// Copyright 2018-2022 the Deno authors. All rights reserved. MIT license.
import { copy as copyBytes } from "../bytes/mod.ts";
import { assert } from "../testing/asserts.ts";
const DEFAULT_BUFFER_SIZE = 32 * 1024;
/**
 * Read a range of bytes from a file or other resource that is readable and
 * seekable.  The range start and end are inclusive of the bytes within that
 * range.
 *
 * ```ts
 * import { assertEquals } from "../testing/asserts.ts";
 * import { readRange } from "./files.ts";
 *
 * // Read the first 10 bytes of a file
 * const file = await Deno.open("example.txt", { read: true });
 * const bytes = await readRange(file, { start: 0, end: 9 });
 * assertEquals(bytes.length, 10);
 * ```
 */ export async function readRange(r, range) {
    // byte ranges are inclusive, so we have to add one to the end
    let length = range.end - range.start + 1;
    assert(length > 0, "Invalid byte range was passed.");
    await r.seek(range.start, Deno.SeekMode.Start);
    const result = new Uint8Array(length);
    let off = 0;
    while(length){
        const p = new Uint8Array(Math.min(length, DEFAULT_BUFFER_SIZE));
        const nread = await r.read(p);
        assert(nread !== null, "Unexpected EOF reach while reading a range.");
        assert(nread > 0, "Unexpected read of 0 bytes while reading a range.");
        copyBytes(p, result, off);
        off += nread;
        length -= nread;
        assert(length >= 0, "Unexpected length remaining after reading range.");
    }
    return result;
}
/**
 * Read a range of bytes synchronously from a file or other resource that is
 * readable and seekable.  The range start and end are inclusive of the bytes
 * within that range.
 *
 * ```ts
 * import { assertEquals } from "../testing/asserts.ts";
 * import { readRangeSync } from "./files.ts";
 *
 * // Read the first 10 bytes of a file
 * const file = Deno.openSync("example.txt", { read: true });
 * const bytes = readRangeSync(file, { start: 0, end: 9 });
 * assertEquals(bytes.length, 10);
 * ```
 */ export function readRangeSync(r, range) {
    // byte ranges are inclusive, so we have to add one to the end
    let length = range.end - range.start + 1;
    assert(length > 0, "Invalid byte range was passed.");
    r.seekSync(range.start, Deno.SeekMode.Start);
    const result = new Uint8Array(length);
    let off = 0;
    while(length){
        const p = new Uint8Array(Math.min(length, DEFAULT_BUFFER_SIZE));
        const nread = r.readSync(p);
        assert(nread !== null, "Unexpected EOF reach while reading a range.");
        assert(nread > 0, "Unexpected read of 0 bytes while reading a range.");
        copyBytes(p, result, off);
        off += nread;
        length -= nread;
        assert(length >= 0, "Unexpected length remaining after reading range.");
    }
    return result;
}
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