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FAQ: Why doesn't cURL error out when the cable is unplugged?

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This one was long overdue to be mentioned in the FAQ. Also, mention the
new ftp wildcard downloading feature.
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Dan Fandrich 2010-07-21 15:15:07 -07:00
parent affff47b3d
commit 7d166b0ef6
1 changed files with 29 additions and 1 deletions
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@ -74,6 +74,7 @@ FAQ
4.16 My HTTP POST or PUT requests are slow!
4.17 Non-functional connect timeouts on Windows
4.18 file:// URLs containing drive letters (Windows, NetWare)
4.19 Why doesn't cURL return an error when the network cable is unplugged?
5. libcurl Issues
5.1 Is libcurl thread-safe?
@ -944,6 +945,31 @@ FAQ
In either case, cURL should now be looking for the correct file.
4.19 Why doesn't cURL return an error when the network cable is unplugged?
Unplugging the cable is not an error situation. The TCP/IP protocol stack
was designed to be fault tolerant, so even though there may be a physical
break somewhere the connection shouldn't be affected, just possibly
delayed. Eventually, the physical break will be fixed or the data will be
re-routed around the physical problem.
In such cases, the TCP/IP stack is responsible for detecting when the
network connection is irrevocably lost. Since with some protocols it is
perfectly legal for the client wait indefinitely for data, the stack may
never report a problem, and even when it does, it can take up to 20 minutes
for it to detect an issue. The curl option --keepalive-time enables
keep-alive support in the TCP/IP stack which makes it periodically probe the
connection to make sure it is still available to send data. That should
reliably detect any TCP/IP network failure.
But even that won't detect the network going down before the TCP/IP
connection is established (e.g. during a DNS lookup) or using protocols that
don't use TCP. To handle those situations, curl offers a number of timeouts
on its own. --speed-limit/--speed-time will abort if the data transfer rate
falls too low, and --connect-timeout and --max-time can be used to put an
overall timeout on the connection phase or the entire transfer.
5. libcurl Issues
5.1 Is libcurl thread-safe?
@ -1182,7 +1208,9 @@ FAQ
to do "LIST -a" or similar to see them.
The application thus needs to parse the LIST output. One such existing
list parser is available at http://cr.yp.to/ftpparse.html
list parser is available at http://cr.yp.to/ftpparse.html Versions of
libcurl since 7.21.0 also provide the ability to specify a wildcard to
download multiple files from one FTP directory.
6. License Issues