1 files changed, 88 insertions, 0 deletions
diff --git a/content/context/google/google.go b/content/context/google/google.go
new file mode 100644
index 0000000..7f8a984
--- /dev/null
+++ b/content/context/google/google.go
@@ -0,0 +1,88 @@
+// Package google provides a function to do Google searches using the Google Web
+// Search API. See https://developers.google.com/web-search/docs/
+package google
+
+import (
+	"encoding/json"
+	"net/http"
+
+	"code.google.com/p/go.blog/content/context/userip"
+	"code.google.com/p/go.net/context"
+)
+
+// Results is an ordered list of search results.
+type Results []Result
+
+// A Result contains the title and URL of a search result.
+type Result struct {
+	Title, URL string
+}
+
+// Search sends query to Google search and returns the results.
+func Search(ctx context.Context, query string) (Results, error) {
+	// Prepare the Google Search API request.
+	req, err := http.NewRequest("GET", "https://ajax.googleapis.com/ajax/services/search/web?v=1.0", nil)
+	if err != nil {
+		return nil, err
+	}
+	q := req.URL.Query()
+	q.Set("q", query)
+
+	// If ctx is carrying the user IP address, forward it to the server.
+	// Google APIs use the user IP to distinguish server-initiated requests
+	// from end-user requests.
+	if userIP, ok := userip.FromContext(ctx); ok {
+		q.Set("userip", userIP.String())
+	}
+	req.URL.RawQuery = q.Encode()
+
+	// Issue the HTTP request and handle the response. The httpDo function
+	// cancels the request if ctx.Done is closed.
+	var results Results
+	err = httpDo(ctx, req, func(resp *http.Response, err error) error {
+		if err != nil {
+			return err
+		}
+		defer resp.Body.Close()
+
+		// Parse the JSON search result.
+		// https://developers.google.com/web-search/docs/#fonje
+		var data struct {
+			ResponseData struct {
+				Results []struct {
+					TitleNoFormatting string
+					URL               string
+				}
+			}
+		}
+		if err := json.NewDecoder(resp.Body).Decode(&data); err != nil {
+			return err
+		}
+		for _, res := range data.ResponseData.Results {
+			results = append(results, Result{Title: res.TitleNoFormatting, URL: res.URL})
+		}
+		return nil
+	})
+	// httpDo waits for the closure we provided to return, so it's safe to
+	// read results here.
+	return results, err
+}
+
+// httpDo issues the HTTP request and calls f with the response. If ctx.Done is
+// closed while the request or f is running, httpDo cancels the request, waits
+// for f to exit, and returns ctx.Err. Otherwise, httpDo returns f's error.
+func httpDo(ctx context.Context, req *http.Request, f func(*http.Response, error) error) error {
+	// Run the HTTP request in a goroutine and pass the response to f.
+	tr := &http.Transport{}
+	client := &http.Client{Transport: tr}
+	c := make(chan error, 1)
+	go func() { c <- f(client.Do(req)) }()
+	select {
+	case <-ctx.Done():
+		tr.CancelRequest(req)
+		<-c // Wait for f to return.
+		return ctx.Err()
+	case err := <-c:
+		return err
+	}
+}