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* Copyright (C) 2015 The Android Open Source Project
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
// This file contains classes and functionality to launch shell subprocesses
// in adbd and communicate between those subprocesses and the adb client.
// The main features exposed here are:
// 1. A ShellPacket class to wrap data in a simple protocol. Both adbd and
// the adb client use this class to transmit data between them.
// 2. Functions to launch a subprocess on the adbd side.
#include <stdint.h>
#include <android-base/macros.h>
#include "adb.h"
// Class to send and receive shell protocol packets.
// To keep things simple and predictable, reads and writes block until an entire
// packet is complete.
// Example: read raw data from |fd| and send it in a packet.
// ShellProtocol* p = new ShellProtocol(protocol_fd);
// int len = adb_read(stdout_fd, p->data(), p->data_capacity());
// packet->WritePacket(ShellProtocol::kIdStdout, len);
// Example: read a packet and print it to |stdout|.
// ShellProtocol* p = new ShellProtocol(protocol_fd);
// if (p->ReadPacket() && p->id() == kIdStdout) {
// fwrite(p->data(), 1, p->data_length(), stdout);
// }
class ShellProtocol {
// This is an unscoped enum to make it easier to compare against raw bytes.
enum Id : uint8_t {
kIdStdin = 0,
kIdStdout = 1,
kIdStderr = 2,
kIdExit = 3,
// Close subprocess stdin if possible.
kIdCloseStdin = 4,
// Window size change (an ASCII version of struct winsize).
kIdWindowSizeChange = 5,
// Indicates an invalid or unknown packet.
kIdInvalid = 255,
// ShellPackets will probably be too large to allocate on the stack so they
// should be dynamically allocated on the heap instead.
// |fd| is an open file descriptor to be used to send or receive packets.
explicit ShellProtocol(int fd);
virtual ~ShellProtocol();
// Returns a pointer to the data buffer.
const char* data() const { return buffer_ + kHeaderSize; }
char* data() { return buffer_ + kHeaderSize; }
// Returns the total capacity of the data buffer.
size_t data_capacity() const { return buffer_end_ - data(); }
// Reads a packet from the FD.
// If a packet is too big to fit in the buffer then Read() will split the
// packet across multiple calls. For example, reading a 50-byte packet into
// a 20-byte buffer would read 20 bytes, 20 bytes, then 10 bytes.
// Returns false if the FD closed or errored.
bool Read();
// Returns the ID of the packet in the buffer.
int id() const { return buffer_[0]; }
// Returns the number of bytes that have been read into the data buffer.
size_t data_length() const { return data_length_; }
// Writes the packet currently in the buffer to the FD.
// Returns false if the FD closed or errored.
bool Write(Id id, size_t length);
// Packets support 4-byte lengths.
typedef uint32_t length_t;
enum {
// It's OK if MAX_PAYLOAD doesn't match on the sending and receiving
// end, reading will split larger packets into multiple smaller ones.
kBufferSize = MAX_PAYLOAD,
// Header is 1 byte ID + 4 bytes length.
kHeaderSize = sizeof(Id) + sizeof(length_t)
int fd_;
char buffer_[kBufferSize];
size_t data_length_ = 0, bytes_left_ = 0;
// We need to be able to modify this value for testing purposes, but it
// will stay constant during actual program use.
char* buffer_end_ = buffer_ + sizeof(buffer_);
friend class ShellProtocolTest;
enum class SubprocessType {
enum class SubprocessProtocol {
// Forks and starts a new shell subprocess. If |name| is empty an interactive
// shell is started, otherwise |name| is executed non-interactively.
// Returns an open FD connected to the subprocess or -1 on failure.
int StartSubprocess(const char* name, const char* terminal_type,
SubprocessType type, SubprocessProtocol protocol);
#endif // !ADB_HOST
#endif // SHELL_SERVICE_H_