Reading a non UTF-8 text file in Go

Try go-iconv. It wraps iconv and implements io.Reader and io.Writer.

This message in golang-china discussion group is mentioning a few examples of go-iconv usage.

Previously (as mentioned in an older answer) the "easy" way to do this involved using third party packages that needed cgo and wrapped the iconv library. That is undesirable for many reasons. Thankfully, for quite a while now there has been a superior all Go way of doing this using only packages provided by the Go Authors (not in the main set of packages but in the Go Sub-Repositories).

The golang.org/x/text/encoding package defines an interface for generic character encodings that can convert to/from UTF-8. The golang.org/x/text/encoding/simplifiedchinese sub-package provides GB18030, GBK and HZ-GB2312 encoding implementations.

Here is an example of reading and writing a GBK encoded file. Note that the io.Reader and io.Writer do the encoding "on the fly" as data is being read/written.

package main

import (
    "bufio"
    "fmt"
    "log"
    "os"

    "golang.org/x/text/encoding/simplifiedchinese"
    "golang.org/x/text/transform"
)

// Encoding to use. Since this implements the encoding.Encoding
// interface from golang.org/x/text/encoding you can trivially
// change this out for any of the other implemented encoders,
// e.g. `traditionalchinese.Big5`, `charmap.Windows1252`,
// `korean.EUCKR`, etc.
var enc = simplifiedchinese.GBK

func main() {
    const filename = "example_GBK_file"
    exampleWriteGBK(filename)
    exampleReadGBK(filename)
}

func exampleReadGBK(filename string) {
    // Read UTF-8 from a GBK encoded file.
    f, err := os.Open(filename)
    if err != nil {
        log.Fatal(err)
    }
    r := transform.NewReader(f, enc.NewDecoder())

    // Read converted UTF-8 from `r` as needed.
    // As an example we'll read line-by-line showing what was read:
    sc := bufio.NewScanner(r)
    for sc.Scan() {
        fmt.Printf("Read line: %s\n", sc.Bytes())
    }
    if err = sc.Err(); err != nil {
        log.Fatal(err)
    }

    if err = f.Close(); err != nil {
        log.Fatal(err)
    }
}

func exampleWriteGBK(filename string) {
    // Write UTF-8 to a GBK encoded file.
    f, err := os.Create(filename)
    if err != nil {
        log.Fatal(err)
    }
    w := transform.NewWriter(f, enc.NewEncoder())

    // Write UTF-8 to `w` as desired.
    // As an example we'll write some text from the Wikipedia
    // GBK page that includes Chinese.
    _, err = fmt.Fprintln(w,
        `In 1995, China National Information Technology Standardization
Technical Committee set down the Chinese Internal Code Specification
(Chinese: 汉字内码扩展规范（GBK）; pinyin: Hànzì Nèimǎ
Kuòzhǎn Guīfàn (GBK)), Version 1.0, known as GBK 1.0, which is a
slight extension of Codepage 936. The newly added 95 characters were not
found in GB 13000.1-1993, and were provisionally assigned Unicode PUA
code points.`)
    if err != nil {
        log.Fatal(err)
    }

    if err = f.Close(); err != nil {
        log.Fatal(err)
    }
}

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