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137 lines
3.0 KiB
Go
137 lines
3.0 KiB
Go
package pager
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import (
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"fmt"
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"io"
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"os"
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"os/exec"
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"strings"
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"sync"
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"github.com/kballard/go-shellquote"
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"github.com/zk-org/zk/internal/util"
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"github.com/zk-org/zk/internal/util/errors"
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executil "github.com/zk-org/zk/internal/util/exec"
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"github.com/zk-org/zk/internal/util/opt"
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osutil "github.com/zk-org/zk/internal/util/os"
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)
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// Pager writes text to a terminal using the user's pager.
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type Pager struct {
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io.WriteCloser
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done chan bool
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isCloseable bool
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closeOnce sync.Once
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}
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// PassthroughPager is a Pager writing the content directly to stdout without
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// pagination.
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var PassthroughPager = &Pager{
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WriteCloser: os.Stdout,
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isCloseable: false,
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}
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// New creates a pager.Pager to be used to write a paginated text to the terminal.
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func New(pagerCmd opt.String, logger util.Logger) (*Pager, error) {
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wrap := errors.Wrapper("failed to paginate the output, try again with --no-pager or fix your PAGER environment variable")
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pagerCmd = selectPagerCmd(pagerCmd)
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if pagerCmd.IsNull() {
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return PassthroughPager, nil
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}
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cmd := executil.CommandFromString(pagerCmd.String())
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r, w, err := os.Pipe()
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if err != nil {
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return nil, wrap(err)
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}
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cmd.Stdin = r
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cmd.Stdout = os.Stdout
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cmd.Stderr = os.Stderr
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done := make(chan bool)
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pager := Pager{
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WriteCloser: w,
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done: done,
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isCloseable: true,
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closeOnce: sync.Once{},
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}
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go func() {
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defer func() {
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close(done)
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// Close manually to make sure that writers are not blocked if the
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// pager process is closed before writing is complete.
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// E.g. when listing a huge number of results.
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pager.Close()
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}()
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err := cmd.Run()
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if err != nil {
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logger.Err(wrap(err))
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os.Exit(1)
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}
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}()
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return &pager, nil
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}
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// Close terminates the pager, waiting for the process to be finished before returning.
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//
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// We make sure Close is called only once, since we don't know how it is
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// implemented in underlying writers.
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func (p *Pager) Close() error {
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if !p.isCloseable {
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return nil
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}
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var err error
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p.closeOnce.Do(func() {
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err = p.WriteCloser.Close()
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})
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<-p.done
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return err
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}
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// WriteString sends the given text to the pager, ending with a newline.
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func (p *Pager) WriteString(text string) error {
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_, err := fmt.Fprintln(p, text)
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return err
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}
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// selectPagerCmd returns the paging command meant to be run.
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//
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// By order of precedence: ZK_PAGER, config.pager, PAGER then the default
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// pagers.
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func selectPagerCmd(userPager opt.String) opt.String {
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return osutil.GetOptEnv("ZK_PAGER").
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Or(userPager).
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Or(osutil.GetOptEnv("PAGER")).
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Or(selectDefaultPager())
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}
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var defaultPagers = []string{
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"less -FIRX", "more -R",
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}
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// selectDefaultPager returns the first pager in the list of defaultPagers
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// available on the execution paths.
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func selectDefaultPager() opt.String {
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for _, pager := range defaultPagers {
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parts, err := shellquote.Split(pager)
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if err != nil {
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continue
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}
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pager, err := exec.LookPath(parts[0])
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parts[0] = pager
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if err == nil {
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return opt.NewNotEmptyString(strings.Join(parts, " "))
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}
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}
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return opt.NullString
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}
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