Fix leading slash for abspath in joinpath (continuation of #62)

Project.toml

@@ -1,7 +1,7 @@
 name = "URIs"
 uuid = "5c2747f8-b7ea-4ff2-ba2e-563bfd36b1d4"
 authors = ["Jacob Quinn", "Sam O'Connor", "contributors: https://github.com/JuliaWeb/URIs.jl/graphs/contributors"]
-version = "1.6.2"
+version = "1.6.3"
 
 [compat]
 julia = "1.6"

src/URIs.jl

@@ -656,6 +656,10 @@ end
     joinpath(uri::URI, path::AbstractString) -> URI
 
 Join the path component of URI and other parts.
+
+If `uri` has no authority (host) component, the resulting path must not begin
+with `"//"`, since such a URI cannot be represented (RFC 3986 Section 3.3);
+an `ArgumentError` is thrown in that case.
 """
 function Base.joinpath(uri::URI, parts::String...)
     path = uri.path
@@ -669,10 +673,15 @@ function Base.joinpath(uri::URI, parts::String...)
         end
     end
 
-    if isempty(uri.path)
+    if isempty(uri.path) && !startswith(path, "/")
         path = "/" * path
     end
-    return URI(uri; path=normpath(path))
+    path = normpath(path)
+    if isabsent(uri.host) && startswith(path, "//")
+        throw(ArgumentError("URI without authority (host) cannot have a path " *
+                            "beginning with \"//\" (RFC 3986 Section 3.3): $(repr(path))"))
+    end
+    return URI(uri; path=path)
 end
 
 """

test/uri.jl

@@ -462,7 +462,7 @@ urltests = URLTest[
         @test URIs.splitpath("/foo/bar") == ["foo", "bar"]
     end
     end
-      
+
     @testset "splitfilepath" begin
         @static if Sys.iswindows()
             data = [
@@ -612,6 +612,29 @@ urltests = URLTest[
         @test joinpath(URIs.URI("http://a.b.c/d/f"), "/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")
         @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/")
+        @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")
+
+        # absolute paths joined to URIs without an authority (host) component
+        @test string(joinpath(URIs.URI("file:"), "/a/b/c")) == "file:/a/b/c"
+        @test string(joinpath(URIs.URI("file://"), "/a/b/c")) == "file:///a/b/c"
+        @test string(joinpath(URIs.URI(), "/a/b")) == "/a/b"
+        # a path beginning with "//" cannot be represented without an authority
+        # component (RFC 3986 Section 3.3)
+        @test_throws ArgumentError joinpath(URIs.URI("file:"), "//server/share")
+        @test_throws ArgumentError joinpath(URIs.URI(), "//server/share")
+        # with an authority component (even an empty one), "//" paths are fine
+        @test string(joinpath(URIs.URI("file://"), "//server/share")) == "file:////server/share"
+        @test string(joinpath(URIs.URI("http://a.b.c"), "//b/c")) == "http://a.b.c//b/c"
+        # results must round-trip through their string representation
+        for u in (joinpath(URIs.URI("file:"), "/a/b/c"),
+                  joinpath(URIs.URI("file://"), "/a/b/c"),
+                  joinpath(URIs.URI(), "/a/b"),
+                  joinpath(URIs.URI("file://"), "//server/share"),
+                  joinpath(URIs.URI("http://a.b.c"), "//b/c"))
+            @test URI(string(u)) == u
+        end
     end
 
     @testset "resolvereference" begin