Bash HTTP image receiver server curl 55 broken pipe error

Question

I'm new to writing bash scripts and mostly using chatgpt to get templates right now. I am trying to create a simple netcat based http server which receives and stores .png files. I have a second script intended to test this and it is currently sending a broken pipe error. I don't entirely know what that means in this context since I'm not really sending data over a network. Any insight appreciated. Not new to programming but new to bash/networking/web dev.

Test script terminal output:

Sending PUT request to http://127.0.0.1:1881...
*   Trying 127.0.0.1:1881...
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0* Connected to 127.0.0.1 (127.0.0.1) port 1881 (#0)
 
PUT /test_image.png HTTP/1.1

Host: 127.0.0.1:1881

User-Agent: curl/7.81.0

Accept: */*

Content-Length: 16074

Expect: 100-continue

* Mark bundle as not supporting multiuse

HTTP/1.1 100-continue 
* Send failure: Broken pipe
  0 16074    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
* Closing connection 0

curl: (55) Send failure: Broken pipe

Test Script:

#!/bin/bash

# Define the server address and port
SERVER_ADDRESS="127.0.0.1"
SERVER_PORT=1881

# File to send
TEST_FILE="test_image.png"

# Check if the test file exists
if [[ ! -f "$TEST_FILE" ]]; then
  echo "Test file '$TEST_FILE' does not exist. Creating a dummy file..."
  echo "This is a test file." > "$TEST_FILE"
fi

# Use curl to send a PUT request with the --upload-file option
echo "Sending PUT request to http://$SERVER_ADDRESS:$SERVER_PORT..."
RESPONSE=$(curl -v http://$SERVER_ADDRESS:$SERVER_PORT --upload-file $TEST_FILE)
# Check the HTTP response code
if [[ "$RESPONSE" == "200" ]]; then
  echo "PUT request was successful. Server returned HTTP 200 OK."
else
  echo "PUT request failed. Server returned HTTP $RESPONSE."
fi

Server Script:

#!/bin/bash

# Define the IP address and port for the HTTP server
IP_ADDRESS="127.0.0.1"
PORT=1881

# Directory to store received data
UPLOAD_DIR="Data"


# Start the HTTP server using netcat
echo "Starting HTTP server on $IP_ADDRESS:$PORT..."
while :
do
  echo -e "HTTP/1.1 100-continue \r\n" | nc -l -s $IP_ADDRESS -p $PORT -q 1 > request.txt
 

    # Generate a timestamp-based file name
    TIMESTAMP=$(date +"%Y%m%d%H%M%S")
    OUTPUT_FILE_PATH="$UPLOAD_DIR/received_$TIMESTAMP.png"

    # Save the received data to the defined output file path
    sed -n '/\r\n\r\n/{n;p;}' request.txt > "$OUTPUT_FILE_PATH"
    echo "Received PUT data saved to $OUTPUT_FILE_PATH"
  

done

Answer 1

For the netcat server, I started with:

while true; do (echo -ne "HTTP/1.1 200 OK\r\nContent-Length: 0\r\n\r\n" && cat | tee $(date +"%Y%m%d%H%M%S").png) | nc -l -p 1881; done

I used this curl command to test:

curl -X POST --data-binary @your_image.png http://localhost:1881

At first glance, it appeared to succeed, but then I noticed the file was 0 bytes.

I tried and tried to get nc to output to a file and it just wouldn't do it. I now understand your frustrations.

#!/bin/bash

while true; do
  filename="$(date +"%Y%m%d%H%M%S").png"

  # Listen (-l), close idle @ 100ms (-i .1), wait avoids truncation (-w 2)
  nc -l -i .1 -w 2 -p 1881 | {

  echo -ne "HTTP/1.1 200 OK\r\nContent-Type: image/png\r\n\r\n"

  # Strip curl's response headers from output
  sed -e '1,7d' > ./"$filename"
  }
done

This script, with the same curl command, should do the trick.