### Hysteria2 Build Targets

Source: https://github.com/herrymeg/hysteria2/blob/master/platforms.txt

Lists the supported operating systems and their corresponding CPU architectures for building Hysteria2. This configuration is used to control cross-compilation targets.

```plaintext
# This file controls what platform/architecture combinations we build for a release.

# Windows
windows/amd64
windows/amd64-avx
windows/386
windows/arm64

# macOS
darwin/amd64
darwin/amd64-avx
darwin/arm64

# Linux
linux/amd64
linux/amd64-avx
linux/386
linux/arm
linux/armv5
linux/arm64
linux/s390x
linux/mipsle
linux/mipsle-sf
linux/riscv64

# Android
android/386
android/amd64
android/armv7
android/arm64

# FreeBSD
freebsd/amd64
freebsd/amd64-avx
freebsd/386
freebsd/arm
freebsd/arm64
```

--------------------------------

### Hysteria Protocol TCP Proxy Request

Source: https://github.com/herrymeg/hysteria2/blob/master/PROTOCOL.md

Details the message format for initiating a TCP proxy connection over a QUIC stream. Includes address and padding information.

```APIDOC
[varint] 0x401 (TCPRequest ID)
[varint] Address length
[bytes] Address string (host:port)
[varint] Padding length
[bytes] Random padding
```

--------------------------------

### Hysteria Protocol Authentication Response

Source: https://github.com/herrymeg/hysteria2/blob/master/PROTOCOL.md

Defines the HTTP/3 response format a Hysteria server MUST send upon successful authentication. Details the status code and optional headers.

```APIDOC
:status: 233 HyOK
Hysteria-UDP: [true/false]
Hysteria-CC-RX: [uint/"auto"]
Hysteria-Padding: [string]

`Hysteria-UDP`: Whether the server supports UDP relay.

`Hysteria-CC-RX`: Server's maximum receive rate in bytes per second. A value of 0 indicates unlimited; "auto" indicates the server refuses to provide a value and ask the client to use congestion control to determine the rate on its own.

`Hysteria-Padding`: A random padding string of variable length.
```

--------------------------------

### Hysteria 2 Congestion Control Headers

Source: https://github.com/herrymeg/hysteria2/blob/master/PROTOCOL.md

Describes how client and server exchange receive rates during authentication using the 'Hysteria-CC-RX' header for congestion control. It outlines special cases for rate negotiation.

```plaintext
Client sends 'Hysteria-CC-RX' header with its rx rate.
Server responds with its rx rate or 'auto'.
```

--------------------------------

### Hysteria Protocol Authentication Request

Source: https://github.com/herrymeg/hysteria2/blob/master/PROTOCOL.md

Specifies the HTTP/3 request format a Hysteria client MUST send to authenticate with a server. Includes details on required headers and their purpose.

```APIDOC
:method: POST
:path: /auth
:host: hysteria
Hysteria-Auth: [string]
Hysteria-CC-RX: [uint]
Hysteria-Padding: [string]

`Hysteria-Auth`: Authentication credentials.

`Hysteria-CC-RX`: Client's maximum receive rate in bytes per second. A value of 0 indicates unknown.

`Hysteria-Padding`: A random padding string of variable length.
```

--------------------------------

### Hysteria 2 'Salamander' Obfuscation

Source: https://github.com/herrymeg/hysteria2/blob/master/PROTOCOL.md

Details the 'Salamander' obfuscation layer, which encapsulates QUIC packets using a salt and BLAKE2b-256 hash for payload obfuscation. It specifies the hashing and XOR obfuscation algorithms.

```plaintext
Format:
[8 bytes] Salt
[bytes] Payload

Hash calculation:
hash = BLAKE2b-256(key + salt)

Obfuscation:
payload[i] ^= hash[i % 32]
```

```python
import hashlib

def obfuscate(payload, key, salt):
    hash_val = hashlib.blake2b(key + salt, digest_size=32).digest()
    obfuscated_payload = bytearray(len(payload))
    for i in range(len(payload)):
        obfuscated_payload[i] = payload[i] ^ hash_val[i % 32]
    return bytes(obfuscated_payload)

def deobfuscate(obfuscated_payload, key, salt):
    return obfuscate(obfuscated_payload, key, salt) # Same algorithm for deobfuscation
```

--------------------------------

### Hysteria 2 UDP Packet Format

Source: https://github.com/herrymeg/hysteria2/blob/master/PROTOCOL.md

Defines the structure of UDP packets encapsulated for Hysteria 2, including session ID, packet ID, fragmentation information, address, and payload. This format is used for unreliable datagrams over QUIC.

```plaintext
[uint32] Session ID
[uint16] Packet ID
[uint8] Fragment ID
[uint8] Fragment count
[varint] Address length
[bytes] Address string (host:port)
[bytes] Payload
```

--------------------------------

### Hysteria Protocol TCP Proxy Response

Source: https://github.com/herrymeg/hysteria2/blob/master/PROTOCOL.md

Specifies the response format from the server for a TCP proxy request, indicating success or failure and providing status messages.

```APIDOC
[uint8] Status (0x00 = OK, 0x01 = Error)
[varint] Message length
[bytes] Message string
[varint] Padding length
[bytes] Random padding
```

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