Troubleshooting Peculiar CSV Results for Quoted Strings in Go Encoding/CSV

The encoding/csv package in Go has been the subject of much debate regarding the handling of quoted strings in CSV files. This article aims to shed light on the issue by exploring an intriguing phenomenon observed by a user encountered extra quotes while writing quoted strings to a CSV file.

The Enigma of Extra Quotes

The user provided the following code snippet to illustrate the issue:

package main

import (
    "encoding/csv"
    "fmt"
    "os"
)

func main() {
    // Create a file to write CSV data
    f, err := os.Create("./test.csv")
    if err != nil {
        log.Fatal("Error: %s", err)
    }
    defer f.Close()

    // Initialize a CSV writer
    w := csv.NewWriter(f)

    // Unquoted string
    var record []string
    record = append(record, "Unquoted string")
    s := "Cr@zy text with , and \\ and \" etc"
    record = append(record, s)
    fmt.Println(record)
    w.Write(record)

    // Quoted string
    record = make([]string, 0)
    record = append(record, "Quoted string")
    s = fmt.Sprintf("%q", s)
    record = append(record, s)
    fmt.Println(record)
    w.Write(record)

    // Flush the writer to save the changes
    w.Flush()
}

When running this code, the expected output for the quoted string would be as follows:

[Quoted string "Cr@zy text with , and \\ and \" etc"]

However, the output actually obtained was:

[Quoted string,"""Cr@zy text with , and \\ and \"" etc"""]

The presence of additional quotes around the quoted string was puzzling and required further investigation.

Understanding the CSV Standard

The root of the issue lies in the CSV (Comma-Separated Values) file format standard itself. According to the standard, double quotation marks (") used within a field must be represented by two double quotation marks (""). This is a means of escaping the character for parsing purposes.

A (double) quote character in a field must be represented by two (double) quote characters.

• [Comma-separated values - Wikipedia](https://en.wikipedia.org/wiki/Comma-separated_values)

Impact on CSV Writing

Applying this rule to the code, the user was indeed correctly escaping the quotation marks within the quoted string by using fmt.Sprintf("%q"). However, the encoding/csv package adds additional escaping by surrou

[Unquoted string Cr@zy text with , and `\` and " etc]
[Quoted string `""""Cr@zy text with , and `\` and \"" etc""""`]

This additional escaping is necessary to adhere to the CSV standard, which requires fields to be optionally enclosed by double quotes, and double quotes within fields must be represented as double double quotes.

Avoiding Extra Quotes

While the extra quotes are added as per the CSV encoding specifications, they can be avoided by opting for an alternative encoding format. Alternatively, if you want to strictly follow the CSV standard, you can manipulate the string manually by replacing each single double quote with a double double quote, like this:

s = strings.ReplaceAll(s, `"`, `""`)

Conclusion

The peculiar behavior observed while writing quoted strings to CSV files in Go's encoding/csv package can be attributed to the CSV standard itself, which requires double quotation marks to be escaped for parsing. By understanding this underlying mechanism, you can either choose alternate encoding formats or manually handle string escaping to achieve your desired results.