Quick Hack of Redis Client

redis.ts

import type { Either } from "fun/either.ts";
import type { Option } from "fun/option.ts";
import type { Hold } from "fun/kind.ts";

import * as A from "fun/array.ts";
import * as E from "fun/either.ts";
import * as O from "fun/option.ts";

import { flow, pipe, todo } from "fun/fn.ts";

import { BufReader, BufWriter } from "https://deno.land/std@0.162.0/io/mod.ts";

const encoder = new TextEncoder();
const decoder = new TextDecoder();

/**
 * A try at implementing the redis RESP protocol detailed here:
 * https://redis.io/docs/reference/protocol-spec/
 */

// === First Byte Consts ===

// Termination
export const CR = "\r";
export const CRLF = "\r\n";
export type CRLF = typeof CRLF;

// Simple String
export const SSTR = "+";
export type SSTR = typeof SSTR;

// Errors
export const ERRS = "-";
export type ERRS = typeof ERRS;

// Integers
export const INTS = ":";
export type INTS = typeof INTS;

// Bulk Strings
export const BSTR = "$";
export type BSTR = typeof BSTR;

// Arrays
export const ARRS = "*";
export type ARRS = typeof ARRS;

export const OK = "OK";
export type OK = typeof OK;

// === Commands ===

// String must not contain \r or \n
export type SimpleString = `${SSTR}${string}${CRLF}`;

// String must not contain \r or \n
export type ErrorString = `${ERRS}${string}${CRLF}`;

// Number must by an integer
// In some cases 0 denotes false and 1 denotes true
export type IntegerString = `${INTS}${number}${CRLF}`;

// Number is the number of bytes of the string payload
export type BulkStringLength = `${BSTR}${number}${CRLF}`;

// -1 denotes a null value, not an empty string
export type BulkNull = `${BSTR}-1${CRLF}`;
export const BulkNull = `${BSTR}-1${CRLF}` as BulkNull;

export type BulkString = `${BulkStringLength}${string}${CRLF}`;

// Number is the number of array entries
// String is a concatenation of RespMessages
export type ArrayStringLength = `${ARRS}${number}${CRLF}`;
export type ArrayString = `${ArrayStringLength}${string}`;

export type RespMessage =
  | SimpleString
  | ErrorString
  | IntegerString
  | BulkString
  | BulkNull
  | ArrayString;

// === Encode Resp Values ===

function removeCRLF(s: string): string {
  return s.replaceAll("\n", "").replaceAll("\r", "");
}

export function simpleString(s: string): SimpleString {
  return `${SSTR}${removeCRLF(s)}${CRLF}`;
}

export function errorString(s: string): ErrorString {
  return `${ERRS}${removeCRLF(s)}${CRLF}`;
}

export function integerString(n: number): IntegerString {
  return `${INTS}${Math.floor(n)}${CRLF}`;
}

export function bulkString(s: string | number): BulkString {
  const length = encoder.encode(`${s}`).length;
  return `${BSTR}${length}${CRLF}${s}${CRLF}`;
}

export function arrayString(...messages: RespMessage[]): ArrayString {
  return `${ARRS}${messages.length}${CRLF}${messages.join("")}`;
}

// === Parsed Responses ===

export type StringResult = string; // Newtype?
export type ErrorResult = string; // Newtype?
export type IntegerResult = number; // Integer?
export type BulkResult = Option<string>;
export type ArrayResult = readonly ParseResult[];
export type ParseResult =
  | StringResult
  | ErrorResult
  | IntegerResult
  | BulkResult
  | ArrayResult;

export type ParsedError = {
  readonly tag: "ParsedError";
  readonly message: string;
};

export function parsedError(message: string): ParsedError {
  return { tag: "ParsedError", message };
}

export type Parsed<A extends ParseResult> = Promise<Either<ParsedError, A>>;

// Parsing a response

export function printParseResult(result: ParseResult): string {
  if (typeof result === "string") {
    return result;
  } else if (typeof result === "number") {
    return result.toString();
  } else if (Array.isArray(result)) {
    return result.map(printParseResult).join("\n");
  } else {
    return pipe(
      result as BulkResult,
      O.fold(() => "nil", (r) => r),
    );
  }
}

async function readFullLine(reader: BufReader): Promise<null | string> {
  const result = await reader.readString(CR);
  if (result !== null) {
    // RESP uses \r\n for termination so here we
    // drop the \n from the buffer
    await reader.readByte();
  }
  // Pop the \r off the result
  return result === null ? result : result.slice(0, result.length - 1);
}

const fromNull = E.fromNullable(() => parsedError("Unexpected null payload"));

// Expects that the initial RESP byte has been read from the buffer.
export async function parseString(reader: BufReader): Parsed<StringResult> {
  const result = await readFullLine(reader);
  return fromNull(result);
}

// Expects that the initial RESP byte has been read from the buffer.
export async function parseError(reader: BufReader): Parsed<ErrorResult> {
  const result = await readFullLine(reader);
  return fromNull(result);
}

// Expects that the initial RESP byte has been read from the buffer.
export async function parseInteger(reader: BufReader): Parsed<IntegerResult> {
  const result = await readFullLine(reader);
  return pipe(
    result,
    fromNull,
    E.chain((str) => {
      const num = parseInt(str, 10);
      return isNaN(num)
        ? E.left(parsedError(`${str} cannot be parsed into an integer`))
        : E.right(num);
    }),
  );
}

// Expects that the initial RESP byte has been read from the buffer.
export async function parseBulk(reader: BufReader): Parsed<BulkResult> {
  const _length = await readFullLine(reader);
  // Ideally we would wrap this nicely in some type classes over Promise<Either>
  // But I'm trying not to yak shave too hard
  if (_length === null) {
    return fromNull(_length);
  }
  const length = parseInt(_length, 10);
  if (isNaN(length)) {
    return E.left(parsedError("Unable to parse length of Bulk String"));
  }
  // This might need to be tightened to only length === -1
  if (length < 0) {
    return E.right(O.none);
  }
  const buffer = new Uint8Array(length);
  const result = await reader.readFull(buffer);
  if (result === null) {
    return fromNull(result);
  }
  // Pop the remaining \r\n off the bulk reply
  const last = await readFullLine(reader);
  if (last === null) {
    return E.left(parsedError("Bulk string must end in CRLF"));
  }
  return E.right(O.some(decoder.decode(result)));
}

// Expects that the initial RESP byte has been read from the buffer.
export async function parseArray(
  reader: BufReader,
): Parsed<ArrayResult> {
  const _length = await readFullLine(reader);
  if (_length === null) {
    return fromNull(_length);
  }
  const length = parseInt(_length, 10);
  const results: ParseResult[] = [];
  let index = -1;
  while (++index < length) {
    const result = await parse(reader);
    if (E.isLeft(result)) {
      return result;
    }
    results[index] = result.right;
  }
  return E.right(results);
}

// This function does not clean up the BufReader
export async function parse(
  reader: BufReader,
): Parsed<ParseResult> {
  const _first = await reader.readByte();
  if (_first === null) {
    return fromNull(_first);
  }
  const first = String.fromCharCode(_first);
  switch (first) {
    case SSTR:
      return parseString(reader);
    case ERRS:
      return parseError(reader);
    case INTS:
      return parseInteger(reader);
    case BSTR:
      return parseBulk(reader);
    case ARRS:
      return parseArray(reader);
    default:
      return E.left(parsedError(`Unknown RESP symbol ${first}`));
  }
}

// === Connection ===

/**
 * When interacting with redis our primary interface is a
 * BufReader and BufWriter pair and a TcpConnection
 */
export type RedisConnection = {
  readonly connection: Deno.TcpConn;
  readonly reader: BufReader;
  readonly writer: BufWriter;
};

/**
 * For now I'm only implementing RedisConnection from a TcpConnection with
 * no concept of retry or error.
 */
export function fromTcpConnection(connection: Deno.TcpConn): RedisConnection {
  // TODO wrap BufReader and BufWriter in tryCatch or reduce the interface
  // so it's not so big
  return {
    connection,
    reader: new BufReader(connection),
    writer: new BufWriter(connection),
  };
}

const sequenceEither = A.createSequence(E.MonadEither);

/**
 * Right now all of our messages are strings and not U8IntArrays. In the future
 * we might want to change this for performance or interop reasons.
 *
 * TODO: Use AsyncEither? FnAsyncEither?
 *
 * TODO: Build on top of sendMessage a "Decoder" interface at
 * the type level and runtime level to ensure correct responses.
 */
export async function sendMessage(
  redis: RedisConnection,
  message: RespMessage,
): Parsed<ParseResult>;
export async function sendMessage(
  redis: RedisConnection,
  message: RespMessage[],
): Parsed<ParseResult[]>;
export async function sendMessage(
  redis: RedisConnection,
  message: RespMessage | RespMessage[],
): Promise<Either<ParsedError, ParseResult | ParseResult[]>> {
  const multi = Array.isArray(message);
  const msg = Array.isArray(message) ? message.join("") : message;
  await redis.writer.write(encoder.encode(msg));
  await redis.writer.flush();
  if (multi) {
    const results: Either<ParsedError, ParseResult>[] = new Array(
      message.length,
    );
    let index = -1;
    while (++index < message.length) {
      results[index] = await parse(redis.reader);
    }
    return sequenceEither(results);
  }
  return parse(redis.reader);
}

// === Basic Commands ===

export type Command<A> = Hold<A> & RespMessage;

// deno-lint-ignore no-explicit-any
export type AnyCommand = Command<any>;

export type FromCommand<T> = T extends Command<infer A> ? A : never;

// Helper
function cmd(...vs: string[]): RespMessage {
  return arrayString(...vs.map(bulkString));
}

export function pipeline<C extends AnyCommand[]>(...cmds: C): C {
  return cmds;
}

// APPEND
export function append(key: string, value: string): Command<number> {
  return cmd("append", key, value);
}

// DECR
export function decr(key: string): Command<number> {
  return cmd("decr", key);
}

// DECRBY
export function decrby(key: string, decrement: number): Command<number> {
  return arrayString(
    bulkString("decrby"),
    bulkString(key),
    integerString(decrement),
  );
}

// GET
export function get(key: string): Command<Option<string>> {
  return cmd("get", key);
}

// GETDEL
export function getdel(key: string): Command<Option<string>> {
  return cmd("getdel", key);
}

// SET
export function set(key: string, value: string): Command<OK> {
  return cmd("set", key, value);
}

// GETRANGE
// GETSET
// INCR
// INCRBY
// INCRBYFLOAT
// LCS
// MGET
// MSET
// MSETNX
// PSETEX
// SETEX
// SETNX
// SETRANGE
// STRLEN
// SUBSTR

// === Testing ===
type Send = {
  (cmd: RespMessage): Parsed<ParseResult>;
  (cmds: RespMessage[]): Parsed<ParseResult[]>;
};

function getSend(port: number): Send {
  return async (cmd) => {
    const conn = await Deno.connect({ port });
    const redis = fromTcpConnection(conn);
    const result = await sendMessage(redis, cmd as any);
    conn.close();
    return result as any;
  };
}

const send = getSend(6379);

// await log(set("hello", "world"));
// await log(get("hello"));
const piped = pipeline(
  get("hello"),
  get("hello"),
  get("hello"),
  get("hello"),
  get("hello"),
  get("hello"),
  get("hello"),
);

const result = await send(piped);
console.log(JSON.stringify(result, null, 2));