resolved path prefix duplication and added unit tests

links/links.go

@@ -3,6 +3,7 @@ package links
 import (
 	"net/http"
 	"net/url"
+	"strings"
 
 	"github.com/pkg/errors"
 )
@@ -43,7 +44,10 @@ func FromHeadersOrDefault(h *http.Header, defaultURL *url.URL) *Builder {
 }
 
 func (b *Builder) BuildURL(oldURL *url.URL) *url.URL {
-	apiURL := b.URL.JoinPath(oldURL.Path)
+	newPath := oldURL.Path
+	newPath = strings.TrimPrefix(newPath, "/v1")
+
+	apiURL := b.URL.JoinPath(newPath)
 	apiURL.RawQuery = oldURL.RawQuery
 	return apiURL
 }

links/links_test.go

@@ -245,6 +245,18 @@ func TestBuilder_BuildLink(t *testing.T) {
 				"http://localhost:8080/some/path?param1=value1&param2=value2",
 				"http://localhost:8080/some/path?param1=value1&param2=value2",
 			},
+			// Old external link to new internal url
+			{
+				"http://localhost:8080/",
+				"https://some.api.host/v1/some/path",
+				"http://localhost:8080/some/path",
+			},
+			// Old external link to new external url
+			{
+				"https://some.api.host/v1",
+				"https://some.api.host/v1/some/path",
+				"https://some.api.host/v1/some/path",
+			},
 			// Old internal link to new external url
 			{
 				"https://some.api.host/v1",