Decode root directory entries

src/components/DiskInfo.vue

@@ -13,6 +13,10 @@ const floppyDisk = computed(() => {
   <section v-if="floppyDisk.bootSectorInfo">
     <h3>Boot Sector</h3>
     <pre>{{ floppyDisk.bootSectorInfo }}</pre>
+    <h3>Root Dir</h3>
+    <pre>{{ floppyDisk.rootDirEntries }}</pre>
+    <h3>Data</h3>
+    <pre>Offset: {{ floppyDisk.dataOffset }}</pre>
   </section>
 </template>
 

src/floppy/disk.ts

@@ -30,6 +30,26 @@ export interface IBiosParameterBlock {
   totalSectorsLarge: number
 }
 
+export interface IStandardDirEntry {
+  type: 'standard-entry'
+  name: string
+  extension: string
+}
+
+export interface ILongFileNameDirEntry {
+  type: 'long-filename-entry'
+}
+
+export interface IFinalDirEntry {
+  type: 'final-entry'
+}
+
+export interface IUnusedDirEntry {
+  type: 'unused-entry'
+}
+
+export type DirEntry = IStandardDirEntry | ILongFileNameDirEntry | IFinalDirEntry | IUnusedDirEntry
+
 export class FloppyDisk {
   private readonly _buffer = new ArrayBuffer(0)
   private _bootSector: IBootSectorInfo | null = null
@@ -38,18 +58,87 @@ export class FloppyDisk {
     this._buffer = buffer
   }
 
+  private _rootDirEntries: DirEntry[] | null = null
+
+  get rootDirEntries() {
+    if (this._rootDirEntries === null) {
+      const offset = this.rootDirOffset
+      const size = this.rootDirSize
+
+      const end = offset + size
+
+      if (this._buffer.byteLength >= end) {
+        this._rootDirEntries = decodeDirectoryEntries(
+          new DataView(this._buffer, this.rootDirOffset, this.rootDirSize),
+        )
+      }
+    }
+    return this._rootDirEntries
+  }
+
   get bootSectorInfo() {
-    return (this._bootSector = this._bootSector ?? decodeBootSector(this._buffer))
+    if (this._buffer.byteLength < 512) {
+      return null
+    }
+    return (this._bootSector =
+      this._bootSector ?? decodeBootSector(new DataView(this._buffer, 0, 512)))
+  }
+
+  get tableSize() {
+    return this.bootSectorInfo?.biosParameterBlock?.sectorsPerTableSmall ?? 0
+  }
+
+  get rootEntryCount() {
+    return this.bootSectorInfo?.biosParameterBlock?.rootEntryCount ?? 0
+  }
+
+  get tableCount() {
+    return this.bootSectorInfo?.biosParameterBlock?.tableCount ?? 0
+  }
+
+  get reservedSectorCount() {
+    return this.bootSectorInfo?.biosParameterBlock?.reservedSectorCount ?? 0
+  }
+
+  get bytesPerSector() {
+    return this.bootSectorInfo?.biosParameterBlock?.bytesPerSector ?? 0
+  }
+
+  get rootDirSectors() {
+    if (this.bytesPerSector === 0) {
+      return 0
+    } else {
+      return Math.ceil((this.rootEntryCount * 32) / this.bytesPerSector)
+    }
+  }
+
+  get firstDataSector() {
+    return this.reservedSectorCount + this.tableCount * this.tableSize + this.rootDirSectors
+  }
+
+  get dataOffset() {
+    return this.firstDataSector * this.bytesPerSector
+  }
+
+  get firstRootDirSector() {
+    return this.firstDataSector - this.rootDirSectors
+  }
+
+  get rootDirOffset() {
+    return this.firstRootDirSector * this.bytesPerSector
+  }
+
+  get rootDirSize() {
+    return this.rootDirSectors * this.bytesPerSector
   }
 }
 
-function decodeBootSector(buffer: ArrayBuffer): IBootSectorInfo | null {
+function decodeBootSector(data: DataView): IBootSectorInfo | null {
-  if (buffer.byteLength < 512) {
+  if (data.byteLength < 512) {
     return null
   }
 
   const asciiDecoder = new TextDecoder('ascii')
-  const data = new DataView(buffer)
 
   const jumpInstruction: [number, number, number] = [
     data.getUint8(0),
@@ -57,7 +146,7 @@ function decodeBootSector(buffer: ArrayBuffer): IBootSectorInfo | null {
     data.getUint8(2),
   ]
 
-  const oemName = asciiDecoder.decode(buffer.slice(3, 11))
+  const oemName = asciiDecoder.decode(data.buffer.slice(3, 11))
   const bytesPerSector = data.getUint16(11, true)
   const sectorsPerCluster = data.getUint8(13)
   const reservedSectorCount = data.getUint16(14, true)
@@ -81,12 +170,12 @@ function decodeBootSector(buffer: ArrayBuffer): IBootSectorInfo | null {
 
   let volumeLabel
   if (bootSignature === 0x29) {
-    volumeLabel = asciiDecoder.decode(buffer.slice(43, 54))
+    volumeLabel = asciiDecoder.decode(data.buffer.slice(43, 54))
   }
 
   let fileSystemType
   if (bootSignature === 0x29) {
-    fileSystemType = asciiDecoder.decode(buffer.slice(54, 62))
+    fileSystemType = asciiDecoder.decode(data.buffer.slice(54, 62))
   }
 
   const bootPartitionSignature = data.getUint16(510, true)
@@ -119,3 +208,54 @@ function decodeBootSector(buffer: ArrayBuffer): IBootSectorInfo | null {
     },
   }
 }
+
+function decodeDirectoryEntry(data: DataView): DirEntry | null {
+  if (data.byteLength < 32) {
+    return null
+  }
+
+  const firstByte = data.getUint8(0)
+  const attributeByte = data.getUint8(11)
+
+  if (firstByte === 0) {
+    return { type: 'final-entry' }
+  } else if (firstByte === 0xe5) {
+    return { type: 'unused-entry' }
+  } else if (attributeByte === 0x0f) {
+    return { type: 'long-filename-entry' }
+  } else {
+    const asciiDecoder = new TextDecoder('ascii')
+    const name = asciiDecoder.decode(data.buffer.slice(data.byteOffset, data.byteOffset + 8))
+    const extension = asciiDecoder.decode(
+      data.buffer.slice(data.byteOffset + 8, data.byteOffset + 11),
+    )
+    return {
+      type: 'standard-entry',
+      name,
+      extension,
+    }
+  }
+}
+
+function decodeDirectoryEntries(data: DataView): DirEntry[] {
+  const entries: DirEntry[] = []
+
+  let offset = 0
+  while (data.byteLength - offset >= 32) {
+    const dirData = new DataView(data.buffer, data.byteOffset + offset, 32)
+    offset += 32
+
+    const entry = decodeDirectoryEntry(dirData)
+    if (entry === null) {
+      break
+    }
+
+    entries.push(entry)
+
+    if (entry.type === 'final-entry') {
+      break
+    }
+  }
+
+  return entries
+}