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rpctest: make test TCP ports unique per process
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This commit adds a new NextAvailablePortForProcess function that takes a
process ID and then assures unique (non-occupied) port numbers are
returned per process.
This uses a temporary file that contains the latest used port and a
secondary temporary lock file to assure only a single goroutine can
request a new port at a time.

The GenerateProcessUniqueListenerAddresses is intened to be used as a
package-level override for the ListenAddressGenerator variable. We don't
use it by default to make sure we don't break any existing assumptions.
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guggero committed Dec 21, 2023
1 parent d33ac28 commit dd5f3bd
Showing 1 changed file with 105 additions and 0 deletions.
105 changes: 105 additions & 0 deletions integration/rpctest/rpc_harness.go
Original file line number Diff line number Diff line change
Expand Up @@ -561,6 +561,111 @@ func NextAvailablePort() int {
panic("no ports available for listening")
}

// NextAvailablePortForProcess returns the first port that is available for
// listening by a new node, using a lock file to make sure concurrent access for
// parallel tasks within the same process don't re-use the same port. It panics
// if no port is found and the maximum available TCP port is reached.
func NextAvailablePortForProcess(pid int) int {
lockFile := filepath.Join(
os.TempDir(), fmt.Sprintf("rpctest-port-pid-%d.lock", pid),
)
timeout := time.After(time.Second)

var (
lockFileHandle *os.File
err error
)
for {
// Attempt to acquire the lock file. If it already exists, wait
// for a bit and retry.
lockFileHandle, err = os.OpenFile(
lockFile, os.O_CREATE|os.O_EXCL, 0600,
)
if err == nil {
// Lock acquired.
break
}

// Wait for a bit and retry.
select {
case <-timeout:
panic("timeout waiting for lock file")
case <-time.After(10 * time.Millisecond):
}
}

// Release the lock file when we're done.
defer func() {
// Always close file first, Windows won't allow us to remove it
// otherwise.
_ = lockFileHandle.Close()
err := os.Remove(lockFile)
if err != nil {
panic(fmt.Errorf("couldn't remove lock file: %w", err))
}
}()

portFile := filepath.Join(
os.TempDir(), fmt.Sprintf("rpctest-port-pid-%d", pid),
)
port, err := os.ReadFile(portFile)
if err != nil {
if !os.IsNotExist(err) {
panic(fmt.Errorf("error reading port file: %w", err))
}
port = []byte(strconv.Itoa(int(defaultNodePort)))
}

lastPort, err := strconv.Atoi(string(port))
if err != nil {
panic(fmt.Errorf("error parsing port: %w", err))
}

// We take the next one.
lastPort++
for lastPort < 65535 {
// If there are no errors while attempting to listen on this
// port, close the socket and return it as available. While it
// could be the case that some other process picks up this port
// between the time the socket is closed and it's reopened in
// the harness node, in practice in CI servers this seems much
// less likely than simply some other process already being
// bound at the start of the tests.
addr := fmt.Sprintf(ListenerFormat, lastPort)
l, err := net.Listen("tcp4", addr)
if err == nil {
err := l.Close()
if err == nil {
err := os.WriteFile(
portFile,
[]byte(strconv.Itoa(lastPort)), 0600,
)
if err != nil {
panic(fmt.Errorf("error updating "+
"port file: %w", err))
}

return lastPort
}
}
lastPort++
}

// No ports available? Must be a mistake.
panic("no ports available for listening")
}

// GenerateProcessUniqueListenerAddresses is a function that returns two
// listener addresses with unique ports per the given process id and should be
// used to overwrite rpctest's default generator which is prone to use colliding
// ports.
func GenerateProcessUniqueListenerAddresses(pid int) (string, string) {
port1 := NextAvailablePortForProcess(pid)
port2 := NextAvailablePortForProcess(pid)
return fmt.Sprintf(ListenerFormat, port1),
fmt.Sprintf(ListenerFormat, port2)
}

// baseDir is the directory path of the temp directory for all rpctest files.
func baseDir() (string, error) {
dirPath := filepath.Join(os.TempDir(), "btcd", "rpctest")
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