packet.md 1.9 KB
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Packet Format
ADB protocol is a bi-directional, packet-oriented protocol. Each packet has a fixed-sized header and an optional, variable-sized payload.
Because it is originally implemented in C for Linux, all multi-byte fields are in little-endian, and all strings are in UTF-8 encoding.
Before Android 9, it used char * for string handling, so null terminators are required. Now it’s transitioning to std::string, which doesn't require null-terminators. But not all places has been changed, and for backward compatibility, adding null-terminators are still recommended.
Each packet contains following fields:
| Byte Offset | Type | Field | Description |
|---|---|---|---|
| 0 | char[4] | command | Packet type |
| 4 | in32 | arg0 | Meaning defined by each packet type |
| 8 | in32 | arg1 | Meaning defined by each packet type |
| 12 | uint32 | payloadLength | Length of payload, in bytes |
| 16 | uint32 | checksum | Checksum for verify data integrity |
| 20 | uint32 | magic | Should equal to command ^ 0xFFFFFFFF |
| 24 | byte[payloadLength] | payload | Meaning defined by each packet type |
Command
The command field consists of four ASCII characters.
For example, "CNXN" packets' command is [0x43, 0x4e, 0x58, 0x4e], or 0x4e584e43 in Hex (Hex strings are big-endian).
arg0/arg1
Two integer parameters for the command.
Checksum
Checksum is calculated by adding up all bytes in payload.
For example, when the payload is [0x01, 0x02, 0x03], the checksum is 0x01 + 0x02 + 0x03 = 0x00000006.