V2 API Version Support

* Update blang/semver to allow ParseTolerant() support
* Provide helper functions for API handlers to obtain client's 'version'
  path variable focused on API endpoint tree: libpod vs. compat
* Introduce new errors:
  * version not given in path, endpoints may determine if this is a hard
    error (ErrVersionNotGiven)
  * given version not supported (ErrVersionNotSupported), only a soft
    error if the handler is going to hijack the connection
* Added unit tests for version parsing
* bindings check version on connect:
  * client <= Server API version connection is continued
  * client >= Server API version connection fails

Signed-off-by: Jhon Honce <jhonce@redhat.com>

5 files changed, 250 insertions, 31 deletions

diff --git a/pkg/api/handlers/compat/ping.go b/pkg/api/handlers/compat/ping.go
index 6e77e270f..abee3d8e8 100644
--- a/pkg/api/handlers/compat/ping.go
+++ b/pkg/api/handlers/compat/ping.go
@@ -5,22 +5,22 @@ import (
 	"net/http"
 
 	"github.com/containers/buildah"
-	"github.com/containers/libpod/pkg/api/handlers"
+	"github.com/containers/libpod/pkg/api/handlers/utils"
 )
 
 // Ping returns headers to client about the service
 //
 // This handler must always be the same for the compatibility and libpod URL trees!
 // Clients will use the Header availability to test which backend engine is in use.
+// Note: Additionally handler supports GET and HEAD methods
 func Ping(w http.ResponseWriter, r *http.Request) {
-	w.Header().Set("API-Version", handlers.DefaultApiVersion)
+	w.Header().Set("API-Version", utils.ApiVersion[utils.CompatTree][utils.CurrentApiVersion].String())
 	w.Header().Set("BuildKit-Version", "")
 	w.Header().Set("Docker-Experimental", "true")
 	w.Header().Set("Cache-Control", "no-cache")
 	w.Header().Set("Pragma", "no-cache")
 
-	// API-Version and Libpod-API-Version may not always be equal
-	w.Header().Set("Libpod-API-Version", handlers.DefaultApiVersion)
+	w.Header().Set("Libpod-API-Version", utils.ApiVersion[utils.LibpodTree][utils.CurrentApiVersion].String())
 	w.Header().Set("Libpod-Buildha-Version", buildah.Version)
 	w.WriteHeader(http.StatusOK)
 
diff --git a/pkg/api/handlers/compat/version.go b/pkg/api/handlers/compat/version.go
index 8786f1d5b..bfc226bb8 100644
--- a/pkg/api/handlers/compat/version.go
+++ b/pkg/api/handlers/compat/version.go
@@ -8,7 +8,6 @@ import (
 
 	"github.com/containers/libpod/libpod"
 	"github.com/containers/libpod/libpod/define"
-	"github.com/containers/libpod/pkg/api/handlers"
 	"github.com/containers/libpod/pkg/api/handlers/utils"
 	"github.com/containers/libpod/pkg/domain/entities"
 	docker "github.com/docker/docker/api/types"
@@ -35,34 +34,35 @@ func VersionHandler(w http.ResponseWriter, r *http.Request) {
 		Name:    "Podman Engine",
 		Version: versionInfo.Version,
 		Details: map[string]string{
-			"APIVersion":    handlers.DefaultApiVersion,
+			"APIVersion":    utils.ApiVersion[utils.LibpodTree][utils.CurrentApiVersion].String(),
 			"Arch":          goRuntime.GOARCH,
 			"BuildTime":     time.Unix(versionInfo.Built, 0).Format(time.RFC3339),
 			"Experimental":  "true",
 			"GitCommit":     versionInfo.GitCommit,
 			"GoVersion":     versionInfo.GoVersion,
 			"KernelVersion": infoData.Host.Kernel,
-			"MinAPIVersion": handlers.MinimalApiVersion,
+			"MinAPIVersion": utils.ApiVersion[utils.LibpodTree][utils.MinimalApiVersion].String(),
 			"Os":            goRuntime.GOOS,
 		},
 	}}
 
-	utils.WriteResponse(w, http.StatusOK, entities.ComponentVersion{Version: docker.Version{
-		Platform: struct {
-			Name string
-		}{
-			Name: fmt.Sprintf("%s/%s/%s-%s", goRuntime.GOOS, goRuntime.GOARCH, infoData.Host.Distribution.Distribution, infoData.Host.Distribution.Version),
-		},
-		APIVersion:    components[0].Details["APIVersion"],
-		Arch:          components[0].Details["Arch"],
-		BuildTime:     components[0].Details["BuildTime"],
-		Components:    components,
-		Experimental:  true,
-		GitCommit:     components[0].Details["GitCommit"],
-		GoVersion:     components[0].Details["GoVersion"],
-		KernelVersion: components[0].Details["KernelVersion"],
-		MinAPIVersion: components[0].Details["MinAPIVersion"],
-		Os:            components[0].Details["Os"],
-		Version:       components[0].Version,
-	}})
+	utils.WriteResponse(w, http.StatusOK, entities.ComponentVersion{
+		Version: docker.Version{
+			Platform: struct {
+				Name string
+			}{
+				Name: fmt.Sprintf("%s/%s/%s-%s", goRuntime.GOOS, goRuntime.GOARCH, infoData.Host.Distribution.Distribution, infoData.Host.Distribution.Version),
+			},
+			APIVersion:    components[0].Details["APIVersion"],
+			Arch:          components[0].Details["Arch"],
+			BuildTime:     components[0].Details["BuildTime"],
+			Components:    components,
+			Experimental:  true,
+			GitCommit:     components[0].Details["GitCommit"],
+			GoVersion:     components[0].Details["GoVersion"],
+			KernelVersion: components[0].Details["KernelVersion"],
+			MinAPIVersion: components[0].Details["MinAPIVersion"],
+			Os:            components[0].Details["Os"],
+			Version:       components[0].Version,
+		}})
 }
diff --git a/pkg/api/handlers/handler.go b/pkg/api/handlers/handler.go
deleted file mode 100644
index 2dd2c886b..000000000
--- a/pkg/api/handlers/handler.go
+++ /dev/null
@@ -1,6 +0,0 @@
-package handlers
-
-const (
-	DefaultApiVersion = "1.40" // See https://docs.docker.com/engine/api/v1.40/
-	MinimalApiVersion = "1.24"
-)
diff --git a/pkg/api/handlers/utils/handler.go b/pkg/api/handlers/utils/handler.go
index b5bd488fb..2f4a54b98 100644
--- a/pkg/api/handlers/utils/handler.go
+++ b/pkg/api/handlers/utils/handler.go
@@ -9,11 +9,55 @@ import (
 	"os"
 	"strings"
 
+	"github.com/blang/semver"
 	"github.com/gorilla/mux"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
 )
 
+type (
+	// VersionTree determines which API endpoint tree for version
+	VersionTree int
+	// VersionLevel determines which API level, current or something from the past
+	VersionLevel int
+)
+
+const (
+	// LibpodTree supports Libpod endpoints
+	LibpodTree = VersionTree(iota)
+	// CompatTree supports Libpod endpoints
+	CompatTree
+
+	// CurrentApiVersion announces what is the current API level
+	CurrentApiVersion = VersionLevel(iota)
+	// MinimalApiVersion announces what is the oldest API level supported
+	MinimalApiVersion
+)
+
+var (
+	// See https://docs.docker.com/engine/api/v1.40/
+	// libpod compat handlers are expected to honor docker API versions
+
+	// ApiVersion provides the current and minimal API versions for compat and libpod endpoint trees
+	// Note: GET|HEAD /_ping is never versioned and provides the API-Version and Libpod-API-Version headers to allow
+	//       clients to shop for the Version they wish to support
+	ApiVersion = map[VersionTree]map[VersionLevel]semver.Version{
+		LibpodTree: {
+			CurrentApiVersion: semver.MustParse("1.0.0"),
+			MinimalApiVersion: semver.MustParse("1.0.0"),
+		},
+		CompatTree: {
+			CurrentApiVersion: semver.MustParse("1.40.0"),
+			MinimalApiVersion: semver.MustParse("1.24.0"),
+		},
+	}
+
+	// ErrVersionNotGiven returned when version not given by client
+	ErrVersionNotGiven = errors.New("version not given in URL path")
+	// ErrVersionNotSupported returned when given version is too old
+	ErrVersionNotSupported = errors.New("given version is not supported")
+)
+
 // IsLibpodRequest returns true if the request related to a libpod endpoint
 // (e.g., /v2/libpod/...).
 func IsLibpodRequest(r *http.Request) bool {
@@ -21,6 +65,48 @@ func IsLibpodRequest(r *http.Request) bool {
 	return len(split) >= 3 && split[2] == "libpod"
 }
 
+// SupportedVersion validates that the version provided by client is included in the given condition
+// https://github.com/blang/semver#ranges provides the details for writing conditions
+// If a version is not given in URL path, ErrVersionNotGiven is returned
+func SupportedVersion(r *http.Request, condition string) (semver.Version, error) {
+	version := semver.Version{}
+	val, ok := mux.Vars(r)["version"]
+	if !ok {
+		return version, ErrVersionNotGiven
+	}
+	safeVal, err := url.PathUnescape(val)
+	if err != nil {
+		return version, errors.Wrapf(err, "unable to unescape given API version: %q", val)
+	}
+	version, err = semver.ParseTolerant(safeVal)
+	if err != nil {
+		return version, errors.Wrapf(err, "unable to parse given API version: %q from %q", safeVal, val)
+	}
+
+	inRange, err := semver.ParseRange(condition)
+	if err != nil {
+		return version, err
+	}
+
+	if inRange(version) {
+		return version, nil
+	}
+	return version, ErrVersionNotSupported
+}
+
+// SupportedVersionWithDefaults validates that the version provided by client valid is supported by server
+// minimal API version <= client path version <= maximum API version focused on the endpoint tree from URL
+func SupportedVersionWithDefaults(r *http.Request) (semver.Version, error) {
+	tree := CompatTree
+	if IsLibpodRequest(r) {
+		tree = LibpodTree
+	}
+
+	return SupportedVersion(r,
+		fmt.Sprintf(">=%s <=%s", ApiVersion[tree][MinimalApiVersion].String(),
+			ApiVersion[tree][CurrentApiVersion].String()))
+}
+
 // WriteResponse encodes the given value as JSON or string and renders it for http client
 func WriteResponse(w http.ResponseWriter, code int, value interface{}) {
 	// RFC2616 explicitly states that the following status codes "MUST NOT
diff --git a/pkg/api/handlers/utils/handler_test.go b/pkg/api/handlers/utils/handler_test.go
new file mode 100644
index 000000000..6009432b5
--- /dev/null
+++ b/pkg/api/handlers/utils/handler_test.go
@@ -0,0 +1,139 @@
+package utils
+
+import (
+	"errors"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/gorilla/mux"
+)
+
+func TestSupportedVersion(t *testing.T) {
+	req, err := http.NewRequest("GET",
+		fmt.Sprintf("/v%s/libpod/testing/versions", ApiVersion[LibpodTree][CurrentApiVersion]),
+		nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	req = mux.SetURLVars(req, map[string]string{"version": ApiVersion[LibpodTree][CurrentApiVersion].String()})
+
+	rr := httptest.NewRecorder()
+	handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_, err := SupportedVersionWithDefaults(r)
+		switch {
+		case errors.Is(err, ErrVersionNotGiven): // for compat endpoints version optional
+			w.WriteHeader(http.StatusInternalServerError)
+			fmt.Fprint(w, err.Error())
+		case errors.Is(err, ErrVersionNotSupported): // version given but not supported
+			w.WriteHeader(http.StatusBadRequest)
+			fmt.Fprint(w, err.Error())
+		case err != nil:
+			w.WriteHeader(http.StatusInternalServerError)
+			fmt.Fprint(w, err.Error())
+		default: // all good
+			w.WriteHeader(http.StatusOK)
+			fmt.Fprint(w, "OK")
+		}
+	})
+	handler.ServeHTTP(rr, req)
+
+	if status := rr.Code; status != http.StatusOK {
+		t.Errorf("handler returned wrong status code: got %v want %v",
+			status, http.StatusOK)
+	}
+
+	// Check the response body is what we expect.
+	expected := `OK`
+	if rr.Body.String() != expected {
+		t.Errorf("handler returned unexpected body: got %q want %q",
+			rr.Body.String(), expected)
+	}
+}
+
+func TestUnsupportedVersion(t *testing.T) {
+	version := "999.999.999"
+	req, err := http.NewRequest("GET",
+		fmt.Sprintf("/v%s/libpod/testing/versions", version),
+		nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	req = mux.SetURLVars(req, map[string]string{"version": version})
+
+	rr := httptest.NewRecorder()
+	handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_, err := SupportedVersionWithDefaults(r)
+		switch {
+		case errors.Is(err, ErrVersionNotGiven): // for compat endpoints version optional
+			w.WriteHeader(http.StatusInternalServerError)
+			fmt.Fprint(w, err.Error())
+		case errors.Is(err, ErrVersionNotSupported): // version given but not supported
+			w.WriteHeader(http.StatusBadRequest)
+			fmt.Fprint(w, err.Error())
+		case err != nil:
+			w.WriteHeader(http.StatusInternalServerError)
+			fmt.Fprint(w, err.Error())
+		default: // all good
+			w.WriteHeader(http.StatusOK)
+			fmt.Fprint(w, "OK")
+		}
+	})
+	handler.ServeHTTP(rr, req)
+
+	if status := rr.Code; status != http.StatusBadRequest {
+		t.Errorf("handler returned wrong status code: got %v want %v",
+			status, http.StatusBadRequest)
+	}
+
+	// Check the response body is what we expect.
+	expected := ErrVersionNotSupported.Error()
+	if rr.Body.String() != expected {
+		t.Errorf("handler returned unexpected body: got %q want %q",
+			rr.Body.String(), expected)
+	}
+}
+
+func TestEqualVersion(t *testing.T) {
+	version := "1.30.0"
+	req, err := http.NewRequest("GET",
+		fmt.Sprintf("/v%s/libpod/testing/versions", version),
+		nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	req = mux.SetURLVars(req, map[string]string{"version": version})
+
+	rr := httptest.NewRecorder()
+	handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_, err := SupportedVersion(r, "=="+version)
+		switch {
+		case errors.Is(err, ErrVersionNotGiven): // for compat endpoints version optional
+			w.WriteHeader(http.StatusInternalServerError)
+			fmt.Fprint(w, err.Error())
+		case errors.Is(err, ErrVersionNotSupported): // version given but not supported
+			w.WriteHeader(http.StatusBadRequest)
+			fmt.Fprint(w, err.Error())
+		case err != nil:
+			w.WriteHeader(http.StatusInternalServerError)
+			fmt.Fprint(w, err.Error())
+		default: // all good
+			w.WriteHeader(http.StatusOK)
+			fmt.Fprint(w, "OK")
+		}
+	})
+	handler.ServeHTTP(rr, req)
+
+	if status := rr.Code; status != http.StatusOK {
+		t.Errorf("handler returned wrong status code: got %v want %v",
+			status, http.StatusOK)
+	}
+
+	// Check the response body is what we expect.
+	expected := http.StatusText(http.StatusOK)
+	if rr.Body.String() != expected {
+		t.Errorf("handler returned unexpected body: got %q want %q",
+			rr.Body.String(), expected)
+	}
+}