std/fs/exists.ts

// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.

/** Options for {@linkcode exists} and {@linkcode existsSync.} */
export interface ExistsOptions {
  /**
   * When `true`, will check if the path is readable by the user as well.
   * @default {false}
   */
  isReadable?: boolean;
  /**
   * When `true`, will check if the path is a directory as well.
   * Directory symlinks are included.
   * @default {false}
   */
  isDirectory?: boolean;
  /**
   * When `true`, will check if the path is a file as well.
   * File symlinks are included.
   * @default {false}
   */
  isFile?: boolean;
}

/**
 * Test whether or not the given path exists by checking with the file system. Please consider to check if the path is readable and either a file or a directory by providing additional `options`:
 *
 * ```ts
 * import { exists } from "https://deno.land/std@$STD_VERSION/fs/mod.ts";
 * const isReadableDir = await exists("./foo", {
 *   isReadable: true,
 *   isDirectory: true
 * });
 * const isReadableFile = await exists("./bar", {
 *   isReadable: true,
 *   isFile: true
 * });
 * ```
 *
 * Note: Do not use this function if performing a check before another operation on that file. Doing so creates a race condition. Instead, perform the actual file operation directly.
 *
 * Bad:
 * ```ts
 * import { exists } from "https://deno.land/std@$STD_VERSION/fs/mod.ts";
 *
 * if (await exists("./foo")) {
 *   await Deno.remove("./foo");
 * }
 * ```
 *
 * Good:
 * ```ts
 * // Notice no use of exists
 * try {
 *   await Deno.remove("./foo", { recursive: true });
 * } catch (error) {
 *   if (!(error instanceof Deno.errors.NotFound)) {
 *     throw error;
 *   }
 *   // Do nothing...
 * }
 * ```
 * @see https://en.wikipedia.org/wiki/Time-of-check_to_time-of-use
 */
export async function exists(
  path: string | URL,
  options?: ExistsOptions,
): Promise<boolean> {
  try {
    const stat = await Deno.stat(path);
    if (
      options &&
      (options.isReadable || options.isDirectory || options.isFile)
    ) {
      if (options.isDirectory && options.isFile) {
        throw new TypeError(
          "ExistsOptions.options.isDirectory and ExistsOptions.options.isFile must not be true together.",
        );
      }
      if (
        (options.isDirectory && !stat.isDirectory) ||
        (options.isFile && !stat.isFile)
      ) {
        return false;
      }
      if (options.isReadable) {
        if (stat.mode === null) {
          return true; // Exclusive on Non-POSIX systems
        }
        if (Deno.uid() === stat.uid) {
          return (stat.mode & 0o400) === 0o400; // User is owner and can read?
        } else if (Deno.gid() === stat.gid) {
          return (stat.mode & 0o040) === 0o040; // User group is owner and can read?
        }
        return (stat.mode & 0o004) === 0o004; // Others can read?
      }
    }
    return true;
  } catch (error) {
    if (error instanceof Deno.errors.NotFound) {
      return false;
    }
    if (error instanceof Deno.errors.PermissionDenied) {
      if (
        (await Deno.permissions.query({ name: "read", path })).state ===
          "granted"
      ) {
        // --allow-read not missing
        return !options?.isReadable; // PermissionDenied was raised by file system, so the item exists, but can't be read
      }
    }
    throw error;
  }
}

/**
 * Test whether or not the given path exists by checking with the file system. Please consider to check if the path is readable and either a file or a directory by providing additional `options`:
 *
 * ```ts
 * import { existsSync } from "https://deno.land/std@$STD_VERSION/fs/mod.ts";
 * const isReadableDir = existsSync("./foo", {
 *   isReadable: true,
 *   isDirectory: true
 * });
 * const isReadableFile = existsSync("./bar", {
 *   isReadable: true,
 *   isFile: true
 * });
 * ```
 *
 * Note: do not use this function if performing a check before another operation on that file. Doing so creates a race condition. Instead, perform the actual file operation directly.
 *
 * Bad:
 * ```ts
 * import { existsSync } from "https://deno.land/std@$STD_VERSION/fs/mod.ts";
 *
 * if (existsSync("./foo")) {
 *   Deno.removeSync("./foo");
 * }
 * ```
 *
 * Good:
 * ```ts
 * // Notice no use of existsSync
 * try {
 *   Deno.removeSync("./foo", { recursive: true });
 * } catch (error) {
 *   if (!(error instanceof Deno.errors.NotFound)) {
 *     throw error;
 *   }
 *   // Do nothing...
 * }
 * ```
 * @see https://en.wikipedia.org/wiki/Time-of-check_to_time-of-use
 */
export function existsSync(
  path: string | URL,
  options?: ExistsOptions,
): boolean {
  try {
    const stat = Deno.statSync(path);
    if (
      options &&
      (options.isReadable || options.isDirectory || options.isFile)
    ) {
      if (options.isDirectory && options.isFile) {
        throw new TypeError(
          "ExistsOptions.options.isDirectory and ExistsOptions.options.isFile must not be true together.",
        );
      }
      if (
        (options.isDirectory && !stat.isDirectory) ||
        (options.isFile && !stat.isFile)
      ) {
        return false;
      }
      if (options.isReadable) {
        if (stat.mode === null) {
          return true; // Exclusive on Non-POSIX systems
        }
        if (Deno.uid() === stat.uid) {
          return (stat.mode & 0o400) === 0o400; // User is owner and can read?
        } else if (Deno.gid() === stat.gid) {
          return (stat.mode & 0o040) === 0o040; // User group is owner and can read?
        }
        return (stat.mode & 0o004) === 0o004; // Others can read?
      }
    }
    return true;
  } catch (error) {
    if (error instanceof Deno.errors.NotFound) {
      return false;
    }
    if (error instanceof Deno.errors.PermissionDenied) {
      if (
        Deno.permissions.querySync({ name: "read", path }).state === "granted"
      ) {
        // --allow-read not missing
        return !options?.isReadable; // PermissionDenied was raised by file system, so the item exists, but can't be read
      }
    }
    throw error;
  }
}