I have a flex scanner that run correctly for a long time, even on files with some Chinese characters.
Recently I want to make it faster, and I add the "%option full", it indeed get 3X faster. but may fail on some files with comments that contain chinese characters.
The error message is "start-condition stack underflow".
I add some printing statement to my lex source code, and find that the scanner print this error in some start condiiton SC, but it have NOT run any code segment that contain "yy_push_state(SC)". So I think there may be some overflow in the flex buffer.
So what to do?
For historical reasons (or something), if you use %option full or %option fast, then flex will default to producing a 7-bit scanner (i.e. %option 7bit).
That's really unsafe, since the 7-bit scanner does not even attempt to verify that the scanned text consists only of 7-bit ("ASCII") characters, and its behaviour in the case that it encounters a character with the high-order bit set is undefined. That will definitely happen if your input is UTF-8 or multibyte.
So you need to specify %option 8bit full. This will increase the size of your scanner tables, but these days that might not matter much. You might want to try %option 8bit full ecs as an intermediate setting. (I'm pretty sure that 8bit is not necessary with ecs, but it can't hurt.)
Related
My non-Unicode Delphi 7 application allows users to open .txt files.
Sometimes UTF-8/UNICODE .txt files are tried to be opened causing a problem.
I need a function that detects if the user is opening a txt file with UTF-8 or Unicode encoding and Converts it to the system's default code page (ANSI) encoding automatically when possible so that it can be used by the app.
In cases when converting is not possible, the function should return an error.
The ReturnAsAnsiText(filename) function should open the txt file, make detection and conversion in steps like this;
If the byte stream has no bytes values over x7F, its ANSI, return as is
If the byte stream has bytes values over x7F, convert from UTF-8
If the stream has BOM; try Unicode conversion
If conversion to the system's current code page is not possible, return NULL to indicate an error.
It will be an OK limit for this function, that the user can open only those files that match their region/codepage (Control Panel Regional Region Settings for non-Unicode apps).
The conversion function ReturnAsAnsiText, as you designed, will have a number of issues:
The Delphi 7 application may not be able to open files where the filename using UTF-8 or UTF-16.
UTF-8 (and other Unicode) usage has increased significantly from 2019. Current web pages are between 98% and 100% UTF-8 depending on the language.
You design will incorrectly translate some text that a standards compliant would handle.
Creating the ReturnAsAnsiText is beyond the scope of an answer, but you should look at locating a library you can use instead of creating a new function. I haven't used Delphi 2005 (I believe that is 7), but I found this MIT licensed library that may get you there. It has a number of caveats:
It doesn't support all forms of BOM.
It doesn't support all encodings.
There is no universal "best-fit" behavior for single-byte character sets.
There are other issues that are tangentially described in this question. You wouldn't use an external command, but I used one here to demonstrate the point:
% iconv -f utf-8 -t ascii//TRANSLIT < hello.utf8
^h'elloe
iconv: (stdin):1:6: cannot convert
% iconv -f utf-8 -t ascii < hello.utf8
iconv: (stdin):1:0: cannot convert
Enabling TRANSLIT in standards based libraries supports converting characters like é to ASCII e. But still fails on characters like π, since there are no similar in form ASCII characters.
Your required answer would need massive UTF-8 and UTF-16 translation tables for every supported code page and BMP, and would still be unable to reliably detect the source encoding.
Notepad has trouble with this issue.
The solution as requested, would probably entail more effort than you put into the original program.
Possible solutions
Add a text editor into your program. If you write it, you will be able to read it.
The following solution pushes the translation to established tables provided by Windows.
Use the Win32 API native calls translate strings using functions like WideCharToMultiByte, but even this has its drawbacks(from the referenced page, the note is more relevant to the topic, but the caution is important for security):
Caution Using the WideCharToMultiByte function incorrectly can compromise the security of your application. Calling this function can easily cause a buffer overrun because the size of the input buffer indicated by lpWideCharStr equals the number of characters in the Unicode string, while the size of the output buffer indicated by lpMultiByteStr equals the number of bytes. To avoid a buffer overrun, your application must specify a buffer size appropriate for the data type the buffer receives.
Data converted from UTF-16 to non-Unicode encodings is subject to data loss, because a code page might not be able to represent every character used in the specific Unicode data. For more information, see Security Considerations: International Features.
Note The ANSI code pages can be different on different computers, or can be changed for a single computer, leading to data corruption. For the most consistent results, applications should use Unicode, such as UTF-8 or UTF-16, instead of a specific code page, unless legacy standards or data formats prevent the use of Unicode. If using Unicode is not possible, applications should tag the data stream with the appropriate encoding name when protocols allow it. HTML and XML files allow tagging, but text files do not.
This solution still has the guess the encoding problem, but if a BOM is present, this is one of the best translators possible.
Simply require the text file to be saved in the local code page.
Other thoughts:
ANSI, ASCII, and UTF-8 are all separate encodings above 127 and the control characters are handled differently.
In UTF-16 every other byte(zero first) of ASCII encoded text is 0. This is not covered in your "rules".
You simply have to search for the Turkish i to understand the complexities of Unicode translations and comparisons.
Leverage any expectations of the file contents to establish a coherent baseline comparison to make an educated guess.
For example, if it is a .csv file, find a comma in the various formats...
Bottom Line
There is no perfect general solution, only specific solutions tailored to your specific needs, which were extremely broad in the question.
I'm playing around with ANSI escape sequences, e.g.
echo -e "\e[91mHello\e[m"
on a Linux console to display colored text.
Now I try to use superscript and subscript output like a=b².
I read here and here about: Partial Line Down (subscript) and Partial Line Up (superscript) but I'm not sure about the exact syntax and even which terminal client might supports this.
Any suggestions about this?
Possibly some commercial product supports it, but it's not supported by any terminal emulator you'll encounter (unless someone modifies one just to prove a point).
The standard describes possible escape sequences, but there is no requirement that any given sequence is supported by any terminal. There are commonly supported (and assumed) sequences such as clearing the screen, but even for that, not all terminals have supported the feature.
The reason is that terminal emulators are generally used with applications (such as text editors) which assume a regular set of rows/columns, and that the text is shown compactly (no extra space such as would be needed to allow for partial line movement. Back in the day when people used typewriters, it was common to have 1.5 or 2.0 line-spacing, and get no more than 33 lines on a page. That changed, long ago.
The need for subscripts/superscripts didn't go away — Unicode provides a usable set of characters with that representation (see Superscripts and Subscripts
Range: 2070–209F)
Further reading:
Your New Royal Portable (1953).
Line Spacing - Butterick's Practical Typography
console_codes - Linux console escape and control sequences
For a work project I am using headless Squeak on a (displayless, remote) Linuxserver and also using Squeak on a Windows developer-machine.
Code on the developer machine is managed using Monticello. I have to copy the mcz to the server using SFTP unfortunately (e.g. having a push-repository on the server is not possible for security reasons). The code is then merged by eg:
MczInstaller installFileNamed: 'name-b.18.mcz'.
Which generally works.
Unfortunately our code-base contains strings that contain Umlauts and other non-ascii characters. During the Monticello-reimport some of them get replaced with other characters and some get replaced with nothing.
I also tried e.g.
MczInstaller installStream: (FileStream readOnlyFileNamed: '...') binary
(note .mcz's are actually .zip's, so binary should be appropriate, i guess it is the default anyway)
Finding out how to make Monticello's transfer preserve the Squeak internal-encoding of non-ascii's is the main Goal of my question. Changing all the source code to only use ascii-strings is (at least in this codebase) much less desirable because manual labor is involved. If you are interested in why it is not a simple grep-replace in this case read this side note:
(Side note: (A simplified/special case) The codebase uses Seaside's #text: method to render strings that contain chars that have to be html-escaped. This works fine with our non-ascii's e.g. it converts ä into ä, if we were to grep-replace the literal ä's by ä explicitly, then we would have to use the #html: method instead (else double-escape), however that would then require that we replace all other characters that have to be html-escaped as well (e.g. &), but then again the source-code itself contains such characters. And there are other cases, like some #text:'s that take third-party strings, they may not be replaced by #html's...)
Squeak does use unicode (ISO 10646) internally for encoding characters in a String.
It might use extension like CP1252 for characters in range 16r80 to: 16r9F, but I'm not really sure anymore.
The characters codes are written as is on the stream source.st, and these codes are made of a single byte for a ByteString when all characters are <= 16rFF. In this case, the file should look like encoded in ISO-8859-L1 or CP1252.
If ever you have character codes > 16rFF, then a WideString is used in Squeak. Once again the codes are written as is on the stream source.st, but this time these are 32 bits codes (written in big-endian order). Technically, the encoding is thus UTF-32BE.
Now what does MczInstaller does? It uses the snapshot/source.st file, and uses setConverterForCode for reading this file, which is either UTF-8 or MacRoman... So non ASCII characters might get changed, and this is even worse in case of WideString which will be re-interpreted as ByteString.
MC itself doesn't use the snapshot/source.st member in the archive.
It rather uses the snapshot.bin (see code in MCMczReader, MCMczWriter).
This is a binary file whose format is governed by DataStream.
The snippet that you should use is rather:
MCMczReader loadVersionFile: 'YourPackage-b.18.mcz'
Monticello isn't really aware of character encoding. I don't know the present situation in squeak but the last time I've looked into it there was an assumed character encoding of latin1. But that would mean it should work flawlessly in your situation.
It should work somehow anyway if you are writing and reading from the same kind of image. If the proper character encoding fails usually the internal byte representation is written from memory to disk. While this prevents any cross dialect exchange of packages it should work if using the same image kind.
Anyway there are things that should or could work but they often go wrong. So most projects try to avoid using non 7bit characters in their code.
You don't need to convert non 7bit characters to HTML entities. You can use
Character value: 228
for producing an ä in your code without using non 7bit characters. On every character you like to add a conversion you can do
$ä asciiValue => 228
I know this is not the kind of answer some would want to get. But monticello is one of these things that still need to be adjusted for proper character encoding.
My application is parsing incoming emails. I try to parse them as best as possible but every now and then I get one with puzzling content. This time is an email that looks to be in ASCII but the specified charset is: ansi_x3.110-1983.
My application handles it correctly by defaulting to ASCII, but it throws a warning which I'd like to stop receiving, so my question is: what is ansi_x3.110-1983 and what should I do with it?
According to this page on the IANA's site, ANSI_X3.110-1983 is also known as:
iso-ir-99
CSA_T500-1983
NAPLPS
csISO99NAPLPS
Of those, only the name NAPLPS seems interesting or informative. If you can, consider getting in touch with the people sending those mails. If they're really using Prodigy in this day and age, I'd be amazed.
The IANA site also has a pointer to RFC 1345, which contains a description of the bytes and the characters that they map to. Compared to ISO-8859-1, the control characters are the same, as are most of the punctuation, all of the numbers and letters, and most of the remaining characters in the first 7 bits.
You could possibly use the guide in the RFC to write a tool to map the characters over, if someone hasn't written a tool for it already. To be honest, it may be easier to simply ignore the whines about the weird character set given that the character mapping is close enough to what is expected anyway...
Even today, one frequently sees character encoding problems with significant frequency. Take for example this recent job post:
(Note: This is an example, not a spam job post... :-)
I have recently seen that exact error on websites, in popular IM programs, and in the background graphics on CNN.
My two-part question:
What causes this particular, common encoding issue?
As a developer, what should I do with user input to avoid common encoding issues like
this one? If this question requires simplification to provide a
meaningful answer, assume content is entered through a web browser.
What causes this particular, common encoding issue?
This will occur when the conversion between characters and bytes has taken place using the wrong charset. Computers handles data as bytes, but to represent the data in a sensible manner to humans, it has to be converted to characters (strings). This conversion takes place based on a charset of which there are many different ones.
In the particular ’ example, this is a typical CP1252 representation of the Unicode Character 'RIGHT SINQLE QUOTATION MARK' (U+2019) ’ which was been read using UTF-8. In UTF-8, that character exist of the bytes 0xE2, 0x80 and 0x99. If you check the CP1252 codepage layout, then you'll see that those bytes represent exactly the characters â, € and ™.
This can be caused by the website not having read in the original source properly (it should have used CP1252 for this), or is displaying an UTF-8 page with the wrong charset=CP1252 attribute in Content-Type response header (or the attribute is missing; on Windows machines the default charset of CP1252 would be used then).
As a developer, what should I do with user input to avoid common encoding issues like this one? If this question requires simplification to provide a meaningful answer, assume content is entered through a web browser.
Ensure that you read the characters from arbitrary byte stream sources (e.g. a file, an URL, a network socket, etc) using a known and predefinied charset. Then, ensure that you're consistently storing, writing and sending it using an Unicode charset, preferably UTF-8.
If you're familiar with Java (your question history confirms this), you may find this article useful.