[bb] Read/Write PureText Strings by _PJ_ [ 1+ years ago ]

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Title : Read/Write PureText Strings
Author : _PJ_
Posted : 1+ years ago

Description : Not sure exactly how practical this is, since it was part of something else I've been working towards.
Essentially, it simplifies the bytes of string data allowing standard alphanumeric characters (plus 1 or two others) to be read/written to files with 64 bytes each character.
Making use of the Bit for 128, I incorporated a very simple randomisation to 'encrypt' the data, making it harder to read by an end user direct from the output. The Read functionality identifies this value.
Limitations & Notes:
I built in some formatting to remove extraneous spaces.
Commas and full-stops (period US) / decimal points are the only accepted punctuation. It's possible to alter these, but only 3 such non-alphanumeric chars are permitted (including SPACE).
String length is limited to 65535 chars, should be enough for anyoine. This limit can be altered if really necessary, so long as Length is read/written as Int for 4-Byte values or perhaps Byte for 255-length strings rather than Short (16-Bit, 65535 limit).
Encryption is very simply substitution and reversal with the cypher given at the top of the code. (Also the byte format for the chars) - whilst it may not be a preferred form of security, it should be adequate in theory for general purposes due to the application of randomised encrypted characters.

Code :

Code: BlitzBasic

1. ;0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz.,
2.  
3. ;------------------------------------------------------------------------------------------------
4. ;EXAMPLE:
5. ;------------------------------------------------------------------------------------------------
6. f=WriteFile("test.txt")
7.  
8. WritePureTextString(f,"Hello World",True)
9.  
10. CloseFile f
11.  
12. f=ReadFile("test.txt")
13.  
14. Print ReadPureTextString(f)
15.  
16. CloseFile f
17.  
18.  
19. ;------------------------------------------------------------------------------------------------
20. ;FUNCTIONS:
21. ;------------------------------------------------------------------------------------------------
22.  
23.  
24. Function ReadPureTextString$(FileStream)
25.         If (Not(Filestream)) Then Return ""
26.        
27.         Local Length%=ReadShort(FileStream)
28.         If (Not (Length)) Then Return ""
29.        
30.         Local sString$=""
31.         Local IterChar%
32.         Local Char$
33.         Local Byte%
34.         For IterChar= 1 To Length
35.                 Byte=ReadByte(Filestream)
36.                 If (Byte>64) Then Byte=Byte-128
37.                 Char=ConvertByteToChar(Byte)
38.                 sString=sString+Char
39.         Next
40.        
41.         sString=Trim(sString)
42.         While Instr(sString,"  ")
43.                 sString=Replace(sString,"  "," ")
44.         Wend
45.        
46.         Return sString
47. End Function
48.  
49. Function WritePureTextString(Filestream%,sString$,Encrypt=False)
50.         If (Not(Filestream)) Then Return
51.        
52.         Local Length=Len(sString)
53.  
54.         ; Zero Length string   
55.         If (Not (Length))
56.                 WriteShort Filestream,0
57.                 Return
58.         End If
59.        
60.         Local IterChar%
61.         Local Char$
62.         Local Byte%
63.                
64.         ;Convert string
65.         For IterChar=1 To Length
66.                 Char=Mid(sString,IterChar,1)
67.                 Byte=ConvertCharToByte(Char)
68.                 Replace(sString,Chr(Char),ConvertByteToChar(Char))
69.         Next
70.  
71.         ;Consecutive spaces count as 1. No leading or trailing spaces.
72.         sString=Trim(sString)
73.         While Instr(sString,"  ")
74.                 sString=Replace(sString,"  "," ")
75.         Wend
76.  
77.         Length=Len(sString)
78.  
79.         ; Zero Length string   
80.         If (Not (Length))
81.                 WriteShort Filestream,0
82.                 Return
83.         End If
84.        
85.         ;Truncate long strings
86.         If (Length>65535)
87.                 Length=65535
88.                 sString=Left(sString,65535)
89.         End If
90.  
91.         ;Consecutive spaces count as 1. No leading or trailing spaces.
92.         sString=Trim(sString)
93.         While Instr(sString,"  ")
94.                 sString=Replace(sString,"  "," ")
95.         Wend
96.  
97.         Length%=Len(sString)
98.  
99.         ;Write Length as short
100.         WriteShort FileStream,Length
101.                        
102.         For IterChar=1 To Length
103.                 Char=Mid(sString,IterChar,1)
104.                 Byte=ConvertCharToByte(Char)
105.                 If (Encrypt)
106.                         SeedRnd MilliSecs()*RndSeed()
107.                         If Rand(0,1) Then Byte=Byte+128
108.                 End If
109.                 WriteByte Filestream,Byte
110.         Next
111. End Function
112.        
113.  
114. Function ConvertCharToByte%(Char$)
115.  
116.         Local Ascii%=Asc(Char)
117.  
118.         If ((Ascii>47) And (Ascii<58))
119.                 ; NUMERAL
120.                 Return (Ascii-48)
121.         Else
122.  
123.                 If ((Ascii>64) And (Ascii<91))
124.                         ; UPPER ALPHA
125.                         Return (Ascii-54)
126.        
127.                 Else
128.        
129.                         If (Ascii>96) And (Ascii<123)
130.                                 ; LOWER ALPHA
131.                         Return (Ascii-61)
132.                
133.                         End If
134.                 End If
135.         End If 
136.        
137.         If Char="." Then Return 62
138.         If Char="," Then Return 63
139.        
140.         ; For everything else, there's mastercard
141.         Return 64
142.                
143. End Function
144.  
145. Function ConvertByteToChar$(Byte)
146.  
147.         If (Byte<10)
148.                 ;NUMERAL
149.                 Return Chr(Byte+48)
150.        
151.         Else
152.                 If ((Byte>9) And (Byte<37))
153.                         ; UPPER ALPHA
154.                         Return Chr(Byte+54)
155.                 Else
156.                         If ((Byte>36) And (Byte<62))
157.                                 ; LOWER ALPHA
158.                                 Return Chr(Byte+61)
159.                
160.                         End If
161.                 End If
162.         End If 
163.        
164.         If Byte=62 Then Return "."
165.         If Byte=63 Then Return ","     
166.         Return " "
167. End Function

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