使用AT指令请求JSON接口返回200，Arduino端获取响应不完整

问题背景 #

使用Arduino UNO搭配SIM800L模块向HTTPS接口发起GET请求，接口返回状态码200，但Arduino终端仅能获取部分JSON响应，Postman测试可完整返回响应。

原代码 #

#include <SoftwareSerial.h>

#define RX_PIN 2
#define TX_PIN 3

SoftwareSerial gsmSerial(RX_PIN, TX_PIN);

void setup() {
  Serial.begin(9600);
  gsmSerial.begin(9600);
  configureAPN();
  Serial.println("Start Actual Communication:---->");

  // Additional setup code for your SIM800L module, if required
  // Ensure that the SIM800L module is configured and connected to the network
}

void loop() {
  // Make HTTP GET request to the specified API endpoint

  another_function("https://just_normal_server.com/user/heartbeat");

  // Adjust the delay based on your application requirements
  delay(2000);
}



void another_function(String url) {
  // Buffer to store the HTTP response data
  char buffer[512];
  int index = 0;

  // Helper function to read and append data to the buffer
  auto readAndAppendToBuffer = [&buffer, &index](int timeout) {
    long startTime = millis();
    while (millis() - startTime < timeout && gsmSerial.available()) {
      char c = gsmSerial.read();
      buffer[index++] = c;
      // Add additional conditions for handling specific characters or patterns if needed
    }
  };

  gsmSerial.println("AT+HTTPINIT");
  delay(1000);
  Serial.println("HTTP INITIALIZATION: " + get_data());

  gsmSerial.println("AT+HTTPPARA=\"CID\",1");
  delay(1000);
  Serial.println("CID PARA: " + get_data());

  gsmSerial.println("AT+HTTPPARA=\"URL\",\"" + url + "\"");
  delay(2000);
  Serial.println("URL Called: " + get_data());

  gsmSerial.println("\"CONTENT\",\"application/json\"");
  delay(2000);
  Serial.println("JSON PARA: " + get_data());

  gsmSerial.println("AT+HTTPPARA=\"REDIR\",1");
  delay(1000);
  Serial.println("REDIR PARA: " + get_data());

  gsmSerial.println("AT+HTTPSSL=1");
  delay(10000);
  Serial.println("SSL PARA: " + get_data());

  gsmSerial.println("AT+HTTPACTION=0");
  delay(10000);
  Serial.println("HTTP ACTION: " + get_data());

  gsmSerial.println("AT+HTTPREAD");
  delay(10000);
  Serial.println("HTTP Read DATA: " + get_data());
  /*
  readAndAppendToBuffer(30000);  // Adjust the timeout based on your server's response time

  // Null-terminate the buffer
  buffer[index] = '\0';

  // Print the entire response data
  Serial.println(buffer);
  */

  gsmSerial.println("AT+HTTPTERM");
  delay(1000);
  Serial.println("HTTP Termination: " + get_data());
}


String get_data() {
  String response = "";  // Initialize an empty string

  while (gsmSerial.available() > 0) {
    char character = gsmSerial.read();
    response += character;  // Append the character to the string
  }

  return response;
}


void configureAPN() {
  gsmSerial.println("AT+SAPBR=3,1,\"CONTYPE\",\"GPRS\"\r");
  delay(1000);
  Serial.println("APN-1: " + get_data());
  gsmSerial.println("AT+SAPBR=3,1,\"APN\",\"airtelgprs.com\"\r");
  delay(1000);
  Serial.println("APN-2: " + get_data());
  gsmSerial.println("AT+SAPBR=1,1\r");
  delay(1000);
  Serial.println("APN-3: " + get_data());
}

实际获取的响应 #

HTTP ACTION: AT+HTTPACTION=0

OK

+HTTPACTION: 0,200,57

HTTP Read DATA: AT+HTTPREAD

+HTTPREAD: 57
{"status":"alive","timestamp":"202
HTTP Termination: AT+HTTPTERM

OK

解决方案 #

1. 修复get_data()的读取逻辑 #

当前get_data()仅读取调用瞬间串口缓冲区的可用数据，SIM800L的响应是分批次发送的，需要添加超时等待，确保读取完所有响应内容。修改后的函数如下：

String get_data() {
  String response = "";
  long timeout = millis() + 1000; // 1秒超时，可根据网络情况调整
  while (millis() < timeout) {
    while (gsmSerial.available() > 0) {
      char character = gsmSerial.read();
      response += character;
      timeout = millis() + 1000; // 每次收到数据就重置超时
    }
  }
  return response;
}

2. 修正无效的AT指令 #

原代码中gsmSerial.println("\"CONTENT\",\"application/json\"");是错误的，缺少AT+HTTPPARA前缀，属于无效指令，会导致模块无法正确识别请求格式。应修改为：

gsmSerial.println("AT+HTTPPARA=\"CONTENT\",\"application/json\"");

3. 优化AT+HTTPREAD后的读取流程 #

去掉固定的delay(10000)，依赖修改后的get_data()超时读取，确保完整获取响应。也可以取消注释原代码中readAndAppendToBuffer相关逻辑，直接用缓冲区存储响应，但需注意避免缓冲区溢出。

4. 调整超时参数 #

根据网络状况调整AT+HTTPSSL=1、AT+HTTPACTION=0后的延迟时间，确保模块完成SSL握手和请求发送。如果网络较慢，可适当延长延迟，比如将delay(10000)调整为delay(15000)。

验证修改效果 #

修改后重新上传代码，终端应能完整输出JSON响应，示例如下：

HTTP Read DATA: AT+HTTPREAD

+HTTPREAD: 57
{"status":"alive","timestamp":"2024-05-20T12:34:56Z"}

OK

内容的提问来源于stack exchange，提问作者Dheeraj SmartIam