Technologies

How to list MongoDB databases on command line

Use this command to list the MongoDB databases on the command line:

echo 'show dbs' | mongo

Example output:

MongoDB shell version v4.0.13
connecting to: mongodb://127.0.0.1:27017/?gssapiServiceName=mongodb
Implicit session: session { "id" : UUID("5c1e505e-9b05-4270-ab20-c537c0760481") }
MongoDB server version: 4.0.13
admin       0.000GB
config      0.000GB
drawing     0.001GB
order       0.000GB
production  0.001GB
standards   0.001GB
user        0.000GB
bye

 

Posted by Uli Köhler in MongoDB

How to fix Puppetteer ‘Running as root without –no-sandbox is not supported’

Problem:

When you try to run your puppetteer application, e.g. under docker, you see this error message:

Solution:

Note: Unless you are running in a Docker or similar container, first consider running the application as non-root-user!

You have to pass the --no-sandbox option to puppeteer.launch():

const browser = await puppeteer.launch({
    headless: true,
    args: ['--no-sandbox']
});

We recommend to use this slightly more complex solution to pass it only if the process is being run as root:

/**
 * Return true if the current process is run by the root user
 * https://techoverflow.net/2019/11/07/how-to-check-if-nodejs-is-run-by-root/
 */
function isCurrentUserRoot() {
   return process.getuid() == 0; // UID 0 is always root
}

const browser = await puppeteer.launch({
    headless: true,
    args: isCurrentUserRoot() ? ['--no-sandbox'] : undefined
});

This ensures Chromium is run in the most secure mode possible with the current user.

Posted by Uli Köhler in Javascript, NodeJS, Puppeteer

How to get schema of SQLite3 table in Python

Also see How to show table schema for SQLite3 table on the command line

Use this function to find the table schema of a SQLite3 table in Python:

def sqlite_table_schema(conn, name):
    """Return a string representing the table's CREATE"""
    cursor = conn.execute("SELECT sql FROM sqlite_master WHERE name=?;", [name])
    sql = cursor.fetchone()[0]
    cursor.close()
    return sql

Usage example:

print(sqlite_table_schema(conn, 'commands'))

Full example:

#!/usr/bin/env python3
import sqlite3
conn = sqlite3.connect('/usr/share/command-not-found/commands.db')

def sqlite_table_schema(conn, name):
    cursor = conn.execute("SELECT sql FROM sqlite_master WHERE name=?;", [name])
    sql = cursor.fetchone()[0]
    cursor.close()
    return sql

print(sqlite_table_schema(conn, 'commands'))

which prints

CREATE TABLE "commands" 
           (
            [cmdID] INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
            [pkgID] INTEGER NOT NULL,
            [command] TEXT,
            FOREIGN KEY ([pkgID]) REFERENCES "pkgs" ([pkgID])
           )

 

 

Posted by Uli Köhler in Python, SQLite

How to fix SQLite3 Python ‘Incorrect number of bindings supplied. The current statement uses 1, … supplied’

Problem:

You are trying to run a simple SQL query with placeholders on a SQLite3 database, e.g.:

name = "mytable"
conn.execute("SELECT sql FROM sqlite_master WHERE name=?;", name)

But you get an exception like this:

---------------------------------------------------------------------------
ProgrammingError                          Traceback (most recent call last)
<ipython-input-55-e385cf40fd72> in <module>
      1 name = "mytable"
----> 2 conn.execute("SELECT sql FROM sqlite_master WHERE type='table' AND name=?;", name)

ProgrammingError: Incorrect number of bindings supplied. The current statement uses 1, and there are 7 supplied.

Solution:

You need to use a list as the second argument to conn.execute(...)!

Since you only gave the function a string, the string is being interpreted as list of characters.

In our example from above, you just need to wrap name in square brackets to read [name]:

name = "mytable"
conn.execute("SELECT sql FROM sqlite_master WHERE name=?;", [name])
Posted by Uli Köhler in Python, SQLite

How to list SQLite3 database tables on command line

Also see How to list tables in SQLite3 database in Python

Use this command to list all the tables in a SQLite3 database using the sqlite3 command line tool:

sqlite3 [database file] "SELECT name FROM sqlite_master WHERE type='table' AND name != 'sqlite_sequence';"

Example:

$ sqlite3 /usr/share/command-not-found/commands.db "SELECT name FROM sqlite_master WHERE type='table' AND name != 'sqlite_sequence';"
commands
packages

 

Posted by Uli Köhler in Databases, SQLite

How to list tables in SQLite3 database in Python

Also see How to list SQLite3 database tables on command line

You can use this snippet to list all the SQL tables in your SQLite 3.x database in Python:

def tables_in_sqlite_db(conn):
    cursor = conn.execute("SELECT name FROM sqlite_master WHERE type='table';")
    tables = [
        v[0] for v in cursor.fetchall()
        if v[0] != "sqlite_sequence"
    ]
    cursor.close()
    return tables

Usage example:

#!/usr/bin/env python3
import sqlite3
# Open database
conn = sqlite3.connect('/usr/share/command-not-found/commands.db')
# List tables
tables = tables_in_sqlite_db(conn)

# Your code goes here!
# Example:
print(tables) # prints ['commands', 'packages']

 

Posted by Uli Köhler in Databases, Python, SQLite

How to dump SQL from SQLite3 database file

If you have a SQLite3 database file (usually the filename extension is .db) and you want to dump it as SQL code, you can use

sqlite3 [database file] .dump

For example:

$ sqlite3 /usr/share/command-not-found/commands.db .dump
[...]
DELETE FROM sqlite_sequence;
INSERT INTO sqlite_sequence VALUES('packages',14669);
INSERT INTO sqlite_sequence VALUES('commands',47706);
CREATE INDEX idx_commands_command ON commands (command);
CREATE INDEX idx_packages_name ON packages (name);
COMMIT;

Missing the sqlite3 executable?

In case you don’t have the sqlite3 executable, you can install it using

sudo apt -y install sqlite3

on Ubuntu/Debian-based system

Posted by Uli Köhler in Allgemein, SQLite

How to emulate the Enter key in Puppeteer

To emulate a keypress to the Enter key in Puppeteer, use

await page.keyboard.press("Enter");

The E needs to be uppercase for this to work!

Posted by Uli Köhler in Javascript, Puppeteer

How to emulate keyboard input in Puppeteer

To emulate the user typing something on the keyboard, use

await page.keyboard.type("the text");

This will type the text extremely fast with virtually no delay between the characters.

In order to simulate the finite typing speed of real users, use

await page.keyboard.type("the text", {delay: 100});

instead. The delay betwen characters in this example is 100 Milliseconds, i.e. the emulated user types 10 characters per second.

Posted by Uli Köhler in Javascript, NodeJS, Puppeteer

How to emulate TAB key press in Puppeteer

In order to emulate a tab key press in Puppeteer, use

await page.keyboard.press("Tab");

Full example:

// Minimal puppeteer example
const puppeteer = require('puppeteer');
(async () => {
  const browser = await puppeteer.launch({defaultViewport: {width: 1920, height: 1080}});
  const page = await browser.newPage();
  await page.goto('https://techoverflow.net', {waitUntil: 'domcontentloaded'});
  // Press tab 10 times (effectively scrolls down on techoverflow.net)
  for (let i = 0; i < 10; i++) {
      await page.keyboard.press("Tab");
  }
  // Screenshot to verify result
  await page.screenshot({path: 'screenshot.png'});
  // Cleanup
  await browser.close();
})();

 

Posted by Uli Köhler in Javascript, Puppeteer

How to set <input> value in Puppeteer

Use this snippet to set the value of an HTML <input> element in Puppeteer:

const newInputValue = "test 123";
await page.evaluate(val => document.querySelector('.search-form-input').value = val, newInputValue);amp

Remember to replace '.search-form-input' by whatever CSS selector is suitable to select your <input>. Examples include 'input[name="username"]' or '.username > input'.

Full example:

// Minimal puppeteer example
const puppeteer = require('puppeteer');
(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  await page.goto('https://techoverflow.net', {waitUntil: 'domcontentloaded'});
  // Set input value
  const newInputValue = "test 123";
  await page.evaluate(val => document.querySelector('.search-form-input').value = val, newInputValue);
  // Screenshot to verify result
  await page.screenshot({path: 'screenshot.png'});
  // Cleanup
  await browser.close();
})();

Note that this method will work for any simple <input>, however it might not work for some heavily Javascripted inputs which you can find on some modern websites.

Posted by Uli Köhler in Javascript, Puppeteer

How to save screenshot in Puppeteer as PNG?

You can take a screenshot in Puppeteer using

await page.screenshot({path: 'screenshot.png'});

The path is relative to the current working directory.

Want to have a screenshot in a size different to 800×600? See How to set screenshot size in Puppeteer?

Full example:

// Minimal puppeteer example
const puppeteer = require('puppeteer');
(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  await page.goto('https://techoverflow.net', {waitUntil: 'domcontentloaded'});
  // Screenshot to verify result
  await page.screenshot({path: 'screenshot.png'});
  // Cleanup
  await browser.close();
})();

 

Posted by Uli Köhler in Javascript, NodeJS, Puppeteer

Minimal puppeteer response interception example

Using Python (pyppeteer)? Check out Pyppetteer minimal network response interception example

This example shows you how to intercept network responses in puppeteer.

Note: This intercepts the response, not the request! This means you can abort the request before it is actually sent to the server, but you can’t read the content of the response! See Minimal puppeteer request interception example for an example on how to intercept requests.

const puppeteer = require('puppeteer');
(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  // Enable response interception
  page.on('response', async (response) => {
      console.info("URL", response.request().url());
      console.info("Method", response.request().method())
      console.info("Response headers", response.headers())
      console.info("Request headers", response.request().headers())
      // Use this to get the content as text
      const responseText = await response.text();
      // ... or as buffer (for binary data)
      const responseBuffer = await response.buffer();
      // ... or as JSON, if it's a JSON (else, this will throw!)
      const responseObj = await response.json();
  })
  await page.goto('https://techoverflow.net', {waitUntil: 'domcontentloaded'});
  // Make a screenshot
  await page.screenshot({path: 'screenshot.png'});
  await browser.close();
})();

 

Posted by Uli Köhler in Javascript, Puppeteer

Minimal puppeteer request interception example

Using Python (pyppeteer)? Check out Pyppetteer minimal network request interception example

This example shows you how to intercept network requests in puppeteer:

Note: This intercepts the request, not the response! This means you can abort the request made, but you can’t read the content of the response! See Minimal puppeteer response interception example for an example on how to intercept responses.

const puppeteer = require('puppeteer');
(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  // Enable request interception
  await page.setRequestInterception(true);
  page.on('request', async (request) => {
      console.info("URL", request.url());
      console.info("Method", request.method())
      console.info("Headers", request.headers())
      return request.continue(); // Allow request to continue
      // return request.abort(); // use this instead to abort the request!
  })
  await page.goto('https://techoverflow.net', {waitUntil: 'domcontentloaded'});
  // Make a screenshot
  await page.screenshot({path: 'screenshot.png'});
  await browser.close();
})();

 

Posted by Uli Köhler in Javascript, Puppeteer

How to fix Puppeteer ‘Error: Protocol error (Emulation.setDeviceMetricsOverride): Invalid parameters width: integer value expected; height: integer value expected’

Problem:

You are trying to set the viewport size in Puppeteer using

const browser = await puppeteer.launch({
    defaultViewport: '1920x1080'
});

but you see an error message like

(node:15692) UnhandledPromiseRejectionWarning: Error: Protocol error (Emulation.setDeviceMetricsOverride): Invalid parameters width: integer value expected; height: integer value expected
    at /home/uli/dev/myproject/node_modules/puppeteer/lib/Connection.js:183:56
    at new Promise (<anonymous>)
    at CDPSession.send (/home/uli/dev/myproject/node_modules/puppeteer/lib/Connection.js:182:12)
    at EmulationManager.emulateViewport (/home/uli/dev/myproject/node_modules/puppeteer/lib/EmulationManager.js:41:20)
    at Page.setViewport (/home/uli/dev/myproject/node_modules/puppeteer/lib/Page.js:808:54)
    at Page.<anonymous> (/home/uli/dev/myproject/node_modules/puppeteer/lib/helper.js:112:23)
    at Function.create (/home/uli/dev/myproject/node_modules/puppeteer/lib/Page.js:49:18)
    at processTicksAndRejections (internal/process/task_queues.js:85:5)
    at async Browser._createPageInContext (/home/uli/dev/myproject/node_modules/puppeteer/lib/Browser.js:177:18)
    at async /home/uli/dev/myproject/index.js:8:16
  -- ASYNC --
    at Target.<anonymous> (/home/uli/dev/myproject/node_modules/puppeteer/lib/helper.js:111:15)
    at Browser._createPageInContext (/home/uli/dev/myproject/node_modules/puppeteer/lib/Browser.js:177:31)
    at processTicksAndRejections (internal/process/task_queues.js:85:5)
    at async /home/uli/dev/myproject/index.js:8:16
  -- ASYNC --
    at Browser.<anonymous> (/home/uli/dev/myproject/node_modules/puppeteer/lib/helper.js:111:15)
    at /home/uli/dev/myproject/index.js:8:30
    at processTicksAndRejections (internal/process/task_queues.js:85:5)
(node:15692) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:15692) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

Solution:

You need to use

{defaultViewport: {width: 1920, height: 1080}}

instead of

{defaultViewport: '1920x1080'}

Full example:

// Minimal puppeteer example
const puppeteer = require('puppeteer');
(async () => {
  const browser = await puppeteer.launch({
      defaultViewport: {width: 1920, height: 1080}
  });
  const page = await browser.newPage();
  await page.goto('https://techoverflow.net', {waitUntil: 'domcontentloaded'});
  // Make a screenshot
  await page.screenshot({path: 'screenshot.png'});
  await browser.close();
})();

 

Posted by Uli Köhler in Javascript, Puppeteer

How to set screenshot size in Puppeteer?

Problem:

You are trying to make a screenshot using Puppeteer like this:

await page.screenshot({path: 'screenshot.png'});

but the screenshot is always 800×600 pixels. How can you increase the size of the screenshot?

Solution:

You can’t set the size for the screenshot, you need to set the size for the viewport in puppeteer.launch:

const browser = await puppeteer.launch({
    defaultViewport: {width: 1920, height: 1080}
});

Full example to produce a 1920x1080 screenshot:

const puppeteer = require('puppeteer');

(async () => {
  const browser = await puppeteer.launch({
      defaultViewport: {width: 1920, height: 1080}
  });
  const page = await browser.newPage();
  await page.goto('https://techoverflow.net', {waitUntil: 'domcontentloaded'});
  // Wait until page has loaded completely
  // Make a screenshot
  await page.screenshot({path: 'screenshot.png'});

  await browser.close();
})();

 

Posted by Uli Köhler in Javascript, Puppeteer

Puppeteer minimal example

You can use this example as a starting point for your puppeteer application.

// Minimal puppeteer example
const puppeteer = require('puppeteer');

(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  await page.goto('https://techoverflow.net', {waitUntil: 'domcontentloaded'});
  //
  // YOUR CODE GOES HERE!
  //
  await browser.close();
})();

The screenshot is 800x600px by default and could look like this:

Posted by Uli Köhler in Javascript, NodeJS, Puppeteer

How to intercept AJAX JSON response in Pyppeteer

This example shows you how to intercept and print the content of a JSON response requested via any AJAX request on a web page by using Pyppeteer:

import asyncio
import json
from pyppeteer import launch

async def intercept_network_response(response):
    # In this example, we care only about responses returning JSONs
    if "application/json" in response.headers.get("content-type", ""):
        # Print some info about the responses
        print("URL:", response.url)
        print("Method:", response.request.method)
        print("Response headers:", response.headers)
        print("Request Headers:", response.request.headers)
        print("Response status:", response.status)
        # Print the content of the response
        try:
            # await response.json() returns the response as Python object
            print("Content: ", await response.json())
        except json.decoder.JSONDecodeError:
            # NOTE: Use await response.text() if you want to get raw response text
            print("Failed to decode JSON from", await response.text())

async def main():
    browser = await launch()
    page = await browser.newPage()
    
    page.on('response', intercept_network_response)
            
    await page.goto('https://instagram.com')
    await browser.close()

asyncio.get_event_loop().run_until_complete(main())
Posted by Uli Köhler in Puppeteer, Python

Pyppetteer minimal network response interception example

Using Javascript (puppeteer)? Check out Minimal puppeteer response interception example

This example shows you how to intercept network responses in pyppeteer.

Note: This intercepts the response, not the request! This means you can abort the request before it is actually sent to the server, but you can’t read the content of the response! See Pyppetteer minimal network request interception example for an example on how to intercept requests.

import asyncio
from pyppeteer import launch

async def intercept_network_response(response):
    # In this example, we only care about HTML responses!
    if "text/html" in response.headers.get("content-type", ""):
        # Print some info about the responses
        print("URL:", response.url)
        print("Method:", response.request.method)
        print("Response headers:", response.headers)
        print("Request Headers:", response.request.headers)
        print("Response status:", response.status)
        # Print the content of the response
        print("Content: ", await response.text())
        # NOTE: Use await response.json() if you want to get the JSON directly

async def main():
    browser = await launch()
    page = await browser.newPage()
    
    page.on('response', intercept_network_response)
            
    await page.goto('https://techoverflow.net')
    await browser.close()

asyncio.get_event_loop().run_until_complete(main())

 

Posted by Uli Köhler in Puppeteer, Python