How to truncate a string in a Golang template

Question

In golang, is there a way to truncate text in an html template?

For example, I have the following in my template:

{{ range .SomeContent }}
 ....
             


        

Answer 1

Needs more magic for Unicode strings

This is not correct, see below

import "unicode/utf8"

func Short( s string, i int) string {
    if len( s ) < i {
        return s
    }
    if utf8.ValidString( s[:i] ) {
        return s[:i]
    }
    // The omission.
    // In reality, a rune can have 1-4 bytes width (not 1 or 2)
    return s[:i+1] // or i-1
}

But i above is not the number of chars. It's the number of bytes. Link to this code on play.golang.org

I hope this helps.

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Edit

Updated: check string length. See @geoff comment below

See that answer, and play here. It's another solution.

package main

import "fmt"

func Short( s string, i int ) string {
    runes := []rune( s )
    if len( runes ) > i {
        return string( runes[:i] )
    }
    return s
}

func main() {
    fmt.Println( Short( "Hello World", 5 ) )
    fmt.Println( Short( "Привет Мир", 5 ) )
}

---

But if you are interested in the length in bytes:

func truncateStrings(s string, n int) string {
    if len(s) <= n {
        return s
    }
    for !utf8.ValidString(s[:n]) {
        n--
    }
    return s[:n]
}

play.golang.org. This function never panics (if n >= 0), but you can obtain an empty string play.golang.org

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Also, keep in mind this experimental package golang.org/x/exp/utf8string

Package utf8string provides an efficient way to index strings by rune rather than by byte.