在Go中获取文件的内容类型时出错

import (
    "mime"
    "fmt"
)

func main() {
    filename := "path/to/file.txt"
    contentType := mime.TypeByExtension(".txt")
    fmt.Println(contentType)
}

import (
    "net/http"
    "fmt"
    "os"
)

func main() {
    file, err := os.Open("path/to/file.txt")
    if err != nil {
        fmt.Println("Error opening file:", err)
        return
    }
    defer file.Close()

    buffer := make([]byte, 512)
    _, err = file.Read(buffer)
    if err != nil {
        fmt.Println("Error reading file:", err)
        return
    }

    contentType := http.DetectContentType(buffer)
    fmt.Println(contentType)
}