std/io/types.ts

// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.

/**
 * An abstract interface which when implemented provides an interface to read
 * bytes into an array buffer asynchronously.
 */
export interface Reader {
  /** Reads up to `p.byteLength` bytes into `p`. It resolves to the number of
   * bytes read (`0` < `n` <= `p.byteLength`) and rejects if any error
   * encountered. Even if `read()` resolves to `n` < `p.byteLength`, it may
   * use all of `p` as scratch space during the call. If some data is
   * available but not `p.byteLength` bytes, `read()` conventionally resolves
   * to what is available instead of waiting for more.
   *
   * When `read()` encounters end-of-file condition, it resolves to EOF
   * (`null`).
   *
   * When `read()` encounters an error, it rejects with an error.
   *
   * Callers should always process the `n` > `0` bytes returned before
   * considering the EOF (`null`). Doing so correctly handles I/O errors that
   * happen after reading some bytes and also both of the allowed EOF
   * behaviors.
   *
   * Implementations should not retain a reference to `p`.
   *
   * Use
   * {@linkcode @std/io/to-iterator.ts?s=toIterator}
   * to turn a {@linkcode Reader} into an {@linkcode AsyncIterableIterator}.
   */
  read(p: Uint8Array): Promise<number | null>;
}

/**
 * An abstract interface which when implemented provides an interface to read
 * bytes into an array buffer synchronously.
 */
export interface ReaderSync {
  /** Reads up to `p.byteLength` bytes into `p`. It resolves to the number
   * of bytes read (`0` < `n` <= `p.byteLength`) and rejects if any error
   * encountered. Even if `read()` returns `n` < `p.byteLength`, it may use
   * all of `p` as scratch space during the call. If some data is available
   * but not `p.byteLength` bytes, `read()` conventionally returns what is
   * available instead of waiting for more.
   *
   * When `readSync()` encounters end-of-file condition, it returns EOF
   * (`null`).
   *
   * When `readSync()` encounters an error, it throws with an error.
   *
   * Callers should always process the `n` > `0` bytes returned before
   * considering the EOF (`null`). Doing so correctly handles I/O errors that happen
   * after reading some bytes and also both of the allowed EOF behaviors.
   *
   * Implementations should not retain a reference to `p`.
   *
   * Use
   * {@linkcode @std/io/to-iterator.ts?s=toIteratorSync}
   * to turn a {@linkcode ReaderSync} into an {@linkcode IterableIterator}.
   */
  readSync(p: Uint8Array): number | null;
}

/**
 * An abstract interface which when implemented provides an interface to write
 * bytes from an array buffer to a file/resource asynchronously.
 */
export interface Writer {
  /** Writes `p.byteLength` bytes from `p` to the underlying data stream. It
   * resolves to the number of bytes written from `p` (`0` <= `n` <=
   * `p.byteLength`) or reject with the error encountered that caused the
   * write to stop early. `write()` must reject with a non-null error if
   * would resolve to `n` < `p.byteLength`. `write()` must not modify the
   * slice data, even temporarily.
   *
   * Implementations should not retain a reference to `p`.
   */
  write(p: Uint8Array): Promise<number>;
}
/**
 * An abstract interface which when implemented provides an interface to write
 * bytes from an array buffer to a file/resource synchronously.
 */
export interface WriterSync {
  /** Writes `p.byteLength` bytes from `p` to the underlying data
   * stream. It returns the number of bytes written from `p` (`0` <= `n`
   * <= `p.byteLength`) and any error encountered that caused the write to
   * stop early. `writeSync()` must throw a non-null error if it returns `n` <
   * `p.byteLength`. `writeSync()` must not modify the slice data, even
   * temporarily.
   *
   * Implementations should not retain a reference to `p`.
   */
  writeSync(p: Uint8Array): number;
}

/**
 * An abstract interface which when implemented provides an interface to close
 * files/resources that were previously opened.
 */
export interface Closer {
  /** Closes the resource, "freeing" the backing file/resource. */
  close(): void;
}

/**
 * A enum which defines the seek mode for IO related APIs that support
 * seeking.
 */
export enum SeekMode {
  /* Seek from the start of the file/resource. */
  Start = 0,
  /* Seek from the current position within the file/resource. */
  Current = 1,
  /* Seek from the end of the current file/resource. */
  End = 2,
}

/**
 * An abstract interface which when implemented provides an interface to seek
 * within an open file/resource asynchronously.
 */
export interface Seeker {
  /** Seek sets the offset for the next `read()` or `write()` to offset,
   * interpreted according to `whence`: `Start` means relative to the
   * start of the file, `Current` means relative to the current offset,
   * and `End` means relative to the end. Seek resolves to the new offset
   * relative to the start of the file.
   *
   * Seeking to an offset before the start of the file is an error. Seeking to
   * any positive offset is legal, but the behavior of subsequent I/O
   * operations on the underlying object is implementation-dependent.
   *
   * It resolves with the updated offset.
   */
  seek(offset: number | bigint, whence: SeekMode): Promise<number>;
}

/**
 * An abstract interface which when implemented provides an interface to seek
 * within an open file/resource synchronously.
 */
export interface SeekerSync {
  /** Seek sets the offset for the next `readSync()` or `writeSync()` to
   * offset, interpreted according to `whence`: `Start` means relative
   * to the start of the file, `Current` means relative to the current
   * offset, and `End` means relative to the end.
   *
   * Seeking to an offset before the start of the file is an error. Seeking to
   * any positive offset is legal, but the behavior of subsequent I/O
   * operations on the underlying object is implementation-dependent.
   *
   * It returns the updated offset.
   */
  seekSync(offset: number | bigint, whence: SeekMode): number;
}