fix(ui): bound the text of a log by its size

docs/allocations.md

@@ -149,8 +149,9 @@ opens the same log in the allocation it replaced.
 where it is. Press it again to go further back, as far as the cluster keeps
 the log; while a read is still out, `e` waits for it. The title then says how
 much of the log is read, for example `last 1.1 MiB of 5.3 MiB`, until the log
-drops lines off its front. It stops at the 50,000 lines a screen keeps. It needs a
-token that can read the files of the allocation, as `b` does.
+drops lines off its front. It stops at what a screen keeps: 50,000 lines or
+64 MiB of text, whichever comes first. It needs a token that can read the files
+of the allocation, as `b` does.
 
 A line under the title shows the state of three toggles:
 

internal/ui/logback_test.go

@@ -290,12 +290,43 @@ func TestLogEarlier_AnAnswerIsDroppedWhenItNoLongerFits(t *testing.T) {
 	r.Equal(flashWarn, m.flash.level)
 }
 
+func TestLogEarlier_AnAnswerIsDroppedWhenItsBytesDoNotFit(t *testing.T) {
+	r := require.New(t)
+
+	eighth := maxTextBytes / 8
+	read := logState{before: midLog, more: true}
+	read.content.add(sizedLines(0, 7, eighth), arrivedAt, nil, nil)
+
+	part := nomad.LogPart{Lines: sizedLines(10, 2, eighth), From: nomad.LogMark{File: midLog.File, Offset: 60_000}, Before: 60_000, Size: 130_000}
+	read, out, ok := read.earlier(logPartMsg{at: midLog, part: part})
+
+	r.True(ok)
+	r.Equal(7, len(read.content.lines))
+	r.Equal(midLog, read.before)
+	r.Len(out.now, 1)
+	r.Equal(warnMsg("The lines read back no longer fit on the screen."), out.now[0])
+}
+
 func TestLogEarlier_AFullTextOffersNoKey(t *testing.T) {
 	m, _ := sentLog(t, &fakeClient{jobs: twoJobs(), allocs: twoAllocs()}, midLog, numberedLines("late", 0, maxTextLines))
 
 	require.False(t, offersLabel(m, "e", "Read Earlier"))
 }
 
+func TestLogEarlier_ATextFullOfBytesOffersNoKey(t *testing.T) {
+	for name, lines := range map[string][]string{
+		"as many bytes as it keeps":     sizedLines(0, 8, maxTextBytes/8),
+		"lines dropped for their bytes": sizedLines(0, 3, maxTextBytes*2/5),
+	} {
+		t.Run(name, func(t *testing.T) {
+			p := logsPage{read: logState{before: midLog, more: true}}
+			p.read.content.add(lines, arrivedAt, nil, nil)
+
+			require.False(t, hasEarlier(p, env{}))
+		})
+	}
+}
+
 func TestLogEarlier_TheLinesReadBackAreCleaned(t *testing.T) {
 	r := require.New(t)
 

internal/ui/logs.go

@@ -215,10 +215,9 @@ func openPrevious(p logsPage, _ env) (logsPage, outcome) {
 }
 
 // hasEarlier says the cluster keeps more of the log before what is shown,
-// no read of it is out, and the screen has room for it: a text that dropped
-// lines is full.
+// no read of it is out, and the screen has room for it.
 func hasEarlier(p logsPage, _ env) bool {
-	return p.read.more && !p.read.asking && len(p.read.content.lines) < maxTextLines
+	return p.read.more && !p.read.asking && !p.read.content.full()
 }
 
 // readEarlier reads the step of the log before what is shown, to put above
@@ -343,9 +342,8 @@ func (l logState) take(msg tea.Msg) (logState, outcome, bool) {
 // earlier puts a part read from before the text in front of it, when it was
 // read for the place the text starts at now. A failed read shows its error.
 // The answer is dropped if the stream took lines off the front meanwhile: the
-// text no longer starts there. It is also dropped if the stream added so many
-// lines meanwhile that it no longer fits under the limit, with a warning: the
-// press shows nothing else.
+// text no longer starts there. It is also dropped if it does not fit under
+// the limits of the text, with a warning: the press shows nothing else.
 func (l logState) earlier(msg logPartMsg) (logState, outcome, bool) {
 	l.asking = false
 
@@ -357,11 +355,10 @@ func (l logState) earlier(msg logPartMsg) (logState, outcome, bool) {
 		return l, outcome{reading: true}, true
 	}
 
-	if len(l.content.lines)+len(msg.part.Lines) > maxTextLines {
+	if !l.content.addBefore(msg.part.Lines) {
 		return l, outcome{now: []tea.Msg{warnMsg("The lines read back no longer fit on the screen.")}, reading: true}, true
 	}
 
-	l.content.addBefore(msg.part.Lines)
 	l.before = msg.part.From
 	l.size, l.from = msg.part.Size, msg.part.Before
 	l.more = msg.part.Before > 0

internal/ui/text.go

@@ -84,6 +84,11 @@ type rowCache struct {
 // or more.
 const maxTextLines = 50_000
 
+// maxTextBytes is how many bytes the lines of a text hold at most. A task can
+// write a line of 64 KiB, and 50,000 of them would take gigabytes. 50,000 lines
+// of up to 1.3 KiB still fit.
+const maxTextBytes = 64 << 20
+
 // textContent is what a text holds, apart from how it is shown: a text page
 // keeps it, and the root model keeps the window over it.
 type textContent struct {
@@ -93,6 +98,9 @@ type textContent struct {
 
 	lines []string
 
+	// size is the bytes of lines.
+	size int
+
 	// dropped are the lines taken off the front so far.
 	dropped int
 
@@ -167,7 +175,9 @@ func (t *textContent) add(lines []string, arrived time.Time, label *tag, style *
 	}
 
 	for _, line := range lines {
-		t.lines = append(t.lines, cleanLine(line))
+		clean := cleanLine(line)
+		t.lines = append(t.lines, clean)
+		t.size += len(clean)
 		t.stamps = append(t.stamps, arrived)
 
 		if tagged {
@@ -191,23 +201,39 @@ func (t *textContent) addChunk(lines []string, old int, arrived time.Time, label
 	t.add(lines[old:], arrived, label, style)
 }
 
-// addBefore puts lines read from before the text in front of it. They have
-// no time, tag or style, and the text gets a new id so that its rows are drawn
-// afresh: the kept ones would take the new lines as added at the end. The
-// caller keeps the text under the limit, so none are dropped.
-func (t *textContent) addBefore(lines []string) {
-	n := len(lines)
+// addBefore puts lines read from before the text in front of it, and says
+// whether they fit under the limits of the text: lines that do not fit are
+// not added, since they would be the first ones dropped. They have no time,
+// tag or style, and the text gets a new id so that its rows are drawn afresh:
+// the kept ones would take the new lines as added at the end.
+func (t *textContent) addBefore(lines []string) bool {
+	n, size := len(lines), t.size
 	front := make([]string, 0, n+len(t.lines))
 
 	for _, line := range lines {
-		front = append(front, cleanLine(line))
+		clean := cleanLine(line)
+		front = append(front, clean)
+		size += len(clean)
+	}
+
+	if n+len(t.lines) > maxTextLines || size > maxTextBytes {
+		return false
 	}
 
-	t.lines = append(front, t.lines...)
+	t.lines, t.size = append(front, t.lines...), size
 	t.stamps = fronted(t.stamps, n, len(t.lines)-n)
 	t.tags = fronted(t.tags, n, len(t.lines)-n)
 	t.paint = fronted(t.paint, n, len(t.lines)-n)
 	t.id = &textID{}
+
+	return true
+}
+
+// full says no lines can be put in front of the text: it holds as many lines
+// or bytes as it keeps, or it dropped lines and no longer starts where the
+// lines before it end.
+func (t textContent) full() bool {
+	return t.dropped > 0 || len(t.lines) >= maxTextLines || t.size >= maxTextBytes
 }
 
 // fronted puts n unset items in front of s, after growing it to total items.
@@ -220,11 +246,21 @@ func fronted[T any](s []T, n, total int) []T {
 	return append(make([]T, n), grown(s, total)...)
 }
 
-// dropOld takes the lines past maxTextLines off the front. The slices are cut,
+// dropOld takes lines off the front while there are more than maxTextLines
+// or more than maxTextBytes, and keeps the newest line. The slices are cut,
 // not copied: the next append grows them anew and frees the old front.
 func (t *textContent) dropOld() {
-	n := len(t.lines) - maxTextLines
-	if n <= 0 {
+	n := max(0, len(t.lines)-maxTextLines)
+	for _, line := range t.lines[:n] {
+		t.size -= len(line)
+	}
+
+	for n < len(t.lines)-1 && t.size > maxTextBytes {
+		t.size -= len(t.lines[n])
+		n++
+	}
+
+	if n == 0 {
 		return
 	}
 

internal/ui/textrows_test.go

@@ -209,6 +209,97 @@ func TestText_AStreamKeepsItsLastLines(t *testing.T) {
 	r.Equal(maxTextLines, len(text.stamps))
 }
 
+// sizedLines are n lines of size bytes, each starting with its place, from
+// first on.
+func sizedLines(first, n, size int) []string {
+	lines := make([]string, 0, n)
+	for i := first; i < first+n; i++ {
+		place := fmt.Sprintf("%02d ", i)
+		lines = append(lines, place+strings.Repeat("x", size-len(place)))
+	}
+
+	return lines
+}
+
+// bytesOf is the bytes of the lines.
+func bytesOf(lines []string) int {
+	n := 0
+	for _, line := range lines {
+		n += len(line)
+	}
+
+	return n
+}
+
+func TestText_CountsTheBytesOfItsLines(t *testing.T) {
+	r := require.New(t)
+
+	// A tab is spaces up to the next stop: the text holds more bytes than
+	// it was given.
+	text := textModel{}
+	text.add([]string{"a\tb", "cd"}, arrivedAt, nil, nil)
+	r.Equal(7, text.size)
+
+	r.True(text.addBefore([]string{"\tx"}))
+	r.Equal(bytesOf(text.lines), text.size)
+
+	// Lines past maxTextLines leave with their bytes.
+	text.add(linesFrom(0, maxTextLines), arrivedAt, nil, nil)
+	r.Equal(bytesOf(text.lines), text.size)
+}
+
+func TestText_AStreamKeepsItsLastBytes(t *testing.T) {
+	r := require.New(t)
+
+	old := &tag{text: "old │ "}
+	own := &tag{text: "own │ "}
+	bold := lipgloss.NewStyle().Bold(true)
+	quarter := maxTextBytes / 4
+
+	text := textModel{}
+	text.add(sizedLines(0, 1, quarter), arrivedAt.Add(-time.Hour), old, nil)
+
+	// The second line is the first one kept, with what it came with.
+	text.add(sizedLines(1, 1, quarter), arrivedAt, own, &bold)
+	text.add(sizedLines(2, 3, quarter), arrivedAt.Add(time.Hour), old, nil)
+
+	r.Equal(4, len(text.lines))
+	r.True(strings.HasPrefix(text.lines[0], "01 "))
+	r.True(strings.HasPrefix(text.lines[3], "04 "))
+	r.Equal(1, text.dropped)
+	r.Equal(5, text.total())
+	r.Equal(bytesOf(text.lines), text.size)
+
+	r.Equal(arrivedAt, text.stampAt(0))
+	r.Same(own, text.tagAt(0))
+	r.Same(&bold, text.paintAt(0))
+	r.Same(old, text.tagAt(1))
+	r.Nil(text.paintAt(1))
+	r.Len(text.stamps, 4)
+	r.Len(text.tags, 4)
+	r.Len(text.paint, 4)
+}
+
+func TestText_KeepsItsNewestLineEvenOverTheByteLimit(t *testing.T) {
+	r := require.New(t)
+
+	text := textModel{}
+	text.add([]string{"first", strings.Repeat("x", maxTextBytes+1)}, arrivedAt, nil, nil)
+
+	r.Equal(1, len(text.lines))
+	r.Equal(maxTextBytes+1, len(text.lines[0]))
+	r.Equal(1, text.dropped)
+	r.Len(text.stamps, 1)
+
+	// The next line takes its place.
+	text.add([]string{"next"}, arrivedAt, nil, nil)
+
+	r.Equal(1, len(text.lines))
+	r.Equal("next", text.lines[0])
+	r.Equal(2, text.dropped)
+	r.Equal(4, text.size)
+}
+
 func TestText_ALongTextHasItsFrontDroppedWithoutMissingRows(t *testing.T) {
 	text := textModel{wrap: true, filter: "5"}
 	text.setSize(8, 6)