HTTP requests from Arduino - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of making HTTP requests from an Arduino?

To communicate with web servers or online services by sending or receiving data over the internet.

beginner

Which Arduino library is commonly used to make HTTP requests over WiFi?

The WiFiClient library combined with HTTPClient is commonly used for HTTP requests on WiFi-enabled Arduino boards.

intermediate

What is the basic sequence to perform an HTTP GET request on Arduino?

1. Connect to WiFi network.
2. Create an HTTPClient object.
3. Begin the request with the URL.
4. Send the GET request.
5. Read the response.
6. End the connection.

intermediate

Why is it important to call http.end() after an HTTP request?

Calling http.end() frees resources and closes the connection properly to avoid memory leaks and connection issues.

beginner

What is the difference between HTTP GET and POST requests on Arduino?

GET requests retrieve data from a server, while POST requests send data to the server, often used to submit form data or update information.

Which Arduino library helps you make HTTP requests over WiFi?

A HTTPClient

B Servo

C Wire

D SPI

HTTPClient is designed for making HTTP requests, while Servo, Wire, and SPI are for other hardware functions.

What function do you use to start an HTTP request with a URL in Arduino's HTTPClient?

A http.begin(url)

B http.start(url)

C http.open(url)

D http.connect(url)

The correct method to initialize the HTTP request is http.begin(url).

After sending an HTTP request, which function reads the response code?

A http.get()

B http.GET()

C http.getResponse()

D http.responseCode()

The http.GET() function sends the GET request and returns the response code.

Why should you call http.end() after an HTTP request?

A To start a new request

B To reset the Arduino board

C To free resources and close the connection

D To send data to the server

http.end() cleans up and closes the connection to avoid memory leaks.

Which HTTP method is used to send data to a server from Arduino?

A PUT

B GET

C DELETE

D POST

POST is used to send data to the server, while GET is for retrieving data.

Explain the steps to perform an HTTP GET request from an Arduino board.

Think about how you connect, ask for data, and then close the connection.

Describe the difference between HTTP GET and POST requests when used on Arduino.

One asks for information, the other sends information.

Practice

1. What is the main purpose of using HTTPClient in Arduino sketches?

easy

A. To control digital pins

B. To connect to WiFi networks

C. To read analog sensor values

D. To send and receive HTTP requests easily

Solution

1. Step 1: Understand the role of HTTPClient

   The HTTPClient library is designed to simplify sending HTTP requests like GET and POST from Arduino.

2. Step 2: Differentiate from other libraries

   Connecting to WiFi is done by WiFiClient, not HTTPClient. Reading sensors or controlling pins is unrelated.

3. Final Answer:

   To send and receive HTTP requests easily -> Option D

4. Quick Check:

   HTTPClient = HTTP requests [OK]

Hint: HTTPClient handles web requests, not WiFi or sensors [OK]

Common Mistakes:

• Confusing HTTPClient with WiFi connection library
• Thinking HTTPClient reads sensors
• Assuming HTTPClient controls pins

2. Which of the following is the correct way to start a GET request using HTTPClient in Arduino?

easy

A. http.connect("http://example.com");

B. http.startGET("http://example.com");

C. http.begin("http://example.com");

D. http.open("http://example.com");

Solution

1. Step 1: Recall HTTPClient method for starting requests

   The correct method to initialize a request is begin() with the URL as argument.

2. Step 2: Check other options

   Methods like connect(), startGET(), or open() do not exist in HTTPClient library.

3. Final Answer:

   http.begin("http://example.com"); -> Option C

4. Quick Check:

   Use begin() to start HTTP request [OK]

Hint: Use begin() to start HTTP requests in Arduino [OK]

Common Mistakes:

• Using non-existent methods like connect() or open()
• Confusing begin() with WiFi connection functions
• Forgetting to pass the URL string

3. What will the following Arduino code print if the HTTP GET request to http://example.com/data returns status 200 and body "OK"?

HTTPClient http;
http.begin("http://example.com/data");
int httpCode = http.GET();
if (httpCode > 0) {
  String payload = http.getString();
  Serial.println(httpCode);
  Serial.println(payload);
} else {
  Serial.println("Error");
}
http.end();

medium

A. 200
OK

B. Error

C. 404
Not Found

D. 0

Solution

1. Step 1: Analyze the HTTP GET response code

   The code checks if httpCode > 0. Since the server returns 200, this condition is true.

2. Step 2: Print status code and response body

   The code prints the status code (200) and then the response body ("OK") on separate lines.

3. Final Answer:

   200 OK -> Option A

4. Quick Check:

   200 status means success, prints code and body [OK]

Hint: Status > 0 means success; print code and body [OK]

Common Mistakes:

• Assuming error when status is 200
• Confusing status code with response body
• Not calling http.end() to close connection

4. Identify the error in this Arduino code snippet for sending a POST request:

HTTPClient http;
http.begin("http://example.com/api");
http.addHeader("Content-Type", "application/json");
int httpCode = http.POST("{\"value\": 42}");
if (httpCode == 200) {
  Serial.println("Success");
}
http.end();

medium

A. Incorrect header name; should be "ContentType"

B. Missing WiFi connection before HTTPClient usage

C. POST method requires no argument

D. http.end() should be called before POST

Solution

1. Step 1: Check prerequisites for HTTP requests

   Before using HTTPClient, Arduino must be connected to WiFi. This code snippet does not show WiFi connection setup.

2. Step 2: Validate headers and method usage

   Header name "Content-Type" is correct, POST accepts a string argument, and http.end() is correctly called after POST.

3. Final Answer:

   Missing WiFi connection before HTTPClient usage -> Option B

4. Quick Check:

   WiFi must connect before HTTPClient [OK]

Hint: Always connect WiFi before HTTP requests [OK]

Common Mistakes:

• Skipping WiFi connection setup
• Using wrong header names
• Calling http.end() too early

5. You want to send sensor data as JSON to a server using Arduino's HTTPClient. Which sequence correctly sends a POST request with JSON data and handles the response?

hard

A. Connect WiFi -> http.begin(url) -> http.addHeader("Content-Type", "application/json") -> http.POST(jsonData) -> check httpCode -> http.end()

B. http.begin(url) -> http.POST(jsonData) -> http.addHeader("Content-Type", "application/json") -> check httpCode -> http.end()

C. Connect WiFi -> http.POST(jsonData) -> http.begin(url) -> http.addHeader("Content-Type", "application/json") -> check httpCode -> http.end()

D. Connect WiFi -> http.addHeader("Content-Type", "application/json") -> http.begin(url) -> http.POST(jsonData) -> check httpCode -> http.end()

Solution

1. Step 1: Establish WiFi connection first

   Arduino must connect to WiFi before making HTTP requests.

2. Step 2: Follow correct HTTPClient method order

   Start with http.begin(url), then set headers, then send POST with data, check response code, and finally call http.end().

3. Final Answer:

   Connect WiFi -> http.begin(url) -> http.addHeader("Content-Type", "application/json") -> http.POST(jsonData) -> check httpCode -> http.end() -> Option A

4. Quick Check:

   WiFi -> begin() -> headers -> POST -> end() [OK]

Hint: Connect WiFi first, then begin(), addHeader(), POST, end() [OK]

Common Mistakes:

• Calling POST before begin()
• Adding headers after POST
• Skipping WiFi connection