terminal: use exact window size for pager (#3249)

Instead of using a fixed 100x30 window size query the operating system
for the exact size, also fixes a bug where the last line before calling
the pager is repeated twice.

pkg/terminal/out.go

@@ -100,6 +100,8 @@ type pagingWriter struct {
 	pager    string
 	lastnl   bool
 	cancel   func()
+
+	lines, columns int
 }
 
 type pagingWriterMode uint8
@@ -108,9 +110,6 @@ const (
 	pagingWriterNormal pagingWriterMode = iota
 	pagingWriterMaybe
 	pagingWriterPaging
-
-	pagingWriterMaxLines    = 30
-	pagingWriterColsPerLine = 100
 )
 
 func (w *pagingWriter) Write(p []byte) (nn int, err error) {
@@ -141,7 +140,7 @@ func (w *pagingWriter) Write(p []byte) (nn int, err error) {
 			w.cmdStdin.Write(w.buf)
 			w.buf = nil
 			w.mode = pagingWriterPaging
-			return w.cmdStdin.Write(p)
+			return len(p), nil
 		} else {
 			if len(p) > 0 {
 				w.lastnl = p[len(p)-1] == '\n'
@@ -202,17 +201,17 @@ func (w *pagingWriter) PageMaybe(cancel func()) {
 	}
 	w.lastnl = true
 	w.cancel = cancel
+	w.getWindowSize()
 }
 
 func (w *pagingWriter) largeOutput() bool {
-	if len(w.buf) > pagingWriterMaxLines*pagingWriterColsPerLine {
-		return true
-	}
-	nl := 0
+	lines := 0
+	lineStart := 0
 	for i := range w.buf {
-		if w.buf[i] == '\n' {
-			nl++
-			if nl > pagingWriterMaxLines {
+		if i-lineStart > w.columns || w.buf[i] == '\n' {
+			lineStart = i
+			lines++
+			if lines > w.lines {
 				return true
 			}
 		}

pkg/terminal/out_unix.go

@@ -0,0 +1,25 @@
+//go:build linux || darwin || freebsd
+// +build linux darwin freebsd
+
+package terminal
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+type winSize struct {
+	row, col       uint16
+	xpixel, ypixel uint16
+}
+
+func (w *pagingWriter) getWindowSize() {
+	var ws winSize
+	ok, _, _ := syscall.Syscall(syscall.SYS_IOCTL, uintptr(syscall.Stdout), syscall.TIOCGWINSZ, uintptr(unsafe.Pointer(&ws)))
+	if int(ok) < 0 {
+		w.mode = pagingWriterNormal
+		return
+	}
+	w.lines = int(ws.row)
+	w.columns = int(ws.col)
+}

pkg/terminal/out_windows.go

@@ -0,0 +1,44 @@
+package terminal
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+var (
+	kernel32                       = syscall.NewLazyDLL("kernel32.dll")
+	procGetStdHandle               = kernel32.NewProc("GetStdHandle")
+	procGetConsoleScreenBufferInfo = kernel32.NewProc("GetConsoleScreenBufferInfo")
+)
+
+type coord struct {
+	x, y int16
+}
+
+type smallRect struct {
+	left, top, right, bottom int16
+}
+
+type consoleScreenBufferInfo struct {
+	dwSize              coord
+	dwCursorPosition    coord
+	wAttributes         int16
+	srWindow            smallRect
+	dwMaximumWindowSize coord
+}
+
+func (w *pagingWriter) getWindowSize() {
+	hout, _, err := procGetStdHandle.Call(uintptr(uint32(-12 & 0xFFFFFFFF))) // stdout handle
+	if err != syscall.Errno(0) {
+		w.mode = pagingWriterNormal
+		return
+	}
+	var sbi consoleScreenBufferInfo
+	_, _, err = procGetConsoleScreenBufferInfo.Call(uintptr(hout), uintptr(unsafe.Pointer(&sbi)))
+	if err != syscall.Errno(0) {
+		w.mode = pagingWriterNormal
+		return
+	}
+	w.columns = int(sbi.srWindow.right - sbi.srWindow.left + 1)
+	w.lines = int(sbi.srWindow.bottom - sbi.srWindow.top + 1)
+}