upload/koji: use the new API of kolo/xmlrpc by default

Fedora 33 ships the new API so let's do the switch now.

But... this would break older Fedoras because they only have the old API,
right?

We have the following options:

1) Ship xmlrpc compat package to Fedora 33+. This would mean that we delay the API switch till F32 EOL. This would be the most elegant solution, yet it has two issues: a) We will surely not be able to deliver the compat package before F33 Final Freeze. b) It's an extra and annoying work.

2) Downstream patch. No.

3) Use build constraints and have two versions of our code for both different
   API.

I chose solution #3. It has an issue though:

%gobuild macro already passes -tags argument to go build. Therefore the
following line fails because it's not possible to use -tags more than once:

%gobuild -tags kolo_xmlrpc_oldapi ...

Therefore I had to come up with manual tinkering with the build constraints
in the spec file. This is pretty ugly but I like that:

1) Go code is actually clean, no weird magic is happening there.
2) We can still ship our software to Fedora/RHEL as we used to
   (no downstream patches)
3) All downstreams can use the upstream spec file directly.

Note that this doesn't affect RHEL in any way as it uses vendored libraries.

go.mod

@@ -20,7 +20,7 @@ require (
 	github.com/google/uuid v1.1.1
 	github.com/gophercloud/gophercloud v0.11.0
 	github.com/julienschmidt/httprouter v1.2.0
-	github.com/kolo/xmlrpc v0.0.0-20190417161013-de6d879202d7
+	github.com/kolo/xmlrpc v0.0.0-20200310150728-e0350524596b
 	github.com/labstack/echo/v4 v4.1.11
 	github.com/pkg/errors v0.9.1 // indirect
 	github.com/stretchr/testify v1.5.1

go.sum

@@ -74,8 +74,8 @@ github.com/jmespath/go-jmespath v0.0.0-20180206201540-c2b33e8439af h1:pmfjZENx5i
 github.com/jmespath/go-jmespath v0.0.0-20180206201540-c2b33e8439af/go.mod h1:Nht3zPeWKUH0NzdCt2Blrr5ys8VGpn0CEB0cQHVjt7k=
 github.com/julienschmidt/httprouter v1.2.0 h1:TDTW5Yz1mjftljbcKqRcrYhd4XeOoI98t+9HbQbYf7g=
 github.com/julienschmidt/httprouter v1.2.0/go.mod h1:SYymIcj16QtmaHHD7aYtjjsJG7VTCxuUUipMqKk8s4w=
-github.com/kolo/xmlrpc v0.0.0-20190417161013-de6d879202d7 h1:kL2yi3DjwkRWFgKwD5COyl4XMLKhfOvqck4xyis7EIw=
-github.com/kolo/xmlrpc v0.0.0-20190417161013-de6d879202d7/go.mod h1:o03bZfuBwAXHetKXuInt4S7omeXUu62/A845kiycsSQ=
+github.com/kolo/xmlrpc v0.0.0-20200310150728-e0350524596b h1:DzHy0GlWeF0KAglaTMY7Q+khIFoG8toHP+wLFBVBQJc=
+github.com/kolo/xmlrpc v0.0.0-20200310150728-e0350524596b/go.mod h1:o03bZfuBwAXHetKXuInt4S7omeXUu62/A845kiycsSQ=
 github.com/kr/pretty v0.1.0 h1:L/CwN0zerZDmRFUapSPitk6f+Q3+0za1rQkzVuMiMFI=
 github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=

golang-github-osbuild-composer.spec

@@ -64,6 +64,20 @@ Provides: weldr
 %goprep
 %endif
 
+%if 0%{?fedora} && 0%{?fedora} <= 32
+# Fedora 32 and older ships a different kolo/xmlrpc API. We cannot specify
+# build tags in gobuild macro because the macro itself specifies build tags.
+# and -tags argument cannot be used more than once.
+# Therefore, this ugly hack with build tags switcharoo is required.
+# Remove when F32 is EOL.
+
+# Remove the build constraint from the wrapper of the old API
+sed -i "s$// +build kolo_xmlrpc_oldapi$// +build !kolo_xmlrpc_oldapi$" internal/upload/koji/xmlrpc-response-oldapi.go
+
+# Add a build constraint to the wrapper of the new API
+sed -i "s$// +build !kolo_xmlrpc_oldapi$// +build kolo_xmlrpc_oldapi$" internal/upload/koji/xmlrpc-response.go
+%endif
+
 %build
 %if 0%{?rhel}
 GO_BUILD_PATH=$PWD/_build

internal/upload/koji/xmlrpc-response-oldapi.go

@@ -1,4 +1,6 @@
-// This files provides a wrapper around kolo/xmlrpc response handling.
+// +build kolo_xmlrpc_oldapi
+//
+// This file provides a wrapper around kolo/xmlrpc response handling.
 //
 // Commit e3ad6d89 of the xmlrpc library changed the API of response handling.
 // This means that different APIs are available in Fedora 32 and 33 (it does

internal/upload/koji/xmlrpc-response.go

@@ -0,0 +1,34 @@
+// +build !kolo_xmlrpc_oldapi
+//
+// This file provides a wrapper around kolo/xmlrpc response handling.
+//
+// Commit e3ad6d89 of the xmlrpc library changed the API of response handling.
+// This means that different APIs are available in Fedora 32 and 33 (it does
+// not matter for RHEL as uses vendored libraries).
+// This wrapper allows us to use both xmlrpc's APIs using buildflags.
+//
+// This file is a wrapper for xmlrpc equal or newer than e3ad6d89.
+
+package koji
+
+import (
+	"fmt"
+
+	"github.com/kolo/xmlrpc"
+)
+
+// processXMLRPCResponse is a wrapper around kolo/xmlrpc
+func processXMLRPCResponse(body []byte, reply interface{}) error {
+	resp := xmlrpc.Response(body)
+
+	if resp.Err() != nil {
+		return fmt.Errorf("xmlrpc server returned an error: %v", resp.Err())
+	}
+
+	err := resp.Unmarshal(reply)
+	if err != nil {
+		return fmt.Errorf("cannot unmarshal the xmlrpc response: %v", err)
+	}
+
+	return nil
+}

osbuild-composer.spec

@@ -87,6 +87,20 @@ Provides:  golang-github-osbuild-composer = %{version}-%{release}
 %goprep
 %endif
 
+%if 0%{?fedora} && 0%{?fedora} <= 32
+# Fedora 32 and older ships a different kolo/xmlrpc API. We cannot specify
+# build tags in gobuild macro because the macro itself specifies build tags.
+# and -tags argument cannot be used more than once.
+# Therefore, this ugly hack with build tags switcharoo is required.
+# Remove when F32 is EOL.
+
+# Remove the build constraint from the wrapper of the old API
+sed -i "s$// +build kolo_xmlrpc_oldapi$// +build !kolo_xmlrpc_oldapi$" internal/upload/koji/xmlrpc-response-oldapi.go
+
+# Add a build constraint to the wrapper of the new API
+sed -i "s$// +build !kolo_xmlrpc_oldapi$// +build kolo_xmlrpc_oldapi$" internal/upload/koji/xmlrpc-response.go
+%endif
+
 %build
 %if 0%{?rhel}
 GO_BUILD_PATH=$PWD/_build