Buffers do no behave properly - string

Question

I am miserable at assembly programming and ask for your help. What I do not understand is why do I lose the characters of a string from my buffer even though there is plenty of room in it?
My readBuffer size is 32 and writeBuffer size is 64, what my program does is add a space after a period and makes the first letter capital.
EXAMPLE:
Good.morning.people hehehe in the jungle the mighty jungle //this is the data
Good. Morning. People hehehe in the jungle the mighty jungle //this is the output
WHAT MY PROGRAM DOES:
Good.morning.people hehehe in the jungle the mighty jungle //this is the data
Good. Morning. People hehehe in e jungle the mighty jungle //this is the output
As you can see I end up with 'e' instead of 'the'
Here is the my code which does the editing:
Read:
MOV bx, DataHandle
CALL ReadBuffer
CMP ax, 0 ;ax = how many symbols did I read
JE closeWrite ;if 0 then close write file
;Editing the string
MOV cx, ax ;CX FOR LOOPING
MOV si, offset rBuff ;read buffer = si
MOV di, offset wBuff ;write buffer = di
Do_It:
MOV dl, [si]
CMP dl, '.' ;comparing to period
JNE Keep_Going ;if not period put it in di (write buffer)
MOV dh, [si+1] ;put the char after the period in dh
CMP dh, ' ' ;check if space is after it
JNE If_capital ;if not I check if it is a capital letter
MOV dh, [si+2] ;if there was a space I add the char after the space
CMP dh, 'a' ;checking if it is a capital letter
JB Keep_Going
CMP dh, 'z'
JA Keep_Going
SUB byte ptr [si+2], 32 ;turn it into a capital letter
Keep_Going:
MOV [di], dl ;put the char into writebuff
INC si
INC di
LOOP Do_It
JMP Finishin
If_capital:
CMP dh, 'a'
JB Add_Space
CMP dh, 'z'
JA Add_Space
SUB byte ptr [si+1], 32
Add_Space:
MOV [di], '.'
INC di
MOV [di], ' '
INC di
INC si
JMP Do_It
;Write the result
Finishin:
MOV cx, ax
CALL checkOnScreen ;print it to command line
MOV bx, WriteHandle
CALL writeBuffer ;print it
CMP ax, rBuffSize ;compare the size to 32
JE Read ;if it was 32 then read again

Answer 1

You write only 32 bytes of wBuff. This is after the first run: "Good. Morning. People hehehe in ". Since the line is longer, the rest is behind the boarder of 32 byte. Then you reset the pointers to rBuff and wBuff and read the next block: "e jungle the mighty jungle". That block is attached to the written line.
Consider that the block to be written has a variable length. You can calculate the length by subtracting the offset of wBuff from DI (sub di, OFFSET wBuff) after changing the JMP Do_It to LOOP Do_It.
I can't show a working example since I can't interpret relevant parts of your code (CMP ax, rBuffSize, JE Read ???).

Answer 2

Thanks for input guys, I managed to do it myself this time. The problem was
Finishin:
MOV cx, ax
CALL checkOnScreen
MOV bx, WriteHandle
CALL writeBuffer
CMP ax, rBuffSize
JE Read
New code:
Finishin:
MOV cx, strLength2 ;length of writebuffer
CALL checkOnScreen
MOV bx, WriteHandle
CALL writeBuffer
CMP ax, rBuffSize ;ax was messed up so I changed it to strLength1 or readBuffer
JE Read