How Can I Serve Static Files Embedded in a Go Binary?

Serving Static Files from Binary in Go: A Custom FileSystem

When serving static files in Go, the FileServer handler simplifies the process. However, for cases where only a few static files need to be deployed, an alternative approach can eliminate the need for managing those files externally.

InMemoryFS Implementation

The FileServer requires a FileSystem object, leading to the question of how to bake static files into a binary. An implementation of InMemoryFS can serve files from memory, eliminating the need to interact with the file system directly.

package main

import (
    "io"
    "net/http"
    "time"
)

type InMemoryFS map[string]io.ReadCloser

// Implements FileSystem interface
func (fs InMemoryFS) Open(name string) (http.File, error) {
    f, ok := fs[name]
    if !ok {
        return nil, os.ErrNotExist
    }
    return &InMemoryFile{
        ReadCloser: f,
    }, nil
}

type InMemoryFile struct {
    io.ReadCloser
}

// Implements http.File interface
func (f *InMemoryFile) Close() error {
    return nil
}
func (f *InMemoryFile) Stat() (os.FileInfo, error) {
    fi, err := f.ReadCloser.Stat()
    if err != nil {
        return nil, err
    }
    return &InMemoryFileInfo{
        name: f.ReadCloser.(os.FileInfo).Name(),
        size: fi.Size(),
        modTime: fi.ModTime(),
    }, nil
}

type InMemoryFileInfo struct {
    name string
    size int64
    modTime time.Time
}

// Implements os.FileInfo
func (s *InMemoryFileInfo) Name() string       { return s.name }
func (s *InMemoryFileInfo) Size() int64        { return s.size }
func (s *InMemoryFileInfo) Mode() os.FileMode  { return 0644 }
func (s *InMemoryFileInfo) ModTime() time.Time { return s.modTime }
func (s *InMemoryFileInfo) IsDir() bool        { return false }
func (s *InMemoryFileInfo) Sys() interface{}   { return nil }

Example Usage

The InMemoryFS implementation can be utilized with the FileServer as follows:

func main() {
    FS := make(InMemoryFS)
    // Load static files into memory
    FS["foo.html"] = os.Open("foo.html")
    FS["bar.css"] = os.Open("bar.css")
    http.Handle("/", http.FileServer(FS))
    http.ListenAndServe(":8080", nil)
}

Alternative Considerations

Instead of creating a custom FileSystem, it might be simpler to rewrite the serving part to handle a small number of static files directly, avoiding the need to emulate a complete file system. Ultimately, the best approach depends on the specific requirements of the project.

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