Create new URI from Base URI and Relative Path - slash makes a difference?

c# .net uri trailing-slash
user2864740 picture user2864740 · Mar 20, 2014 · Viewed 16.4k times · Source

Why does a slash make difference when using new URI(baseUri, relativePath)?

This constructor creates a Uri instance by combining the baseUri and the relativeUri ..

And, how can can a relative path be appended safely/consistently to a URI?

var badBase = new Uri("http://amee/noTrailingSlash");
var goodBase = new Uri("http://amee/trailingSlash/");
var f = "relPath";
new Uri(badBase, f)     // BAD  -> http://amee/relPath
new Uri(goodBase, f)    // GOOD -> http://amee/trailingSlash/relPath

The desired output is "good" case, even when the initial URI does not have a trailing slash.

Answer

Jon Skeet picture Jon Skeet · Mar 20, 2014

Why does a slash make difference when using new URI(baseUri, relativePath)?

Well, that's what happens on the web normally.

For example, suppose I'm looking at http://foo.com/some/file1.html and there's a link to file2.html - that link goes to http://foo.com/some/file2.html, right? Not http://foo.com/some/file1.html/file2.html.

More specifically though, this follows section 5.2.3 of RFC 3986.

5.2.3. Merge Paths

The pseudocode above refers to a "merge" routine for merging a relative-path reference with the path of the base URI. This is accomplished as follows:

  • If the base URI has a defined authority component and an empty path, then return a string consisting of "/" concatenated with the reference's path; otherwise,

  • return a string consisting of the reference's path component appended to all but the last segment of the base URI's path (i.e., excluding any characters after the right-most "/" in the base URI path, or excluding the entire base URI path if it does not contain any "/" characters).

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