cogito: add support for Github Enterprise API endpoint

Initial implementation by @wanderanimrod and @dev-jin
Co-authored-by: Nimrod Wandera <wanderanimrod@gmail.com>
Co-authored-by: Jin-Chun <Jin.Chun@ibm.com>

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [v0.12.0] - Unreleased
+
+### Added
+
+- Support GitHub Enterprise (see `source.github_hostname` in the README). Initial implementation by @wanderanimrod and @dev-jin.
+
 ## [v0.11.0] - 2023-09-22
 
 ### Added 

README.md

@@ -198,6 +198,10 @@ With reference to the [GitHub Commit status API], the `POST` parameters (`state`
   The log level (one of `debug`, `info`, `warn`, `error`, `silent`).\
   Default: `info`.
 
+- `github_hostname`:\
+  Override the default GitHub hostname. This allows you to post commit statuses to repositories hosted by GitHub Enterprise (GHE) instances. e.g, `github.mycompany.org`, without protocol (only HTTPS is supported) and without API endpoint suffix (`/api/v3/`).
+  Default: `github.com`
+
 - `log_url`. **DEPRECATED, no-op, will be removed**\
   A Google Hangout Chat webhook. Useful to obtain logging for the `check` step for Concourse < v7.x
 

cogito/ghcommitsink.go

@@ -93,9 +93,21 @@ func ghMakeContext(request PutRequest) string {
 }
 
 func apiEndpoint(h string) string {
-	hostname := strings.ToLower(h)
+	hostname := normalizeHostname(h) // not really required; already called during protocol init
+	if hostname == github.GhDefaultHostname {
+		return github.API
+	}
 	if strings.Contains(hostname, "127.0.0.1") {
 		return fmt.Sprintf("http://%s", hostname)
 	}
-	return github.API
+	return fmt.Sprintf("https://%s/api/v3", hostname)
+}
+
+func normalizeHostname(h string) string {
+	hostname := strings.ToLower(h)
+	hostname = strings.TrimSuffix(hostname, "/")
+	hostname = strings.TrimSuffix(hostname, "/api/v3")
+	hostname = strings.TrimPrefix(hostname, "http://")
+	hostname = strings.TrimPrefix(hostname, "https://")
+	return hostname
 }

cogito/protocol.go

@@ -260,7 +260,9 @@ func (src *Source) Validate() error {
 	//
 	// Validate optional fields.
 	//
-	// In this case, nothing to validate.
+	if src.GhHostname != "" {
+		src.GhHostname = normalizeHostname(src.GhHostname)
+	}
 
 	//
 	// Apply defaults.