A brief analysis of golang's method of removing BOM characters in UTF-8 encoding

UTF-8 is an encoding method of the Unicode character set, which uses variable byte length to represent characters. However, in UTF-8 encoding, there is a special character called BOM (Byte Order Mark), which is used to identify the byte order of text, so it is also called a byte order identifier.

In some scenarios, BOM may cause some problems. For example, when using certain tools to process text, errors may occur due to BOM. Therefore, this article will introduce how to use Golang to remove BOM characters in UTF-8 encoding.

The role of BOM

In the Unicode character set, there are multiple encoding methods, such as UTF-8, UTF-16, etc. Among them, UTF-16 uses double-byte encoding, and each character occupies 2 bytes. In UTF-16 encoding, the representation of a character is divided into two bytes, high-order and low-order. However, due to different CPU processors of computers, some CPU processors store data in a big-endian (Big-Endian) manner, while other CPUs store data in a low-endian (Little-Endian) manner.

Therefore, in non-UTF-8 encoding, in order for the decoder to correctly determine the byte order of characters, a special character, the BOM character, needs to be inserted at the beginning of the text. There are two forms of BOM characters, namely U FEFF and U FFFE. Among them, U FEFF represents Big-Endian byte order, and U FFFE represents Little-Endian byte order. BOM characters are often used in UTF-16 and UTF-32 encodings.

However, in UTF-8 encoding, since the byte length of each character is different, there is no need to use BOM characters to identify the byte order of text like UTF-16 and UTF-32. However, in order to be compatible with other encoding methods, the UTF-8 encoding method can also insert BOM characters at the beginning of the text to identify the encoding method of the text.

How to remove BOM

Although not all UTF-8 text will insert BOM characters, in some cases, we still need to remove BOM characters. For example:

• You want to perform some specific processing on the text, but for BOM characters, the processing tool may not be able to handle it;
• You need to convert the text into other formats, such as JSON, XML, etc., and these formats are very sensitive to BOM characters and will cause parsing errors.

In Golang, you can use some methods in the unicode/utf8 library and bytes library to remove BOM characters. Below, we will introduce the implementation of these two methods respectively.

Method 1: Use the unicode/utf8 library

The unicode/utf8 library provides a function called SkipBOM, which can be used to skip the BOM characters in UTF-8 encoding. The definition of this function is as follows:

func SkipBOM(p []byte) []byte

The parameters of this function are byte arrays, and the return value is also a byte array, with the BOM characters removed.

The following is a specific example:

package main

import (
    "fmt"
    "unicode/utf8"
)

func main() {
    str := "\ufeffHello World"
    b := []byte(str)

    // 去除BOM字符
    b = utf8.SkipBOM(b)
    str = string(b)

    fmt.Println(str)
}

The output result is:

Hello World

Using the SkipBOM function is very simple, you only need to convert the string to be processed into a byte array , and then call the SkipBOM function. In this example, we first define a string with BOM characters and then convert it to a byte array. Then, call the SkipBOM function to remove the BOM characters, and finally convert the byte array into a string for output.

It should be noted that when calling the SkipBOM function, if there is no BOM character in the byte array, the function will directly return the original byte array without any impact.

Method 2: Use bytes library

bytes library also provides a method to remove BOM characters, the specific implementation is as follows:

func TrimBOM(s []byte) []byte {
    if len(s) >= 3 && s[0] == 0xef && s[1] == 0xbb && s[2] == 0xbf {
        return s[3:]
    }
    return s
}

This method receives a byte array parameter , returns a new byte array with the BOM characters removed. If the BOM character does not exist in the parameter byte array, this method will directly return the original byte array.

The following is a specific example:

package main

import (
    "bytes"
    "fmt"
)

func main() {
    str := "\ufeffHello World"
    b := []byte(str)

    // 去除BOM字符
    b = bytes.TrimPrefix(b, []byte{0xef, 0xbb, 0xbf})
    str = string(b)

    fmt.Println(str)
}

The output result is:

Hello World

In this example, we use the TrimPrefix method in the bytes library to remove BOM characters. This method Receives two parameters, the first parameter is the byte array to be processed, and the second parameter is the prefix to be deleted. Since the UTF-8 encoding of the BOM character is 0xefbbbf, we remove the BOM character by passing []byte{0xef, 0xbb, 0xbf} as the second parameter. Finally, the processed byte array is converted into a string for output.

It should be noted that when calling the TrimPrefix method, you need to use the []byte type BOM character as a parameter.

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