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princepdf.go
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/
princepdf.go
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package princepdf
import (
"bufio"
"encoding/json"
"fmt"
"io"
"os/exec"
"strconv"
"strings"
)
const (
chunkJob = "job"
chunkData = "dat"
chunkEnd = "end"
chunkErr = "err"
chunkLog = "log"
chunkPDF = "pdf"
strJobResource = "job-resource:%d"
strFilesFmt = "files:%s"
cmdPrince = "prince"
workerCountDefault = 1
)
var (
cmdPrinceOpts = []string{"--control"}
)
// Client provides a client interface to be able to stream commands to the prince
// controller.
type Client struct {
in chan *Job
workerCount int
workers []*worker
}
// Option defines a functional option to configure the Client
type Option func(*Client)
// WithWorkerCounter sets the number of prince processes to launch
// thus increasing the number of concurrent requests that can be handled.
// The default is 1.
func WithWorkerCount(i int) Option {
return func(c *Client) {
c.workerCount = i
}
}
// New instantiates a new PrincePDF client
func New(opts ...Option) *Client {
c := &Client{
in: make(chan *Job),
workerCount: workerCountDefault,
}
for _, opt := range opts {
opt(c)
}
c.workers = make([]*worker, c.workerCount)
return c
}
// Start begins the workers and prepares to run jobs
func (c *Client) Start() error {
var err error
for i := range c.workers {
c.workers[i], err = newWorker(c.in)
if err != nil {
return fmt.Errorf("starting: %w", err)
}
go c.workers[i].start()
}
return nil
}
// Stop ends the workers and closes the client.
func (c *Client) Stop() error {
close(c.in)
for _, w := range c.workers {
w.stop()
}
return nil
}
// Run sends a job to the prince controller and returns the output.
func (c *Client) Run(job *Job) ([]byte, error) {
job.reply = make(chan *output)
defer close(job.reply)
c.in <- job
out := <-job.reply
return out.data, out.err
}
// worker represents and individual execution of a prince command that can
// respond to an process a single stream of requests.
type worker struct {
cmd *exec.Cmd
in chan *Job
stderr *bufio.Reader
stdout *bufio.Reader
stdin io.Writer
}
func newWorker(in chan *Job) (*worker, error) {
w := &worker{
cmd: exec.Command(cmdPrince, cmdPrinceOpts...),
in: in,
}
stderr, err := w.cmd.StderrPipe()
if err != nil {
return nil, fmt.Errorf("preparing stderr: %w", err)
}
w.stderr = bufio.NewReader(stderr)
stdout, err := w.cmd.StdoutPipe()
if err != nil {
return nil, fmt.Errorf("preparing stdout: %w", err)
}
w.stdout = bufio.NewReader(stdout)
if w.stdin, err = w.cmd.StdinPipe(); err != nil {
return nil, fmt.Errorf("preparing stdin: %w", err)
}
if err := w.cmd.Start(); err != nil {
return nil, err
}
return w, nil
}
func (w *worker) start() {
// first grab the version information which is sent automatically by prince
out := w.read()
fmt.Printf("started version: '%s'\n", string(out.data))
go w.printStderr()
for job := range w.in {
w.run(job)
}
}
func (w *worker) printStderr() {
for {
line, err := w.stderr.ReadString('\n')
if err != nil {
if err != io.EOF {
fmt.Printf("reading stderr: %s\n", err.Error())
}
return
}
fmt.Printf("stderr: %s\n", line)
}
}
func (w *worker) stop() {
if err := w.end(); err != nil {
fmt.Printf("ending session: %s\n", err.Error())
}
if err := w.cmd.Wait(); err != nil {
fmt.Printf("waiting for command to close: %s\n", err.Error())
}
}
func (w *worker) run(job *Job) {
// send request to command
req := job.request()
data, err := json.Marshal(req)
if err != nil {
fmt.Printf("failed to marshal job: %s\n", err.Error())
return
}
// Send to the stream
w.write(chunkJob, data)
for _, d := range req.resources {
w.write(chunkData, d)
}
job.reply <- w.read()
}
func (w *worker) end() error {
return w.write(chunkEnd, nil)
}
func (w *worker) write(msg string, data []byte) error {
if len(data) == 0 {
w.stdin.Write([]byte(msg + "\n"))
}
msg = fmt.Sprintf("%s %d", msg, len(data))
w.stdin.Write([]byte(msg + "\n"))
if _, err := w.stdin.Write(data); err != nil {
return fmt.Errorf("writing data: %w", err)
}
if _, err := w.stdin.Write([]byte("\n")); err != nil {
return fmt.Errorf("writing last newline: %w", err)
}
return nil
}
func (w *worker) read() *output {
o := new(output)
// Read the first line
var line string
var err error
line, err = w.stdout.ReadString('\n')
if err != nil {
o.err = fmt.Errorf("reading string: %w", err)
return o
}
line = strings.TrimSpace(line)
fmt.Printf("line: '%s'\n", line)
parts := strings.Fields(line)
if len(parts) == 0 {
o.err = fmt.Errorf("invalid empty response")
return o
}
o.msg = parts[0]
// read data
if len(parts) > 1 {
l, err := strconv.Atoi(parts[1])
if err != nil {
o.err = fmt.Errorf("invalid length: %w", err)
return o
}
o.data = make([]byte, l)
_, err = io.ReadFull(w.stdout, o.data)
if err != nil {
o.err = fmt.Errorf("reading data: %w", err)
return o
}
_, err = w.stdout.ReadString('\n') // read the newline at the end
if err != nil {
o.err = fmt.Errorf("reading newline: %w", err)
return o
}
}
switch o.msg {
case chunkErr:
o.err = fmt.Errorf("prince error: %s", string(o.data))
o.data = nil
case chunkPDF:
// pdf messages are always followed by a 'log' message
w.read()
case chunkLog:
fmt.Printf("log: %s\n", string(o.data))
}
return o
}
// output wraps around output provided from a job
type output struct {
msg string // type of message from prince
data []byte
err error
}