Is there an upper limit on how many characters you can send at a time with client.print()?
I am seeing some problems when I sent a string 112 bytes long, problem when I send a string 100 bytes long, but no problem with 89 byte long string.
Then I cut the long string in half and did two client.print() and no more problem. What is the maximal length then? Thanks.
Yes, there is an upper limit, but you are not even close. The max you can send at a time is about 1400 characters, but most Arduinos do not have enough SRAM for a buffer that big. If you try that with an Uno, you would run out of SRAM.
edit: This applies to the ethernet shield. I don't know about the Wifi shield. I have sent 500 characters at a time with my Mega/ethernet shield, but the code would not run on an Uno due to SRAM limitations.
Thanks SurferTim. I am using a MEGA so memory should not be the problem. I will also check with the web master for more clues. I suppose the lower layer SPI functions might have limit on max length?! But I client.write somehow fragments the packet as needed?
Maybe if you post your code, it will help me or someone else see the problem.
SurferTim,
Thanks for your help. Here is the code that sends the packet to the server:
Original code that stops working (returning 0) when the string becomes too long (100 bytes is too long, 90 is not. I wasn't patient enough to find the exact limit)
int SendPacket(char* buffer)
{
unsigned long connect_time;
if (client.connect(server, 1035))
{
connect_time=millis();
Debug->println("Connected to server");
client.println(buffer);
}
else return 0;
while (!client.available())
{
if (millis()-connect_time>server_response_time)
{
client.stop();
return 0;
}
}
return client.read();
}
Modified code that does multiple client.println(), which works. In this code, the caller needs to intentionally insert separators (I chose '~') within the long string so this function will replace them with '\0' (fragment the long message) and send the long message one fragment at a time.
int SendPacket(char* buffer)
{
int nptr=1,i=0;
int ptrs[10];
ptrs[0]=0;
unsigned long connect_time;
if (client.connect(server, 1035))
{
connect_time=millis();
Debug->println(F("Connected to server"));
while ((buffer[i]!='\0'))
{
if (buffer[i]==string_segment_marker) // found one marker
{
buffer[i]='\0'; // replace with \0
ptrs[nptr]=i+1; // store the pointer to the next string segments
nptr++; // increment the number of pointers or segments
}
i++;
}
for (byte j=0;j<nptr;j++) // print strings segment by segment
{
client.println(buffer+ptrs[j]);
}
}
else return 0;
while (!client.available())
{
if (millis()-connect_time>server_response_time)
{
client.stop();
return 0;
}
}
return client.read();
}
The server was working fine with a cell modem and library but I recently added more digits to each value in the long message and have not tested it since. I could reassemble the other prototype that has cell modem and test the long message via cell modem just to make sure the server is not to be blamed.
Search shankar108's comment. I checked with the web master and he said there is no limit on his end. This may be a real limit.
The same person also reported a possible reason here:
I don't know enough of SPI bus to know if there can be any timing issue.
Hello, I using ESP8266 there is a lot of memory. I discovereded that the upper limit for client.println() function is 2922bytes. Is it possible to pull up this limit? I using ESP8266 for webserver and html(where I have lot of code, javascripth graphs, etc..) page going through this function. Thank You.
woodwax:
Hello, I using ESP8266 there is a lot of memory. I discovereded that the upper limit for client.println() function is 2922bytes. Is it possible to pull up this limit? I using ESP8266 for webserver and html(where I have lot of code, javascripth graphs, etc..) page going through this function. Thank You.
How did you determine the ESP8266 can send a packet larger than 1492 bytes? What code did you use to send the 2922 bytes?
On page about println() is:
"return the number of bytes written"
And here is my code:
String s = "var temperature=[";
for (i=0; i < temperature.count; i++)
{
s += temperature.saved[i];
s += ",";
}
s += "];\n var epoch=[";
for (i=0; i < temperature.count; i++)
{
s += temperature.epoch_saved[i]-7200;
s += ",";
}
s += "];\n";
Serial.print("Bytes sent:");
Serial.println(client->println(s));
The String s is enough large. The data sent by client->println(s) function is in file sent_data.txt. You can clearly see the epoch array is not comleted (lack of some characters and ]; ) and it contains 2921 characters + maybe terminating.
On picture bytes_sent.png is the serial output an there is the 2922 bytes sent.
Obviously not an Uno. String s would be grow to be too large for an Uno's SRAM.
Sorry I forget the atachments.
The question is still available, can I extend the number of characters sent by function client.print()?
sent_data.txt (2.85 KB)
I send 26.5K in one upload, but not all as one client.print. Why is it necessary to send that all in one client.print?
Because, I think send data in one client.print() is a bit faster.
woodwax:
Because, I think send data in one client.print() is a bit faster.
Then what is stopping you?
Because, I think send data in one client.print() is a bit faster.
If it isn't possible, then your assertion is clearly false.
I have just been writing a program using ESP8266 WifiClient client.print. And I can verify that the maximum is just under 3000 bytes. I believe the size stated above (2922) is probably correct. I wish it was larger and don't yet know why but will investigate. It does not cause an error to try to print a longer string but it does truncate it so there must be a buffer somewhere that is limiting the size.
It has been found by several people that multiple client.print statements are slow so I build up the string as long as I can before doing the client.print. Doing that, it is reasonably fast. Also, using WiFiClient allows me to leave the connection open for more speed.
Previously, I was using ESP8266WebServer and there is a limit there, too. It is larger. Something around 8KB and it won't go above that. I was not able to find how to do multiple httpServer.send(200, "text/html" style commands so I converted to the lower level WifiClient library code. This gives me access to all of the input lines from the browser and I can track browser type, environment and IP address:port.
There is a hierachy here:
ESP8266HTTPUpdateServer (OTA server) is on top of ESP8266WebServer which is on top of WiFiServer.
The program is currently 1600 lines. If someone wants it, I can send it or put it on my web server and post a link. It reads 3 types of temp sensors, also reads Barometric Pressure and Humidity, writes to OLED and SD (history files) and sends out a web page with lots of information including an .svg graphic with 3 symbols and two text lines. If the sensors are missing, it goes on with what it has. I tried to make it not break so easily as some programs.
Mike
