api,libcni: add network config list-based plugin chaining

Using a new ".configlist" file format that allows specifying
a list of CNI network configurations to run, add new libcni
helper functions to call each plugin in the list, injecting
the overall name, CNI version, and previous plugin's Result
structure into the configuration of the next plugin.

libcni/conf_test.go

@@ -26,29 +26,25 @@ import (
 )
 
 var _ = Describe("Loading configuration from disk", func() {
-	var (
-		configDir     string
-		pluginConfig  []byte
-		testNetConfig *libcni.NetworkConfig
-	)
-
-	BeforeEach(func() {
-		var err error
-		configDir, err = ioutil.TempDir("", "plugin-conf")
-		Expect(err).NotTo(HaveOccurred())
-
-		pluginConfig = []byte(`{ "name": "some-plugin", "some-key": "some-value" }`)
-		Expect(ioutil.WriteFile(filepath.Join(configDir, "50-whatever.conf"), pluginConfig, 0600)).To(Succeed())
-
-		testNetConfig = &libcni.NetworkConfig{Network: &types.NetConf{Name: "some-plugin"},
-			Bytes: []byte(`{ "name": "some-plugin" }`)}
-	})
-
-	AfterEach(func() {
-		Expect(os.RemoveAll(configDir)).To(Succeed())
-	})
-
 	Describe("LoadConf", func() {
+		var (
+			configDir    string
+			pluginConfig []byte
+		)
+
+		BeforeEach(func() {
+			var err error
+			configDir, err = ioutil.TempDir("", "plugin-conf")
+			Expect(err).NotTo(HaveOccurred())
+
+			pluginConfig = []byte(`{ "name": "some-plugin", "some-key": "some-value" }`)
+			Expect(ioutil.WriteFile(filepath.Join(configDir, "50-whatever.conf"), pluginConfig, 0600)).To(Succeed())
+		})
+
+		AfterEach(func() {
+			Expect(os.RemoveAll(configDir)).To(Succeed())
+		})
+
 		It("finds the network config file for the plugin of the given type", func() {
 			netConfig, err := libcni.LoadConf(configDir, "some-plugin")
 			Expect(err).NotTo(HaveOccurred())
@@ -128,7 +124,137 @@ var _ = Describe("Loading configuration from disk", func() {
 		})
 	})
 
+	Describe("LoadConfList", func() {
+		var (
+			configDir  string
+			configList []byte
+		)
+
+		BeforeEach(func() {
+			var err error
+			configDir, err = ioutil.TempDir("", "plugin-conf")
+			Expect(err).NotTo(HaveOccurred())
+
+			configList = []byte(`{
+  "name": "some-list",
+  "cniVersion": "0.2.0",
+  "plugins": [
+    {
+      "type": "host-local",
+      "subnet": "10.0.0.1/24"
+    },
+    {
+      "type": "bridge",
+      "mtu": 1400
+    },
+    {
+      "type": "port-forwarding",
+      "ports": {"20.0.0.1:8080": "80"}
+    }
+  ]
+}`)
+			Expect(ioutil.WriteFile(filepath.Join(configDir, "50-whatever.conflist"), configList, 0600)).To(Succeed())
+		})
+
+		AfterEach(func() {
+			Expect(os.RemoveAll(configDir)).To(Succeed())
+		})
+
+		It("finds the network config file for the plugin of the given type", func() {
+			netConfigList, err := libcni.LoadConfList(configDir, "some-list")
+			Expect(err).NotTo(HaveOccurred())
+			Expect(netConfigList).To(Equal(&libcni.NetworkConfigList{
+				Name:       "some-list",
+				CNIVersion: "0.2.0",
+				Plugins: []*libcni.NetworkConfig{
+					{
+						Network: &types.NetConf{Type: "host-local"},
+						Bytes:   []byte(`{"subnet":"10.0.0.1/24","type":"host-local"}`),
+					},
+					{
+						Network: &types.NetConf{Type: "bridge"},
+						Bytes:   []byte(`{"mtu":1400,"type":"bridge"}`),
+					},
+					{
+						Network: &types.NetConf{Type: "port-forwarding"},
+						Bytes:   []byte(`{"ports":{"20.0.0.1:8080":"80"},"type":"port-forwarding"}`),
+					},
+				},
+				Bytes: configList,
+			}))
+		})
+
+		Context("when the config directory does not exist", func() {
+			BeforeEach(func() {
+				Expect(os.RemoveAll(configDir)).To(Succeed())
+			})
+
+			It("returns a useful error", func() {
+				_, err := libcni.LoadConfList(configDir, "some-plugin")
+				Expect(err).To(MatchError("no net configuration lists found"))
+			})
+		})
+
+		Context("when there is no config for the desired plugin list", func() {
+			It("returns a useful error", func() {
+				_, err := libcni.LoadConfList(configDir, "some-other-plugin")
+				Expect(err).To(MatchError(ContainSubstring(`no net configuration list with name "some-other-plugin" in`)))
+			})
+		})
+
+		Context("when a config file is malformed", func() {
+			BeforeEach(func() {
+				Expect(ioutil.WriteFile(filepath.Join(configDir, "00-bad.conflist"), []byte(`{`), 0600)).To(Succeed())
+			})
+
+			It("returns a useful error", func() {
+				_, err := libcni.LoadConfList(configDir, "some-plugin")
+				Expect(err).To(MatchError(`error parsing configuration list: unexpected end of JSON input`))
+			})
+		})
+
+		Context("when the config is in a nested subdir", func() {
+			BeforeEach(func() {
+				subdir := filepath.Join(configDir, "subdir1", "subdir2")
+				Expect(os.MkdirAll(subdir, 0700)).To(Succeed())
+
+				configList = []byte(`{
+  "name": "deep",
+  "cniVersion": "0.2.0",
+  "plugins": [
+    {
+      "type": "host-local",
+      "subnet": "10.0.0.1/24"
+    },
+  ]
+}`)
+				Expect(ioutil.WriteFile(filepath.Join(subdir, "90-deep.conflist"), configList, 0600)).To(Succeed())
+			})
+
+			It("will not find the config", func() {
+				_, err := libcni.LoadConfList(configDir, "deep")
+				Expect(err).To(MatchError(HavePrefix("no net configuration list with name")))
+			})
+		})
+	})
+
+	Describe("ConfListFromFile", func() {
+		Context("when the file cannot be opened", func() {
+			It("returns a useful error", func() {
+				_, err := libcni.ConfListFromFile("/tmp/nope/not-here")
+				Expect(err).To(MatchError(HavePrefix(`error reading /tmp/nope/not-here: open /tmp/nope/not-here`)))
+			})
+		})
+	})
+
 	Describe("InjectConf", func() {
+		var testNetConfig *libcni.NetworkConfig
+
+		BeforeEach(func() {
+			testNetConfig = &libcni.NetworkConfig{Network: &types.NetConf{Name: "some-plugin"},
+				Bytes: []byte(`{ "name": "some-plugin" }`)}
+		})
+
 		Context("when function parameters are incorrect", func() {
 			It("returns unmarshal error", func() {
 				conf := &libcni.NetworkConfig{Network: &types.NetConf{Name: "some-plugin"},