Combine URL paths with path.Join()

Question

Is there a way in Go to combine URL paths similarly as we can do with filepaths using path.Join()?

For example see e.g. Combine absolute path and relative path to get a new absolute path.

When I use path.Join("http://foo", "bar"), I get http:/foo/bar.

See in Golang Playground.

Answer 1

ResolveReference() in net/url package

The accepted answer will not work for relative url paths containing file endings like .html or .img. The ResolveReference() function is the correct way to join url paths in go.

package main

import (
    "fmt"
    "log"
    "net/url"
)

func main() {
    u, err := url.Parse("../../..//search?q=dotnet")
    if err != nil {
        log.Fatal(err)
    }
    base, err := url.Parse("http://example.com/directory/")
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println(base.ResolveReference(u))
}

Answer 2

A simple approach to this would be to trim the /'s you don't want and join. Here is an example func

func JoinURL(base string, paths ...string) string {
    p := path.Join(paths...)
    return fmt.Sprintf("%s/%s", strings.TrimRight(base, "/"), strings.TrimLeft(p, "/"))
}

Usage would be

b := "http://my.domain.com/api/"
u := JoinURL(b, "/foo", "bar/", "baz")
fmt.Println(u)

This removes the need for checking/returning errors

Answer 3

To join a URL with another URL or a path, there is URL.Parse():

func (u *URL) Parse(ref string) (*URL, error)

Parse parses a URL in the context of the receiver. The provided URL may be relative or absolute. Parse returns nil, err on parse failure, otherwise its return value is the same as ResolveReference.

func TestURLParse(t *testing.T) {
    baseURL, _ := url.Parse("http://foo/a/b/c")

    url1, _ := baseURL.Parse("d/e")
    require.Equal(t, "http://foo/a/b/d/e", url1.String())

    url2, _ := baseURL.Parse("../d/e")
    require.Equal(t, "http://foo/a/d/e", url2.String())

    url3, _ := baseURL.Parse("/d/e")
    require.Equal(t, "http://foo/d/e", url3.String())
}

Answer 4

In 1.19 there will be a new function in the standard library that solves this very neatly.

u := url.JoinPath("http://host/foo", "bar/")

https://go.dev/play/p/xCJcVPN5pPh?v=gotip

Answer 5

I wrote this utility function that works for my purposes:

func Join(basePath string, paths ...string) (*url.URL, error) {

    u, err := url.Parse(basePath)

    if err != nil {
        return nil, fmt.Errorf("invalid url")
    }

    p2 := append([]string{u.Path}, paths...)

    result := path.Join(p2...)

    u.Path = result

    return u, nil
}

https://play.golang.org/p/-QNVvyzacMM