1 files changed, 143 insertions, 0 deletions
diff --git a/src/os/error.go b/src/os/error.go
new file mode 100644
index 0000000..704a6fb
--- /dev/null
+++ b/src/os/error.go
@@ -0,0 +1,143 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os
+
+import (
+	"internal/oserror"
+	"internal/poll"
+	"io/fs"
+)
+
+// Portable analogs of some common system call errors.
+//
+// Errors returned from this package may be tested against these errors
+// with errors.Is.
+var (
+	// ErrInvalid indicates an invalid argument.
+	// Methods on File will return this error when the receiver is nil.
+	ErrInvalid = fs.ErrInvalid // "invalid argument"
+
+	ErrPermission = fs.ErrPermission // "permission denied"
+	ErrExist      = fs.ErrExist      // "file already exists"
+	ErrNotExist   = fs.ErrNotExist   // "file does not exist"
+	ErrClosed     = fs.ErrClosed     // "file already closed"
+
+	ErrNoDeadline       = errNoDeadline()       // "file type does not support deadline"
+	ErrDeadlineExceeded = errDeadlineExceeded() // "i/o timeout"
+)
+
+func errClosed() error     { return oserror.ErrClosed }
+func errNoDeadline() error { return poll.ErrNoDeadline }
+
+// errDeadlineExceeded returns the value for os.ErrDeadlineExceeded.
+// This error comes from the internal/poll package, which is also
+// used by package net. Doing this this way ensures that the net
+// package will return os.ErrDeadlineExceeded for an exceeded deadline,
+// as documented by net.Conn.SetDeadline, without requiring any extra
+// work in the net package and without requiring the internal/poll
+// package to import os (which it can't, because that would be circular).
+func errDeadlineExceeded() error { return poll.ErrDeadlineExceeded }
+
+type timeout interface {
+	Timeout() bool
+}
+
+// PathError records an error and the operation and file path that caused it.
+type PathError = fs.PathError
+
+// SyscallError records an error from a specific system call.
+type SyscallError struct {
+	Syscall string
+	Err     error
+}
+
+func (e *SyscallError) Error() string { return e.Syscall + ": " + e.Err.Error() }
+
+func (e *SyscallError) Unwrap() error { return e.Err }
+
+// Timeout reports whether this error represents a timeout.
+func (e *SyscallError) Timeout() bool {
+	t, ok := e.Err.(timeout)
+	return ok && t.Timeout()
+}
+
+// NewSyscallError returns, as an error, a new SyscallError
+// with the given system call name and error details.
+// As a convenience, if err is nil, NewSyscallError returns nil.
+func NewSyscallError(syscall string, err error) error {
+	if err == nil {
+		return nil
+	}
+	return &SyscallError{syscall, err}
+}
+
+// IsExist returns a boolean indicating whether the error is known to report
+// that a file or directory already exists. It is satisfied by ErrExist as
+// well as some syscall errors.
+//
+// This function predates errors.Is. It only supports errors returned by
+// the os package. New code should use errors.Is(err, os.ErrExist).
+func IsExist(err error) bool {
+	return underlyingErrorIs(err, ErrExist)
+}
+
+// IsNotExist returns a boolean indicating whether the error is known to
+// report that a file or directory does not exist. It is satisfied by
+// ErrNotExist as well as some syscall errors.
+//
+// This function predates errors.Is. It only supports errors returned by
+// the os package. New code should use errors.Is(err, os.ErrNotExist).
+func IsNotExist(err error) bool {
+	return underlyingErrorIs(err, ErrNotExist)
+}
+
+// IsPermission returns a boolean indicating whether the error is known to
+// report that permission is denied. It is satisfied by ErrPermission as well
+// as some syscall errors.
+//
+// This function predates errors.Is. It only supports errors returned by
+// the os package. New code should use errors.Is(err, os.ErrPermission).
+func IsPermission(err error) bool {
+	return underlyingErrorIs(err, ErrPermission)
+}
+
+// IsTimeout returns a boolean indicating whether the error is known
+// to report that a timeout occurred.
+//
+// This function predates errors.Is, and the notion of whether an
+// error indicates a timeout can be ambiguous. For example, the Unix
+// error EWOULDBLOCK sometimes indicates a timeout and sometimes does not.
+// New code should use errors.Is with a value appropriate to the call
+// returning the error, such as os.ErrDeadlineExceeded.
+func IsTimeout(err error) bool {
+	terr, ok := underlyingError(err).(timeout)
+	return ok && terr.Timeout()
+}
+
+func underlyingErrorIs(err, target error) bool {
+	// Note that this function is not errors.Is:
+	// underlyingError only unwraps the specific error-wrapping types
+	// that it historically did, not all errors implementing Unwrap().
+	err = underlyingError(err)
+	if err == target {
+		return true
+	}
+	// To preserve prior behavior, only examine syscall errors.
+	e, ok := err.(syscallErrorType)
+	return ok && e.Is(target)
+}
+
+// underlyingError returns the underlying error for known os error types.
+func underlyingError(err error) error {
+	switch err := err.(type) {
+	case *PathError:
+		return err.Err
+	case *LinkError:
+		return err.Err
+	case *SyscallError:
+		return err.Err
+	}
+	return err
+}