Warp/apps/desktop/internal/shell/links.go

package shell

import (
	"bytes"
	"io/fs"
	"time"
)

// linkScriptPath serves linkScript, which withLinkScript adds to the
// client's index.html. A script of the page's own, rather than one the
// webview injects, runs before the app on every platform and is allowed by
// the client's Content-Security-Policy (script-src 'self').
const linkScriptPath = "/_desktop/links.js"

// linkScript makes links to other sites open in the system browser. A URL
// in a message would otherwise replace the app in its own window, or open a
// bare webview window for target="_blank"; this sends those to openPath
// instead. Links within the app, and blob: URLs for downloads, are left
// alone.
const linkScript = `(() => {
  if (window.__warpDesktopLinks) return
  window.__warpDesktopLinks = true
  const external = (href) => {
    try {
      const u = new URL(href, location.href)
      return u.origin !== location.origin && ['http:', 'https:', 'mailto:'].includes(u.protocol) ? u.href : null
    } catch { return null }
  }
  const open = (href) => fetch('/_desktop/open', {
    method: 'POST', credentials: 'omit',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({ url: href }),
  }).catch(() => {})
  const onClick = (e) => {
    if (e.defaultPrevented || e.button > 1) return
    const a = e.target instanceof Element ? e.target.closest('a[href]') : null
    const href = a && external(a.href)
    if (!href) return
    e.preventDefault()
    open(href)
  }
  // auxclick is the middle button, which would open a new window.
  document.addEventListener('click', onClick, true)
  document.addEventListener('auxclick', onClick, true)
  const windowOpen = window.open
  window.open = function (url, ...rest) {
    const href = url == null ? null : external(String(url))
    if (href) { open(href); return null }
    return windowOpen.call(window, url, ...rest)
  }
})()
`

// withLinkScript returns the client with a script tag for linkScript at the
// top of index.html's head. ok is false when index.html has no <head> to
// add it to; the client is then returned unchanged.
func withLinkScript(client fs.FS) (_ fs.FS, ok bool, _ error) {
	index, err := fs.ReadFile(client, "index.html")
	if err != nil {
		return nil, false, err
	}
	tag := []byte(`<head>` + "\n    " + `<script src="` + linkScriptPath + `"></script>`)
	patched := bytes.Replace(index, []byte("<head>"), tag, 1)
	if bytes.Equal(patched, index) {
		return client, false, nil
	}
	return indexFS{FS: client, index: patched}, true, nil
}

// indexFS is a client whose index.html is replaced.
type indexFS struct {
	fs.FS
	index []byte
}

func (f indexFS) Open(name string) (fs.File, error) {
	if name != "index.html" {
		return f.FS.Open(name)
	}
	return &memFile{Reader: bytes.NewReader(f.index), size: int64(len(f.index))}, nil
}

func (f indexFS) ReadFile(name string) ([]byte, error) {
	if name != "index.html" {
		return fs.ReadFile(f.FS, name)
	}
	return bytes.Clone(f.index), nil
}

type memFile struct {
	*bytes.Reader
	size int64
}

func (m *memFile) Stat() (fs.FileInfo, error) { return memInfo{m.size}, nil }
func (m *memFile) Close() error               { return nil }

type memInfo struct{ size int64 }

func (i memInfo) Name() string       { return "index.html" }
func (i memInfo) Size() int64        { return i.size }
func (i memInfo) Mode() fs.FileMode  { return 0o444 }
func (i memInfo) ModTime() time.Time { return time.Time{} }
func (i memInfo) IsDir() bool        { return false }
func (i memInfo) Sys() any           { return nil }