src/pkg/tabwriter/tabwriter.go - go - Git at Google

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 // Package tabwriter implements a write filter (tabwriter.Writer) that
 // translates tabbed columns in input into properly aligned text.
 //
 // The package is using the Elastic Tabstops algorithm described at
 // http://nickgravgaard.com/elastictabstops/index.html.
 //
 package tabwriter

 import (
 	"bytes"
 	"io"
 	"os"
 	"utf8"
 )


 // ----------------------------------------------------------------------------
 // Filter implementation

 // A cell represents a segment of text terminated by tabs or line breaks.
 // The text itself is stored in a separate buffer; cell only describes the
 // segment's size in bytes, its width in runes, and whether it's an htab
 // ('\t') terminated cell.
 //
 type cell struct {
 	size  int  // cell size in bytes
 	width int  // cell width in runes
 	htab  bool // true if the cell is terminated by an htab ('\t')
 }


 // A Writer is a filter that inserts padding around tab-delimited
 // columns in its input to align them in the output.
 //
 // The Writer treats incoming bytes as UTF-8 encoded text consisting
 // of cells terminated by (horizontal or vertical) tabs or line
 // breaks (newline or formfeed characters). Cells in adjacent lines
 // constitute a column. The Writer inserts padding as needed to
 // make all cells in a column have the same width, effectively
 // aligning the columns. It assumes that all characters have the
 // same width except for tabs for which a tabwidth must be specified.
 // Note that cells are tab-terminated, not tab-separated: trailing
 // non-tab text at the end of a line does not form a column cell.
 //
 // The Writer assumes that all Unicode code points have the same width;
 // this may not be true in some fonts.
 //
 // If DiscardEmptyColumns is set, empty columns that are terminated
 // entirely by vertical (or "soft") tabs are discarded. Columns
 // terminated by horizontal (or "hard") tabs are not affected by
 // this flag.
 //
 // If a Writer is configured to filter HTML, HTML tags and entities
 // are simply passed through. The widths of tags and entities are
 // assumed to be zero (tags) and one (entities) for formatting purposes.
 //
 // A segment of text may be escaped by bracketing it with Escape
 // characters. The tabwriter passes escaped text segments through
 // unchanged. In particular, it does not interpret any tabs or line
 // breaks within the segment. If the StripEscape flag is set, the
 // Escape characters are stripped from the output; otherwise they
 // are passed through as well. For the purpose of formatting, the
 // width of the escaped text is always computed excluding the Escape
 // characters.
 //
 // The formfeed character ('\f') acts like a newline but it also
 // terminates all columns in the current line (effectively calling
 // Flush). Cells in the next line start new columns. Unless found
 // inside an HTML tag or inside an escaped text segment, formfeed
 // characters appear as newlines in the output.
 //
 // The Writer must buffer input internally, because proper spacing
 // of one line may depend on the cells in future lines. Clients must
 // call Flush when done calling Write.
 //
 type Writer struct {
 	// configuration
 	output   io.Writer
 	minwidth int
 	tabwidth int
 	padding  int
 	padbytes [8]byte
 	flags    uint

 	// current state
 	buf     bytes.Buffer // collected text excluding tabs or line breaks
 	pos     int          // buffer position up to which cell.width of incomplete cell has been computed
 	cell    cell         // current incomplete cell; cell.width is up to buf[pos] excluding ignored sections
 	endChar byte         // terminating char of escaped sequence (Escape for escapes, '>', ';' for HTML tags/entities, or 0)
 	lines   [][]cell     // list of lines; each line is a list of cells
 	widths  []int        // list of column widths in runes - re-used during formatting
 }


 func (b *Writer) addLine() { b.lines = append(b.lines, []cell{}) }


 // Reset the current state.
 func (b *Writer) reset() {
 	b.buf.Reset()
 	b.pos = 0
 	b.cell = cell{}
 	b.endChar = 0
 	b.lines = b.lines[0:0]
 	b.widths = b.widths[0:0]
 	b.addLine()
 }


 // Internal representation (current state):
 //
 // - all text written is appended to buf; tabs and line breaks are stripped away
 // - at any given time there is a (possibly empty) incomplete cell at the end
 //   (the cell starts after a tab or line break)
 // - cell.size is the number of bytes belonging to the cell so far
 // - cell.width is text width in runes of that cell from the start of the cell to
 //   position pos; html tags and entities are excluded from this width if html
 //   filtering is enabled
 // - the sizes and widths of processed text are kept in the lines list
 //   which contains a list of cells for each line
 // - the widths list is a temporary list with current widths used during
 //   formatting; it is kept in Writer because it's re-used
 //
 //                    |<---------- size ---------->|
 //                    |                            |
 //                    |<- width ->|<- ignored ->|  |
 //                    |           |             |  |
 // [---processed---tab------------<tag>...</tag>...]
 // ^                  ^                         ^
 // |                  |                         |
 // buf                start of incomplete cell  pos


 // Formatting can be controlled with these flags.
 const (
 	// Ignore html tags and treat entities (starting with '&'
 	// and ending in ';') as single characters (width = 1).
 	FilterHTML uint = 1 << iota

 	// Strip Escape characters bracketing escaped text segments
 	// instead of passing them through unchanged with the text.
 	StripEscape

 	// Force right-alignment of cell content.
 	// Default is left-alignment.
 	AlignRight

 	// Handle empty columns as if they were not present in
 	// the input in the first place.
 	DiscardEmptyColumns

 	// Always use tabs for indentation columns (i.e., padding of
 	// leading empty cells on the left) independent of padchar.
 	TabIndent

 	// Print a vertical bar ('|') between columns (after formatting).
 	// Discarded columns appear as zero-width columns ("||").
 	Debug
 )


 // A Writer must be initialized with a call to Init. The first parameter (output)
 // specifies the filter output. The remaining parameters control the formatting:
 //
 //	minwidth	minimal cell width including any padding
 //	tabwidth	width of tab characters (equivalent number of spaces)
 //	padding		padding added to a cell before computing its width
 //	padchar		ASCII char used for padding
 //			if padchar == '\t', the Writer will assume that the
 //			width of a '\t' in the formatted output is tabwidth,
 //			and cells are left-aligned independent of align_left
 //			(for correct-looking results, tabwidth must correspond
 //			to the tab width in the viewer displaying the result)
 //	flags		formatting control
 //
 // To format in tab-separated columns with a tab stop of 8:
 //	b.Init(w, 8, 1, 8, '\t', 0);
 //
 // To format in space-separated columns with at least 4 spaces between columns:
 //	b.Init(w, 0, 4, 8, ' ', 0);
 //
 func (b *Writer) Init(output io.Writer, minwidth, tabwidth, padding int, padchar byte, flags uint) *Writer {
 	if minwidth < 0 || tabwidth < 0 || padding < 0 {
 		panic("negative minwidth, tabwidth, or padding")
 	}
 	b.output = output
 	b.minwidth = minwidth
 	b.tabwidth = tabwidth
 	b.padding = padding
 	for i := range b.padbytes {
 		b.padbytes[i] = padchar
 	}
 	if padchar == '\t' {
 		// tab padding enforces left-alignment
 		flags &^= AlignRight
 	}
 	b.flags = flags

 	b.reset()

 	return b
 }


 // debugging support (keep code around)
 func (b *Writer) dump() {
 	pos := 0
 	for i, line := range b.lines {
 		print("(", i, ") ")
 		for _, c := range line {
 			print("[", string(b.buf.Bytes()[pos:pos+c.size]), "]")
 			pos += c.size
 		}
 		print("\n")
 	}
 	print("\n")
 }


 // local error wrapper so we can distinguish os.Errors we want to return
 // as errors from genuine panics (which we don't want to return as errors)
 type osError struct {
 	err os.Error
 }


 func (b *Writer) write0(buf []byte) {
 	n, err := b.output.Write(buf)
 	if n != len(buf) && err == nil {
 		err = os.EIO
 	}
 	if err != nil {
 		panic(osError{err})
 	}
 }


 func (b *Writer) writeN(src []byte, n int) {
 	for n > len(src) {
 		b.write0(src)
 		n -= len(src)
 	}
 	b.write0(src[0:n])
 }


 var (
 	newline = []byte{'\n'}
 	tabs    = []byte("\t\t\t\t\t\t\t\t")
 )


 func (b *Writer) writePadding(textw, cellw int, useTabs bool) {
 	if b.padbytes[0] == '\t' || useTabs {
 		// padding is done with tabs
 		if b.tabwidth == 0 {
 			return // tabs have no width - can't do any padding
 		}
 		// make cellw the smallest multiple of b.tabwidth
 		cellw = (cellw + b.tabwidth - 1) / b.tabwidth * b.tabwidth
 		n := cellw - textw // amount of padding
 		if n < 0 {
 			panic("internal error")
 		}
 		b.writeN(tabs, (n+b.tabwidth-1)/b.tabwidth)
 		return
 	}

 	// padding is done with non-tab characters
 	b.writeN(b.padbytes[0:], cellw-textw)
 }


 var vbar = []byte{'|'}

 func (b *Writer) writeLines(pos0 int, line0, line1 int) (pos int) {
 	pos = pos0
 	for i := line0; i < line1; i++ {
 		line := b.lines[i]

 		// if TabIndent is set, use tabs to pad leading empty cells
 		useTabs := b.flags&TabIndent != 0

 		for j, c := range line {
 			if j > 0 && b.flags&Debug != 0 {
 				// indicate column break
 				b.write0(vbar)
 			}

 			if c.size == 0 {
 				// empty cell
 				if j < len(b.widths) {
 					b.writePadding(c.width, b.widths[j], useTabs)
 				}
 			} else {
 				// non-empty cell
 				useTabs = false
 				if b.flags&AlignRight == 0 { // align left
 					b.write0(b.buf.Bytes()[pos : pos+c.size])
 					pos += c.size
 					if j < len(b.widths) {
 						b.writePadding(c.width, b.widths[j], false)
 					}
 				} else { // align right
 					if j < len(b.widths) {
 						b.writePadding(c.width, b.widths[j], false)
 					}
 					b.write0(b.buf.Bytes()[pos : pos+c.size])
 					pos += c.size
 				}
 			}
 		}

 		if i+1 == len(b.lines) {
 			// last buffered line - we don't have a newline, so just write
 			// any outstanding buffered data
 			b.write0(b.buf.Bytes()[pos : pos+b.cell.size])
 			pos += b.cell.size
 		} else {
 			// not the last line - write newline
 			b.write0(newline)
 		}
 	}
 	return
 }


 // Format the text between line0 and line1 (excluding line1); pos
 // is the buffer position corresponding to the beginning of line0.
 // Returns the buffer position corresponding to the beginning of
 // line1 and an error, if any.
 //
 func (b *Writer) format(pos0 int, line0, line1 int) (pos int) {
 	pos = pos0
 	column := len(b.widths)
 	for this := line0; this < line1; this++ {
 		line := b.lines[this]

 		if column < len(line)-1 {
 			// cell exists in this column => this line
 			// has more cells than the previous line
 			// (the last cell per line is ignored because cells are
 			// tab-terminated; the last cell per line describes the
 			// text before the newline/formfeed and does not belong
 			// to a column)

 			// print unprinted lines until beginning of block
 			pos = b.writeLines(pos, line0, this)
 			line0 = this

 			// column block begin
 			width := b.minwidth // minimal column width
 			discardable := true // true if all cells in this column are empty and "soft"
 			for ; this < line1; this++ {
 				line = b.lines[this]
 				if column < len(line)-1 {
 					// cell exists in this column
 					c := line[column]
 					// update width
 					if w := c.width + b.padding; w > width {
 						width = w
 					}
 					// update discardable
 					if c.width > 0 || c.htab {
 						discardable = false
 					}
 				} else {
 					break
 				}
 			}
 			// column block end

 			// discard empty columns if necessary
 			if discardable && b.flags&DiscardEmptyColumns != 0 {
 				width = 0
 			}

 			// format and print all columns to the right of this column
 			// (we know the widths of this column and all columns to the left)
 			b.widths = append(b.widths, width) // push width
 			pos = b.format(pos, line0, this)
 			b.widths = b.widths[0 : len(b.widths)-1] // pop width
 			line0 = this
 		}
 	}

 	// print unprinted lines until end
 	return b.writeLines(pos, line0, line1)
 }


 // Append text to current cell.
 func (b *Writer) append(text []byte) {
 	b.buf.Write(text)
 	b.cell.size += len(text)
 }


 // Update the cell width.
 func (b *Writer) updateWidth() {
 	b.cell.width += utf8.RuneCount(b.buf.Bytes()[b.pos:b.buf.Len()])
 	b.pos = b.buf.Len()
 }


 // To escape a text segment, bracket it with Escape characters.
 // For instance, the tab in this string "Ignore this tab: \xff\t\xff"
 // does not terminate a cell and constitutes a single character of
 // width one for formatting purposes.
 //
 // The value 0xff was chosen because it cannot appear in a valid UTF-8 sequence.
 //
 const Escape = '\xff'


 // Start escaped mode.
 func (b *Writer) startEscape(ch byte) {
 	switch ch {
 	case Escape:
 		b.endChar = Escape
 	case '<':
 		b.endChar = '>'
 	case '&':
 		b.endChar = ';'
 	}
 }


 // Terminate escaped mode. If the escaped text was an HTML tag, its width
 // is assumed to be zero for formatting purposes; if it was an HTML entity,
 // its width is assumed to be one. In all other cases, the width is the
 // unicode width of the text.
 //
 func (b *Writer) endEscape() {
 	switch b.endChar {
 	case Escape:
 		b.updateWidth()
 		if b.flags&StripEscape == 0 {
 			b.cell.width -= 2 // don't count the Escape chars
 		}
 	case '>': // tag of zero width
 	case ';':
 		b.cell.width++ // entity, count as one rune
 	}
 	b.pos = b.buf.Len()
 	b.endChar = 0
 }


 // Terminate the current cell by adding it to the list of cells of the
 // current line. Returns the number of cells in that line.
 //
 func (b *Writer) terminateCell(htab bool) int {
 	b.cell.htab = htab
 	line := &b.lines[len(b.lines)-1]
 	*line = append(*line, b.cell)
 	b.cell = cell{}
 	return len(*line)
 }


 func handlePanic(err *os.Error) {
 	if e := recover(); e != nil {
 		*err = e.(osError).err // re-panics if it's not a local osError
 	}
 }


 // Flush should be called after the last call to Write to ensure
 // that any data buffered in the Writer is written to output. Any
 // incomplete escape sequence at the end is simply considered
 // complete for formatting purposes.
 //
 func (b *Writer) Flush() (err os.Error) {
 	defer b.reset() // even in the presence of errors
 	defer handlePanic(&err)

 	// add current cell if not empty
 	if b.cell.size > 0 {
 		if b.endChar != 0 {
 			// inside escape - terminate it even if incomplete
 			b.endEscape()
 		}
 		b.terminateCell(false)
 	}

 	// format contents of buffer
 	b.format(0, 0, len(b.lines))

 	return
 }


 var hbar = []byte("---\n")

 // Write writes buf to the writer b.
 // The only errors returned are ones encountered
 // while writing to the underlying output stream.
 //
 func (b *Writer) Write(buf []byte) (n int, err os.Error) {
 	defer handlePanic(&err)

 	// split text into cells
 	n = 0
 	for i, ch := range buf {
 		if b.endChar == 0 {
 			// outside escape
 			switch ch {
 			case '\t', '\v', '\n', '\f':
 				// end of cell
 				b.append(buf[n:i])
 				b.updateWidth()
 				n = i + 1 // ch consumed
 				ncells := b.terminateCell(ch == '\t')
 				if ch == '\n' || ch == '\f' {
 					// terminate line
 					b.addLine()
 					if ch == '\f' || ncells == 1 {
 						// A '\f' always forces a flush. Otherwise, if the previous
 						// line has only one cell which does not have an impact on
 						// the formatting of the following lines (the last cell per
 						// line is ignored by format()), thus we can flush the
 						// Writer contents.
 						if err = b.Flush(); err != nil {
 							return
 						}
 						if ch == '\f' && b.flags&Debug != 0 {
 							// indicate section break
 							b.write0(hbar)
 						}
 					}
 				}

 			case Escape:
 				// start of escaped sequence
 				b.append(buf[n:i])
 				b.updateWidth()
 				n = i
 				if b.flags&StripEscape != 0 {
 					n++ // strip Escape
 				}
 				b.startEscape(Escape)

 			case '<', '&':
 				// possibly an html tag/entity
 				if b.flags&FilterHTML != 0 {
 					// begin of tag/entity
 					b.append(buf[n:i])
 					b.updateWidth()
 					n = i
 					b.startEscape(ch)
 				}
 			}

 		} else {
 			// inside escape
 			if ch == b.endChar {
 				// end of tag/entity
 				j := i + 1
 				if ch == Escape && b.flags&StripEscape != 0 {
 					j = i // strip Escape
 				}
 				b.append(buf[n:j])
 				n = i + 1 // ch consumed
 				b.endEscape()
 			}
 		}
 	}

 	// append leftover text
 	b.append(buf[n:])
 	n = len(buf)
 	return
 }


 // NewWriter allocates and initializes a new tabwriter.Writer.
 // The parameters are the same as for the the Init function.
 //
 func NewWriter(output io.Writer, minwidth, tabwidth, padding int, padchar byte, flags uint) *Writer {
 	return new(Writer).Init(output, minwidth, tabwidth, padding, padchar, flags)
 }
	// Copyright 2009 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	// Package tabwriter implements a write filter (tabwriter.Writer) that
	// translates tabbed columns in input into properly aligned text.
	//
	// The package is using the Elastic Tabstops algorithm described at
	// http://nickgravgaard.com/elastictabstops/index.html.
	//
	package tabwriter

	import (
	"bytes"
	"io"
	"os"
	"utf8"
	)


	// ----------------------------------------------------------------------------
	// Filter implementation

	// A cell represents a segment of text terminated by tabs or line breaks.
	// The text itself is stored in a separate buffer; cell only describes the
	// segment's size in bytes, its width in runes, and whether it's an htab
	// ('\t') terminated cell.
	//
	type cell struct {
	size int // cell size in bytes
	width int // cell width in runes
	htab bool // true if the cell is terminated by an htab ('\t')
	}


	// A Writer is a filter that inserts padding around tab-delimited
	// columns in its input to align them in the output.
	//
	// The Writer treats incoming bytes as UTF-8 encoded text consisting
	// of cells terminated by (horizontal or vertical) tabs or line
	// breaks (newline or formfeed characters). Cells in adjacent lines
	// constitute a column. The Writer inserts padding as needed to
	// make all cells in a column have the same width, effectively
	// aligning the columns. It assumes that all characters have the
	// same width except for tabs for which a tabwidth must be specified.
	// Note that cells are tab-terminated, not tab-separated: trailing
	// non-tab text at the end of a line does not form a column cell.
	//
	// The Writer assumes that all Unicode code points have the same width;
	// this may not be true in some fonts.
	//
	// If DiscardEmptyColumns is set, empty columns that are terminated
	// entirely by vertical (or "soft") tabs are discarded. Columns
	// terminated by horizontal (or "hard") tabs are not affected by
	// this flag.
	//
	// If a Writer is configured to filter HTML, HTML tags and entities
	// are simply passed through. The widths of tags and entities are
	// assumed to be zero (tags) and one (entities) for formatting purposes.
	//
	// A segment of text may be escaped by bracketing it with Escape
	// characters. The tabwriter passes escaped text segments through
	// unchanged. In particular, it does not interpret any tabs or line
	// breaks within the segment. If the StripEscape flag is set, the
	// Escape characters are stripped from the output; otherwise they
	// are passed through as well. For the purpose of formatting, the
	// width of the escaped text is always computed excluding the Escape
	// characters.
	//
	// The formfeed character ('\f') acts like a newline but it also
	// terminates all columns in the current line (effectively calling
	// Flush). Cells in the next line start new columns. Unless found
	// inside an HTML tag or inside an escaped text segment, formfeed
	// characters appear as newlines in the output.
	//
	// The Writer must buffer input internally, because proper spacing
	// of one line may depend on the cells in future lines. Clients must
	// call Flush when done calling Write.
	//
	type Writer struct {
	// configuration
	output io.Writer
	minwidth int
	tabwidth int
	padding int
	padbytes [8]byte
	flags uint

	// current state
	buf bytes.Buffer // collected text excluding tabs or line breaks
	pos int // buffer position up to which cell.width of incomplete cell has been computed
	cell cell // current incomplete cell; cell.width is up to buf[pos] excluding ignored sections
	endChar byte // terminating char of escaped sequence (Escape for escapes, '>', ';' for HTML tags/entities, or 0)
	lines [][]cell // list of lines; each line is a list of cells
	widths []int // list of column widths in runes - re-used during formatting
	}


	func (b *Writer) addLine() { b.lines = append(b.lines, []cell{}) }


	// Reset the current state.
	func (b *Writer) reset() {
	b.buf.Reset()
	b.pos = 0
	b.cell = cell{}
	b.endChar = 0
	b.lines = b.lines[0:0]
	b.widths = b.widths[0:0]
	b.addLine()
	}


	// Internal representation (current state):
	//
	// - all text written is appended to buf; tabs and line breaks are stripped away
	// - at any given time there is a (possibly empty) incomplete cell at the end
	// (the cell starts after a tab or line break)
	// - cell.size is the number of bytes belonging to the cell so far
	// - cell.width is text width in runes of that cell from the start of the cell to
	// position pos; html tags and entities are excluded from this width if html
	// filtering is enabled
	// - the sizes and widths of processed text are kept in the lines list
	// which contains a list of cells for each line
	// - the widths list is a temporary list with current widths used during
	// formatting; it is kept in Writer because it's re-used
	//
	// \|<---------- size ---------->\|
	// \| \|
	// \|<- width ->\|<- ignored ->\| \|
	// \| \| \| \|
	// [---processed---tab------------<tag>...</tag>...]
	// ^ ^ ^
	// \| \| \|
	// buf start of incomplete cell pos


	// Formatting can be controlled with these flags.
	const (
	// Ignore html tags and treat entities (starting with '&'
	// and ending in ';') as single characters (width = 1).
	FilterHTML uint = 1 << iota

	// Strip Escape characters bracketing escaped text segments
	// instead of passing them through unchanged with the text.
	StripEscape

	// Force right-alignment of cell content.
	// Default is left-alignment.
	AlignRight

	// Handle empty columns as if they were not present in
	// the input in the first place.
	DiscardEmptyColumns

	// Always use tabs for indentation columns (i.e., padding of
	// leading empty cells on the left) independent of padchar.
	TabIndent

	// Print a vertical bar ('\|') between columns (after formatting).
	// Discarded columns appear as zero-width columns ("\|\|").
	Debug
	)


	// A Writer must be initialized with a call to Init. The first parameter (output)
	// specifies the filter output. The remaining parameters control the formatting:
	//
	// minwidth minimal cell width including any padding
	// tabwidth width of tab characters (equivalent number of spaces)
	// padding padding added to a cell before computing its width
	// padchar ASCII char used for padding
	// if padchar == '\t', the Writer will assume that the
	// width of a '\t' in the formatted output is tabwidth,
	// and cells are left-aligned independent of align_left
	// (for correct-looking results, tabwidth must correspond
	// to the tab width in the viewer displaying the result)
	// flags formatting control
	//
	// To format in tab-separated columns with a tab stop of 8:
	// b.Init(w, 8, 1, 8, '\t', 0);
	//
	// To format in space-separated columns with at least 4 spaces between columns:
	// b.Init(w, 0, 4, 8, ' ', 0);
	//
	func (b Writer) Init(output io.Writer, minwidth, tabwidth, padding int, padchar byte, flags uint) Writer {
	if minwidth < 0 \|\| tabwidth < 0 \|\| padding < 0 {
	panic("negative minwidth, tabwidth, or padding")
	}
	b.output = output
	b.minwidth = minwidth
	b.tabwidth = tabwidth
	b.padding = padding
	for i := range b.padbytes {
	b.padbytes[i] = padchar
	}
	if padchar == '\t' {
	// tab padding enforces left-alignment
	flags &^= AlignRight
	}
	b.flags = flags

	b.reset()

	return b
	}


	// debugging support (keep code around)
	func (b *Writer) dump() {
	pos := 0
	for i, line := range b.lines {
	print("(", i, ") ")
	for _, c := range line {
	print("[", string(b.buf.Bytes()[pos:pos+c.size]), "]")
	pos += c.size
	}
	print("\n")
	}
	print("\n")
	}


	// local error wrapper so we can distinguish os.Errors we want to return
	// as errors from genuine panics (which we don't want to return as errors)
	type osError struct {
	err os.Error
	}


	func (b *Writer) write0(buf []byte) {
	n, err := b.output.Write(buf)
	if n != len(buf) && err == nil {
	err = os.EIO
	}
	if err != nil {
	panic(osError{err})
	}
	}


	func (b *Writer) writeN(src []byte, n int) {
	for n > len(src) {
	b.write0(src)
	n -= len(src)
	}
	b.write0(src[0:n])
	}


	var (
	newline = []byte{'\n'}
	tabs = []byte("\t\t\t\t\t\t\t\t")
	)


	func (b *Writer) writePadding(textw, cellw int, useTabs bool) {
	if b.padbytes[0] == '\t' \|\| useTabs {
	// padding is done with tabs
	if b.tabwidth == 0 {
	return // tabs have no width - can't do any padding
	}
	// make cellw the smallest multiple of b.tabwidth
	cellw = (cellw + b.tabwidth - 1) / b.tabwidth * b.tabwidth
	n := cellw - textw // amount of padding
	if n < 0 {
	panic("internal error")
	}
	b.writeN(tabs, (n+b.tabwidth-1)/b.tabwidth)
	return
	}

	// padding is done with non-tab characters
	b.writeN(b.padbytes[0:], cellw-textw)
	}


	var vbar = []byte{'\|'}

	func (b *Writer) writeLines(pos0 int, line0, line1 int) (pos int) {
	pos = pos0
	for i := line0; i < line1; i++ {
	line := b.lines[i]

	// if TabIndent is set, use tabs to pad leading empty cells
	useTabs := b.flags&TabIndent != 0

	for j, c := range line {
	if j > 0 && b.flags&Debug != 0 {
	// indicate column break
	b.write0(vbar)
	}

	if c.size == 0 {
	// empty cell
	if j < len(b.widths) {
	b.writePadding(c.width, b.widths[j], useTabs)
	}
	} else {
	// non-empty cell
	useTabs = false
	if b.flags&AlignRight == 0 { // align left
	b.write0(b.buf.Bytes()[pos : pos+c.size])
	pos += c.size
	if j < len(b.widths) {
	b.writePadding(c.width, b.widths[j], false)
	}
	} else { // align right
	if j < len(b.widths) {
	b.writePadding(c.width, b.widths[j], false)
	}
	b.write0(b.buf.Bytes()[pos : pos+c.size])
	pos += c.size
	}
	}
	}

	if i+1 == len(b.lines) {
	// last buffered line - we don't have a newline, so just write
	// any outstanding buffered data
	b.write0(b.buf.Bytes()[pos : pos+b.cell.size])
	pos += b.cell.size
	} else {
	// not the last line - write newline
	b.write0(newline)
	}
	}
	return
	}


	// Format the text between line0 and line1 (excluding line1); pos
	// is the buffer position corresponding to the beginning of line0.
	// Returns the buffer position corresponding to the beginning of
	// line1 and an error, if any.
	//
	func (b *Writer) format(pos0 int, line0, line1 int) (pos int) {
	pos = pos0
	column := len(b.widths)
	for this := line0; this < line1; this++ {
	line := b.lines[this]

	if column < len(line)-1 {
	// cell exists in this column => this line
	// has more cells than the previous line
	// (the last cell per line is ignored because cells are
	// tab-terminated; the last cell per line describes the
	// text before the newline/formfeed and does not belong
	// to a column)

	// print unprinted lines until beginning of block
	pos = b.writeLines(pos, line0, this)
	line0 = this

	// column block begin
	width := b.minwidth // minimal column width
	discardable := true // true if all cells in this column are empty and "soft"
	for ; this < line1; this++ {
	line = b.lines[this]
	if column < len(line)-1 {
	// cell exists in this column
	c := line[column]
	// update width
	if w := c.width + b.padding; w > width {
	width = w
	}
	// update discardable
	if c.width > 0 \|\| c.htab {
	discardable = false
	}
	} else {
	break
	}
	}
	// column block end

	// discard empty columns if necessary
	if discardable && b.flags&DiscardEmptyColumns != 0 {
	width = 0
	}

	// format and print all columns to the right of this column
	// (we know the widths of this column and all columns to the left)
	b.widths = append(b.widths, width) // push width
	pos = b.format(pos, line0, this)
	b.widths = b.widths[0 : len(b.widths)-1] // pop width
	line0 = this
	}
	}

	// print unprinted lines until end
	return b.writeLines(pos, line0, line1)
	}


	// Append text to current cell.
	func (b *Writer) append(text []byte) {
	b.buf.Write(text)
	b.cell.size += len(text)
	}


	// Update the cell width.
	func (b *Writer) updateWidth() {
	b.cell.width += utf8.RuneCount(b.buf.Bytes()[b.pos:b.buf.Len()])
	b.pos = b.buf.Len()
	}


	// To escape a text segment, bracket it with Escape characters.
	// For instance, the tab in this string "Ignore this tab: \xff\t\xff"
	// does not terminate a cell and constitutes a single character of
	// width one for formatting purposes.
	//
	// The value 0xff was chosen because it cannot appear in a valid UTF-8 sequence.
	//
	const Escape = '\xff'


	// Start escaped mode.
	func (b *Writer) startEscape(ch byte) {
	switch ch {
	case Escape:
	b.endChar = Escape
	case '<':
	b.endChar = '>'
	case '&':
	b.endChar = ';'
	}
	}


	// Terminate escaped mode. If the escaped text was an HTML tag, its width
	// is assumed to be zero for formatting purposes; if it was an HTML entity,
	// its width is assumed to be one. In all other cases, the width is the
	// unicode width of the text.
	//
	func (b *Writer) endEscape() {
	switch b.endChar {
	case Escape:
	b.updateWidth()
	if b.flags&StripEscape == 0 {
	b.cell.width -= 2 // don't count the Escape chars
	}
	case '>': // tag of zero width
	case ';':
	b.cell.width++ // entity, count as one rune
	}
	b.pos = b.buf.Len()
	b.endChar = 0
	}


	// Terminate the current cell by adding it to the list of cells of the
	// current line. Returns the number of cells in that line.
	//
	func (b *Writer) terminateCell(htab bool) int {
	b.cell.htab = htab
	line := &b.lines[len(b.lines)-1]
	line = append(line, b.cell)
	b.cell = cell{}
	return len(*line)
	}


	func handlePanic(err *os.Error) {
	if e := recover(); e != nil {
	*err = e.(osError).err // re-panics if it's not a local osError
	}
	}


	// Flush should be called after the last call to Write to ensure
	// that any data buffered in the Writer is written to output. Any
	// incomplete escape sequence at the end is simply considered
	// complete for formatting purposes.
	//
	func (b *Writer) Flush() (err os.Error) {
	defer b.reset() // even in the presence of errors
	defer handlePanic(&err)

	// add current cell if not empty
	if b.cell.size > 0 {
	if b.endChar != 0 {
	// inside escape - terminate it even if incomplete
	b.endEscape()
	}
	b.terminateCell(false)
	}

	// format contents of buffer
	b.format(0, 0, len(b.lines))

	return
	}


	var hbar = []byte("---\n")

	// Write writes buf to the writer b.
	// The only errors returned are ones encountered
	// while writing to the underlying output stream.
	//
	func (b *Writer) Write(buf []byte) (n int, err os.Error) {
	defer handlePanic(&err)

	// split text into cells
	n = 0
	for i, ch := range buf {
	if b.endChar == 0 {
	// outside escape
	switch ch {
	case '\t', '\v', '\n', '\f':
	// end of cell
	b.append(buf[n:i])
	b.updateWidth()
	n = i + 1 // ch consumed
	ncells := b.terminateCell(ch == '\t')
	if ch == '\n' \|\| ch == '\f' {
	// terminate line
	b.addLine()
	if ch == '\f' \|\| ncells == 1 {
	// A '\f' always forces a flush. Otherwise, if the previous
	// line has only one cell which does not have an impact on
	// the formatting of the following lines (the last cell per
	// line is ignored by format()), thus we can flush the
	// Writer contents.
	if err = b.Flush(); err != nil {
	return
	}
	if ch == '\f' && b.flags&Debug != 0 {
	// indicate section break
	b.write0(hbar)
	}
	}
	}

	case Escape:
	// start of escaped sequence
	b.append(buf[n:i])
	b.updateWidth()
	n = i
	if b.flags&StripEscape != 0 {
	n++ // strip Escape
	}
	b.startEscape(Escape)

	case '<', '&':
	// possibly an html tag/entity
	if b.flags&FilterHTML != 0 {
	// begin of tag/entity
	b.append(buf[n:i])
	b.updateWidth()
	n = i
	b.startEscape(ch)
	}
	}

	} else {
	// inside escape
	if ch == b.endChar {
	// end of tag/entity
	j := i + 1
	if ch == Escape && b.flags&StripEscape != 0 {
	j = i // strip Escape
	}
	b.append(buf[n:j])
	n = i + 1 // ch consumed
	b.endEscape()
	}
	}
	}

	// append leftover text
	b.append(buf[n:])
	n = len(buf)
	return
	}


	// NewWriter allocates and initializes a new tabwriter.Writer.
	// The parameters are the same as for the the Init function.
	//
	func NewWriter(output io.Writer, minwidth, tabwidth, padding int, padchar byte, flags uint) *Writer {
	return new(Writer).Init(output, minwidth, tabwidth, padding, padchar, flags)
	}