I want to extract the data of the body of a POST request from the browser to a Bash server with Ncat using only Bash Scripting, I have tried AI tools and searched and tried for days but I can't access the data, I am new to Bash Scripting.
Most of the time the browser and the server freeze probably due to an infinite loop or problem in the htttp response despite the presence of both in the code.
I would really appreciate if you can demonstrate with a code block on how to extract all the data needed from a POST request coming from the browser to a Bash Server that uses Ncat such as the http method, route, data of the body request...etc, thanks in advance.
Here is one of my many trials:
#!/bin/bash
PORT=8080
DIR="/var/www/html"
setup_nginx(){
sudo apt-get update
sudo apt-get install -y nginx
}
configure_nginx(){
cat > /etc/nginx/sites-enabled/default << EOF
server {
listen 80;
server_name localhost;
root /var/www/html;
index index.html index.htm index.nginx-debian.html;
# Timeouts
proxy_connect_timeout 60;
proxy_read_timeout 60;
proxy_send_timeout 60;
# Buffer settings
proxy_buffering off;
proxy_request_buffering off;
location / {
proxy_pass http://localhost:$PORT;
}
}
EOF
sudo nginx -t && systemctl reload nginx
}
setup_ncat(){
sudo apt-get update
sudo apt-get install -y ncat
}
create_HTML_page(){
cat > $DIR/index.html << EOF
<!DOCTYPE html>
<html>
<head>
<title>Bash Web Application</title>
</head>
<body>
<h1>Save Messages</h1>
<form action="/messages" method="POST">
<input type="text" name="message" placeholder="Enter your message">
<input type="submit" value="Submit">
</form>
<br/>
<a href="http://localhost:$PORT/messages">Messages Page</a>
<br/>
<a href="http://localhost:$PORT/deleteAll">Delete All Messages</a>
</body>
</html>
EOF
cat > $DIR/success.html << EOF
<!DOCTYPE html>
<html>
<head>
<title>Success</title>
</head>
<body>
<h1>Your operation has been done successfully</h1>
<a href="http://localhost:$PORT">Home Page</a>
<br/>
<a href="http://localhost:$PORT/messages">Messages Page</a>
<br/>
<a href="http://localhost:$PORT/deleteAll">Delete All Messages</a>
</body>
</html>
EOF
}
# File to store messages
DATA_FILE="$DIR/messages.txt"
# Ensure the data file exists
if [ ! -f "$DATA_FILE" ]; then
cd "$DIR"
touch messages.txt
fi
create_server(){
echo "Starting web server on port $PORT..."
echo "Visit http://localhost:$PORT to view the website."
while true; do
# Listen for connections and process requests
ncat -l -p $PORT -c '
DIR=/var/www/html
set -x
# Read the first line of the HTTP request (e.g., POST /endpoint HTTP/1.1)
read -r REQUEST_FIRST_LINE
METHOD=$(echo "$REQUEST_FIRST_LINE" | cut -d" " -f1)
ROUTE=$(echo "$REQUEST_FIRST_LINE" | cut -d" " -f2)
REQUEST=""
if [ "$METHOD" = "POST" ]; then
while IFS= read -r line; do
# Extract Content-Length if present
if echo "$line" | grep -q "^Content-Length:"; then
CONTENT_LENGTH=$(echo "$line" | cut -d" " -f2)
fi
line=${line%%$'\r'}
REQUEST+="$line"$'\n'
if [ "$line" = " " ]; then
# If we have Content-Length, read the body
if [ ! -z "$CONTENT_LENGTH" ]; then
# Read the POST body
body=$(dd bs=1 count=$CONTENT_LENGTH 2>/dev/null)
# Add body to complete request
REUQEST+="$body"
fi
break
fi
done
fi
# Determine which file to serve based on the requested route
case "$ROUTE" in
"/")
if [ "$METHOD" = "GET" ]; then
FILE="$DIR/index.html"
STATUS="200 OK"
fi
;;
"/messages")
if [ "$METHOD" = "GET" ]; then
FILE="$DIR/messages.txt"
STATUS="200 OK"
today=$(date +"%Y-%m-%d")
elif [ "$METHOD" = "POST" ]; then
read -r request
# data=$(echo "$request" | sed -e "s/+/ /g" -e "s/.*message=\([^&]*\).*/\1/")
data= $(echo "$request")
echo "$data" >> $DIR/messages.txt
FILE="$DIR/success.html"
STATUS="200 OK"
today=$(date +"%Y-%m-%d")
fi
;;
"/deleteAll")
if [ "$METHOD" = "GET" ]; then
> $DIR/messages.txt
FILE="$DIR/success.html"
STATUS="200 OK"
today=$(date +"%Y-%m-%d")
fi
;;
*)
FILE="templates/404.html"
STATUS="404 Not Found"
;;
esac
# Check if the requested file exists
if [ -f "$FILE" ]; then
RESPONSE_BODY=$(cat "$FILE")
RESPONSE_BODY=$(eval "echo \"$RESPONSE_BODY\"")
else
RESPONSE_BODY="<html><body><h1>404 Not Found</h1></body></html>"
fi
# Send the HTTP response headers and body
echo "HTTP/1.1 $STATUS\r"
echo "Content-Type: text/html\r"
echo "Connection: close\r"
echo "\r" # This is the required blank line separating headers from the body
echo "$RESPONSE_BODY"
'
if [[ "$?" -ne 0 ]]; then
echo "Error happened during connection";
exit 1;
fi
done
}
# handle_http_request(){
# while true; do
# echo "Listening on port $PORT..."
# # Use netcat to listen for incoming connections
# {
# # Read the request line
# read request
# log_request "$request"
# # Extract HTTP method and resource path
# method=$(echo "$request" | awk '{print $1}')
# resource=$(echo "$request" | awk '{print $2}')
# # Process GET request
# if [[ $method == "GET" ]]; then
# echo -e "HTTP/1.1 200 OK\r\nContent-Type: text/plain\r\n\r\nGET request received: $resource"
# # Process POST request
# elif [[ $method == "POST" ]]; then
# # Read Content-Length header
# while read header; do
# [[ $header == $'\r' ]] && break
# if [[ $header == Content-Length:* ]]; then
# length=${header#Content-Length: }
# fi
# done
# # Read the payload
# read -n $length payload
# echo "$payload" >> "$DATAFILE"
# echo -e "HTTP/1.1 200 OK\r\nContent-Type: text/plain\r\n\r\nPOST data saved: $payload"
# # Handle unknown methods
# else
# echo -e "HTTP/1.1 405 Method Not Allowed\r\nContent-Type: text/plain\r\n\r\nUnsupported HTTP method: $method"
# fi
# } | nc -l -p "$PORT" -q 1
# done
# }
setup(){
command -v nginx
if [[ "$?" -ne 0 ]]; then
echo "nginx is not installed, it will be installed now"
setup_nginx
fi
command -v ncat
if [[ "$?" -ne 0 ]]; then
echo "ncat is not installed, it will be installed now"
setup_ncat
fi
configure_nginx
create_HTML_page
create_server
}
setup
I tested with 2 different clients:
\r after each line)#!/bin/bash
ncat --no-shutdown localhost 8080 <<@
POST /messages HTTP/1.1
Host: example.com
Content-Type: application/json
Content-Length: 50
{
"username": "johndoe",
"password": "1234"
}
@
curl http://localhost:8080/messages -H "Content-Type: application/json" --data '{"username": "johndoe", "password": "1234"}'
When removing the \r fails, the first program might work while the second fails.
I tried to make minimal changes to your original script:
# Changedprintf as a replacement for the echo commands.The script in the ncat part is not bash, some commands are not available.
When you write line=${line%%$'\r'}, the first single quote matches the opening quote in ncat -l -p $PORT -c ', so removing the \r fails
An assignment like data= $(echo "$request") won't work because of the space after the =.
See the changed code beneath, and look at the lines marked with Changed.
#!/bin/bash
PORT=8080
DIR="/var/www/html"
setup_nginx(){
sudo apt-get update
sudo apt-get install -y nginx
}
configure_nginx(){
# Changed: Added sudo creating and chmodding file
sudo touch /etc/nginx/sites-enabled/default
sudo chmod 666 /etc/nginx/sites-enabled/default
cat > /etc/nginx/sites-enabled/default << EOF
server {
listen 80;
server_name localhost;
root /var/www/html;
index index.html index.htm index.nginx-debian.html;
# Timeouts
proxy_connect_timeout 60;
proxy_read_timeout 60;
proxy_send_timeout 60;
# Buffer settings
proxy_buffering off;
proxy_request_buffering off;
location / {
proxy_pass http://localhost:$PORT;
}
}
EOF
sudo nginx -t && systemctl reload nginx
}
setup_ncat(){
sudo apt-get update
sudo apt-get install -y ncat
}
create_HTML_page(){
# Changed: Added sudo
sudo touch $DIR/index.html
sudo chmod 666 $DIR/index.html
cat > $DIR/index.html << EOF
<!DOCTYPE html>
<html>
<head>
<title>Bash Web Application</title>
</head>
<body>
<h1>Save Messages</h1>
<form action="/messages" method="POST">
<input type="text" name="message" placeholder="Enter your message">
<input type="submit" value="Submit">
</form>
<br/>
<a href="http://localhost:$PORT/messages">Messages Page</a>
<br/>
<a href="http://localhost:$PORT/deleteAll">Delete All Messages</a>
</body>
</html>
EOF
# Changed: Added sudo
sudo touch $DIR/success.html
sudo chmod 666 $DIR/success.html
cat > $DIR/success.html << EOF
<!DOCTYPE html>
<html>
<head>
<title>Success</title>
</head>
<body>
<h1>Your operation has been done successfully</h1>
<a href="http://localhost:$PORT">Home Page</a>
<br/>
<a href="http://localhost:$PORT/messages">Messages Page</a>
<br/>
<a href="http://localhost:$PORT/deleteAll">Delete All Messages</a>
</body>
</html>
EOF
}
# File to store messages
DATA_FILE="$DIR/messages.txt"
# Ensure the data file exists
if [ ! -f "$DATA_FILE" ]; then
cd "$DIR"
# Changed: Added sudo
sudo touch messages.txt
fi
create_server(){
echo "Starting web server on port $PORT..."
echo "Visit http://localhost:$PORT to view the website."
while true; do
# Listen for connections and process requests
ncat -l -p $PORT -c '
DIR=/var/www/html
# Changed: removed the `set -x`, which was a good approach for debugging
# Read the first line of the HTTP request (e.g., POST /endpoint HTTP/1.1)
read -r REQUEST_FIRST_LINE
METHOD=$(echo "$REQUEST_FIRST_LINE" | cut -d" " -f1)
# Changed: Remove \r from ROUTE
ROUTE=$(echo "$REQUEST_FIRST_LINE" | cut -d" " -f2 | tr -d "\r")
REQUEST=""
if [ "$METHOD" = "POST" ]; then
while read -r line; do
# Extract Content-Length if present
if echo "$line" | grep -q "^Content-Length:"; then
# Changed: Remove \r from CONTENT_LENGTH
CONTENT_LENGTH=$(echo "$line" | cut -d" " -f2 | tr -d "\r")
fi
# Changed: delete \r without use of single quotes
line=$(echo "${line}" | tr -d "\r")
# Changed: Added debug line and commented that line.
# echo >&2 "Line: [${line}], ${#line} chars long"
# Changed: The '+=' does not work fine here
REQUEST="${REQUEST}${line}\n"
# Changed: Do not compare $line with a space, it should be empty
if [ -z "$line" ]; then
# If we have Content-Length, read the body
if [ ! -z "$CONTENT_LENGTH" ]; then
# Read the POST body
body=$(dd bs=1 count=$CONTENT_LENGTH 2>/dev/null)
# Changed: Debug show body
echo >&2 "Body=[$body]"
# Add body to complete request
# Changed: Typo REUQEST changed in REQUEST and replaced += operator
REQUEST="${REQUEST}${body}\n"
fi
# Changed: Added indent
break
fi
done
fi
# Changed: write $REQUEST (never used) to console
echo >&2 "Request:\n${REQUEST}"
# Determine which file to serve based on the requested route
case "$ROUTE" in
"/")
if [ "$METHOD" = "GET" ]; then
FILE="$DIR/index.html"
STATUS="200 OK"
fi
;;
"/messages")
if [ "$METHOD" = "GET" ]; then
FILE="$DIR/messages.txt"
STATUS="200 OK"
today=$(date +"%Y-%m-%d")
elif [ "$METHOD" = "POST" ]; then
# Changed: Replaced "read -r request" and assigning $request to $data with data=${body}
data="${body}"
# data=$(echo "$request" | sed -e "s/+/ /g" -e "s/.*message=\([^&]*\).*/\1/")
echo "$data" >> $DIR/messages.txt
FILE="$DIR/success.html"
STATUS="200 OK"
today=$(date +"%Y-%m-%d")
fi
;;
"/deleteAll")
if [ "$METHOD" = "GET" ]; then
> $DIR/messages.txt
FILE="$DIR/success.html"
STATUS="200 OK"
today=$(date +"%Y-%m-%d")
fi
;;
*)
FILE="templates/404.html"
STATUS="404 Not Found"
;;
esac
# Check if the requested file exists
if [ -f "$FILE" ]; then
RESPONSE_BODY=$(cat "$FILE")
RESPONSE_BODY=$(eval "echo \"$RESPONSE_BODY\"")
else
RESPONSE_BODY="<html><body><h1>404 Not Found</h1></body></html>"
fi
# Send the HTTP response headers and body
# Changed: added next comment
# When you dont want \n in the output, use printf
echo "HTTP/1.1 $STATUS\r"
echo "Content-Type: text/html\r"
echo "Connection: close\r"
# Changed: added content-length
echo "Content-Length: ${#RESPONSE_BODY}\r"
echo "\r" # This is the required blank line separating headers from the body
echo "$RESPONSE_BODY"
'
if [[ "$?" -ne 0 ]]; then
echo "Error happened during connection";
exit 1;
fi
done
}
# handle_http_request(){
# while true; do
# echo "Listening on port $PORT..."
# # Use netcat to listen for incoming connections
# {
# # Read the request line
# read request
# log_request "$request"
# # Extract HTTP method and resource path
# method=$(echo "$request" | awk '{print $1}')
# resource=$(echo "$request" | awk '{print $2}')
# # Process GET request
# if [[ $method == "GET" ]]; then
# echo -e "HTTP/1.1 200 OK\r\nContent-Type: text/plain\r\n\r\nGET request received: $resource"
# # Process POST request
# elif [[ $method == "POST" ]]; then
# # Read Content-Length header
# while read header; do
# [[ $header == $'\r' ]] && break
# if [[ $header == Content-Length:* ]]; then
# length=${header#Content-Length: }
# fi
# done
# # Read the payload
# read -n $length payload
# echo "$payload" >> "$DATAFILE"
# echo -e "HTTP/1.1 200 OK\r\nContent-Type: text/plain\r\n\r\nPOST data saved: $payload"
# # Handle unknown methods
# else
# echo -e "HTTP/1.1 405 Method Not Allowed\r\nContent-Type: text/plain\r\n\r\nUnsupported HTTP method: $method"
# fi
# } | nc -l -p "$PORT" -q 1
# done
# }
setup(){
command -v nginx
if [[ "$?" -ne 0 ]]; then
echo "nginx is not installed, it will be installed now"
setup_nginx
fi
command -v ncat
if [[ "$?" -ne 0 ]]; then
echo "ncat is not installed, it will be installed now"
setup_ncat
fi
configure_nginx
create_HTML_page
create_server
}
setup
Result:
curl http://localhost:8080/messages -H "Content-Type: application/json" --data '{"username": "johndoe", "password": "1234"}'
<!DOCTYPE html>
<html>
<head>
<title>Success</title>
</head>
<body>
<h1>Your operation has been done successfully</h1>
<a href=http://localhost:8080>Home Page</a>
<br/>
<a href=http://localhost:8080/messages>Messages Page</a>
<br/>
<a href=http://localhost:8080/deleteAll>Delete All Messages</a>
</body>
</html>