HTTP requests from Arduino - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to include the library needed for HTTP requests.

Arduino

#include <[1]>

void setup() {
  Serial.begin(9600);
}

Drag options to blanks, or click blank then click option'

AWire.h

BWiFi.h

CSPI.h

DHTTPClient.h

Attempts:

3 left

💡 Hint

Common Mistakes

Including WiFi.h instead of HTTPClient.h

Forgetting to include any HTTP-related library

The HTTPClient.h library is needed to make HTTP requests from Arduino.

2fill in blank

medium

Complete the code to start an HTTP GET request to the URL.

Arduino

HTTPClient http;
http.begin("[1]");
int httpCode = http.GET();

Drag options to blanks, or click blank then click option'

ASerial.begin(9600)

Bhttp://example.com

Cdelay(1000)

DWiFi.begin()

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a function call instead of a URL string

Forgetting to put the URL in quotes

The http.begin() function needs the URL string to start the HTTP request.

3fill in blank

hard

Fix the error in reading the HTTP response payload.

Arduino

if (httpCode > 0) {
  String payload = http.[1]();
  Serial.println(payload);
}

Drag options to blanks, or click blank then click option'

AgetResponse

BreadPayload

CgetString

DreadString

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-existent function like getResponse()

Using readString() which is not part of HTTPClient

The correct function to get the response body as a string is getString().

4fill in blank

hard

Fill both blanks to properly close the HTTP connection and free resources.

Arduino

http.[1]();
http.[2]();

Drag options to blanks, or click blank then click option'

Aend

Bclose

Cdisconnect

Dstop

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'close' or 'stop' which are not functions of HTTPClient

Not calling end() to free resources

The end() function closes the connection and frees resources. It should be called once after the request.

5fill in blank

hard

Fill all three blanks to create a dictionary of HTTP headers and print a specific header value.

Arduino

http.begin("http://example.com");
http.addHeader([1], [2]);
String headerValue = http.header([3]);
Serial.println(headerValue);

Drag options to blanks, or click blank then click option'

A"Content-Type"

B"application/json"

D"Authorization"

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong header keys or values

Mixing up the order of key and value in addHeader

You add a header with key "Content-Type" and value "application/json". Then you get the header value by key "Content-Type".

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