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Bun.write: apply mode for string, buffer, Blob and stream sources on POSIX #32885

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Bun.write: apply mode for string, buffer, Blob and stream sources on POSIX #32885

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Bun.write: apply `mode` for string, buffer, Blob and stream sources o…
robobun Oct 24, 2026
806df88
bun-types: document `mode` on every `Bun.write` overload and on `BunF…
robobun Oct 24, 2026
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136 changes: 128 additions & 8 deletions packages/bun-types/bun.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -2153,7 +2153,28 @@ declare module "bun" {
input: Blob | NodeJS.TypedArray | ArrayBufferLike | string | BlobPart[] | Archive | ReadableStream,
options?: {
/**
* If writing to a PathLike, set the permissions of the file.
* Set the Unix permissions of the destination file to exactly this mode.
* The process umask does not apply, and a file that already exists is
* changed too.
*
* The new data is never readable through permissions that the mode does
* not give. If the operating system refuses the change, the write is
* rejected and an existing file keeps its contents. A `Bun.file()` input
* is the exception: it is copied first, and the mode is set after the
* copy.
*
* If omitted, an existing file keeps its permissions, and a new file gets
* the default ones, which the process umask limits (typically 0o644).
*
* It has no effect when the destination is a file descriptor. For an input
* other than a `Bun.file()`, it also has no effect on a FIFO or a device.
* Windows has no Unix permissions, so the mode is not applied in this way
* there.
*
* Must be an integer from 0 to 0o777 (511 in decimal).
*
* @throws {TypeError} If the mode is not a number.
* @throws {RangeError} If the mode is not an integer in that range.
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*/
mode?: number;
/**
Expand Down Expand Up @@ -2183,6 +2204,31 @@ declare module "bun" {
destination: BunFile,
input: Response | Request,
options?: {
/**
* Set the Unix permissions of the destination file to exactly this mode.
* The process umask does not apply, and a file that already exists is
* changed too.
*
* The new data is never readable through permissions that the mode does
* not give. If the operating system refuses the change, the write is
* rejected and an existing file keeps its contents. A `Bun.file()` input
* is the exception: it is copied first, and the mode is set after the
* copy.
*
* If omitted, an existing file keeps its permissions, and a new file gets
* the default ones, which the process umask limits (typically 0o644).
*
* It has no effect when the destination is a file descriptor. For an input
* other than a `Bun.file()`, it also has no effect on a FIFO or a device.
* Windows has no Unix permissions, so the mode is not applied in this way
* there.
*
* Must be an integer from 0 to 0o777 (511 in decimal).
*
* @throws {TypeError} If the mode is not a number.
* @throws {RangeError} If the mode is not an integer in that range.
*/
mode?: number;
/**
* If `true`, create the parent directory if it doesn't exist.
*
Expand All @@ -2208,6 +2254,31 @@ declare module "bun" {
destinationPath: PathLike,
input: Response | Request,
options?: {
/**
* Set the Unix permissions of the destination file to exactly this mode.
* The process umask does not apply, and a file that already exists is
* changed too.
*
* The new data is never readable through permissions that the mode does
* not give. If the operating system refuses the change, the write is
* rejected and an existing file keeps its contents. A `Bun.file()` input
* is the exception: it is copied first, and the mode is set after the
* copy.
*
* If omitted, an existing file keeps its permissions, and a new file gets
* the default ones, which the process umask limits (typically 0o644).
*
* It has no effect when the destination is a file descriptor. For an input
* other than a `Bun.file()`, it also has no effect on a FIFO or a device.
* Windows has no Unix permissions, so the mode is not applied in this way
* there.
*
* Must be an integer from 0 to 0o777 (511 in decimal).
*
* @throws {TypeError} If the mode is not a number.
* @throws {RangeError} If the mode is not an integer in that range.
*/
mode?: number;
/**
* If `true`, create the parent directory if it doesn't exist.
*
Expand Down Expand Up @@ -2242,12 +2313,23 @@ declare module "bun" {
input: BunFile,
options?: {
/**
* Set the file permissions of the destination when it is created or overwritten.
* Set the Unix permissions of the destination file to exactly this mode.
* The process umask does not apply, and a file that already exists is
* changed too.
*
* The file is copied first, and the mode is set after the copy. If the
* operating system refuses the change, the write is rejected after the
* copy.
*
* Must be a valid Unix permission mode (0 to 0o777 / 511 in decimal).
* If omitted, defaults to the system default based on umask (typically 0o644).
*
* @throws {RangeError} If the mode is outside the valid range (0 to 0o777).
* It has no effect when the destination is a file descriptor. Windows has
* no Unix permissions, so the mode is not applied in this way there.
*
* Must be an integer from 0 to 0o777 (511 in decimal).
*
* @throws {TypeError} If the mode is not a number.
* @throws {RangeError} If the mode is not an integer in that range.
*
* @example
* ```ts
Expand Down Expand Up @@ -2288,12 +2370,23 @@ declare module "bun" {
input: BunFile,
options?: {
/**
* Set the file permissions of the destination when it is created or overwritten.
* Set the Unix permissions of the destination file to exactly this mode.
* The process umask does not apply, and a file that already exists is
* changed too.
*
* The file is copied first, and the mode is set after the copy. If the
* operating system refuses the change, the write is rejected after the
* copy.
*
* Must be a valid Unix permission mode (0 to 0o777 / 511 in decimal).
* If omitted, defaults to the system default based on umask (typically 0o644).
*
* @throws {RangeError} If the mode is outside the valid range (0 to 0o777).
* It has no effect when the destination is a file descriptor. Windows has
* no Unix permissions, so the mode is not applied in this way there.
*
* Must be an integer from 0 to 0o777 (511 in decimal).
*
* @throws {TypeError} If the mode is not a number.
* @throws {RangeError} If the mode is not an integer in that range.
*
* @example
* ```ts
Expand Down Expand Up @@ -2759,7 +2852,34 @@ declare module "bun" {
*/
write(
data: string | ArrayBufferView | ArrayBuffer | SharedArrayBuffer | Request | Response | BunFile | ReadableStream,
options?: { highWaterMark?: number },
options?: {
highWaterMark?: number;
/**
* Set the Unix permissions of this file to exactly this mode.
* The process umask does not apply, and a file that already exists is
* changed too.
*
* The new data is never readable through permissions that the mode does
* not give. If the operating system refuses the change, the write is
* rejected and an existing file keeps its contents. A `Bun.file()` input
* is the exception: it is copied first, and the mode is set after the
* copy.
*
* If omitted, an existing file keeps its permissions, and a new file gets
* the default ones, which the process umask limits (typically 0o644).
*
* It has no effect when this file is a file descriptor. For an input
* other than a `Bun.file()`, it also has no effect on a FIFO or a device.
* Windows has no Unix permissions, so the mode is not applied in this way
* there.
*
* Must be an integer from 0 to 0o777 (511 in decimal).
*
* @throws {TypeError} If the mode is not a number.
* @throws {RangeError} If the mode is not an integer in that range.
*/
mode?: number;
},
): Promise<number>;

/**
Expand Down
5 changes: 5 additions & 0 deletions src/runtime/webcore/Blob.bind.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -57,5 +57,10 @@ export const BunWriteOptions = b.dictionary(
{ createPath: b.bool.emptyStringAsNull, mode: b.f64.nullable },
{ allowArray: true, fromJS: true, reportedAs: "options" },
);
/** The `mode` that `BunFile.prototype.write` reads of its options. It does not read one for an S3 file. */
export const BunWriteMode = b.dictionary(
{ mode: b.f64.nullable },
{ allowArray: true, fromJS: true, reportedAs: "options" },
);
/** `options` is also what a write to S3 takes. */
export const write = b.fn({ ...method, args: { destination: b.any, data: b.any, options: b.any } });
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