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Source file src/k8s.io/cli-runtime/pkg/printers/terminal.go

Documentation: k8s.io/cli-runtime/pkg/printers

     1  /*
     2  Copyright 2022 The Kubernetes Authors.
     3  
     4  Licensed under the Apache License, Version 2.0 (the "License");
     5  you may not use this file except in compliance with the License.
     6  You may obtain a copy of the License at
     7  
     8      http://www.apache.org/licenses/LICENSE-2.0
     9  
    10  Unless required by applicable law or agreed to in writing, software
    11  distributed under the License is distributed on an "AS IS" BASIS,
    12  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13  See the License for the specific language governing permissions and
    14  limitations under the License.
    15  */
    16  
    17  package printers
    18  
    19  import (
    20  	"io"
    21  	"os"
    22  	"runtime"
    23  	"strings"
    24  
    25  	"github.com/moby/term"
    26  )
    27  
    28  // terminalEscaper replaces ANSI escape sequences and other terminal special
    29  // characters to avoid terminal escape character attacks (issue #101695).
    30  var terminalEscaper = strings.NewReplacer("\x1b", "^[", "\r", "\\r")
    31  
    32  // WriteEscaped replaces unsafe terminal characters with replacement strings
    33  // and writes them to the given writer.
    34  func WriteEscaped(writer io.Writer, output string) error {
    35  	_, err := terminalEscaper.WriteString(writer, output)
    36  	return err
    37  }
    38  
    39  // EscapeTerminal escapes terminal special characters in a human readable (but
    40  // non-reversible) format.
    41  func EscapeTerminal(in string) string {
    42  	return terminalEscaper.Replace(in)
    43  }
    44  
    45  // IsTerminal returns whether the passed object is a terminal or not
    46  func IsTerminal(i interface{}) bool {
    47  	_, terminal := term.GetFdInfo(i)
    48  	return terminal
    49  }
    50  
    51  // AllowsColorOutput returns true if the specified writer is a terminal and
    52  // the process environment indicates color output is supported and desired.
    53  func AllowsColorOutput(w io.Writer) bool {
    54  	if !IsTerminal(w) {
    55  		return false
    56  	}
    57  
    58  	// https://en.wikipedia.org/wiki/Computer_terminal#Dumb_terminals
    59  	if os.Getenv("TERM") == "dumb" {
    60  		return false
    61  	}
    62  
    63  	// https://no-color.org/
    64  	if _, nocolor := os.LookupEnv("NO_COLOR"); nocolor {
    65  		return false
    66  	}
    67  
    68  	// On Windows WT_SESSION is set by the modern terminal component.
    69  	// Older terminals have poor support for UTF-8, VT escape codes, etc.
    70  	if runtime.GOOS == "windows" && os.Getenv("WT_SESSION") == "" {
    71  		return false
    72  	}
    73  
    74  	return true
    75  }
    76  

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