What is the maximum URL length you can pass to the Wininet function, HttpOpenRequest?

Question

What is the maximum URL length you can pass to the Wininet function, HttpOpenRequest?

Answer 1

I would suggest less than 2000 characters., but this KB article suggests Internet Explorer has a limit of 2083, which may well apply to your case too.

Answer 2

HttpOpenRequest does not have a maximum length but server software you are targeting will likely have a limit on your URL length.

Apache (Server)

My early attempts to measure the maximum URL length in web browsers bumped into a server URL length limit of approximately 4,000 characters, after which Apache produces a "413 Entity Too Large" error. I used the current up to date Apache build found in Red Hat Enterprise Linux 4. The official Apache documentation only mentions an 8,192-byte limit on an individual field in a request.

Microsoft Internet Information Server (Server)

The default limit is 16,384 characters (yes, Microsoft's web server accepts longer URLs than Microsoft's web browser). This is configurable.

Perl HTTP::Daemon (Server)

Up to 8,000 bytes will work. Those constructing web application servers with Perl's HTTP::Daemon module will encounter a 16,384 byte limit on the combined size of all HTTP request headers. This does not include POST-method form data, file uploads, etc., but it does include the URL. In practice this resulted in a 413 error when a URL was significantly longer than 8,000 characters. This limitation can be easily removed. Look for all occurrences of 16x1024 in Daemon.pm and replace them with a larger value. Of course, this does increase your exposure to denial of service attacks.

(from Boutell.com)

Answer 3

There are some max length consts in WinInet.h:

...
//
// maximum field lengths (arbitrary)
//

#define INTERNET_MAX_HOST_NAME_LENGTH   256
#define INTERNET_MAX_USER_NAME_LENGTH   128
#define INTERNET_MAX_PASSWORD_LENGTH    128
#define INTERNET_MAX_PORT_NUMBER_LENGTH 5           // INTERNET_PORT is unsigned short
#define INTERNET_MAX_PORT_NUMBER_VALUE  65535       // maximum unsigned short value
#define INTERNET_MAX_PATH_LENGTH        2048
#define INTERNET_MAX_SCHEME_LENGTH      32          // longest protocol name length
#define INTERNET_MAX_URL_LENGTH         (INTERNET_MAX_SCHEME_LENGTH \
                                        + sizeof("://") \
                                        + INTERNET_MAX_PATH_LENGTH)
...