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fromFile.go
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fromFile.go
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package library
import (
"bufio"
"encoding/json"
"github.com/nytlabs/streamtools/st/blocks" // blocks
"github.com/nytlabs/streamtools/st/util"
"os"
)
// specify those channels we're going to use to communicate with streamtools
type FromFile struct {
blocks.Block
queryrule chan chan interface{}
inrule chan interface{}
in chan interface{}
out chan interface{}
quit chan interface{}
}
// we need to build a simple factory so that streamtools can make new blocks of this kind
func NewFromFile() blocks.BlockInterface {
return &FromFile{}
}
// Setup is called once before running the block. We build up the channels and specify what kind of block this is.
func (b *FromFile) Setup() {
b.Kind = "FromFile"
b.Desc = "reads in a file specified by the block's rule, emitting a message for each line"
b.in = b.InRoute("in")
b.inrule = b.InRoute("rule")
b.queryrule = b.QueryRoute("rule")
b.quit = b.Quit()
b.out = b.Broadcast()
}
// Run is the block's main loop. Here we listen on the different channels we set up.
func (b *FromFile) Run() {
var file *os.File
var filename string
for {
select {
case msgI := <-b.inrule:
// set a parameter of the block
filename, err := util.ParseString(msgI, "Filename")
if err != nil {
b.Error(err)
continue
}
file, err := os.Open(filename)
if err != nil {
b.Error(err)
continue
}
scanner := bufio.NewScanner(file)
for scanner.Scan() {
var outMsg interface{}
lineBytes := scanner.Bytes()
err := json.Unmarshal(lineBytes, &outMsg)
// if the json parsing fails, store data unparsed as "data"
if err != nil {
outMsg = map[string]interface{}{
"data": lineBytes,
}
}
b.out <- outMsg
}
if err := scanner.Err(); err != nil {
b.Error(err)
continue
}
case <-b.quit:
// quit the block
if file != nil {
file.Close()
}
return
case c := <-b.queryrule:
c <- map[string]interface{}{
"Filename": filename,
}
}
}
}