Add framing README

protocols/v2/framing-sv2/README.md

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+# `framing_sv2`
+
+[![crates.io](https://img.shields.io/crates/v/framing_sv2.svg)](https://crates.io/crates/framing_sv2)
+[![docs.rs](https://docs.rs/framing_sv2/badge.svg)](https://docs.rs/framing_sv2)
+[![rustc+](https://img.shields.io/badge/rustc-1.75.0%2B-lightgrey.svg)](https://blog.rust-lang.org/2023/12/28/Rust-1.75.0.html)
+[![license](https://img.shields.io/badge/license-MIT%2FApache--2.0-blue.svg)](https://github.com/stratum-mining/stratum/blob/main/LICENSE.md)
+[![codecov](https://codecov.io/gh/stratum-mining/stratum/branch/main/graph/badge.svg?flag=framing_sv2-coverage)](https://codecov.io/gh/stratum-mining/stratum)
+
+`framing_sv2` provides utilities for framing messages sent between Sv2 roles, handling both Sv2
+message and Noise handshake frames.
+
+The Sv2 protocol is binary, with fixed message framing. Each message begins with the extension
+type, message type, and message length (six bytes in total), followed by a variable length
+message. The message framing is outlined below ([according to Sv2 specs
+](https://github.com/stratum-mining/sv2-spec/blob/main/03-Protocol-Overview.md#32-framing)):
+
+| Protocol Type  | Byte Length | Description |
+|----------------|-------------|-------------|
+| `extension_type` | `U16` | Unique identifier of the extension describing this protocol message. <br><br> Most significant bit (i.e.bit `15`, `0`-indexed, aka `channel_msg`) indicates a message which is specific to a channel, whereas if the most significant bit is unset, the message is to be interpreted by the immediate receiving device. <br><br> Note that the `channel_msg` bit is ignored in the extension lookup, i.e.an `extension_type` of `0x8ABC` is for the same "extension" as `0x0ABC`. <br><br> If the `channel_msg` bit is set, the first four bytes of the payload field is a `U32` representing the `channel_id` this message is destined for (these bytes are repeated in the message framing descriptions below). <br><br> Note that for the Job Declaration and Template Distribution Protocols the `channel_msg` bit is always unset. |
+| `msg_type` | `U8` | Unique identifier of the extension describing this protocol message. |
+| `msg_length` | `U24` | Length of the protocol message, not including this header. |
+| `payload` | `BYTES` | Message-specific payload of length `msg_length`. If the MSB in `extension_type` (the `channel_msg` bit) is set the first four bytes are defined as a `U32` `"channel_id"`, though this definition is repeated in the message definitions below and these 4 bytes are included in `msg_length`. |
+
+## Main Components
+
+- **Header**: Defines the 6-byte Sv2 message header with information about the message payload,
+  including its extension type, if it is associated with a specific mining channel, the type of
+  message (e.g. `SetupConnection`, `NewMiningJob`, etc.) and the payload length.
+- **Sv2 Framing**: Use for serializing Sv2 messages.
+- **Noise Handshake Framing**: Use for serializing Noise protocol handshake messages.
+
+## Usage
+
+To include this crate in your project, run:
+
+```bash
+cargo add framing_sv2
+```
+
+This crate can be built with the following feature flags:
+
+- `with_buffer_pool`: Enables buffer pooling for more efficient memory management.
+- `with_serde`: builds [`binary_sv2`](https://crates.io/crates/binary_sv2) and
+  [`buffer_sv2`](https://crates.io/crates/buffer_sv2) crates with `serde`-based encoding and
+  decoding. Note that this feature flag is only used for the Message Generator, and deprecated
+  for any other kind of usage. It will likely be fully deprecated in the future.
+
+### Examples
+
+This crate provides two examples demonstrating how to serialize and deserialize Sv2 and Noise
+handshake message frames:
+
+1. **[Sv2 Frame](https://github.com/stratum-mining/stratum/blob/main/protocols/v2/framing-sv2/examples/sv2_frame.rs)**:
+    Constructs, serializes, and deserializes a regular Sv2 message frame (`Sv2Frame`).
+
+2. **[Noise Handshake Frame](https://github.com/stratum-mining/stratum/blob/main/protocols/v2/framing-sv2/examples/handshake_frame.rs)**:
+   Constructs, serializes, and deserializes a handshake message frame (`HandShakeFrame`).