cmd

package
v1.0.0 Latest Latest
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 Go to latest Published: Dec 27, 2022 License: MIT, MIT Imports: 13 Imported by: 0

README

Stop Order

  • Process exits or is terminated

Modification

  • Always run with bash -c
    • Helps to run bash commands (e.g., echo, sleep, ...)
    • Helps to use EnvVars in .bashrc
  • Add StdoutPub and StderrPub to collect logs
  • Add log file writer
  • Use Name as identifier
  • Add OnStop() func to call when the proc ends

Go-Cmd Advantages

  • Kill the process group
  • Status checking (e.g., exit status)
  • Thoroughly tested
  • Safe cleanup

Documentation

Overview

Package cmd runs external commands with concurrent access to output and status. It wraps the Go standard library os/exec.Command to correctly handle reading output (STDOUT and STDERR) while a command is running and killing a command. All operations are safe to call from multiple goroutines.

A basic example that runs env and prints its output: 

import (
    "fmt"
    "github.com/go-cmd/cmd"
)

func main() {
    // Create Cmd, buffered output
    envCmd := cmd.NewCmd("env")

    // Run and wait for Cmd to return Status
    status := <-envCmd.Start()

    // Print each line of STDOUT from Cmd
    for _, line := range status.Stdout {
        fmt.Println(line)
    }
}

Commands can be ran synchronously (blocking) or asynchronously (non-blocking): 

envCmd := cmd.NewCmd("env") // create

status := <-envCmd.Start() // run blocking

statusChan := envCmd.Start() // run non-blocking
// Do other work while Cmd is running...
status <- statusChan // blocking

Start returns a channel to which the final Status is sent when the command finishes for any reason. The first example blocks receiving on the channel. The second example is non-blocking because it saves the channel and receives on it later. Only one final status is sent to the channel; use Done for multiple goroutines to wait for the command to finish, then call Status to get the final status.

Index

Constants

View Source 
const (
	// DEFAULT_LINE_BUFFER_SIZE is the default size of the OutputStream line buffer.
	// The default value is usually sufficient, but if ErrLineBufferOverflow errors
	// occur, try increasing the size by calling OutputBuffer.SetLineBufferSize.
	DEFAULT_LINE_BUFFER_SIZE = 16384

	// DEFAULT_STREAM_CHAN_SIZE is the default string channel size for a Cmd when
	// Options.Streaming is true. The string channel size can have a minor
	// performance impact if too small by causing OutputStream.Write to block
	// excessively.
	DEFAULT_STREAM_CHAN_SIZE = 1000
)

Variables

View Source 
var (
	// ErrNotStarted is returned by Stop if called before Start or StartWithStdin.
	ErrNotStarted = errors.New("command not running")
)

Functions

func CreateLogFile 

func CreateLogFile(logdir, name string, stdout bool) (*os.File, error)

CreateLogFile helps to create a log file for a command.

Types

type Cmd 

type Cmd struct {
	// Name of binary (command) to run. This is the only required value.
	// No path expansion is done.
	// Used to set underlying os/exec.Cmd.Path.
	Name string

	// Commands line arguments passed to the command.
	// Args are optional.
	// Used to set underlying os/exec.Cmd.Args.
	Args []string

	// Environment variables set before running the command.
	// Env is optional.
	Env []string

	// Current working directory from which to run the command.
	// Dir is optional; default is current working directory
	// of calling process.
	// Used to set underlying os/exec.Cmd.Dir.
	Dir string

	// If set, log files are generated as `${LogDir}/${id}.{stdout,stderr}.log`.
	LogDir string

	// StdoutPub publishes the stdout to multiple subscribers and is created only when Streaming option is true.
	StdoutPub *StringPublisher

	// StderrPub publishes the stderr to multiple subscribers and is created only when Streaming option is true.
	StderrPub *StringPublisher

	Shell string // shell binary to execute

	*sync.Mutex
	// contains filtered or unexported fields
}

Cmd represents an external command, similar to the Go built-in os/exec.Cmd. A Cmd cannot be reused after calling Start. Exported fields are read-only and should not be modified, except Env which can be set before calling Start. To create a new Cmd, call NewCmd or NewCmdOptions.

func NewCmd 

func NewCmd(name string, execmd string) *Cmd

NewCmd creates a new Cmd for the given command name and arguments. The command is not started until Start is called. Output buffering is on, streaming output is off. To control output, use NewCmdOptions instead.

func NewCmdOptions 

func NewCmdOptions(options Options, name string, execmd string) *Cmd

NewCmdOptions creates a new Cmd with options. The command is not started until Start is called.

func (*Cmd) Clone 

func (c *Cmd) Clone() *Cmd

Clone clones a Cmd. All the options are transferred, but the internal state of the original object is lost. Cmd is one-use only, so if you need to re-start a Cmd, you need to Clone it.

func (*Cmd) Done 

func (c *Cmd) Done() <-chan struct{}

Done returns a channel that's closed when the command stops running. This method is useful for multiple goroutines to wait for the command to finish.Call Status after the command finishes to get its final status.

func (*Cmd) IsDone 

func (c *Cmd) IsDone() bool

IsDone returns true if the Cmd is done and exited; otherwise, return false

func (*Cmd) Start 

func (c *Cmd) Start() <-chan Status

Start starts the command and immediately returns a channel that the caller can use to receive the final Status of the command when it ends. The caller can start the command and wait like, 

status := <-myCmd.Start() // blocking

or start the command asynchronously and be notified later when it ends, 

statusChan := myCmd.Start() // non-blocking
// Do other work while Cmd is running...
status := <-statusChan // blocking

Exactly one Status is sent on the channel when the command ends. The channel is not closed. Any Go error is set to Status.Error. Start is idempotent; it always returns the same channel.

func (*Cmd) StartWithStdin 

func (c *Cmd) StartWithStdin(in io.Reader) <-chan Status

StartWithStdin is the same as Start but uses in for STDIN.

func (*Cmd) Status 

func (c *Cmd) Status() Status

Status returns the Status of the command at any time. It is safe to call concurrently by multiple goroutines.

With buffered output, Status.Stdout and Status.Stderr contain the full output as of the Status call time. For example, if the command counts to 3 and three calls are made between counts, Status.Stdout contains: 

"1"
"1 2"
"1 2 3"

The caller is responsible for tailing the buffered output if needed. Else, consider using streaming output. When the command finishes, buffered output is complete and final.

Status.Runtime is updated while the command is running and final when it finishes.

func (*Cmd) Stop 

func (c *Cmd) Stop() error

Stop stops the command by sending its process group a SIGTERM signal. Stop is idempotent. Stopping and already stopped command returns nil.

Stop returns ErrNotStarted if called before Start or StartWithStdin. If the command is very slow to start, Stop can return ErrNotStarted after calling Start or StartWithStdin because this package is still waiting for the system to start the process. All other return errors are from the low-level system function for process termination.

type ErrLineBufferOverflow 

type ErrLineBufferOverflow struct {
	Line       string // Unterminated line that caused the error
	BufferSize int    // Internal line buffer size
	BufferFree int    // Free bytes in line buffer
}

ErrLineBufferOverflow is returned by OutputStream.Write when the internal line buffer is filled before a newline character is written to terminate a line. Increasing the line buffer size by calling OutputStream.SetLineBufferSize can help prevent this error.

func (ErrLineBufferOverflow) Error 

func (e ErrLineBufferOverflow) Error() string

type Options 

type Options struct {
	// If Buffered is true, STDOUT and STDERR are written to Status.Stdout and
	// Status.Stderr. The caller can call Cmd.Status to read output at intervals.
	// See Cmd.Status for more info.
	Buffered bool

	// If Streaming is true, Cmd.Stdout and Cmd.Stderr channels are created and
	// STDOUT and STDERR output lines are written them in real time. This is
	// faster and more efficient than polling Cmd.Status. The caller must read both
	// streaming channels, else lines are dropped silently.
	Streaming bool

	// BeforeExec is a list of functions called immediately before starting
	// the real command. These functions can be used to customize the underlying
	// os/exec.Cmd. For example, to set SysProcAttr.
	BeforeExec []func(cmd *exec.Cmd)

	// BeforeExec is a list of functions called immediately after the real command exits.
	AfterDone []func(cmd *Cmd)
}

Options represents customizations for NewCmdOptions.

type OutputBuffer 

type OutputBuffer struct {
	*sync.Mutex
	// contains filtered or unexported fields
}

OutputBuffer represents command output that is saved, line by line, in an unbounded buffer. It is safe for multiple goroutines to read while the command is running and after it has finished. If output is small (a few megabytes) and not read frequently, an output buffer is a good solution.

A Cmd in this package uses an OutputBuffer for both STDOUT and STDERR by default when created by calling NewCmd. To use OutputBuffer directly with a Go standard library os/exec.Command: 

import "os/exec"
import "github.com/go-cmd/cmd"
runnableCmd := exec.Command(...)
stdout := cmd.NewOutputBuffer()
runnableCmd.Stdout = stdout

While runnableCmd is running, call stdout.Lines() to read all output currently written.

func NewOutputBuffer 

func NewOutputBuffer() *OutputBuffer

NewOutputBuffer creates a new output buffer. The buffer is unbounded and safe for multiple goroutines to read while the command is running by calling Lines.

func (*OutputBuffer) Lines 

func (rw *OutputBuffer) Lines() []string

Lines returns lines of output written by the Cmd. It is safe to call while the Cmd is running and after it has finished. Subsequent calls returns more lines, if more lines were written. "\r\n" are stripped from the lines.

func (*OutputBuffer) Write 

func (rw *OutputBuffer) Write(p []byte) (n int, err error)

Write makes OutputBuffer implement the io.Writer interface. Do not call this function directly.

type OutputStream 

type OutputStream struct {
	// contains filtered or unexported fields
}

OutputStream represents real time, line by line output from a running Cmd. Lines are terminated by a single newline preceded by an optional carriage return. Both newline and carriage return are stripped from the line when sent to a caller-provided channel.

The caller must begin receiving before starting the Cmd. Write blocks on the channel; the caller must always read the channel. The channel is closed when the Cmd exits and all output has been sent.

A Cmd in this package uses an OutputStream for both STDOUT and STDERR when created by calling NewCmdOptions and Options.Streaming is true. To use OutputStream directly with a Go standard library os/exec.Command: 

import "os/exec"
import "github.com/go-cmd/cmd"

stdoutChan := make(chan string, 100)
go func() {
    for line := range stdoutChan {
        // Do something with the line
    }
}()

runnableCmd := exec.Command(...)
stdout := cmd.NewOutputStream(stdoutChan)
runnableCmd.Stdout = stdout

While runnableCmd is running, lines are sent to the channel as soon as they are written and newline-terminated by the command.

func NewOutputStream 

func NewOutputStream(streamChan chan string) *OutputStream

NewOutputStream creates a new streaming output on the given channel. The caller must begin receiving on the channel before the command is started. The OutputStream never closes the channel.

func (*OutputStream) Flush 

func (rw *OutputStream) Flush()

Flush empties the buffer of its last line.

func (*OutputStream) Lines 

func (rw *OutputStream) Lines() <-chan string

Lines returns the channel to which lines are sent. This is the same channel passed to NewOutputStream.

func (*OutputStream) SetLineBufferSize 

func (rw *OutputStream) SetLineBufferSize(n int)

SetLineBufferSize sets the internal line buffer size. The default is DEFAULT_LINE_BUFFER_SIZE. This function must be called immediately after NewOutputStream, and it is not safe to call by multiple goroutines.

Increasing the line buffer size can help reduce ErrLineBufferOverflow errors.

func (*OutputStream) Write 

func (rw *OutputStream) Write(p []byte) (n int, err error)

Write makes OutputStream implement the io.Writer interface. Do not call this function directly.

type Status 

type Status struct {
	Name     string
	Cmd      string
	PID      int
	Complete bool     // false if stopped or signaled
	Exit     int      // exit code of process
	Error    error    // Go error
	StartTs  int64    // Unix ts (nanoseconds), zero if Cmd not started
	StopTs   int64    // Unix ts (nanoseconds), zero if Cmd not started or running
	Runtime  float64  // seconds, zero if Cmd not started
	Stdout   []string // buffered STDOUT; see Cmd.Status for more info
	Stderr   []string // buffered STDERR; see Cmd.Status for more info
}

Status represents the running status and consolidated return of a Cmd. It can be obtained any time by calling Cmd.Status. If StartTs > 0, the command has started. If StopTs > 0, the command has stopped. After the command finishes for any reason, this combination of values indicates success (presuming the command only exits zero on success): 

Exit     = 0
Error    = nil
Complete = true

Error is a Go error from the underlying os/exec.Cmd.Start or os/exec.Cmd.Wait. If not nil, the command either failed to start (it never ran) or it started but was terminated unexpectedly (probably signaled). In either case, the command failed. Callers should check Error first. If nil, then check Exit and Complete.

type StringPublisher 

type StringPublisher struct {
	// contains filtered or unexported fields
}

StringPublisher is basic pub/sub structure. Allows to send events and subscribe to them. Can be safely used from multiple goroutines.

func NewStringPublisher 

func NewStringPublisher(publishTimeout time.Duration, buffer int) *StringPublisher

NewStringPublisher creates a new pub/sub publisher to broadcast messages. The duration is used as the send timeout as to not block the publisher publishing messages to other clients if one client is slow or unresponsive. The buffer is used when creating new channels for subscribers.

func (*StringPublisher) Close 

func (p *StringPublisher) Close()

Close closes the channels to all subscribers registered with the publisher.

func (*StringPublisher) Evict 

func (p *StringPublisher) Evict(sub chan string)

Evict removes the specified subscriber from receiving any more messages.

func (*StringPublisher) Len 

func (p *StringPublisher) Len() int

Len returns the number of subscribers for the publisher

func (*StringPublisher) Publish 

func (p *StringPublisher) Publish(v string)

Publish sends the data in v to all subscribers currently registered with the publisher.

func (*StringPublisher) Subscribe 

func (p *StringPublisher) Subscribe() chan string

Subscribe adds a new subscriber to the publisher returning the channel.

func (*StringPublisher) SubscribeTopic 

func (p *StringPublisher) SubscribeTopic(topic _StringTopicFunc) chan string

SubscribeTopic adds a new subscriber that filters messages sent by a topic.

func (*StringPublisher) SubscribeTopicWithBuffer 

func (p *StringPublisher) SubscribeTopicWithBuffer(topic _StringTopicFunc, buffer int) chan string

SubscribeTopicWithBuffer adds a new subscriber that filters messages sent by a topic. The returned channel has a buffer of the specified size.

type StringsPublisher 

type StringsPublisher struct {
	// contains filtered or unexported fields
}

StringsPublisher is basic pub/sub structure. Allows to send events and subscribe to them. Can be safely used from multiple goroutines.

func NewStringsPublisher 

func NewStringsPublisher(publishTimeout time.Duration, buffer int) *StringsPublisher

NewStringsPublisher creates a new pub/sub publisher to broadcast messages. The duration is used as the send timeout as to not block the publisher publishing messages to other clients if one client is slow or unresponsive. The buffer is used when creating new channels for subscribers.

func (*StringsPublisher) Close 

func (p *StringsPublisher) Close()

Close closes the channels to all subscribers registered with the publisher.

func (*StringsPublisher) Evict 

func (p *StringsPublisher) Evict(sub chan []string)

Evict removes the specified subscriber from receiving any more messages.

func (*StringsPublisher) Len 

func (p *StringsPublisher) Len() int

Len returns the number of subscribers for the publisher

func (*StringsPublisher) Publish 

func (p *StringsPublisher) Publish(v []string)

Publish sends the data in v to all subscribers currently registered with the publisher.

func (*StringsPublisher) Subscribe 

func (p *StringsPublisher) Subscribe() chan []string

Subscribe adds a new subscriber to the publisher returning the channel.

func (*StringsPublisher) SubscribeTopic 

func (p *StringsPublisher) SubscribeTopic(topic _StringsTopicFunc) chan []string

SubscribeTopic adds a new subscriber that filters messages sent by a topic.

func (*StringsPublisher) SubscribeTopicWithBuffer 

func (p *StringsPublisher) SubscribeTopicWithBuffer(topic _StringsTopicFunc, buffer int) chan []string

SubscribeTopicWithBuffer adds a new subscriber that filters messages sent by a topic. The returned channel has a buffer of the specified size.

Source Files

View all Source files

Directories

Path Synopsis
examples
blocking-buffered command

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