How Can I Serve Static Files from Memory in Go?

Serving Static Files from Memory in Go

Web applications often require serving static files, such as JavaScript, CSS, and images. Typically, the FileServer handler is used in Go for this purpose. However, there are scenarios where it is more efficient to embed a few static files within the binary and serve them from memory.

One approach is to utilize a custom FileSystem interface implementation. FileServer requires a FileSystem for its constructor. While http.Dir is typically used to create the FileSystem, it is possible to implement our own.

InMemoryFS Implementation

The following InMemoryFS implementation simulates a file system in memory:

type InMemoryFS map[string]http.File

func (fs InMemoryFS) Open(name string) (http.File, error) {
    if f, ok := fs[name]; ok {
        return f, nil
    }
    panic("No file")
}

InMemoryFile Implementation

The InMemoryFile struct serves as a file within the InMemoryFS:

type InMemoryFile struct {
    at   int64
    Name string
    data []byte
    fs   InMemoryFS
}

func LoadFile(name string, val string, fs InMemoryFS) *InMemoryFile {
    return &InMemoryFile{at: 0,
        Name: name,
        data: []byte(val),
        fs:   fs}
}

Note that this implementation has certain limitations and is primarily used for demonstrative purposes.

Serving Static Files from Memory

Once the InMemoryFS is implemented, we can serve the static files from memory:

FS := make(InMemoryFS)
FS["foo.html"] = LoadFile("foo.html", HTML, FS)
FS["bar.css"] = LoadFile("bar.css", CSS, FS)
http.Handle("/", http.FileServer(FS))
http.ListenAndServe(":8080", nil)

Alternative Approach

Alternatively, instead of reimplementing the FileSystem interface, one could modify the FileServer handler to serve files from memory. This may be more convenient for simpler use cases.

Conclusion

By using a custom FileServer implementation or reimplementing the FileSystem interface, it is possible to embed and serve static files from memory in Go applications. This approach can be beneficial when deploying a small number of static files that do not require complex file serving logic.

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