1 2 --- a replacement for aproto ------------------------------------------- 3 4 When it comes down to it, aproto's primary purpose is to forward 5 various streams between the host computer and client device (in either 6 direction). 7 8 This replacement further simplifies the concept, reducing the protocol 9 to an extremely straightforward model optimized to accomplish the 10 forwarding of these streams and removing additional state or 11 complexity. 12 13 The host side becomes a simple comms bridge with no "UI", which will 14 be used by either commandline or interactive tools to communicate with 15 a device or emulator that is connected to the bridge. 16 17 The protocol is designed to be straightforward and well-defined enough 18 that if it needs to be reimplemented in another environment (Java 19 perhaps), there should not problems ensuring perfect interoperability. 20 21 The protocol discards the layering aproto has and should allow the 22 implementation to be much more robust. 23 24 25 --- protocol overview and basics --------------------------------------- 26 27 The transport layer deals in "messages", which consist of a 24 byte 28 header followed (optionally) by a payload. The header consists of 6 29 32 bit words which are sent across the wire in little endian format. 30 31 struct 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 40 Receipt of an invalid message header, corrupt message payload, or an 41 unrecognized command MUST result in the closing of the remote 42 connection. The protocol depends on shared state and any break in the 43 message stream will result in state getting out of sync. 44 45 The following sections describe the six defined message types in 46 detail. Their format is COMMAND(arg0, arg1, payload) where the payload 47 is represented by a quoted string or an empty string if none should be 48 sent. 49 50 The identifiers "local-id" and "remote-id" are always relative to the 51 *sender* of the message, so for a receiver, the meanings are effectively 52 reversed. 53 54 55 56 --- CONNECT(version, maxdata, "system-identity-string") ---------------- 57 58 The CONNECT message establishes the presence of a remote system. 59 The version is used to ensure protocol compatibility and maxdata 60 declares the maximum message body size that the remote system 61 is willing to accept. 62 63 Currently, version=0x01000000 and maxdata=4096 64 65 Both sides send a CONNECT message when the connection between them is 66 established. Until a CONNECT message is received no other messages may 67 be sent. Any messages received before a CONNECT message MUST be ignored. 68 69 If a CONNECT message is received with an unknown version or insufficiently 70 large maxdata value, the connection with the other side must be closed. 71 72 The system identity string should be "<systemtype>:<serialno>:<banner>" 73 where systemtype is "bootloader", "device", or "host", serialno is some 74 kind of unique ID (or empty), and banner is a human-readable version 75 or identifier string (informational only). 76 77 78 --- OPEN(local-id, 0, "destination") ----------------------------------- 79 80 The OPEN message informs the recipient that the sender has a stream 81 identified by local-id that it wishes to connect to the named 82 destination in the message payload. The local-id may not be zero. 83 84 The OPEN message MUST result in either a READY message indicating that 85 the connection has been established (and identifying the other end) or 86 a CLOSE message, indicating failure. An OPEN message also implies 87 a READY message sent at the same time. 88 89 Common destination naming conventions include: 90 91 * "tcp:<host>:<port>" - host may be omitted to indicate localhost 92 * "udp:<host>:<port>" - host may be omitted to indicate localhost 93 * "local-dgram:<identifier>" 94 * "local-stream:<identifier>" 95 * "shell" - local shell service 96 * "upload" - service for pushing files across (like aproto's /sync) 97 * "fs-bridge" - FUSE protocol filesystem bridge 98 99 100 --- READY(local-id, remote-id, "") ------------------------------------- 101 102 The READY message informs the recipient that the sender's stream 103 identified by local-id is ready for write messages and that it is 104 connected to the recipient's stream identified by remote-id. 105 106 Neither the local-id nor the remote-id may be zero. 107 108 A READY message containing a remote-id which does not map to an open 109 stream on the recipient's side is ignored. The stream may have been 110 closed while this message was in-flight. 111 112 The local-id is ignored on all but the first READY message (where it 113 is used to establish the connection). Nonetheless, the local-id MUST 114 not change on later READY messages sent to the same stream. 115 116 117 118 --- WRITE(0, remote-id, "data") ---------------------------------------- 119 120 The WRITE message sends data to the recipient's stream identified by 121 remote-id. The payload MUST be <= maxdata in length. 122 123 A WRITE message containing a remote-id which does not map to an open 124 stream on the recipient's side is ignored. The stream may have been 125 closed while this message was in-flight. 126 127 A WRITE message may not be sent until a READY message is received. 128 Once a WRITE message is sent, an additional WRITE message may not be 129 sent until another READY message has been received. Recipients of 130 a WRITE message that is in violation of this requirement will CLOSE 131 the connection. 132 133 134 --- CLOSE(local-id, remote-id, "") ------------------------------------- 135 136 The CLOSE message informs recipient that the connection between the 137 sender's stream (local-id) and the recipient's stream (remote-id) is 138 broken. The remote-id MUST not be zero, but the local-id MAY be zero 139 if this CLOSE indicates a failed OPEN. 140 141 A CLOSE message containing a remote-id which does not map to an open 142 stream on the recipient's side is ignored. The stream may have 143 already been closed by the recipient while this message was in-flight. 144 145 The recipient should not respond to a CLOSE message in any way. The 146 recipient should cancel pending WRITEs or CLOSEs, but this is not a 147 requirement, since they will be ignored. 148 149 150 --- SYNC(online, sequence, "") ----------------------------------------- 151 152 The SYNC message is used by the io pump to make sure that stale 153 outbound messages are discarded when the connection to the remote side 154 is broken. It is only used internally to the bridge and never valid 155 to send across the wire. 156 157 * when the connection to the remote side goes offline, the io pump 158 sends a SYNC(0, 0) and starts discarding all messages 159 * when the connection to the remote side is established, the io pump 160 sends a SYNC(1, token) and continues to discard messages 161 * when the io pump receives a matching SYNC(1, token), it once again 162 starts accepting messages to forward to the remote side 163 164 165 --- message command constants ------------------------------------------ 166 167 #define A_SYNC 0x434e5953 168 #define A_CNXN 0x4e584e43 169 #define A_OPEN 0x4e45504f 170 #define A_OKAY 0x59414b4f 171 #define A_CLSE 0x45534c43 172 #define A_WRTE 0x45545257 173 174 175 176 --- implementation details --------------------------------------------- 177 178 The core of the bridge program will use three threads. One thread 179 will be a select/epoll loop to handle io between various inbound and 180 outbound connections and the connection to the remote side. 181 182 The remote side connection will be implemented as two threads (one for 183 reading, one for writing) and a datagram socketpair to provide the 184 channel between the main select/epoll thread and the remote connection 185 threadpair. The reason for this is that for usb connections, the 186 kernel interface on linux and osx does not allow you to do meaningful 187 nonblocking IO. 188 189 The endian swapping for the message headers will happen (as needed) in 190 the remote connection threadpair and that the rest of the program will 191 always treat message header values as native-endian. 192 193 The bridge program will be able to have a number of mini-servers 194 compiled in. They will be published under known names (examples 195 "shell", "fs-bridge", etc) and upon receiving an OPEN() to such a 196 service, the bridge program will create a stream socketpair and spawn 197 a thread or subprocess to handle the io. 198 199 200 --- simplified / embedded implementation ------------------------------- 201 202 For limited environments, like the bootloader, it is allowable to 203 support a smaller, fixed number of channels using pre-assigned channel 204 ID numbers such that only one stream may be connected to a bootloader 205 endpoint at any given time. The protocol remains unchanged, but the 206 "embedded" version of it is less dynamic. 207 208 The bootloader will support two streams. A "bootloader:debug" stream, 209 which may be opened to get debug messages from the bootloader and a 210 "bootloader:control", stream which will support the set of basic 211 bootloader commands. 212 213 Example command stream dialogues: 214 "flash_kernel,2515049,........\n" "okay\n" 215 "flash_ramdisk,5038,........\n" "fail,flash write error\n" 216 "bogus_command......" <CLOSE> 217 218 219 --- future expansion --------------------------------------------------- 220 221 I plan on providing either a message or a special control stream so that 222 the client device could ask the host computer to setup inbound socket 223 translations on the fly on behalf of the client device. 224 225 226 The initial design does handshaking to provide flow control, with a 227 message flow that looks like: 228 229 >OPEN <READY >WRITE <READY >WRITE <READY >WRITE <CLOSE 230 231 The far side may choose to issue the READY message as soon as it receives 232 a WRITE or it may defer the READY until the write to the local stream 233 succeeds. A future version may want to do some level of windowing where 234 multiple WRITEs may be sent without requiring individual READY acks. 235 236 ------------------------------------------------------------------------ 237 238 --- smartsockets ------------------------------------------------------- 239 240 Port 5037 is used for smart sockets which allow a client on the host 241 side to request access to a service in the host adb daemon or in the 242 remote (device) daemon. The service is requested by ascii name, 243 preceeded by a 4 digit hex length. Upon successful connection an 244 "OKAY" response is sent, otherwise a "FAIL" message is returned. Once 245 connected the client is talking to that (remote or local) service. 246 247 client: <hex4> <service-name> 248 server: "OKAY" 249 250 client: <hex4> <service-name> 251 server: "FAIL" <hex4> <reason> 252 253
