使用 curl 实现 MQTT 通信：通过 MQTT/TLS 进行安全连接、发布与订阅

curl --version

curl 8.19.0-DEV (aarch64-apple-darwin25.2.0) libcurl/8.19.0-DEV OpenSSL/3.6.0 zlib/1.2.12 brotli/1.2.0 zstd/1.5.7 AppleIDN libssh2/1.11.1 nghttp2/1.68.0 ngtcp2/1.20.0 nghttp3/1.15.0 librtmp/2.3 mit-krb5/1.7-prerelease OpenLDAP/2.4.28/Apple
Release-Date: [unreleased]
Protocols: dict file ftp ftps gopher gophers http https imap imaps ipfs ipns ldap ldaps mqtt mqtts pop3 pop3s rtmp rtsp scp sftp smb smbs smtp smtps telnet tftp ws wss
Features: alt-svc AppleSecTrust AsynchDNS brotli GSS-API HSTS HTTP2 HTTP3 HTTPS-proxy IDN IPv6 Kerberos Largefile libz NTLM SPNEGO SSL threadsafe TLS-SRP UnixSockets zstd

mqtt[s]://[user:password@]broker[:port]/topic

[2 bytes: topic length (big-endian)] [topic string] [payload]

00 09 c u r l / t e s t h e l l o
└─┬─┘ └───────┬───────┘ └───┬───┘
  │           │             │
  │           │             └── payload (no length prefix)
  │           └── topic: "curl/test" (9 bytes)
  └── topic length: 9 (0x0009)

curl/testhello

# Subscribe to the "curl/test" topic on the public EMQX broker
curl -N mqtt://broker.emqx.io/curl/test --output messages.bin

# Subscribe over TLS
curl -N mqtts://broker.emqx.io/curl/test --output messages.bin

# Replace with your actual credentials curl -N -u "your-username:your-password" mqtts://your-broker.emqxsl.com/curl/test --output messages.bin

curl -sN mqtt://broker.emqx.io/curl/test | \
  while IFS= read -r -d $'\0' d; \
    do \
      [ -n "$d" ] && \
        l=$(printf "%d" "'${d:0:1}") && \
        echo "[${d:1:$l}] ${d:1+$l}"; \
    done

# Save raw output to file (Ctrl+C to stop)
curl -sN mqtt://broker.emqx.io/curl/test > messages.bin

# View with hexdump to see the structure
hexdump -C messages.bin

mqtt_subscribe() {
  curl -sN "$1" | while IFS= read -r -d $'\0' d; do
    [ -n "$d" ] && l=$(printf "%d" "'${d:0:1}") && echo "[${d:1:$l}] ${d:1+$l}"
  done
}

# Usage
mqtt_subscribe "mqtt://broker.emqx.io/curl/test"

# Publish "Hello from curl" to the "curl/test" topic
curl -v -d "Hello from curl" mqtt://broker.emqx.io/curl/test

# Publish over TLS
curl -v -d "Secure message from curl" mqtts://broker.emqx.io/curl/test

# Publish a JSON temperature reading
curl -v -d '{"sensor_id": "temp-001", "value": 23.5, "unit": "celsius"}' \
  mqtt://broker.emqx.io/sensors/temperature

curl -v -u "your-username:your-password" \
  -d '{"status": "online", "timestamp": 1706000000}' \
  mqtts://your-broker.emqxsl.com/devices/status

# With CA certificate verification
curl --cacert /etc/ssl/certs/emqx-ca.crt \
  -d "Verified secure message" \
  mqtts://your-broker.emqxsl.com/secure/topic

# With mutual TLS (mTLS) client authentication
curl --cacert /etc/ssl/certs/ca.crt \
  --cert /etc/ssl/certs/client.crt \
  --key /etc/ssl/private/client.key \
  -d "mTLS authenticated message" \
  mqtts://your-broker.emqxsl.com/secure/topic

curl -v mqtt://broker.emqx.io/test

curl -v mqtt://broker.emqx.io:1883/curl/test
* Host broker.emqx.io:1883 was resolved.
* IPv6: (none)
* IPv4: 34.243.217.54, 35.172.255.228, 44.232.241.40
*   Trying 34.243.217.54:1883...
* Connected to broker.emqx.io (34.243.217.54) port 1883
* Using client id 'curlblZBtS6c'
> MQTT<
       curlblZBtS6cmqtt_doing: state [0]

#!/bin/bash
# simulate-sensor.sh

BROKER="mqtt://broker.emqx.io"
TOPIC="sensors/room1/temperature"

while true; do
  # Generate random temperature between 20-30°C
  TEMP=$(awk -v min=20 -v max=30 'BEGIN{srand(); print min+rand()*(max-min)}')
  PAYLOAD="{\"temperature\": $TEMP, \"timestamp\": $(date +%s)}"
  
  curl -s -d "$PAYLOAD" "$BROKER/$TOPIC"
  echo "Published: $PAYLOAD"
  
  sleep 5
done

# Check if mqtt is listed in protocols
curl --version | grep -i protocols

# Test MQTT support explicitly
curl -V 2>&1 | grep -q mqtt && echo "MQTT supported" || echo "MQTT NOT supported"