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assethandler.go
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/
assethandler.go
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package assetserver
import (
"bytes"
"embed"
"errors"
"fmt"
"io"
iofs "io/fs"
"net/http"
"os"
"path"
"strings"
"github.com/ciderapp/wails/v2/pkg/options/assetserver"
)
type Logger interface {
Debug(message string, args ...interface{})
Error(message string, args ...interface{})
}
//go:embed defaultindex.html
var defaultHTML []byte
const (
indexHTML = "index.html"
)
type assetHandler struct {
fs iofs.FS
handler http.Handler
logger Logger
retryMissingFiles bool
}
func NewAssetHandler(options assetserver.Options, log Logger) (http.Handler, error) {
vfs := options.Assets
if vfs != nil {
if _, err := vfs.Open("."); err != nil {
return nil, err
}
subDir, err := FindPathToFile(vfs, indexHTML)
if err != nil {
if errors.Is(err, os.ErrNotExist) {
msg := "no `index.html` could be found in your Assets fs.FS"
if embedFs, isEmbedFs := vfs.(embed.FS); isEmbedFs {
rootFolder, _ := FindEmbedRootPath(embedFs)
msg += fmt.Sprintf(", please make sure the embedded directory '%s' is correct and contains your assets", rootFolder)
}
return nil, fmt.Errorf(msg)
}
return nil, err
}
vfs, err = iofs.Sub(vfs, path.Clean(subDir))
if err != nil {
return nil, err
}
}
var result http.Handler = &assetHandler{
fs: vfs,
handler: options.Handler,
logger: log,
}
if middleware := options.Middleware; middleware != nil {
result = middleware(result)
}
return result, nil
}
func (d *assetHandler) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
url := req.URL.Path
handler := d.handler
if strings.EqualFold(req.Method, http.MethodGet) {
filename := path.Clean(strings.TrimPrefix(url, "/"))
d.logDebug("Handling request '%s' (file='%s')", url, filename)
if err := d.serveFSFile(rw, req, filename); err != nil {
if os.IsNotExist(err) {
if handler != nil {
d.logDebug("File '%s' not found, serving '%s' by AssetHandler", filename, url)
handler.ServeHTTP(rw, req)
err = nil
} else {
rw.WriteHeader(http.StatusNotFound)
err = nil
}
}
if err != nil {
d.logError("Unable to handle request '%s': %s", url, err)
http.Error(rw, err.Error(), http.StatusInternalServerError)
}
}
} else if handler != nil {
d.logDebug("No GET request, serving '%s' by AssetHandler", url)
handler.ServeHTTP(rw, req)
} else {
rw.WriteHeader(http.StatusMethodNotAllowed)
}
}
// serveFile will try to load the file from the fs.FS and write it to the response
func (d *assetHandler) serveFSFile(rw http.ResponseWriter, req *http.Request, filename string) error {
if d.fs == nil {
return os.ErrNotExist
}
file, err := d.fs.Open(filename)
if err != nil {
return err
}
defer file.Close()
statInfo, err := file.Stat()
if err != nil {
return err
}
url := req.URL.Path
isDirectoryPath := url == "" || url[len(url)-1] == '/'
if statInfo.IsDir() {
if !isDirectoryPath {
// If the URL doesn't end in a slash normally a http.redirect should be done, but that currently doesn't work on
// WebKit WebViews (macOS/Linux).
// So we handle this as a specific error
return fmt.Errorf("a directory has been requested without a trailing slash, please add a trailing slash to your request")
}
filename = path.Join(filename, indexHTML)
file, err = d.fs.Open(filename)
if err != nil {
return err
}
defer file.Close()
statInfo, err = file.Stat()
if err != nil {
return err
}
} else if isDirectoryPath {
return fmt.Errorf("a file has been requested with a trailing slash, please remove the trailing slash from your request")
}
var buf [512]byte
var n int
if _, haveType := rw.Header()[HeaderContentType]; !haveType {
// Detect MimeType by sniffing the first 512 bytes
n, err = file.Read(buf[:])
if err != nil && err != io.EOF {
return err
}
// Do the custom MimeType sniffing even though http.ServeContent would do it in case
// of an io.ReadSeeker. We would like to have a consistent behaviour in both cases.
if contentType := GetMimetype(filename, buf[:n]); contentType != "" {
rw.Header().Set(HeaderContentType, contentType)
}
}
if fileSeeker, _ := file.(io.ReadSeeker); fileSeeker != nil {
if _, err := fileSeeker.Seek(0, io.SeekStart); err != nil {
return fmt.Errorf("seeker can't seek")
}
http.ServeContent(rw, req, statInfo.Name(), statInfo.ModTime(), fileSeeker)
return nil
}
rw.Header().Set(HeaderContentLength, fmt.Sprintf("%d", statInfo.Size()))
// Write the first 512 bytes used for MimeType sniffing
_, err = io.Copy(rw, bytes.NewReader(buf[:n]))
if err != nil {
return err
}
// Copy the remaining content of the file
_, err = io.Copy(rw, file)
return err
}
func (d *assetHandler) logDebug(message string, args ...interface{}) {
if d.logger != nil {
d.logger.Debug("[AssetHandler] "+message, args...)
}
}
func (d *assetHandler) logError(message string, args ...interface{}) {
if d.logger != nil {
d.logger.Error("[AssetHandler] "+message, args...)
}
}