I think you need to research the POST command. The specification says the POST is unlimited but most browser and Web Servers limit it to about 2K characters. I appears your web site allows for a longer URL to be used, close to 8MB.
Have you tried the FileMaker HTTPPOST command: (From the Help system).
httppost and httpspost are custom schemes defined by FileMaker Pro that enable you to send HTTP POST data.
When your URL begins with http or https, FileMaker Pro sends the URL unchanged. However, httppost and httpspost are custom schemes defined by FileMaker Pro and are handled differently. When your URL begins with httppost or httpspost, FileMaker Pro sends the URL beginning with http:// or https:// followed by the text before the first “?” character. All the text after the first “?” character is sent as POST data in the message body.
This URL specifies a POST request and two key-value pairs:
FileMaker Pro sends this URL:
The text after the “?” is sent as POST data:
I found this on line
The HTTP protocol does not place any a priori limit on the length of a URI. Servers MUST be able to handle the URI of any resource they serve, and SHOULD be able to handle URIs of unbounded length if they provide GET-based forms that could generate such URIs. A server SHOULD return 414 (Request-URI Too Long) status if a URI is longer than the server can handle (see section 10.4.15)''
Extremely long URLs are usually a mistake. URLs over 2,000 characters will not work in the most popular web browsers. Don't use them if you intend your site to work for the majority of Internet users.
So the practical limit is about 2000 characters. Tests referenced on-line indicate 2K is probably the max you should use with most web sites. Since you testing shows you can use closer to 8MB your web server is probably set unto support it. If you have control of the Web Server code you can up this to whatever the RAM supports.
Be grateful you aren't using the IE browser.
From support.microsoft.com/kb/208427 "Maximum URL length is 2,083 characters in Internet Explorer"
What is the server that you're sending this to running? The max POST limit default for PHP is 8MB, so anything larger than that will throw error 10 in the latest FMP 14.
If you're able to control the server then increase the post limit in the php ini settings, or if not then you're going to have to reduce the amount of data you send.
At some point it gets too large, so the time will be too long and it could timeout without finishing.
Or user is impatient and force quits FileMaker.
In that case you may prefer to use e.g. MBS Plugin to have more control over download.
Set your own timeouts, show progress dialog and stream data directly for upload/download.
The specification for the POST command does indeed state that there are no limits imposed on it - however...
The ENVIRONMENT the command is executed from (i.e. the server or web browser or in this case FileMaker itself) CAN and often DOES place limits on the POST command. Examples here: http://www.boutell.com/newfaq/misc/urllength.html
I was using the FileMaker "Insert from URL" script step to submit a URL that started with "httppost://" and then gave the URL of the server, the path and filename of the PHP script I was calling, a couple other parameters and then also added on the final parameter which WAS the Base64Encoded file I was wanting to upload. Yes, the URL was rather long.
As I indicated in my original post, this is working great for files < 8MB but apparently Filemaker's binding of the URL is limited to somewhere around 8MB and doesn't like anything larger. Again - the HTTPOST command itself doesn't have any limits but the environment ISSUING the command (normally a browser or server) DOES - but in this case since FileMaker is issuing the command the issue appears to be on FileMaker's side of the fence.
I'm also aware that just two days ago FileMaker updated FileMaker Server to 14.0.4a to FIX an issue with the "Insert from URL" command. I've tested my DB with both a local copy AND on the server (although it hasn't been upgraded to this new version yet) and am still experiencing issues. I'll see if I can get the server updated and re-test.
There doesn't appera to be any way to adjust this within the FileMaker client or server software.
If anyone else has any ideas I'd love to hear them.