Backend plugins: Implement support for resources (#21805)

Implements initial support for resources using v0.14.0 of SDK.

Ref #21512

pkg/plugins/backendplugin/resource/response_writer.go

@@ -0,0 +1,137 @@
+package resource
+
+import (
+	"bytes"
+	"net/http"
+
+	"github.com/grafana/grafana-plugin-sdk-go/genproto/pluginv2"
+)
+
+// ResourceResponseWriter is an implementation of http.ResponseWriter that
+// records its mutations for later inspection in tests.
+type ResourceResponseWriter struct {
+	// Code is the HTTP response code set by WriteHeader.
+	//
+	// Note that if a Handler never calls WriteHeader or Write,
+	// this might end up being 0, rather than the implicit
+	// http.StatusOK. To get the implicit value, use the Result
+	// method.
+	Code int
+
+	// HeaderMap contains the headers explicitly set by the Handler.
+	// It is an internal detail.
+	//
+	// Deprecated: HeaderMap exists for historical compatibility
+	// and should not be used. To access the headers returned by a handler,
+	// use the Response.Header map as returned by the Result method.
+	HeaderMap http.Header
+
+	// Body is the buffer to which the Handler's Write calls are sent.
+	// If nil, the Writes are silently discarded.
+	Body *bytes.Buffer
+
+	// Flushed is whether the Handler called Flush.
+	Flushed bool
+
+	wroteHeader bool
+}
+
+// NewResourceResponseWriter returns an initialized ResponseWriter.
+func NewResourceResponseWriter() *ResourceResponseWriter {
+	return &ResourceResponseWriter{
+		HeaderMap: make(http.Header),
+		Body:      new(bytes.Buffer),
+		Code:      200,
+	}
+}
+
+// Header implements http.ResponseWriter. It returns the response
+// headers to mutate within a handler. To test the headers that were
+// written after a handler completes, use the Result method and see
+// the returned Response value's Header.
+func (rw *ResourceResponseWriter) Header() http.Header {
+	m := rw.HeaderMap
+	if m == nil {
+		m = make(http.Header)
+		rw.HeaderMap = m
+	}
+	return m
+}
+
+// writeHeader writes a header if it was not written yet and
+// detects Content-Type if needed.
+//
+// bytes or str are the beginning of the response body.
+// We pass both to avoid unnecessarily generate garbage
+// in rw.WriteString which was created for performance reasons.
+// Non-nil bytes win.
+func (rw *ResourceResponseWriter) writeHeader(b []byte, str string) {
+	if rw.wroteHeader {
+		return
+	}
+	if len(str) > 512 {
+		str = str[:512]
+	}
+
+	m := rw.Header()
+
+	_, hasType := m["Content-Type"]
+	hasTE := m.Get("Transfer-Encoding") != ""
+	if !hasType && !hasTE {
+		if b == nil {
+			b = []byte(str)
+		}
+		m.Set("Content-Type", http.DetectContentType(b))
+	}
+
+	rw.WriteHeader(200)
+}
+
+// Write implements http.ResponseWriter. The data in buf is written to
+// rw.Body, if not nil.
+func (rw *ResourceResponseWriter) Write(buf []byte) (int, error) {
+	rw.writeHeader(buf, "")
+	if rw.Body != nil {
+		rw.Body.Write(buf)
+	}
+	return len(buf), nil
+}
+
+// WriteHeader implements http.ResponseWriter.
+func (rw *ResourceResponseWriter) WriteHeader(code int) {
+	if rw.wroteHeader {
+		return
+	}
+	rw.Code = code
+	rw.wroteHeader = true
+	if rw.HeaderMap == nil {
+		rw.HeaderMap = make(http.Header)
+	}
+}
+
+// Flush implements http.Flusher.
+func (rw *ResourceResponseWriter) Flush() {
+	if !rw.wroteHeader {
+		rw.WriteHeader(200)
+	}
+}
+
+// Result returns the response generated by the handler.
+func (rw *ResourceResponseWriter) Result() *pluginv2.CallResource_Response {
+	res := &pluginv2.CallResource_Response{
+		Code:    int32(rw.Code),
+		Headers: map[string]*pluginv2.CallResource_StringList{},
+	}
+
+	if rw.Body != nil {
+		res.Body = rw.Body.Bytes()
+	}
+
+	for key, values := range rw.Header().Clone() {
+		res.Headers[key] = &pluginv2.CallResource_StringList{
+			Values: values,
+		}
+	}
+
+	return res
+}