1 2--- a replacement for aproto ------------------------------------------- 3 4When it comes down to it, aproto's primary purpose is to forward 5various streams between the host computer and client device (in either 6direction). 7 8This replacement further simplifies the concept, reducing the protocol 9to an extremely straightforward model optimized to accomplish the 10forwarding of these streams and removing additional state or 11complexity. 12 13The host side becomes a simple comms bridge with no "UI", which will 14be used by either commandline or interactive tools to communicate with 15a device or emulator that is connected to the bridge. 16 17The protocol is designed to be straightforward and well-defined enough 18that if it needs to be reimplemented in another environment (Java 19perhaps), there should not problems ensuring perfect interoperability. 20 21The protocol discards the layering aproto has and should allow the 22implementation to be much more robust. 23 24 25--- protocol overview and basics --------------------------------------- 26 27The transport layer deals in "messages", which consist of a 24 byte 28header followed (optionally) by a payload. The header consists of 6 2932 bit words which are sent across the wire in little endian format. 30 31struct message { 32 unsigned command; /* command identifier constant */ 33 unsigned arg0; /* first argument */ 34 unsigned arg1; /* second argument */ 35 unsigned data_length; /* length of payload (0 is allowed) */ 36 unsigned data_crc32; /* crc32 of data payload */ 37 unsigned magic; /* command ^ 0xffffffff */ 38}; 39 40Receipt of an invalid message header, corrupt message payload, or an 41unrecognized command MUST result in the closing of the remote 42connection. The protocol depends on shared state and any break in the 43message stream will result in state getting out of sync. 44 45The following sections describe the six defined message types in 46detail. Their format is COMMAND(arg0, arg1, payload) where the payload 47is represented by a quoted string or an empty string if none should be 48sent. 49 50The identifiers "local-id" and "remote-id" are always relative to the 51*sender* of the message, so for a receiver, the meanings are effectively 52reversed. 53 54 55 56--- CONNECT(version, maxdata, "system-identity-string") ---------------- 57 58The CONNECT message establishes the presence of a remote system. 59The version is used to ensure protocol compatibility and maxdata 60declares the maximum message body size that the remote system 61is willing to accept. 62 63Currently, version=0x01000000 and maxdata=256*1024. Older versions of adb 64hard-coded maxdata=4096, so CONNECT and AUTH packets sent to a device must not 65be larger than that because they're sent before the CONNECT from the device 66that tells the adb server what maxdata the device can support. 67 68Both sides send a CONNECT message when the connection between them is 69established. Until a CONNECT message is received no other messages may 70be sent. Any messages received before a CONNECT message MUST be ignored. 71 72If a CONNECT message is received with an unknown version or insufficiently 73large maxdata value, the connection with the other side must be closed. 74 75The system identity string should be "<systemtype>:<serialno>:<banner>" 76where systemtype is "bootloader", "device", or "host", serialno is some 77kind of unique ID (or empty), and banner is a human-readable version 78or identifier string. The banner is used to transmit useful properties. 79 80 81--- AUTH(type, 0, "data") ---------------------------------------------- 82 83The AUTH message informs the recipient that authentication is required to 84connect to the sender. If type is TOKEN(1), data is a random token that 85the recipient can sign with a private key. The recipient replies with an 86AUTH packet where type is SIGNATURE(2) and data is the signature. If the 87signature verification succeeds, the sender replies with a CONNECT packet. 88 89If the signature verification fails, the sender replies with a new AUTH 90packet and a new random token, so that the recipient can retry signing 91with a different private key. 92 93Once the recipient has tried all its private keys, it can reply with an 94AUTH packet where type is RSAPUBLICKEY(3) and data is the public key. If 95possible, an on-screen confirmation may be displayed for the user to 96confirm they want to install the public key on the device. 97 98 99--- OPEN(local-id, 0, "destination") ----------------------------------- 100 101The OPEN message informs the recipient that the sender has a stream 102identified by local-id that it wishes to connect to the named 103destination in the message payload. The local-id may not be zero. 104 105The OPEN message MUST result in either a READY message indicating that 106the connection has been established (and identifying the other end) or 107a CLOSE message, indicating failure. An OPEN message also implies 108a READY message sent at the same time. 109 110Common destination naming conventions include: 111 112* "tcp:<host>:<port>" - host may be omitted to indicate localhost 113* "udp:<host>:<port>" - host may be omitted to indicate localhost 114* "local-dgram:<identifier>" 115* "local-stream:<identifier>" 116* "shell" - local shell service 117* "upload" - service for pushing files across (like aproto's /sync) 118* "fs-bridge" - FUSE protocol filesystem bridge 119 120 121--- READY(local-id, remote-id, "") ------------------------------------- 122 123The READY message informs the recipient that the sender's stream 124identified by local-id is ready for write messages and that it is 125connected to the recipient's stream identified by remote-id. 126 127Neither the local-id nor the remote-id may be zero. 128 129A READY message containing a remote-id which does not map to an open 130stream on the recipient's side is ignored. The stream may have been 131closed while this message was in-flight. 132 133The local-id is ignored on all but the first READY message (where it 134is used to establish the connection). Nonetheless, the local-id MUST 135not change on later READY messages sent to the same stream. 136 137 138 139--- WRITE(local-id, remote-id, "data") --------------------------------- 140 141The WRITE message sends data to the recipient's stream identified by 142remote-id. The payload MUST be <= maxdata in length. 143 144A WRITE message containing a remote-id which does not map to an open 145stream on the recipient's side is ignored. The stream may have been 146closed while this message was in-flight. 147 148A WRITE message may not be sent until a READY message is received. 149Once a WRITE message is sent, an additional WRITE message may not be 150sent until another READY message has been received. Recipients of 151a WRITE message that is in violation of this requirement will CLOSE 152the connection. 153 154 155--- CLOSE(local-id, remote-id, "") ------------------------------------- 156 157The CLOSE message informs recipient that the connection between the 158sender's stream (local-id) and the recipient's stream (remote-id) is 159broken. The remote-id MUST not be zero, but the local-id MAY be zero 160if this CLOSE indicates a failed OPEN. 161 162A CLOSE message containing a remote-id which does not map to an open 163stream on the recipient's side is ignored. The stream may have 164already been closed by the recipient while this message was in-flight. 165 166The recipient should not respond to a CLOSE message in any way. The 167recipient should cancel pending WRITEs or CLOSEs, but this is not a 168requirement, since they will be ignored. 169 170 171--- SYNC(online, sequence, "") ----------------------------------------- 172 173The SYNC message is used by the io pump to make sure that stale 174outbound messages are discarded when the connection to the remote side 175is broken. It is only used internally to the bridge and never valid 176to send across the wire. 177 178* when the connection to the remote side goes offline, the io pump 179 sends a SYNC(0, 0) and starts discarding all messages 180* when the connection to the remote side is established, the io pump 181 sends a SYNC(1, token) and continues to discard messages 182* when the io pump receives a matching SYNC(1, token), it once again 183 starts accepting messages to forward to the remote side 184 185 186--- message command constants ------------------------------------------ 187 188#define A_SYNC 0x434e5953 189#define A_CNXN 0x4e584e43 190#define A_AUTH 0x48545541 191#define A_OPEN 0x4e45504f 192#define A_OKAY 0x59414b4f 193#define A_CLSE 0x45534c43 194#define A_WRTE 0x45545257 195 196 197 198--- implementation details --------------------------------------------- 199 200The core of the bridge program will use three threads. One thread 201will be a select/epoll loop to handle io between various inbound and 202outbound connections and the connection to the remote side. 203 204The remote side connection will be implemented as two threads (one for 205reading, one for writing) and a datagram socketpair to provide the 206channel between the main select/epoll thread and the remote connection 207threadpair. The reason for this is that for usb connections, the 208kernel interface on linux and osx does not allow you to do meaningful 209nonblocking IO. 210 211The endian swapping for the message headers will happen (as needed) in 212the remote connection threadpair and that the rest of the program will 213always treat message header values as native-endian. 214 215The bridge program will be able to have a number of mini-servers 216compiled in. They will be published under known names (examples 217"shell", "fs-bridge", etc) and upon receiving an OPEN() to such a 218service, the bridge program will create a stream socketpair and spawn 219a thread or subprocess to handle the io. 220 221 222--- simplified / embedded implementation ------------------------------- 223 224For limited environments, like the bootloader, it is allowable to 225support a smaller, fixed number of channels using pre-assigned channel 226ID numbers such that only one stream may be connected to a bootloader 227endpoint at any given time. The protocol remains unchanged, but the 228"embedded" version of it is less dynamic. 229 230The bootloader will support two streams. A "bootloader:debug" stream, 231which may be opened to get debug messages from the bootloader and a 232"bootloader:control", stream which will support the set of basic 233bootloader commands. 234 235Example command stream dialogues: 236 "flash_kernel,2515049,........\n" "okay\n" 237 "flash_ramdisk,5038,........\n" "fail,flash write error\n" 238 "bogus_command......" <CLOSE> 239 240 241--- future expansion --------------------------------------------------- 242 243I plan on providing either a message or a special control stream so that 244the client device could ask the host computer to setup inbound socket 245translations on the fly on behalf of the client device. 246 247 248The initial design does handshaking to provide flow control, with a 249message flow that looks like: 250 251 >OPEN <READY >WRITE <READY >WRITE <READY >WRITE <CLOSE 252 253The far side may choose to issue the READY message as soon as it receives 254a WRITE or it may defer the READY until the write to the local stream 255succeeds. A future version may want to do some level of windowing where 256multiple WRITEs may be sent without requiring individual READY acks. 257 258------------------------------------------------------------------------ 259 260--- smartsockets ------------------------------------------------------- 261 262Port 5037 is used for smart sockets which allow a client on the host 263side to request access to a service in the host adb daemon or in the 264remote (device) daemon. The service is requested by ascii name, 265preceeded by a 4 digit hex length. Upon successful connection an 266"OKAY" response is sent, otherwise a "FAIL" message is returned. Once 267connected the client is talking to that (remote or local) service. 268 269client: <hex4> <service-name> 270server: "OKAY" 271 272client: <hex4> <service-name> 273server: "FAIL" <hex4> <reason> 274 275