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‎content/blog/resp.md‎

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---
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author: Nimendra
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title: "System Design Notes: Redis Serialization Protocol (RESP)"
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date: 2025-07-12
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description: "Explore the Redis Serialization Protocol (RESP)"
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tags: ["redis", "protocols", "networking", "RESP", "System-Design"]
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categories: ["Backend", "Redis"]
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lastmod: 2025-07-12
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URL: "https://github.com/nmdra/nmdra.github.io/tree/main/content"
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---
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Redis is a high-performance in-memory data store, widely used as a database, cache, and message broker. Unlike many web services that use HTTP, Redis uses a custom protocol known as the **Redis Serialization Protocol (RESP)** for communication between clients and servers.
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In this article, we’ll explore RESP, how it compares to HTTP, and what makes it ideal for Redis’s design philosophy.
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## What is RESP?
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RESP, or **Redis Serialization Protocol**, is the **wire protocol** used by Redis clients (including `redis-cli`) to communicate with the Redis server. It defines the way data is serialized and transmitted over the network.
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> A **wire protocol** is the formal specification of how data is formatted and exchanged between two systems over a network connection.
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> — [Wikipedia](https://en.wikipedia.org/wiki/Wire_protocol)
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RESP is lightweight, efficient, and designed specifically for Redis — but it can be reused in any client-server software.
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## RESP vs HTTP
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Redis does **not** use HTTP. Instead, it defines its own set of commands and responses via RESP. Here’s how RESP equivalents map to typical HTTP operations:
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| **HTTP Feature** | **Redis Equivalent** |
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|------------------------|--------------------------------------------------|
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| `GET /resource` | `GET key` |
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| `POST /resource` | `SET key value` |
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| `PUT /resource` | `SET key value`, or `HSET`, `JSON.SET` (module) |
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| `DELETE /resource` | `DEL key` |
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| `200 OK` | `+OK` |
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| `404 Not Found` | `(nil)` |
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| `500 Internal Error` | `-ERR <message>` |
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| `403 Forbidden` | `-NOAUTH Authentication required.` |
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Unlike HTTP, RESP is not based on request methods or status codes. Instead, Redis commands and responses follow a minimal and efficient format optimized for performance.
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## RESP Characteristics
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| Feature | Description |
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|----------------------------|-----------------------------------------------------------------------------------------|
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| **Text-based** | Commands and responses are human-readable (but binary-safe for values). |
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| **Persistent TCP** | Communication happens over a persistent TCP connection (default port: `6379`). |
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| **Request/Response Model** | Clients issue commands (e.g. `SET key value`) and Redis replies with a response. |
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RESP works over **TCP or Unix sockets**, not HTTP. You can even **telnet** into Redis and type RESP commands manually.
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## RESP Data Types
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RESP supports the following basic data types:
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| **Type** | **Prefix** | **Description** |
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| --------------- | ---------- | ----------------------------------------------------------- |
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| Simple String | `+` | Usually used for status replies. |
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| Error | `-` | Used to signal errors. |
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| Integer | `:` | Used to return numeric values (e.g. result of `INCR`). |
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| Bulk String | `$` | String with specified length, can include binary-safe data. |
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| Null Bulk | `$-1` | Used to represent a null value. |
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| Array | `*` | List of other RESP types. |
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| Null Array | `*-1` | Used to represent a null array (RESP3). |
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| Map (RESP3) | `%` | Key-value pairs (available in RESP3). |
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| Set (RESP3) | `~` | Unordered collection of unique elements (RESP3). |
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| Boolean (RESP3) | `#` | `true` or `false` in RESP3. |
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| Double (RESP3) | `,` | Floating point number in RESP3. |
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## Security in RESP
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Security in RESP is **minimal by default**, because Redis was designed for **trusted local environments**. Here’s what that means:
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- RESP is **plaintext**, meaning commands and data are sent unencrypted.
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- Optional password authentication via `requirepass`.
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- No user roles (before Redis 6).
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- Redis will accept any client connection if the port is reachable.
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- From Redis 6 onward, **SSL/TLS** support is available (needs to be compiled in), enabling **encrypted RESP communication** over TLS — just like HTTPS vs HTTP.
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More on [Redis TLS support](https://redis.io/docs/latest/operate/oss_and_stack/management/security/encryption/)
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## RESP Versions
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| Version | Introduced In | Features |
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|-----------|---------------|--------------------------------------------------------------------------|
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| **RESP2** | Redis 2.x | Basic protocol used by most clients today. Fast and text-based. |
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| **RESP3** | Redis 6.0 | Supports richer data types, attribute metadata, and **introspection**. |
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> **Introspection** in RESP3 allows clients to query metadata about the server or connection, improving diagnostics and tooling.
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## Summary
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Redis’s RESP protocol is a prime example of designing a protocol specifically for performance, simplicity, and predictability. While it lacks the verbosity and feature set of HTTP, it excels in its intended domain — powering fast, efficient key-value operations over a lightweight protocol.
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---
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- Official RESP Spec: [redis.io/docs/latest/develop/reference/protocol-spec](https://redis.io/docs/latest/develop/reference/protocol-spec)
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- Build Your Own Redis (CodeCrafters): [codecrafters.io](https://app.codecrafters.io/r/gentle-armadillo-148010)
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