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libxo output breaks if buffer exceeds 8kb #37

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allanjude opened this issue May 4, 2015 · 4 comments
Closed

libxo output breaks if buffer exceeds 8kb #37

allanjude opened this issue May 4, 2015 · 4 comments

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@allanjude
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While converting the FreeBSD procstat utility to libxo, I noticed that if the output exceeds 8kb, and stdout is a file or a pipe, the content is truncated.

to reproduce, run some command that produces more than 8192 bytes of data via libxo, and redirect stdout to a file, or pipe it to less or similar. The output will be truncated.
@allanjude
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I could be wrong, but it looks like the problem is caused by the call to xo_buf_has_room() not considering some part of the pretty printing:

ALLAN: xo_buf_has_room: xb_size: 8192, curp: 8154, len: 12
ALLAN: xo_buf_has_room: xb_size: 8192, curp: 8166, len: 1
ALLAN: xo_buf_has_room: xb_size: 8192, curp: 8167, len: 5
ALLAN: xo_buf_has_room: xb_size: 8192, curp: 8172, len: 2
ALLAN: xo_buf_has_room: xb_size: 8192, curp: 8174, len: 1
ALLAN: xo_buf_has_room: xb_size: 8192, curp: 8175, len: 5
ALLAN: xo_buf_has_room: xb_size: 8192, curp: 8212, len: 12
ALLAN: Expanded buffer
ALLAN: xo_buf_has_room: xb_size: 16384, curp: 8224, len: 1
ALLAN: xo_buf_has_room: xb_size: 16384, curp: 8225, len: 4

It doesn't appear to expand the buffer until the cur pointer has passed the end of the buffer.

@philshafer
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Could you please retry with the current code? I fixed an embarrassingly bad issue in xo_vsnprintf:

  • if (rc > xbp->xb_size) {
  • if (rc >= left) {

in commit 1f66642 that’s part of libxo-0.3.3. IIRC the fix is in 0.3.2 also.

But I’m fairly confident this was the issue you are seeing.

Thanks,
Phil

On May 4, 2015, at 12:40 AM, Allan Jude notifications@github.com wrote:

I could be wrong, but it looks like the problem is caused by the call to xo_buf_has_room() not considering some part of the pretty printing:

ALLAN: xo_buf_has_room: xb_size: 8192, curp: 8154, len: 12
ALLAN: xo_buf_has_room: xb_size: 8192, curp: 8166, len: 1
ALLAN: xo_buf_has_room: xb_size: 8192, curp: 8167, len: 5
ALLAN: xo_buf_has_room: xb_size: 8192, curp: 8172, len: 2
ALLAN: xo_buf_has_room: xb_size: 8192, curp: 8174, len: 1
ALLAN: xo_buf_has_room: xb_size: 8192, curp: 8175, len: 5
ALLAN: xo_buf_has_room: xb_size: 8192, curp: 8212, len: 12
ALLAN: Expanded buffer
ALLAN: xo_buf_has_room: xb_size: 16384, curp: 8224, len: 1
ALLAN: xo_buf_has_room: xb_size: 16384, curp: 8225, len: 4

It doesn't appear to expand the buffer until the cur pointer has passed the end of the buffer.

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@allanjude
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I have 0.3.2 with that fix.

The issue seems to be that the exact same bug exists in:
xo_printf_v()

ALLAN: xo_buf_has_room: xb_size: 8192, curp: 8166, len: 1
ALLAN: xo_buf_has_room: xb_size: 8192, curp: 8167, len: 5
ALLAN: xo_buf_has_room: xb_size: 8192, curp: 8172, len: 2
ALLAN: xo_buf_has_room: xb_size: 8192, curp: 8174, len: 1
ALLAN: xo_buf_has_room: xb_size: 8192, curp: 8175, len: 5
ALLAN: xo_printf_v: wrote 12 of 12 bytes
ALLAN: xo_printf_v: wrote 20 of 0 bytes
ALLAN: xo_buf_has_room: xb_size: 8192, curp: 8212, len: 12
ALLAN: Expanding Buffer
ALLAN: xo_buf_has_room: xb_size: 16384, curp: 8224, len: 1
ALLAN: xo_buf_has_room: xb_size: 16384, curp: 8225, len: 4

allanjude added a commit to allanjude/libxo that referenced this issue May 4, 2015
@allanjude
fix buffer checking in xo_printf_v, xo_warn_hcv, and xo_message_hcv
56b8b35 
When checking the return value of vsnprintf, these functions compared against the size of the buffer, rather than the number of bytes remaining in the buffer, and so fail to grow the buffer when it was insufficient to fit the new content.

Related to: 1f66642
Fixes: Juniper#37
@allanjude allanjude mentioned this issue May 4, 2015
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@philshafer
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Fixed in 0.3.4

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@allanjude @philshafer