Add a function to resolve URI references relative to a base URI

docs/src/index.md

@@ -57,6 +57,7 @@ absuri
 escapeuri
 unescapeuri
 escapepath
+resolvereference
 URIs.splitpath
 Base.isvalid(::URI)
 ```

src/URIs.jl

@@ -2,7 +2,8 @@ module URIs
 
 export URI,
        queryparams, absuri,
-       escapeuri, unescapeuri, escapepath
+       escapeuri, unescapeuri, escapepath,
+       resolvereference
 
 import Base.==
 
@@ -523,6 +524,88 @@ function Base.joinpath(uri::URI, parts::String...)
     return URI(uri; path=normpath(path))
 end
 
+"""
+    resolvereference(base::Union{URI,AbstractString}, ref::Union{URI,AbstractString}) -> URI
+
+Resolve a URI reference `ref` relative to the absolute base URI `base`,
+complying with [RFC 3986 Section 5.2](https://tools.ietf.org/html/rfc3986#section-5.2).
+
+If `ref` is an absolute URI, return `ref` unchanged.
+
+# Examples
+
+```jldoctest; setup = :(using URIs)
+julia> u = resolvereference("http://example.org/foo/bar/", "/baz/")
+URI("http://example.org/baz/")
+
+julia> resolvereference(u, "./hello/world")
+URI("http://example.org/baz/hello/world")
+
+julia> resolvereference(u, "http://localhost:8000")
+URI("http://localhost:8000")
+```
+"""
+function resolvereference(base::URI, ref::URI)
+    # In the case where the second URI is absolute, we just return the
+    # reference URI. Refer to https://tools.ietf.org/html/rfc3986#section-5.2.2
+    #
+    # We also default to just returning the reference when the base URI is
+    # non-absolute.
+    if isempty(base.scheme) || !isempty(ref.scheme)
+        return ref
+    end
+
+    host, port, path, query = if !isempty(ref.host)
+        ref.host, ref.port, ref.path, ref.query
+    else
+        path, query = if isempty(ref.path)
+            base.path, isempty(ref.query) ? base.query : ref.query
+        else
+            path = startswith(ref.path, "/") ? ref.path : resolveref_merge(base, ref)
+            path, ref.query
+        end
+        base.host, base.port, path, query
+    end
+
+    path = normpath(path)
+    scheme = base.scheme
+    fragment = ref.fragment
+    userinfo = isempty(ref.userinfo) ? base.userinfo : ref.userinfo
+
+    URI(;
+        scheme=scheme,
+        userinfo=userinfo,
+        host=host,
+        port=port,
+        path=path,
+        query=query,
+        fragment=fragment
+    )
+end
+
+resolvereference(base, ref) = resolvereference(URI(base), URI(ref))
+
+"""
+    resolveref_merge(base, ref)
+
+Implementation of the "merge" routine described in RFC 3986 Sec. 5.2.3 for merging
+a relative-path reference with the path of the base URI.
+"""
+function resolveref_merge(base, ref)
+    if !isempty(base.host) && isempty(base.path)
+        "/" * ref.path
+    else
+        last_slash = findprev("/", base.path, lastindex(base.path))
+        if last_slash === nothing
+            ref.path
+        else
+            last_slash = first(last_slash)
+            base.path[1:last_slash] * ref.path
+        end
+    end
+end
+
+
 function access_threaded(f, v::Vector)
     tid = Threads.threadid()
     0 < tid <= length(v) || _length_assert()

test/uri.jl

@@ -547,4 +547,55 @@ urltests = URLTest[
         @test joinpath(URIs.URI("http://a.b.c/"), "b", "c") == URI("http://a.b.c/b/c")
         @test joinpath(URIs.URI("http://a.b.c"), "b", "c") == URI("http://a.b.c/b/c")
     end
+
+    @testset "resolvereference" begin
+        # Tests for resolving URI references, as defined in Section 5.4
+
+        # Perform some basic tests resolving absolute and relative references to a base URI
+        uri = URI("http://example.org/foo/bar/")
+        @test resolvereference(uri, "/baz") == URI("http://example.org/baz")
+        @test resolvereference(uri, "baz/") == URI("http://example.org/foo/bar/baz/")
+        @test resolvereference(uri, "../baz/") == URI("http://example.org/foo/baz/")
+
+        # If the base URI's path doesn't end with a /, we handle relative URIs a little differently
+        uri = URI("http://example.org/foo/bar")
+        @test resolvereference(uri, "baz") == URI("http://example.org/foo/baz")
+        @test resolvereference(uri, "../baz") == URI("http://example.org/baz")
+
+        # If the second URI is absolute, or the first URI isn't, we should just return the
+        # second URI.
+        @test resolvereference("http://www.example.org", "http://example.com") == URI("http://example.com")
+        @test resolvereference("http://example.org/foo", "http://example.org/bar") == URI("http://example.org/bar")
+        @test resolvereference("/foo", "/bar/baz") == URI("/bar/baz")
+
+        # "Normal examples" specified in Section 5.4.1
+        base = URI("http://a/b/c/d;p?q")
+        @test resolvereference(base, "g:h") == URI("g:h")
+        @test resolvereference(base, "g") == URI("http://a/b/c/g")
+        @test resolvereference(base, "./g") == URI("http://a/b/c/g")
+        @test resolvereference(base, "g/") == URI("http://a/b/c/g/")
+        @test resolvereference(base, "/g") == URI("http://a/g")
+        @test resolvereference(base, "//g") == URI("http://g")
+        @test resolvereference(base, "?y") == URI("http://a/b/c/d;p?y")
+        @test resolvereference(base, "g?y") == URI("http://a/b/c/g?y")
+        @test resolvereference(base, "#s") == URI("http://a/b/c/d;p?q#s")
+        @test resolvereference(base, "g#s") == URI("http://a/b/c/g#s")
+        @test resolvereference(base, "g?y#s") == URI("http://a/b/c/g?y#s")
+        @test resolvereference(base, ";x") == URI("http://a/b/c/;x")
+        @test resolvereference(base, "g;x") == URI("http://a/b/c/g;x")
+        @test resolvereference(base, "g;x?y#s") == URI("http://a/b/c/g;x?y#s")
+        @test resolvereference(base, "") == URI("http://a/b/c/d;p?q")
+        @test resolvereference(base, ".") == URI("http://a/b/c/")
+        @test resolvereference(base, "./") == URI("http://a/b/c/")
+        @test resolvereference(base, "..") == URI("http://a/b/")
+        @test resolvereference(base, "../") == URI("http://a/b/")
+        @test resolvereference(base, "../g") == URI("http://a/b/g")
+        @test resolvereference(base, "../..") == URI("http://a/")
+        @test resolvereference(base, "../../") == URI("http://a/")
+        @test resolvereference(base, "../../g") == URI("http://a/g")
+
+        # "Abnormal examples" specified in Section 5.4.2
+        @test resolvereference(base, "../../../g") == URI("http://a/g")
+        @test resolvereference(base, "../../../../g") == URI("http://a/g")
+    end
 end