fix(collector): link a failed repository to the configured host

When the first scan of a repository failed, the repository link pointed at github.com. It now follows github.api_url: Enterprise Server hosts drop the /api/v3 suffix and Enterprise Cloud hosts drop the api. prefix.

internal/config/config.go

@@ -4,6 +4,7 @@ package config
 import (
 	"errors"
 	"fmt"
+	"net/url"
 	"os"
 	"strings"
 	"time"
@@ -161,3 +162,24 @@ func normalizeRepos(in []string) ([]string, error) {
 	}
 	return out, nil
 }
+
+const (
+	defaultWebURL = "https://github.com"
+	apiV3Suffix   = "/api/v3"
+	apiHostPrefix = "api."
+)
+
+// WebBase returns the address of the web interface that belongs to a GitHub API address:
+// github.com for the public API, the host without /api/v3 for Enterprise Server, and the host
+// without its "api." prefix for Enterprise Cloud with data residency.
+func WebBase(apiURL string) string {
+	u, err := url.Parse(strings.TrimRight(apiURL, "/"))
+	if err != nil || u.Host == "" || strings.EqualFold(u.Host, "api.github.com") {
+		return defaultWebURL
+	}
+	u.Path = strings.TrimSuffix(u.Path, apiV3Suffix)
+	if u.Path == "" {
+		u.Host = strings.TrimPrefix(u.Host, apiHostPrefix)
+	}
+	return strings.TrimRight(u.String(), "/")
+}

internal/config/config_test.go

@@ -126,3 +126,22 @@ func TestManualRefreshCanBeDisabled(t *testing.T) {
 		t.Fatal("explicit false must stay off")
 	}
 }
+
+func TestWebBase(t *testing.T) {
+	tests := map[string]string{
+		"":                                      "https://github.com",
+		"https://api.github.com":                "https://github.com",
+		"https://api.github.com/":               "https://github.com",
+		"https://ghe.example.com/api/v3":        "https://ghe.example.com",
+		"https://ghe.example.com/api/v3/":       "https://ghe.example.com",
+		"http://ghe.internal:8080/api/v3":       "http://ghe.internal:8080",
+		"https://api.acme.ghe.com":              "https://acme.ghe.com",
+		"https://github.example.com/sub/api/v3": "https://github.example.com/sub",
+		"not a url":                             "https://github.com",
+	}
+	for in, want := range tests {
+		if got := WebBase(in); got != want {
+			t.Errorf("WebBase(%q) = %q, want %q", in, got, want)
+		}
+	}
+}