@nick/is/reader-sync

isReaderSync

Signature

function isReaderSync(it: unknown): it is ReaderSync;

Checks if a given value is a synchronous reader, which is an object that implements the readSync method as per Deno's ReaderSync interface.

Parameters

Name	Info
it	The value to check.

Returns

true if the value is a synchronous Reader, false otherwise.

Category

I/O

Examples

import { isReaderSync } from "jsr:@nick/is/reader-sync";

const file = Deno.openSync("file.txt");
isReaderSync(file); // true

const socket = new WebSocket("ws://example.com");
isReaderSync(socket); // false

ReaderSync

An abstract interface which when implemented provides an interface to read bytes into an array buffer synchronously.

Category

I/O

Methods

readSync

readSync(
    p: Uint8Array,
  ): number | null;

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 readSync() 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, readSync() 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.

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