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=4096 64 65Both sides send a CONNECT message when the connection between them is 66established. Until a CONNECT message is received no other messages may 67be sent. Any messages received before a CONNECT message MUST be ignored. 68 69If a CONNECT message is received with an unknown version or insufficiently 70large maxdata value, the connection with the other side must be closed. 71 72The system identity string should be "<systemtype>:<serialno>:<banner>" 73where systemtype is "bootloader", "device", or "host", serialno is some 74kind of unique ID (or empty), and banner is a human-readable version 75or identifier string. The banner is used to transmit useful properties. 76 77 78--- AUTH(type, 0, "data") ---------------------------------------------- 79 80The AUTH message informs the recipient that authentication is required to 81connect to the sender. If type is TOKEN(1), data is a random token that 82the recipient can sign with a private key. The recipient replies with an 83AUTH packet where type is SIGNATURE(2) and data is the signature. If the 84signature verification succeeds, the sender replies with a CONNECT packet. 85 86If the signature verification fails, the sender replies with a new AUTH 87packet and a new random token, so that the recipient can retry signing 88with a different private key. 89 90Once the recipient has tried all its private keys, it can reply with an 91AUTH packet where type is RSAPUBLICKEY(3) and data is the public key. If 92possible, an on-screen confirmation may be displayed for the user to 93confirm they want to install the public key on the device. 94 95 96--- OPEN(local-id, 0, "destination") ----------------------------------- 97 98The OPEN message informs the recipient that the sender has a stream 99identified by local-id that it wishes to connect to the named 100destination in the message payload. The local-id may not be zero. 101 102The OPEN message MUST result in either a READY message indicating that 103the connection has been established (and identifying the other end) or 104a CLOSE message, indicating failure. An OPEN message also implies 105a READY message sent at the same time. 106 107Common destination naming conventions include: 108 109* "tcp:<host>:<port>" - host may be omitted to indicate localhost 110* "udp:<host>:<port>" - host may be omitted to indicate localhost 111* "local-dgram:<identifier>" 112* "local-stream:<identifier>" 113* "shell" - local shell service 114* "upload" - service for pushing files across (like aproto's /sync) 115* "fs-bridge" - FUSE protocol filesystem bridge 116 117 118--- READY(local-id, remote-id, "") ------------------------------------- 119 120The READY message informs the recipient that the sender's stream 121identified by local-id is ready for write messages and that it is 122connected to the recipient's stream identified by remote-id. 123 124Neither the local-id nor the remote-id may be zero. 125 126A READY message containing a remote-id which does not map to an open 127stream on the recipient's side is ignored. The stream may have been 128closed while this message was in-flight. 129 130The local-id is ignored on all but the first READY message (where it 131is used to establish the connection). Nonetheless, the local-id MUST 132not change on later READY messages sent to the same stream. 133 134 135 136--- WRITE(0, remote-id, "data") ---------------------------------------- 137 138The WRITE message sends data to the recipient's stream identified by 139remote-id. The payload MUST be <= maxdata in length. 140 141A WRITE message containing a remote-id which does not map to an open 142stream on the recipient's side is ignored. The stream may have been 143closed while this message was in-flight. 144 145A WRITE message may not be sent until a READY message is received. 146Once a WRITE message is sent, an additional WRITE message may not be 147sent until another READY message has been received. Recipients of 148a WRITE message that is in violation of this requirement will CLOSE 149the connection. 150 151 152--- CLOSE(local-id, remote-id, "") ------------------------------------- 153 154The CLOSE message informs recipient that the connection between the 155sender's stream (local-id) and the recipient's stream (remote-id) is 156broken. The remote-id MUST not be zero, but the local-id MAY be zero 157if this CLOSE indicates a failed OPEN. 158 159A CLOSE message containing a remote-id which does not map to an open 160stream on the recipient's side is ignored. The stream may have 161already been closed by the recipient while this message was in-flight. 162 163The recipient should not respond to a CLOSE message in any way. The 164recipient should cancel pending WRITEs or CLOSEs, but this is not a 165requirement, since they will be ignored. 166 167 168--- SYNC(online, sequence, "") ----------------------------------------- 169 170The SYNC message is used by the io pump to make sure that stale 171outbound messages are discarded when the connection to the remote side 172is broken. It is only used internally to the bridge and never valid 173to send across the wire. 174 175* when the connection to the remote side goes offline, the io pump 176 sends a SYNC(0, 0) and starts discarding all messages 177* when the connection to the remote side is established, the io pump 178 sends a SYNC(1, token) and continues to discard messages 179* when the io pump receives a matching SYNC(1, token), it once again 180 starts accepting messages to forward to the remote side 181 182 183--- message command constants ------------------------------------------ 184 185#define A_SYNC 0x434e5953 186#define A_CNXN 0x4e584e43 187#define A_AUTH 0x48545541 188#define A_OPEN 0x4e45504f 189#define A_OKAY 0x59414b4f 190#define A_CLSE 0x45534c43 191#define A_WRTE 0x45545257 192 193 194 195--- implementation details --------------------------------------------- 196 197The core of the bridge program will use three threads. One thread 198will be a select/epoll loop to handle io between various inbound and 199outbound connections and the connection to the remote side. 200 201The remote side connection will be implemented as two threads (one for 202reading, one for writing) and a datagram socketpair to provide the 203channel between the main select/epoll thread and the remote connection 204threadpair. The reason for this is that for usb connections, the 205kernel interface on linux and osx does not allow you to do meaningful 206nonblocking IO. 207 208The endian swapping for the message headers will happen (as needed) in 209the remote connection threadpair and that the rest of the program will 210always treat message header values as native-endian. 211 212The bridge program will be able to have a number of mini-servers 213compiled in. They will be published under known names (examples 214"shell", "fs-bridge", etc) and upon receiving an OPEN() to such a 215service, the bridge program will create a stream socketpair and spawn 216a thread or subprocess to handle the io. 217 218 219--- simplified / embedded implementation ------------------------------- 220 221For limited environments, like the bootloader, it is allowable to 222support a smaller, fixed number of channels using pre-assigned channel 223ID numbers such that only one stream may be connected to a bootloader 224endpoint at any given time. The protocol remains unchanged, but the 225"embedded" version of it is less dynamic. 226 227The bootloader will support two streams. A "bootloader:debug" stream, 228which may be opened to get debug messages from the bootloader and a 229"bootloader:control", stream which will support the set of basic 230bootloader commands. 231 232Example command stream dialogues: 233 "flash_kernel,2515049,........\n" "okay\n" 234 "flash_ramdisk,5038,........\n" "fail,flash write error\n" 235 "bogus_command......" <CLOSE> 236 237 238--- future expansion --------------------------------------------------- 239 240I plan on providing either a message or a special control stream so that 241the client device could ask the host computer to setup inbound socket 242translations on the fly on behalf of the client device. 243 244 245The initial design does handshaking to provide flow control, with a 246message flow that looks like: 247 248 >OPEN <READY >WRITE <READY >WRITE <READY >WRITE <CLOSE 249 250The far side may choose to issue the READY message as soon as it receives 251a WRITE or it may defer the READY until the write to the local stream 252succeeds. A future version may want to do some level of windowing where 253multiple WRITEs may be sent without requiring individual READY acks. 254 255------------------------------------------------------------------------ 256 257--- smartsockets ------------------------------------------------------- 258 259Port 5037 is used for smart sockets which allow a client on the host 260side to request access to a service in the host adb daemon or in the 261remote (device) daemon. The service is requested by ascii name, 262preceeded by a 4 digit hex length. Upon successful connection an 263"OKAY" response is sent, otherwise a "FAIL" message is returned. Once 264connected the client is talking to that (remote or local) service. 265 266client: <hex4> <service-name> 267server: "OKAY" 268 269client: <hex4> <service-name> 270server: "FAIL" <hex4> <reason> 271 272