logclient: buffer JSON request body

This permits us to detect JSON marshalling errors, and makes it easy to
retry the request.

Request bodies are short so this should have negligible performance impact.

ct/client/logclient.go

@@ -11,7 +11,6 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"io"
 	"io/ioutil"
 	"net/http"
 	"net/url"
@@ -124,12 +123,11 @@ func (c *LogClient) fetchAndParse(uri string, respBody interface{}) error {
 }
 
 func (c *LogClient) postAndParse(uri string, body interface{}, respBody interface{}) error {
-	bodyReader, bodyWriter := io.Pipe()
-	go func() {
-		json.NewEncoder(bodyWriter).Encode(body)
-		bodyWriter.Close()
-	}()
-	req, err := http.NewRequest("POST", uri, bodyReader)
+	bodyBytes, err := json.Marshal(body)
+	if err != nil {
+		return err
+	}
+	req, err := http.NewRequest("POST", uri, bytes.NewReader(bodyBytes))
 	if err != nil {
 		return fmt.Errorf("POST %s: Sending request failed: %s", uri, err)
 	}