Return package-specific error messagesformat-errors-and-use-error-values

Instead of passing errors through to clients, wrap them with a
"browserenv" error message to add context.

Add new error types that can be matched against.

2 files changed, 87 insertions, 6 deletions

diff --git a/browserenv.go b/browserenv.go
index 6812700..eaff96e 100644
--- a/browserenv.go
+++ b/browserenv.go
@@ -50,7 +50,7 @@ func OpenFile(path string) error {
 	if envCommand != "" {
 		path, err := filepath.Abs(path)
 		if err != nil {
-			return err
+			return &PathResolutionError{path, err}
 		}
 
 		url := "file://" + path
@@ -70,12 +70,12 @@ func OpenReader(r io.Reader) error {
 	if envCommand != "" {
 		tempFile, err := ioutil.TempFile("", "browserenv")
 		if err != nil {
-			return err
+			return &TempFileError{err}
 		}
 
 		_, err = io.Copy(tempFile, r)
 		if err != nil {
-			return err
+			return &CopyError{err}
 		}
 
 		return OpenFile(tempFile.Name())
@@ -110,18 +110,23 @@ func runBrowserCommand(commands, url string) error {
 	commandList := strings.Split(commands, commandSeparator)
 
 	var err error
+	var lastCommand string
 	for _, command := range commandList {
 		cmd := browserCommand(command, url)
 
 		// Keep running commands from left to right until one of them exits
 		// successfully.
 		err = cmd.Run()
-		if err == nil || cmd.ProcessState.ExitCode() == 0 {
-			return err
+		if err == nil {
+			return nil
+		} else if cmd.ProcessState.ExitCode() == 0 {
+			return &ExecZeroError{command, err}
 		}
+
+		lastCommand = command
 	}
 
-	return err
+	return &ExecError{lastCommand, err}
 }
 
 // browserCommand sets up an exec.Cmd to run command, attaching Stdout and
diff --git a/error.go b/error.go
new file mode 100644
index 0000000..d90d1b8
--- /dev/null
+++ b/error.go
@@ -0,0 +1,76 @@
+package browserenv
+
+import "fmt"
+
+const errorPrefix = "browserenv: "
+
+// CopyError represents a failure to copy data.
+type CopyError struct {
+	err error
+}
+
+func (e *CopyError) Error() string {
+	return fmt.Sprintf(errorPrefix+"can't copy from reader: %v", e.err)
+}
+
+func (e *CopyError) Unwrap() error { return e.err }
+
+// ExecError results from executing an external command.
+type ExecError struct {
+	command string
+	err     error
+}
+
+func (e *ExecError) Error() string {
+	return fmt.Sprintf(
+		errorPrefix+"failed to run BROWSER command %q: %v",
+		e.command,
+		e.err,
+	)
+}
+
+func (e *ExecError) Unwrap() error { return e.err }
+
+// ExecZeroError results from executing an external command that produces an
+// error with an exit code of 0.
+type ExecZeroError struct {
+	command string
+	err     error
+}
+
+func (e *ExecZeroError) Error() string {
+	return fmt.Sprintf(
+		errorPrefix+"error running command %q: %v",
+		e.command,
+		e.err,
+	)
+}
+
+func (e *ExecZeroError) Unwrap() error { return e.err }
+
+// PathResolutionError means the given path couldn't be resolved.
+type PathResolutionError struct {
+	path string
+	err  error
+}
+
+func (e *PathResolutionError) Error() string {
+	return fmt.Sprintf(
+		errorPrefix+"can't resolve path for %q: %v",
+		e.path,
+		e.err,
+	)
+}
+
+func (e *PathResolutionError) Unwrap() error { return e.err }
+
+// TempFileError corresponds to an error while creating a temporary file.
+type TempFileError struct {
+	err error
+}
+
+func (e *TempFileError) Error() string {
+	return fmt.Sprintf(errorPrefix+"can't create temporary file: %v", e.err)
+}
+
+func (e *TempFileError) Unwrap() error { return e.err }