ESP8266与Arduino Uno的SoftwareSerial通信POST请求失败问题

Hey Raphael, let's break down the two key problems you're facing: partial postRequest output in the Serial Monitor and the persistent "ESP8266 is not listening for incoming data" error. These issues are likely tied to how you're constructing your request string and handling SoftwareSerial communication with the ESP8266. Here's how to fix them:

1. Fix the postRequest Construction #

Your one-line string concatenation is error-prone and can cause unexpected truncation or formatting issues. Let's split it into manageable chunks for clarity and reliability:

void httppost(){
  // Build the POST request step-by-step to avoid formatting errors
  String postRequest = "POST " + uri + " HTTP/1.1\r\n";
  postRequest += "Host: " + server + ":" + port + "\r\n";
  postRequest += "Accept: */*\r\n"; // Simplify this line instead of splitting */*
  postRequest += "Content-Length: " + String(data.length()) + "\r\n";
  postRequest += "Content-Type: application/x-www-form-urlencoded\r\n";
  postRequest += "\r\n"; // Blank line separating headers from body
  postRequest += data + "\r\n";

  // Debug: Print full request and its length to verify
  Serial.println("=== Full POST Request ===");
  Serial.println(postRequest);
  Serial.println("Request byte length: " + String(postRequest.length()));
  Serial.println("=========================");

Key Improvements: #

• Splitting the request into lines makes it easier to spot typos (like incorrect header formatting).
• The Accept: */* header is now a single string instead of concatenated parts, eliminating potential whitespace issues.
• Adding a debug print of the request length ensures you're sending the correct value in AT+CIPSEND.

2. Fix the "Not Listening" Error #

The root cause here is almost certainly a mismatch between what you're searching for (>) and what the ESP8266 actually sends (> , with a trailing space). Additionally, SoftwareSerial's default buffer size (64 bytes) can truncate long requests, causing unexpected behavior.

Update the ESP8266 Response Handling #

Modify the code after sending AT+CIPSEND to look for the correct prompt, and add debug output to see what the ESP8266 is actually returning:

String tcpStart = "AT+CIPSTART=\"TCP\",\"" + server + "\"," + port; // Port doesn't need quotes if it's an integer
  esp.println(tcpStart);
  delay(1000); // Reduce delay from 3000ms - 1s is sufficient for most cases

  if(esp.find("OK")){
    Serial.println("TCP connection OK");
    String sendCmd = "AT+CIPSEND=" + String(postRequest.length());
    esp.println(sendCmd);
    delay(1000);

    // Look for the correct ESP8266 prompt ("> " with space)
    if(esp.find("> ")){
      Serial.println("Sending data");
      esp.print(postRequest); // Use print() instead of println() - your request already ends with \r\n
      delay(1000);

      if(esp.find("SEND OK")){
        Serial.println("Packet sent");
        // Print the full HTTP response from your API
        Serial.println("=== API Response ===");
        while(esp.available()){
          Serial.write(esp.read());
        }
        Serial.println("\n===================");
        esp.println("AT+CIPCLOSE");
      }else{
        Serial.println("--> An error occurred while sending packet");
      }
    }else{
      Serial.println("--> ESP8266 is not listening for incoming data");
      // Debug: Print all unread ESP8266 output to diagnose the issue
      Serial.println("ESP8266 response after CIPSEND:");
      while(esp.available()){
        Serial.write(esp.read());
      }
      Serial.println();
    }
  }else{
    Serial.println("--> Cannot initiate TCP connection");
    // Debug: Print ESP8266's error response
    Serial.println("ESP8266 response after CIPSTART:");
    while(esp.available()){
      Serial.write(esp.read());
    }
    Serial.println();
  }
}

Increase SoftwareSerial Buffer Size #

If your postRequest is longer than 64 bytes, SoftwareSerial will truncate it. Initialize the SoftwareSerial with a larger buffer in your setup():

#include <SoftwareSerial.h>
SoftwareSerial esp(2, 3); // RX pin 2, TX pin 3

void setup() {
  Serial.begin(9600);
  // Initialize SoftwareSerial with 256-byte send/receive buffers
  esp.begin(115200, SWSERIAL_8N1, 2, 3, false, 256, 256);
  // Rest of your setup code...
}

Final Notes #

• The debug prints added in error branches will help you see exactly what the ESP8266 is returning, which is critical for diagnosing edge cases.
• Using esp.print() instead of esp.println() for the POST request avoids adding an extra newline that could break your API's parsing.

These changes should resolve both the truncated request output and the "not listening" error. Let me know if you need further tweaks based on the debug output!

内容的提问来源于stack exchange，提问作者Raphael