strings.Contains() returns always false

Question

In Go, I want to check if the following string contains text/plain in a string. The function strings.Contains() returns always false.

My local go version is go1.14.3 windows/amd64, my server version is go1.13.3 linux/amd64

Test code (play.golang.org/p/_ikCzWd6438)

var test = "text/plain; charset=utf-8"

fmt.Println("my string:", test)
fmt.Println("strings.Contains(text/plain)", strings.Contains("text/plain", test))
fmt.Println("strings.Contains(text)", strings.Contains("text", test))
fmt.Println("strings.Contains(charset)", strings.Contains("charset", test))

var test2 = strings.ReplaceAll(test, "/", "") // remove slash
fmt.Println("my second string:", test2)
fmt.Println("strings.Contains(textplain)", strings.Contains("textplain", test2))
fmt.Println("strings.Contains(text)", strings.Contains("text", test2))
fmt.Println("strings.Contains(charset)", strings.Contains("charset", test2))

Output

my string: text/plain; charset=utf-8
strings.Contains(text/plain) false
strings.Contains(text) false
strings.Contains(charset) false
my second string: textplain; charset=utf-8
strings.Contains(textplain) false
strings.Contains(text) false
strings.Contains(charset) false

So why returns strings.Contains() always 'false'?

Answer 1

According to the docs:

func Contains(s, substr string) bool

Contains reports whether substr is within s.

The first parameter s is the original string and the second, substr, is the substring you search for. In your case, it is the other way around.

For example instead of strings.Contains("charset", test), it should be strings.Contains(test, "charset")