Support prow

Instead of requiring to map the prow env vars to other values, directly
use the env vars defined here:

https://github.com/kubernetes/test-infra/blob/master/prow/jobs.md#job-environment-variables

Add paragraph to README.md explaining the usage.

README.md

@@ -332,6 +332,38 @@ If you are using Coveralls Enterprise and have a self-signed certificate, you ne
 $ goveralls -insecure
 ```
 
+## Prow
+
+Goveralls can be used in [prow](https://github.com/kubernetes/test-infra/tree/master/prow) presubmit jobs, picking up the prow [environment variables](https://github.com/kubernetes/test-infra/blob/master/prow/jobs.md#job-environment-variables) `PULL_PULL_SHA`, `PULL_BASE_REF` and `PULL_NUMBER` to determine the original git commit id, the branch and the PR number automatically.
+
+To avoid leaking your coveralls repo token you can use the `COVERALLS_TOKEN_FILE` env variable, so that a token gets read and used in the API call.
+
+When configuring your prow job you can mount a defined secret containing your token like this:
+
+```yaml
+  ...
+  - name: coveralls
+    always_run: true
+    optional: false
+    spec:
+      containers:
+      - image: gcr.io/k8s-testimages/...
+        env:
+          - name: COVERALLS_TOKEN_FILE
+            value: /etc/secrets/coveralls/token
+        command:
+          - "goveralls -service=prow"
+        volumeMounts:
+          - name: coveralls
+            mountPath: /etc/secrets/coveralls
+            readOnly: true
+      volumes:
+        - name: coveralls
+          secret:
+            secretName: coveralls-token
+  ...
+```
+
 # Authors
 
 * Yasuhiro Matsumoto (a.k.a. mattn)

gitinfo.go

@@ -65,6 +65,15 @@ func collectGitInfo(ref string) (*Git, error) {
 				continue
 			}
 		}
+		if key == "GIT_ID" {
+			if envGitId := loadGitIdFromEnv(); envGitId != "" {
+				err := os.Setenv(key, envGitId)
+				if err != nil {
+					return nil, err
+				}
+				continue
+			}
+		}
 		if os.Getenv(key) != "" {
 			// metadata already available via environment variable
 			continue
@@ -129,7 +138,7 @@ var varNames = [...]string{
 	"CI_BRANCH", "APPVEYOR_REPO_BRANCH",
 	"WERCKER_GIT_BRANCH", "DRONE_BRANCH",
 	"BUILDKITE_BRANCH", "BRANCH_NAME",
-	"CI_COMMIT_REF_NAME",
+	"CI_COMMIT_REF_NAME", "PULL_BASE_REF",
 }
 
 func loadBranchFromEnv() string {
@@ -144,3 +153,19 @@ func loadBranchFromEnv() string {
 
 	return ""
 }
+
+var gitIdVarNames = [...]string{
+	"GIT_ID",
+
+	"PULL_PULL_SHA",
+}
+
+func loadGitIdFromEnv() string {
+	for _, gitIdVarName := range gitIdVarNames {
+		if gitId := os.Getenv(gitIdVarName); gitId != "" {
+			return gitId
+		}
+	}
+
+	return ""
+}

gitinfo_test.go

@@ -114,6 +114,13 @@ func TestLoadBranchFromEnv(t *testing.T) {
 			},
 			"github-master",
 		},
+		{
+			"Prow PULL_BASE_REF defined",
+			map[string]string{
+				"PULL_BASE_REF": "prow-master",
+			},
+			"prow-master",
+		},
 		{
 			"no branch var defined",
 			map[string]string{},
@@ -137,3 +144,50 @@ func resetBranchEnvs(values map[string]string) {
 		os.Setenv(k, v)
 	}
 }
+
+func TestLoadGitIdFromEnv(t *testing.T) {
+	t.Parallel()
+
+	var tests = []struct {
+		testCase      string
+		envs          map[string]string
+		expectedGitId string
+	}{
+		{
+			"all vars defined",
+			map[string]string{
+				"GIT_ID":           "git-id",
+				"PULL_PULL_SHA": "prow-git-id",
+			},
+			"git-id",
+		},
+		{
+			"all except GIT_ID",
+			map[string]string{
+				"PULL_PULL_SHA": "prow-git-id",
+			},
+			"prow-git-id",
+		},
+		{
+			"no git id defined",
+			map[string]string{},
+			"",
+		},
+	}
+	for _, test := range tests {
+		resetGitIdEnvs(test.envs)
+		envGitId := loadGitIdFromEnv()
+		if envGitId != test.expectedGitId {
+			t.Errorf("%s: wrong git id returned. Expected %q, but got %q", test.testCase, test.expectedGitId, envGitId)
+		}
+	}
+}
+
+func resetGitIdEnvs(values map[string]string) {
+	for _, envVar := range gitIdVarNames {
+		os.Unsetenv(envVar)
+	}
+	for k, v := range values {
+		os.Setenv(k, v)
+	}
+}

goveralls.go

@@ -402,6 +402,8 @@ func process() error {
 	} else if prURL := os.Getenv("CI_PULL_REQUEST"); prURL != "" {
 		// for Circle CI
 		pullRequest = regexp.MustCompile(`[0-9]+$`).FindString(prURL)
+	} else if prNumber := os.Getenv("PULL_NUMBER"); prNumber != "" {
+		pullRequest = prNumber
 	} else if os.Getenv("GITHUB_EVENT_NAME") == "pull_request" {
 		number := githubEvent["number"].(float64)
 		pullRequest = strconv.Itoa(int(number))