initial implementation for git resource for pipeline

docs/pipeline-resources.md

@@ -0,0 +1,83 @@
+### Pipeline Resources
+
+## Git Resource
+
+Git resource represents a [git](https://git-scm.com/) repository, that containes the source code to be built by the pipeline. Adding the git resource as an input to a task will clone this repository and allow the task to perform the required actions on the contents of the repo.  
+
+Use the following example to understand the syntax and strucutre of a Git Resource
+
+ #### Create a git resource using the `PipelineResource` CRD
+
+ ```
+apiVersion: pipeline.knative.dev/v1alpha1
+kind: Resource
+metadata:
+  name: wizzbang-git
+  namespace: default
+spec:
+  type: git
+  params:
+  - name: url
+    value: github.com/wizzbangcorp/wizzbang
+  - name: Revision
+    value: master
+  - name: ServiceAccount
+    value: pipeline-sa    
+ ```
+
+   Params that can be added are the following:
+
+   1. URL: represents the location of the git repository 
+   1. Revision: Git [revision](https://git-scm.com/docs/gitrevisions#_specifying_revisions ) (branch, tag, commit SHA or ref) to clone. If no revision is specified, the resource will default to `latest` from `master`
+   1. Service Account: specifies the `name` of a `ServiceAccount` resource object. Add this paramater to run your task with the privileges of the specified service account. If no serviceAccountName field is specified, your task runs using the default service account that is in the namespace of the Pipeline resource object.  
+
+ #### Use the defined git resource in a `Task` definition
+
+```
+apiVersion: pipeline.knative.dev/v1alpha1
+kind: Task
+metadata:
+  name: build-push-task
+  namespace: default
+spec:
+    inputs:
+        resources:
+           - name: wizzbang-git
+             type: git
+        params:
+           - name: PATH_TO_DOCKERFILE
+             value: string
+    outputs:
+        resources:
+          - name: builtImage 
+    buildSpec:
+        template:
+            name: kaniko
+            arguments:
+                - name: DOCKERFILE
+                  value: ${PATH_TO_DOCKERFILE}
+                - name: REGISTRY
+                  value: ${REGISTRY}
+``` 
+
+ #### And finally set the version in the `TaskRun` definition
+
+```
+apiVersion: pipeline.knative.dev/v1alpha1
+kind: TaskRun
+metadata:
+  name: build-push-task-run
+  namespace: default
+spec:
+    taskRef:
+        name: build-push-task
+    inputs:
+        resourcesVersion:
+          - resourceRef:
+              name: wizzbang-git
+            version: HEAD
+    outputs:
+        artifacts:
+          - name: builtImage
+            type: image
+``` 

pkg/apis/pipeline/v1alpha1/git_resource.go

@@ -16,6 +16,11 @@ limitations under the License.
 
 package v1alpha1
 
+import (
+	"fmt"
+	"strings"
+)
+
 // GitResource is an endpoint from which to get data which is required
 // by a Build/Task for context (e.g. a repo from which to build an image).
 type GitResource struct {
@@ -30,6 +35,32 @@ type GitResource struct {
 	ServiceAccount string `json:"serviceAccount,omitempty"`
 }
 
+// NewGitResource create a new git resource to pass to Knative Build
+func NewGitResource(r *PipelineResource) (*GitResource, error) {
+	if r.Spec.Type != PipelineResourceTypeGit {
+		return nil, fmt.Errorf("GitResource: Cannot create a Git resource from a %s Pipeline Resource", r.Spec.Type)
+	}
+	gitResource := GitResource{
+		Name: r.Name,
+		Type: r.Spec.Type,
+	}
+	for _, param := range r.Spec.Params {
+		switch {
+		case strings.EqualFold(param.Name, "URL"):
+			gitResource.URL = param.Value
+		case strings.EqualFold(param.Name, "serviceAccount"):
+			gitResource.ServiceAccount = param.Value
+		case strings.EqualFold(param.Name, "Revision"):
+			gitResource.Revision = param.Value
+		}
+	}
+	// default revision to master is nothing is provided
+	if gitResource.Revision == "" {
+		gitResource.Revision = "master"
+	}
+	return &gitResource, nil
+}
+
 // GetName returns the name of the resource
 func (s GitResource) GetName() string {
 	return s.Name
@@ -52,5 +83,10 @@ func (s *GitResource) GetServiceAccountName() string {
 	return s.ServiceAccount
 }
 
+// GetURL returns the url to be used with this resource
+func (s *GitResource) GetURL() string {
+	return s.URL
+}
+
 // GetParams returns the resoruce params
 func (s GitResource) GetParams() []Param { return []Param{} }