wait_for Library

Functions for waiting on resources to become available. Useful for coordination between services, waiting for files, ports, or HTTP endpoints.

Setup

The wait_for library is available by default in the scriptling-cli.

Available Functions

Function	Description
`file(path, timeout=30, poll_rate=1)`	Wait for file to exist
`dir(path, timeout=30, poll_rate=1)`	Wait for directory to exist
`port(host, port, timeout=30, ...)`	Wait for TCP port to accept connections
`http(url, timeout=30, ...)`	Wait for HTTP endpoint to return 200
`tcp(host, port, timeout=30, ...)`	Wait for TCP connection

Functions

wait_for.file(path, timeout=30, poll_rate=1)

Waits for a file to exist.

Parameters:

path (string): Path to the file to wait for
timeout (int, optional): Maximum time to wait in seconds (default: 30)
poll_rate (float, optional): Time between checks in seconds (default: 1)

Returns: bool - True if file exists, False if timeout exceeded

Example:

    
    
  
import wait_for

# Wait for a file to be created (up to 2 minutes)
if wait_for.file("/mnt/nas/index_ready", timeout=120):
    print("File is ready!")
else:
    print("Timeout waiting for file")

wait_for.dir(path, timeout=30, poll_rate=1)

Waits for a directory to exist.

Parameters:

path (string): Path to the directory to wait for
timeout (int, optional): Maximum time to wait in seconds (default: 30)
poll_rate (float, optional): Time between checks in seconds (default: 1)

Returns: bool - True if directory exists, False if timeout exceeded

Example:

    
import wait_for

# Wait for a backup directory to be created
if wait_for.dir("/mnt/nas/backups", timeout=60):
    print("Backup directory exists")

wait_for.port(host, port, timeout=30, poll_rate=1)

Waits for a TCP port to accept connections.

Parameters:

host (string): Hostname or IP address
port (int|string): Port number
timeout (int, optional): Maximum time to wait in seconds (default: 30)
poll_rate (float, optional): Time between checks in seconds (default: 1)

Returns: bool - True if port is open, False if timeout exceeded

Example:

    
    
  
import wait_for

# Wait for PostgreSQL to be ready
if wait_for.port("localhost", 5432, timeout=60):
    print("PostgreSQL is ready")
else:
    print("PostgreSQL did not start in time")

wait_for.http(url, timeout=30, poll_rate=1, status_code=200)

Waits for an HTTP endpoint to respond with the expected status code.

Parameters:

url (string): URL to check
timeout (int, optional): Maximum time to wait in seconds (default: 30)
poll_rate (float, optional): Time between checks in seconds (default: 1)
status_code (int, optional): Expected HTTP status code (default: 200)

Returns: bool - True if endpoint responds with expected status, False if timeout exceeded

Example:

    
import wait_for

# Wait for a health check endpoint
if wait_for.http("http://localhost:8080/health", timeout=60):
    print("Service is healthy")

# Wait for a specific status code
if wait_for.http("http://api.example.com/ready", timeout=30, status_code=200):
    print("API is ready")

wait_for.file_content(path, content, timeout=30, poll_rate=1)

Waits for a file to exist and contain specific content.

Parameters:

path (string): Path to the file to check
content (string): Content to search for in the file
timeout (int, optional): Maximum time to wait in seconds (default: 30)
poll_rate (float, optional): Time between checks in seconds (default: 1)

Returns: bool - True if file contains the content, False if timeout exceeded

Example:

    
import wait_for

# Wait for a readiness file to contain "ready=true"
if wait_for.file_content("/tmp/service.status", "ready=true", timeout=120):
    print("Service is ready")

# Wait for a specific pattern in a log file
if wait_for.file_content("/var/log/app.log", "Server started", timeout=30):
    print("Application has started")

wait_for.process_name(name, timeout=30, poll_rate=1)

Waits for a process with the specified name to be running.

Parameters:

name (string): Process name to search for
timeout (int, optional): Maximum time to wait in seconds (default: 30)
poll_rate (float, optional): Time between checks in seconds (default: 1)

Returns: bool - True if process is running, False if timeout exceeded

Example:

    
import wait_for

# Wait for nginx to start
if wait_for.process_name("nginx", timeout=30):
    print("nginx is running")

# Wait for a custom application
if wait_for.process_name("my-app", timeout=60):
    print("Application is running")

Complete Examples

Database Migration Coordination

    
    
  
import wait_for

# Wait for PostgreSQL to be ready
if not wait_for.port("localhost", 5432, timeout=60):
    print("ERROR: PostgreSQL did not start")
    exit(1)

# Run migrations
import subprocess
subprocess.run(["python", "manage.py", "migrate"])

# Wait for the migration lock file to be removed
while wait_for.file("/tmp/migration.lock", timeout=1):
    print("Waiting for migrations to complete...")

print("Migrations complete, starting application")

Multi-Service Startup Coordination

    
    
  
import wait_for
import time

# Start Redis in background
import subprocess
subprocess.Popen(["redis-server"])

# Start PostgreSQL in background
subprocess.Popen(["postgres", "-D", "/usr/local/var/postgres"])

# Wait for both services
print("Waiting for services...")
if wait_for.port("localhost", 6379, timeout=30):
    print("  ✓ Redis is ready")
else:
    print("  ✗ Redis failed to start")
    exit(1)

if wait_for.port("localhost", 5432, timeout=30):
    print("  ✓ PostgreSQL is ready")
else:
    print("  ✗ PostgreSQL failed to start")
    exit(1)

print("All services are ready!")

HTTP Service Health Check

    
    
  
import wait_for

services = [
    ("http://localhost:8080/health", "API Gateway"),
    ("http://localhost:8081/health", "Auth Service"),
    ("http://localhost:8082/health", "Data Service"),
]

print("Waiting for services to be healthy...")
for url, name in services:
    if wait_for.http(url, timeout=60):
        print(f"  ✓ {name}")
    else:
        print(f"  ✗ {name} failed health check")
        exit(1)

print("All services are healthy!")

Waiting for File Changes

    
    
  
import wait_for

# Wait for an index build to complete
# The index_ready file is created when indexing starts
# and contains "complete" when done

print("Waiting for index build...")
if wait_for.file("/data/index_ready", timeout=300):
    print("Index build started...")
    if wait_for.file_content("/data/index_ready", "complete", timeout=600):
        print("Index build complete!")
    else:
        print("Index build timed out")
else:
    print("Index build never started")

Custom Poll Rate

    
import wait_for

# Poll more frequently for quick checks (every 0.5 seconds)
if wait_for.port("localhost", 8080, timeout=10, poll_rate=0.5):
    print("Port opened quickly")

# Poll less frequently for long waits (every 5 seconds)
if wait_for.file("/mnt/nas/large_file.zip", timeout=600, poll_rate=5):
    print("File is ready")

Notes

All functions return True if the resource became available, False if timeout was exceeded
The default timeout is 30 seconds for all functions
The default poll rate is 1 second (checks once per second)
For HTTP checks, the default expected status code is 200
Process name matching is platform-dependent (uses /proc on Linux, ps on macOS/BSD)
Port checking uses TCP connection attempts with a 1-second timeout per attempt

Navigation

wait_for Library

Setup

Available Functions

Functions

wait_for.file(path, timeout=30, poll_rate=1)

wait_for.dir(path, timeout=30, poll_rate=1)

wait_for.port(host, port, timeout=30, poll_rate=1)

wait_for.http(url, timeout=30, poll_rate=1, status_code=200)

wait_for.file_content(path, content, timeout=30, poll_rate=1)

wait_for.process_name(name, timeout=30, poll_rate=1)

Complete Examples

Database Migration Coordination

Multi-Service Startup Coordination

HTTP Service Health Check

Waiting for File Changes

Custom Poll Rate

Notes

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