blob: 5c7c6ba8142a322c657f128b4d1069964106ff56 [file] [log] [blame]
The Android Open Source Project9ca14dc2009-03-03 19:32:55 -08001
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 ---------------------------------------
David 'Digit' Turner1f1efb52009-05-18 17:36:28 +020026
The Android Open Source Project9ca14dc2009-03-03 19:32:55 -080027The 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
David 'Digit' Turner1f1efb52009-05-18 17:36:28 +020055
The Android Open Source Project9ca14dc2009-03-03 19:32:55 -080056--- 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
Tamas Berghammera1c60c02015-07-13 19:12:28 +010063Currently, 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.
The Android Open Source Project9ca14dc2009-03-03 19:32:55 -080067
68Both sides send a CONNECT message when the connection between them is
69established. Until a CONNECT message is received no other messages may
Tamas Berghammera1c60c02015-07-13 19:12:28 +010070be sent. Any messages received before a CONNECT message MUST be ignored.
The Android Open Source Project9ca14dc2009-03-03 19:32:55 -080071
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
Scott Andersonfa020922012-05-25 14:10:02 -070078or identifier string. The banner is used to transmit useful properties.
The Android Open Source Project9ca14dc2009-03-03 19:32:55 -080079
80
Benoit Goby2cc19e42012-04-12 12:23:49 -070081--- 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
The Android Open Source Project9ca14dc2009-03-03 19:32:55 -080099--- 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
David 'Digit' Turner1f1efb52009-05-18 17:36:28 +0200138
Derrick Bonafilia65f76dd2015-07-06 10:19:28 -0700139--- WRITE(local-id, remote-id, "data") ---------------------------------
The Android Open Source Project9ca14dc2009-03-03 19:32:55 -0800140
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
Benoit Goby2cc19e42012-04-12 12:23:49 -0700190#define A_AUTH 0x48545541
The Android Open Source Project9ca14dc2009-03-03 19:32:55 -0800191#define A_OPEN 0x4e45504f
192#define A_OKAY 0x59414b4f
193#define A_CLSE 0x45534c43
194#define A_WRTE 0x45545257
195
196
David 'Digit' Turner1f1efb52009-05-18 17:36:28 +0200197
The Android Open Source Project9ca14dc2009-03-03 19:32:55 -0800198--- 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