Move description of message binary format into new document

Xaeroxe · Xaeroxe · commit 224715f95b51 · 2023-01-23T11:35:20.000-07:00
diff --git a/MESSAGE_BINARY_FORMAT.md b/MESSAGE_BINARY_FORMAT.md
@@ -0,0 +1,92 @@
+### Introduction
+
+The main offering of this crate is a consistent and known representation of Rust types. As such, the format is
+considered to be part of our stable API, and changing the format requires a major version number bump. To aid you
+in debugging, the current version of that format is documented here.
+
+### High-level overview
+
+***Connection Initial Description***
+
+Version 1 of the protocol did not send this description. Version 2 is the first version that sends a startup description.
+The first 8 bytes sent on the channel are the little endian protocol version number. If the reader is not compatible with the message version provided, it must
+terminate immediately. Immediately following the version, the sender will describe the features of the message stream it is about to send. Those features are as follows.
+
+**Version 1**
+
+Version 1 did not send an initial description. All optional features are disabled in version 1.
+
+**Version 2**
+- `name`: checksum_enabled, `size`: 1 byte, `possible values`: 2 or 3, `notes`: 2 indicates checksums will be sent, 3 indicates checksums will not be sent.
+
+***Message stream***
+
+After the initial description, the byte stream is split up into messages. Every message begins with a `length` value. After `length` bytes have
+been read, a new message can begin immediately afterward. This `length` value is the entirety of the header of a
+message. If checksums are enabled, the 8 bytes immediately following the message are the checksum of the message. This checksum is determined by hashing
+the bytes of the message using SipHash 2-4. If checksums are disabled, instead the next message begins immediately. The bytes from the message are then
+deserialized into a Rust type via [`bincode`](https://github.com/bincode-org/bincode), using the following configuration.
+
+```rust,ignore
+bincode::DefaultOptions::new()
+    .with_limit(size_limit)
+    .with_little_endian()
+    .with_varint_encoding()
+    .reject_trailing_bytes()
+```
+
+### Length encoding
+
+The length is encoded using a variably sized integer encoding scheme. To understand this scheme, first we need a few constant values.
+
+```ignore
+u16_marker; decimal: 252, hex: FC
+u32_marker; decimal: 253, hex: FD
+u64_marker; decimal: 254, hex: FE
+zst_marker; decimal: 255, hex: FF
+stream_end; decimal: 0,   hex: 00
+```
+
+Any length less than `u16_marker` and greater than 0 is encoded as a single byte whose value is the length.
+A length of zero is encoded with the `zst_marker`. The stream is ended with the `stream_end` value. When this is
+read the peer is expected to close the connection.
+
+`async-io-typed` always uses little-endian. The user data being sent may contain values that are not
+little-endian, but `async-io-typed` itself always uses little-endian.
+
+If the first byte is `u16_marker`, then the length is 16 bits wide, and encoded in the following 2 bytes. Once
+those 2 bytes are read, the message begins. `u32_marker` and `u64_marker` are used in a similar way, each of
+those being 4 bytes, and 8 bytes respectively.
+
+### Examples
+
+
+Length 12
+```ignore
+0C
+```
+
+Length 0
+```ignore
+FF
+```
+
+Length 252 (First byte is u16_marker)
+```ignore
+FC, FC, 00
+```
+
+Length 253 (First byte is u16_marker)
+```ignore
+FC, FD, 00
+```
+
+Length 65,536 (aka 2^16) (First byte is u32_marker)
+```ignore
+FD, 00, 00, 01, 00
+```
+
+Length 4,294,967,296 (aka 2^32) (First byte is u64_marker)
+```ignore
+FE, 00, 00, 00, 00, 01, 00, 00, 00
+```
diff --git a/README.md b/README.md
@@ -31,95 +31,4 @@ it will help. Consider using protobufs or JSON if Rust adoption is a blocker.
 
 ## Binary format
 
-### Introduction
-
-The main offering of this crate is a consistent and known representation of Rust types. As such, the format is 
-considered to be part of our stable API, and changing the format requires a major version number bump. To aid you 
-in debugging, that format is documented here.
-
-### High-level overview
-
-***Connection Initial Description***
-
-Version 1 of the protocol did not send this description. Version 2 is the first version that sends a startup description.
-The first 8 bytes sent on the channel are the little endian protocol version number. If the reader is not compatible with the message version provided, it must
-terminate immediately. Immediately following the version, the sender will describe the features of the message stream it is about to send. Those features are as follows.
-
-**Version 1**
-
-Version 1 did not send an initial description. All optional features are disabled in version 1.
-
-**Version 2**
-- `name`: checksum_enabled, `size`: 1 byte, `possible values`: 2 or 3, `notes`: 2 indicates checksums will be sent, 3 indicates checksums will not be sent.
-
-***Message stream***
-
-After the initial description, the byte stream is split up into messages. Every message begins with a `length` value. After `length` bytes have 
-been read, a new message can begin immediately afterward. This `length` value is the entirety of the header of a 
-message. If checksums are enabled, the 8 bytes immediately following the message are the checksum of the message. This checksum is determined by hashing
-the bytes of the message using SipHash 2-4. If checksums are disabled, instead the next message begins immediately. The bytes from the message are then
-deserialized into a Rust type via [`bincode`](https://github.com/bincode-org/bincode), using the following configuration.
-
-```rust,ignore
-bincode::DefaultOptions::new()
-    .with_limit(size_limit)
-    .with_little_endian()
-    .with_varint_encoding()
-    .reject_trailing_bytes()
-```
-
-### Length encoding
-
-The length is encoded using a variably sized integer encoding scheme. To understand this scheme, first we need a few constant values.
-
-```ignore
-u16_marker; decimal: 252, hex: FC
-u32_marker; decimal: 253, hex: FD
-u64_marker; decimal: 254, hex: FE
-zst_marker; decimal: 255, hex: FF
-stream_end; decimal: 0,   hex: 00
-```
-
-Any length less than `u16_marker` and greater than 0 is encoded as a single byte whose value is the length.
-A length of zero is encoded with the `zst_marker`. The stream is ended with the `stream_end` value. When this is
-read the peer is expected to close the connection.
-
-`async-io-typed` always uses little-endian. The user data being sent may contain values that are not 
-little-endian, but `async-io-typed` itself always uses little-endian.
-
-If the first byte is `u16_marker`, then the length is 16 bits wide, and encoded in the following 2 bytes. Once
-those 2 bytes are read, the message begins. `u32_marker` and `u64_marker` are used in a similar way, each of 
-those being 4 bytes, and 8 bytes respectively.
-
-### Examples
-
-
-Length 12
-```ignore
-0C
-```
-
-Length 0
-```ignore
-FF
-```
-
-Length 252 (First byte is u16_marker)
-```ignore
-FC, FC, 00
-```
-
-Length 253 (First byte is u16_marker)
-```ignore
-FC, FD, 00
-```
-
-Length 65,536 (aka 2^16) (First byte is u32_marker)
-```ignore
-FD, 00, 00, 01, 00
-```
-
-Length 4,294,967,296 (aka 2^32) (First byte is u64_marker)
-```ignore
-FE, 00, 00, 00, 00, 01, 00, 00, 00
-```
+Details on the binary format used by this crate can be found in [the binary format specification](https://github.com/Xaeroxe/async-io-typed/blob/main/MESSAGE_BINARY_FORMAT.md).
