chore: panic if a random name cannot be created

If that happens so much will go wrong that there is no point in
continuing to do anything. It simplifies the requirements of the
caller: it may be a function that is assumed to never error.

act/cacheproxy/handler.go

@@ -167,11 +167,7 @@ func (h *Handler) ExternalURL() string {
 // The function returns the 32-bit random key which the run will use to identify itself.
 func (h *Handler) AddRun(data RunData) (string, error) {
 	for retries := 0; retries < 3; retries++ {
-		key, err := common.RandName(4)
-		if err != nil {
-			return "", errors.New("Could not generate the run id")
-		}
-
+		key := common.MustRandName(4)
 		_, loaded := h.runs.LoadOrStore(key, data)
 		if !loaded {
 			// The key was unique and added successfully

act/common/randname.go

@@ -5,12 +5,21 @@ package common
 import (
 	"crypto/rand"
 	"encoding/hex"
+	"fmt"
 )
 
-func RandName(size int) (string, error) {
+func randName(size int) (string, error) {
 	randBytes := make([]byte, size)
 	if _, err := rand.Read(randBytes); err != nil {
 		return "", err
 	}
 	return hex.EncodeToString(randBytes), nil
 }
+
+func MustRandName(size int) string {
+	name, err := randName(size)
+	if err != nil {
+		panic(fmt.Errorf("RandName(%d): %v", size, err))
+	}
+	return name
+}

act/runner/action_cache.go

@@ -39,10 +39,7 @@ func (c GoGitActionCache) Fetch(ctx context.Context, cacheDir, url, ref, token s
 	if err != nil {
 		return "", err
 	}
-	branchName, err := common.RandName(12)
-	if err != nil {
-		return "", err
-	}
+	branchName := common.MustRandName(12)
 
 	var auth transport.AuthMethod
 	if token != "" {

act/runner/run_context.go

@@ -283,10 +283,7 @@ func (rc *RunContext) startHostEnvironment() common.Executor {
 			return true
 		})
 		cacheDir := rc.ActionCacheDir()
-		randName, err := common.RandName(8)
-		if err != nil {
-			return err
-		}
+		randName := common.MustRandName(8)
 		miscpath := filepath.Join(cacheDir, randName)
 		actPath := filepath.Join(miscpath, "act")
 		if err := os.MkdirAll(actPath, 0o777); err != nil {
@@ -626,10 +623,7 @@ func (rc *RunContext) sh(ctx context.Context, script string) (stdout, stderr str
 		env[k] = v
 	}
 
-	base, err := common.RandName(8)
-	if err != nil {
-		return "", "", err
-	}
+	base := common.MustRandName(8)
 	name := base + ".sh"
 	oldStdout, oldStderr := rc.JobContainer.ReplaceLogWriter(hout, herr)
 	err = rc.JobContainer.Copy(rc.JobContainer.GetActPath(), &container.FileEntry{