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+Implementation notes regarding ADB.
+
+I. General Overview:
+
+The Android Debug Bridge (ADB) is used to:
+
+- keep track of all Android devices and emulators instances
+  connected to or running on a given host developer machine
+
+- implement various control commands (e.g. "adb shell", "adb pull", etc..)
+  for the benefit of clients (command-line users, or helper programs like
+  DDMS). These commands are what is called a 'service' in ADB.
+
+As a whole, everything works through the following components:
+
+  1. The ADB server
+
+    This is a background process that runs on the host machine. Its purpose
+    if to sense the USB ports to know when devices are attached/removed,
+    as well as when emulator instances start/stop.
+
+    It thus maintains a list of "connected devices" and assigns a 'state'
+    to each one of them: OFFLINE, BOOTLOADER, RECOVERY or ONLINE (more on
+    this below).
+
+    The ADB server is really one giant multiplexing loop whose purpose is
+    to orchestrate the exchange of data (packets, really) between clients,
+    services and devices.
+
+
+  2. The ADB daemon (adbd)
+
+    The 'adbd' program runs as a background process within an Android device
+    or emulated system. Its purpose is to connect to the ADB server
+    (through USB for devices, through TCP for emulators) and provide a
+    few services for clients that run on the host.
+
+    The ADB server considers that a device is ONLINE when it has succesfully
+    connected to the adbd program within it. Otherwise, the device is OFFLINE,
+    meaning that the ADB server detected a new device/emulator, but could not
+    connect to the adbd daemon.
+
+    the BOOTLOADER and RECOVERY states correspond to alternate states of
+    devices when they are in the bootloader or recovery mode.
+
+  3. The ADB command-line client
+
+    The 'adb' command-line program is used to run adb commands from a shell
+    or a script. It first tries to locate the ADB server on the host machine,
+    and will start one automatically if none is found.
+
+    then, the client sends its service requests to the ADB server. It doesn't
+    need to know.
+
+    Currently, a single 'adb' binary is used for both the server and client.
+    this makes distribution and starting the server easier.
+
+
+  4. Services
+
+    There are essentially two kinds of services that a client can talk to.
+
+    Host Services:
+      these services run within the ADB Server and thus do not need to
+      communicate with a device at all. A typical example is "adb devices"
+      which is used to return the list of currently known devices and their
+      state. They are a few couple other services though.
+
+    Local Services:
+      these services either run within the adbd daemon, or are started by
+      it on the device. The ADB server is used to multiplex streams
+      between the client and the service running in adbd. In this case
+      its role is to initiate the connection, then of being a pass-through
+      for the data.
+
+
+II. Protocol details:
+
+  1. Client <-> Server protocol:
+
+    This details the protocol used between ADB clients and the ADB
+    server itself. The ADB server listens on TCP:localhost:5037.
+
+    A client sends a request using the following format:
+
+        1. A 4-byte hexadecimal string giving the length of the payload
+        2. Followed by the payload itself.
+
+    For example, to query the ADB server for its internal version number,
+    the client will do the following:
+
+        1. Connect to tcp:localhost:5037
+        2. Send the string "000Chost:version" to the corresponding socket
+
+    The 'host:' prefix is used to indicate that the request is addressed
+    to the server itself (we will talk about other kinds of requests later).
+    The content length is encoded in ASCII for easier debugging.
+
+    The server should answer a request with one of the following:
+
+        1. For success, the 4-byte "OKAY" string
+
+        2. For failure, the 4-byte "FAIL" string, followed by a
+           4-byte hex length, followed by a string giving the reason
+           for failure.
+
+        3. As a special exception, for 'host:version', a 4-byte
+           hex string corresponding to the server's internal version number
+
+    Note that the connection is still alive after an OKAY, which allows the
+    client to make other requests. But in certain cases, an OKAY will even
+    change the state of the connection. 
+
+    For example, the case of the 'host:transport:<serialnumber>' request,
+    where '<serialnumber>' is used to identify a given device/emulator; after
+    the "OKAY" answer, all further requests made by the client will go
+    directly to the corresponding adbd daemon.
+
+    The file SERVICES.TXT lists all services currently implemented by ADB.
+
+
+  2. Transports:
+
+    An ADB transport models a connection between the ADB server and one device
+    or emulator. There are currently two kinds of transports:
+
+       - USB transports, for physical devices through USB
+
+       - Local transports, for emulators running on the host, connected to
+         the server through TCP
+
+    In theory, it should be possible to write a local transport that proxies
+    a connection between an ADB server and a device/emulator connected to/
+    running on another machine. This hasn't been done yet though.
+
+    Each transport can carry one or more multiplexed streams between clients
+    and the device/emulator they point to. The ADB server must handle
+    unexpected transport disconnections (e.g. when a device is physically
+    unplugged) properly.