So, yeah, i got the same problem. Since yesterday I'm trying to download the Forge source, but i got the same problems as the Threadopener.
I got to download the ZIP with a trick - i paused and resumed the download (direct, not adfly) every 2 - 5 minutes (otherwise it will fail, see Openers pic).
But downloading the source, with
gradlew setupDecompWorkspace --refresh-dependencies
will work for the first few minutes, but fail after some time.
As you can see in this picture, it starts downloading the files, but will pause/crash after some time (it's on 22 KB since over 20 minutes now).
I'm running Windows 7 64 bit, having no internet connection problems (tested both, connection and installation of forge thw whole day). While i have a quite good speed with other downloads (minecraft-server.jar from Mojang, about 500kb/s - 1,5Mb/s), the speed of the download of the forge-src zip (recommended version, 1.7.10) was only about less than 100kb/s.
Edit:
So, i tried it again today, and got to about 50 KB, and got this error:
Currently I'm running the same command with the additional "--stacktrace" parameter, as the message said.
I'll post the result as soon it's completed.
Edit 2:
I ran the command now with the "--info" parameter and saved the log into a file.
The console showed the same error as previously.
I don't think the log can really help, though i found no stacktrace, etc. But here it is: