|
| 1 | +--- |
| 2 | +pcx_content_type: configuration |
| 3 | +title: fs |
| 4 | +--- |
| 5 | + |
| 6 | +import { Render } from "~/components"; |
| 7 | + |
| 8 | +<Render file="nodejs-compat-howto" product="workers" /> |
| 9 | + |
| 10 | +You can use [`node:fs`](https://nodejs.org/api/fs.html) to access a virtual file |
| 11 | +system in Workers. |
| 12 | + |
| 13 | +The `node:fs` module is available in Workers runtimes that support Node.js |
| 14 | +compatibility using the `nodejs_compat` compatibility flag. Any Worker |
| 15 | +running with `nodejs_compat` enabled and with a compatibility date of |
| 16 | +`2025-09-01` or later will have access to `node:fs` by default. It is |
| 17 | +also possible to enable `node:fs` on Workers with an earlier compatibility |
| 18 | +date using a combination of the `nodejs_compat` and `enable_nodejs_fs_module` |
| 19 | +flags. To disable `node:fs` you can set the `disable_nodejs_fs_module` flag. |
| 20 | + |
| 21 | +```js |
| 22 | +import { readFileSync, writeFileSync } from "node:fs"; |
| 23 | + |
| 24 | +const config = readFileSync("/bundle/config.txt", "utf8"); |
| 25 | + |
| 26 | +writeFileSync("/tmp/abc.txt", "Hello, world!"); |
| 27 | +``` |
| 28 | + |
| 29 | +The Workers Virtual File System (VFS) is a memory-based file system that allows |
| 30 | +you to read modules included in your Worker bundle as read-only files, access a |
| 31 | +directory for writing temporary files, or access common |
| 32 | +[character devices](https://linux-kernel-labs.github.io/refs/heads/master/labs/device_drivers.html) like |
| 33 | +`/dev/null`, `/dev/random`, `/dev/full`, and `/dev/zero`. |
| 34 | + |
| 35 | +The directory structure initially looks like: |
| 36 | + |
| 37 | +``` |
| 38 | +
|
| 39 | +/bundle |
| 40 | +└── (one file for each module in your Worker bundle) |
| 41 | +/tmp |
| 42 | +└── (empty, but you can write files, create directories, symlinks, etc) |
| 43 | +/dev |
| 44 | +├── null |
| 45 | +├── random |
| 46 | +├── full |
| 47 | +└── zero |
| 48 | +
|
| 49 | +``` |
| 50 | + |
| 51 | +The `/bundle` directory contains the files for all modules included in your |
| 52 | +Worker bundle, which you can read using APIs like `readFileSync` or |
| 53 | +`read(...)`, etc. These are always read-only. Reading from the bundle |
| 54 | +can be useful when you need to read a config file or a template. |
| 55 | + |
| 56 | +```js |
| 57 | +import { readFileSync } from "node:fs"; |
| 58 | + |
| 59 | +// The config.txt file would be included in your Worker bundle. |
| 60 | +// Refer to the Wrangler documentation for details on how to |
| 61 | +// include additional files. |
| 62 | +const config = readFileSync("/bundle/config.txt", "utf8"); |
| 63 | + |
| 64 | +export default { |
| 65 | + async fetch(request) { |
| 66 | + return new Response(`Config contents: ${config}`); |
| 67 | + }, |
| 68 | +}; |
| 69 | +``` |
| 70 | + |
| 71 | +The `/tmp` directory is writable, and you can use it to create temporary files |
| 72 | +or directories. You can also create symlinks in this directory. However, the |
| 73 | +contents of `/tmp` are not persistent and are unique to each request. This means |
| 74 | +that files created in `/tmp` within the context of one request will not be |
| 75 | +available in other concurrent or subsequent requests. |
| 76 | + |
| 77 | +```js |
| 78 | +import { writeFileSync, readFileSync } from "node:fs"; |
| 79 | + |
| 80 | +export default { |
| 81 | + fetch(request) { |
| 82 | + // The file `/tmp/hello.txt` will only exist for the duration |
| 83 | + // of this request. |
| 84 | + writeFileSync("/tmp/hello.txt", "Hello, world!"); |
| 85 | + const contents = readFileSync("/tmp/hello.txt", "utf8"); |
| 86 | + return new Response(`File contents: ${contents}`); |
| 87 | + }, |
| 88 | +}; |
| 89 | +``` |
| 90 | + |
| 91 | +The `/dev` directory contains common character devices: |
| 92 | + |
| 93 | +- `/dev/null`: A null device that discards all data written to it and returns |
| 94 | + EOF on read. |
| 95 | +- `/dev/random`: A device that provides random bytes on reads and discards all |
| 96 | + data written to it. Reading from `/dev/random` is only permitted when within |
| 97 | + the context of a request. |
| 98 | +- `/dev/full`: A device that always returns EOF on reads and discards all data |
| 99 | + written to it. |
| 100 | +- `/dev/zero`: A device that provides an infinite stream of zero bytes on reads |
| 101 | + and discards all data written to it. |
| 102 | + |
| 103 | +All operations on the VFS are synchronous. You can use the synchronous, |
| 104 | +asynchronous callback, or promise-based APIs provided by the `node:fs` module |
| 105 | +but all operations will be performed synchronously. |
| 106 | + |
| 107 | +Timestamps for files in the VFS are currently always set to the Unix epoch |
| 108 | +(`1970-01-01T00:00:00Z`). This means that operations that rely on timestamps, |
| 109 | +like `fs.stat`, will always return the same timestamp for all files in the VFS. |
| 110 | +This is a temporary limitation that will be addressed in a future release. |
| 111 | + |
| 112 | +Since all temporary files are held in memory, the total size of all temporary |
| 113 | +files and directories created count towards your Worker’s memory limit. If you |
| 114 | +exceed this limit, the Worker instance will be terminated and restarted. |
| 115 | + |
| 116 | +The file system implementation has the following limits: |
| 117 | + |
| 118 | +- The maximum total length of a file path is 4096 characters, including path |
| 119 | + separators. Because paths are handled as file URLs internally, the limit |
| 120 | + accounts for percent-encoding of special characters, decoding characters |
| 121 | + that do not need encoding before the limit is checked. For example, the |
| 122 | + path `/tmp/abcde%66/ghi%zz' is 18 characters long because the `%66`does |
| 123 | +not need to be percent-encoded and is therefore counted as one character, |
| 124 | +while the`%zz` is an invalid percent-encoding that is counted as 3 characters. |
| 125 | +- The maximum number of path segments is 48. For example, the path `/a/b/c` is |
| 126 | + 3 segments. |
| 127 | +- The maximum size of an individual file is 128 MB total. |
| 128 | + |
| 129 | +The following `node:fs` APIs are not supported in Workers, or are only partially |
| 130 | +supported: |
| 131 | + |
| 132 | +- `fs.watch` and `fs.watchFile` operations for watching for file changes. |
| 133 | +- The `fs.globSync()` and other glob APIs have not yet been implemented. |
| 134 | +- The `force` option in the `fs.rm` API has not yet bee implemented. |
| 135 | +- Timestamps for files are always set to the Unix epoch (`1970-01-01T00:00:00Z`). |
| 136 | +- File permissions and ownership are not supported. |
| 137 | + |
| 138 | +The full `node:fs` API is documented in the [Node.js documentation for `node:fs`](https://nodejs.org/api/fs.html). |
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