open-consul/command/agent/watch_handler.go

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package agent
import (
"bytes"
"encoding/json"
"fmt"
"io"
"log"
"os"
"strconv"
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"sync"
"github.com/armon/circbuf"
"github.com/hashicorp/consul/watch"
)
const (
// Limit the size of a watch handlers's output to the
// last WatchBufSize. Prevents an enormous buffer
// from being captured
WatchBufSize = 4 * 1024 // 4KB
)
// verifyWatchHandler does the pre-check for our handler configuration
func verifyWatchHandler(params interface{}) error {
if params == nil {
return fmt.Errorf("Must provide watch handler")
}
_, ok := params.(string)
if !ok {
return fmt.Errorf("Watch handler must be a string")
}
return nil
}
// makeWatchHandler returns a handler for the given watch
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func makeWatchHandler(logOutput io.Writer, params interface{}, reapLock *sync.RWMutex) watch.HandlerFunc {
script := params.(string)
logger := log.New(logOutput, "", log.LstdFlags)
fn := func(idx uint64, data interface{}) {
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// Disable child process reaping so that we can get this command's
// return value. Note that we take the read lock here since we are
// waiting on a specific PID and don't need to serialize all waits.
reapLock.RLock()
defer reapLock.RUnlock()
// Create the command
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cmd, err := ExecScript(script)
if err != nil {
logger.Printf("[ERR] agent: Failed to setup watch: %v", err)
return
}
cmd.Env = append(os.Environ(),
"CONSUL_INDEX="+strconv.FormatUint(idx, 10),
)
// Collect the output
output, _ := circbuf.NewBuffer(WatchBufSize)
cmd.Stdout = output
cmd.Stderr = output
// Setup the input
var inp bytes.Buffer
enc := json.NewEncoder(&inp)
if err := enc.Encode(data); err != nil {
logger.Printf("[ERR] agent: Failed to encode data for watch '%s': %v", script, err)
return
}
cmd.Stdin = &inp
// Run the handler
if err := cmd.Run(); err != nil {
logger.Printf("[ERR] agent: Failed to invoke watch handler '%s': %v", script, err)
}
// Get the output, add a message about truncation
outputStr := string(output.Bytes())
if output.TotalWritten() > output.Size() {
outputStr = fmt.Sprintf("Captured %d of %d bytes\n...\n%s",
output.Size(), output.TotalWritten(), outputStr)
}
// Log the output
logger.Printf("[DEBUG] agent: watch handler '%s' output: %s", script, outputStr)
}
return fn
}