Add error helper, supermon write/delete

lib/errors/errors.go

@@ -0,0 +1,114 @@
+// Copyright © 2016 Zellyn Hunter <zellyn@gmail.com>
+
+// Package errors contains helpers for creating and testing for
+// certain types of errors.
+package errors
+
+import (
+	"errors"
+	"fmt"
+)
+
+// Copy of errors.New, so you this package can be imported instead.
+func New(text string) error {
+	return errors.New(text)
+}
+
+// --------------------- Out of space
+
+// outOfSpace is an error that signals being out of space on a disk
+// image.
+type outOfSpace string
+
+// OutOfSpaceI is the tag interface used to mark out of space errors.
+type OutOfSpaceI interface {
+	IsOutOfSpace()
+}
+
+var _ OutOfSpaceI = outOfSpace("test")
+
+// Error returns the string message of an OutOfSpace error.
+func (o outOfSpace) Error() string {
+	return string(o)
+}
+
+// Tag method on our outOfSpace implementation.
+func (o outOfSpace) IsOutOfSpace() {
+}
+
+// OutOfSpacef is fmt.Errorf for OutOfSpace errors.
+func OutOfSpacef(format string, a ...interface{}) error {
+	return outOfSpace(fmt.Sprintf(format, a...))
+}
+
+// IsOutOfSpace returns true if a given error is an OutOfSpace error.
+func IsOutOfSpace(err error) bool {
+	_, ok := err.(OutOfSpaceI)
+	return ok
+}
+
+// --------------------- File exists
+
+// fileExists is an error returned when a problem is caused by a file
+// with the given name already existing.
+type fileExists string
+
+// FileExistsI is the tag interface used to mark FileExists errors.
+type FileExistsI interface {
+	IsFileExists()
+}
+
+var _ FileExistsI = fileExists("test")
+
+// Error returns the string message of a FileExists error.
+func (o fileExists) Error() string {
+	return string(o)
+}
+
+// Tag method on our fileExists implementation.
+func (o fileExists) IsFileExists() {
+}
+
+// FileExistsf is fmt.Errorf for FileExists errors.
+func FileExistsf(format string, a ...interface{}) error {
+	return fileExists(fmt.Sprintf(format, a...))
+}
+
+// IsFileExists returns true if a given error is a FileExists error.
+func IsFileExists(err error) bool {
+	_, ok := err.(FileExistsI)
+	return ok
+}
+
+// --------------------- File not found
+
+// fileNotFound is an error returned when a file with the given name
+// cannot be found.
+type fileNotFound string
+
+// FileNotFoundI is the tag interface used to mark FileNotFound errors.
+type FileNotFoundI interface {
+	IsFileNotFound()
+}
+
+var _ FileNotFoundI = fileNotFound("test")
+
+// Error returns the string message of a FileNotFound error.
+func (o fileNotFound) Error() string {
+	return string(o)
+}
+
+// Tag method on our fileNotFound implementation.
+func (o fileNotFound) IsFileNotFound() {
+}
+
+// FileNotFoundf is fmt.Errorf for FileNotFound errors.
+func FileNotFoundf(format string, a ...interface{}) error {
+	return fileNotFound(fmt.Sprintf(format, a...))
+}
+
+// IsFileNotFound returns true if a given error is a FileNotFound error.
+func IsFileNotFound(err error) bool {
+	_, ok := err.(FileNotFoundI)
+	return ok
+}

lib/supermon/supermon.go

@@ -11,6 +11,7 @@ import (
 	"strings"
 
 	"github.com/zellyn/diskii/lib/disk"
+	"github.com/zellyn/diskii/lib/errors"
 )
 
 const (
@@ -47,6 +48,37 @@ func LoadSectorMap(sd disk.SectorDisk) (SectorMap, error) {
 	return sm, nil
 }
 
+// Persist writes the current contenst of a sector map back back to
+// disk.
+func (sm SectorMap) Persist(sd disk.SectorDisk) error {
+	sector09, err := sd.ReadPhysicalSector(0, 9)
+	if err != nil {
+		return err
+	}
+	copy(sector09[0xd0:], sm[0:0x30])
+	if err := sd.WritePhysicalSector(0, 9, sector09); err != nil {
+		return err
+	}
+	if err := sd.WritePhysicalSector(0, 0xA, sm[0x30:0x130]); err != nil {
+		return err
+	}
+	if err := sd.WritePhysicalSector(0, 0xB, sm[0x130:0x230]); err != nil {
+		return err
+	}
+	return nil
+}
+
+// FreeSectors returns the number of blocks free in a sector map.
+func (sm SectorMap) FreeSectors() int {
+	count := 0
+	for _, file := range sm {
+		if file == FileFree {
+			count++
+		}
+	}
+	return count
+}
+
 // Verify checks that we actually have a NakedOS disk.
 func (sm SectorMap) Verify() error {
 	for sector := byte(0); sector <= 0xB; sector++ {
@@ -118,6 +150,49 @@ func (sm SectorMap) ReadFile(sd disk.SectorDisk, file byte) ([]byte, error) {
 	return result, nil
 }
 
+// Delete deletes a file from the sector map. It does not persist the changes.
+func (sm SectorMap) Delete(file byte) {
+	for i, f := range sm {
+		if f == file {
+			sm[i] = FileFree
+		}
+	}
+}
+
+// WriteFile writes the contents of a file.
+func (sm SectorMap) WriteFile(sd disk.SectorDisk, file byte, contents []byte, overwrite bool) error {
+	sectorsNeeded := (len(contents) + 255) / 256
+	cts := make([]byte, 256*sectorsNeeded)
+	copy(cts, contents)
+	free := sm.FreeSectors() + len(sm.SectorsForFile(file))
+	if free < sectorsNeeded {
+		return errors.OutOfSpacef("file requires %d sectors, but only %d are available")
+	}
+	sm.Delete(file)
+
+	// TODO(zellyn): continue implementation.
+	return fmt.Errorf("WriteFile not implemented yet")
+	i := 0
+OUTER:
+	for track := byte(0); track < sd.Tracks(); track++ {
+		for sector := byte(0); sector < sd.Sectors(); sector++ {
+			if sm.FileForSector(track, sector) == file {
+				if err := sd.WritePhysicalSector(track, sector, cts[i*256:(i+1)*256]); err != nil {
+					return err
+				}
+				i++
+				if i == sectorsNeeded {
+					break OUTER
+				}
+			}
+		}
+	}
+	if err := sm.Persist(sd); err != nil {
+		return err
+	}
+	return nil
+}
+
 // Symbol represents a single Super-Mon symbol.
 type Symbol struct {
 	// Address is the memory address the symbol points to, or 0 for an