Identify the type of file and call the respective parser

Since bunny wants to keep backwards compatibility with pun, we need to
keep the handling of Dockerfile-like files. Hence, we need to identofy
the format of the given file between a Dockerfile and a bunnyfile. For
that purpose, we check the first non-empty line of the file under
@syntax and if it starts with FROM we assume a Dockerfile and call the
respective function. Otherwise, we call the bunnyfile handler.

Signed-off-by: Charalampos Mainas <[email protected]>

cmd/main.go

@@ -154,7 +154,7 @@ func bunnyBuilder(ctx context.Context, c client.Client) (*client.Result, error)
 	}
 
 	// Parse packaging/building instructions
-	packInst, err := hops.ParseDockerFile(fileBytes)
+	packInst, err := hops.ParseFile(fileBytes)
 	if err != nil {
 		return nil, fmt.Errorf("Error parsing building instructions: %v", err)
 	}
@@ -218,7 +218,7 @@ func main() {
 	}
 
 	// Parse file with packaging/building instructions
-	packInst, err = hops.ParseDockerFile(CntrFileContent)
+	packInst, err = hops.ParseFile(CntrFileContent)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "Error: Could not parse building instructions: %v\n", err)
 		os.Exit(1)

hops/package.go

@@ -206,6 +206,32 @@ func ParseDockerFile(fileBytes []byte) (*PackInstructions, error) {
 	return instr, nil
 }
 
+// ParseFile identifies the format of the given file and either calls
+// ParseDockerFile or ParseBunnyFile
+func ParseFile(fileBytes []byte) (*PackInstructions, error) {
+	lines := bytes.Split(fileBytes, []byte("\n"))
+
+	// First line is always the #syntax
+	if len(lines) <= 1 {
+		return nil, fmt.Errorf("Invalid format of file")
+	}
+
+	// Simply check if the first non-empty line starts with FROM
+	// If it starts we assume a Dockerfile
+	// otherwise a bunnyfile
+	for _, line := range lines[1:] {
+		if len(bytes.TrimSpace(line)) > 0 {
+			if strings.HasPrefix(string(line), "FROM") {
+				return ParseDockerFile(fileBytes)
+			} else {
+				break
+			}
+		}
+	}
+
+	return ParseBunnyFile(fileBytes)
+}
+
 func copyIn(base llb.State, from string, src string, dst string) llb.State {
 	var copyState llb.State
 	var localSrc llb.State