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digitalmars.D.bugs - [Issue 9421] New: (Compiler internals) Change OutBuffer's interface

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=9421

           Summary: (Compiler internals) Change OutBuffer's interface
           Product: D
           Version: D1 & D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: yebblies gmail.com



Using OutBuffer makes it easy to forget to zero-terminate strings and create
dangling pointers.  I'm think we should make OutBuffer a little less error
prone.

Changes:
- Get rid of toChars
- Add extractString which checks for a '\0' then takes ownership of the
internal buffer
- Add scopedString which checks for a '\0' then return a reference to the
internal buffer
- Add scopedData which returns a reference to the internal buffer

Benefit:
- Nobody will use toChars thinking that it copies/owns the data
- Harder to forget to zero-terminate strings
- Hopefully less casting

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Jan 29 2013
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=9421


Andrej Mitrovic <andrej.mitrovich gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |andrej.mitrovich gmail.com



18:22:42 PST ---


 Using OutBuffer makes it easy to forget to zero-terminate strings and create
 dangling pointers.  I'm think we should make OutBuffer a little less error
 prone.
 
 Changes:
 - Get rid of toChars


There's also toString, which seems to be almost the same as toChars. And the
OutBuffer implementation is split across src/root/root.c and
src/backend/outbuf.c

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Feb 06 2013
prev sibling next sibling parent d-bugmail puremagic.com writes:
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18:29:02 PST ---
So if I got it right we'd have:

char *OutBuffer::extractString()
{
    writeByte(0);
    char *p;
    p = (char *)data;
    data = NULL;
    offset = 0;
    size = 0;
    return p;
}

char *OutBuffer::scopedString()
{
    writeByte(0);
    return (char *)data;
}

char *OutBuffer::scopedData()
{
    return (char *)data;
}

Is that right?

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Feb 06 2013
prev sibling next sibling parent d-bugmail puremagic.com writes:
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The functions shouldn't append a '\0' if data already ends with one, and I'm
not sure scopedString should _ever_ modify it.  Other than that it looks right.

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11:44:09 PST ---



 
 The functions shouldn't append a '\0' if data already ends with one, and I'm
 not sure scopedString should _ever_ modify it.  Other than that it looks right.


Then I don't understand what you mean by: "Add scopedString which checks for a
'\0' then return a reference to the internal buffer".

It checks for a \0, and does what if it doesn't find it?

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Feb 07 2013
prev sibling next sibling parent d-bugmail puremagic.com writes:
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 The functions shouldn't append a '\0' if data already ends with one, and I'm
 not sure scopedString should _ever_ modify it.  Other than that it looks right.


 
 Then I don't understand what you mean by: "Add scopedString which checks for a
 '\0' then return a reference to the internal buffer".
 
 It checks for a \0, and does what if it doesn't find it?


assert(0)

The idea being that getting a pointer to the internal string shouldn't change
the contents.  Maybe it would be more useful to append a zero, I don't know.

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20:30:07 PST ---


 The idea being that getting a pointer to the internal string shouldn't change
 the contents.


Ok, but then what do we need scopedData for? If we're returning a char* and
it's not zero-terminated I don't see how it can be used.

So far I've got this:

/** Extract a zero-terminated string.
    The caller takes ownership. */
const char *OutBuffer::extractString()
{
    if (!data || data[offset] != '\0')
        writeByte(0);
    char *p;
    p = (char *)data;
    data = NULL;
    offset = 0;
    size = 0;
    return p;
}

/** Verify the internal buffer is zero-terminated
    and return a reference to it. */
const char *OutBuffer::scopedString()
{
    assert(data && data[offset] == '\0');
    return (char *)data;
}

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Feb 12 2013
prev sibling next sibling parent d-bugmail puremagic.com writes:
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20:31:04 PST ---




 The idea being that getting a pointer to the internal string shouldn't change
 the contents.


 
 Ok, but then what do we need scopedData for? If we're returning a char* and
 it's not zero-terminated I don't see how it can be used.
 
 So far I've got this:


Those casts should have been (const char*).

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20:37:10 PST ---






 The idea being that getting a pointer to the internal string shouldn't change
 the contents.


 
 Ok, but then what do we need scopedData for? If we're returning a char* and
 it's not zero-terminated I don't see how it can be used.
 
 So far I've got this:


 
 Those casts should have been (const char*).


Or maybe they should remain (char *) if ownership is taken. :)

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 The idea being that getting a pointer to the internal string shouldn't change
 the contents.


 
 Ok, but then what do we need scopedData for? If we're returning a char* and
 it's not zero-terminated I don't see how it can be used.
 


You would use it in the same places as scopedString, but when using OutBuffer
for binary instead of text.  i.e. when you know the data won't be escaped.

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20:44:36 PST ---






 The idea being that getting a pointer to the internal string shouldn't change
 the contents.


 
 Ok, but then what do we need scopedData for? If we're returning a char* and
 it's not zero-terminated I don't see how it can be used.
 


 
 You would use it in the same places as scopedString, but when using OutBuffer
 for binary instead of text.  i.e. when you know the data won't be escaped.


Code in DMD already uses .data directly though.

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