x9d5bc31b;
+
+static const uint SM_HEADER_LEN = 8;
+
 // the unix socket StorageManager is listening on
 static const char *socket_name = "\0storagemanager";
 
@@ -46,6 +55,8 @@ enum Opcodes {
     value for errno follows.  On success, no errno is sent.
 
     On success, what follows is any output parameters from the call.
+    
+    TBD: Require filenames to be NULL-terminated.  Currently they are not.
 
     OPEN
     ----
@@ -66,7 +77,7 @@ enum Opcodes {
     WRITE
     -----
     command format:
-    1-byte opcode|4-byte filename length|filename|size_t count|off_t offset|data
+    1-byte opcode|size_t count|off_t offset|4-byte filename length|filename|data
 
     response format: