Bug 1364727 - Prevent libcurl from printing received data to stdout; r=Dexter

By default libcurl prints all the data it receives to stdout. By providing a
dummy write function that drops incoming data and setting it via
CURLOPT_WRITEFUNCTION we can quiet the pingsender operation entirely.

MozReview-Commit-ID: BsgaUWxtLn9

--HG--
extra : rebase_source : 62e7d56206c07fb21886b1431707611225fe5a8a

toolkit/components/telemetry/pingsender/pingsender_unix_common.cpp

@@ -12,10 +12,14 @@
 
 #include "third_party/curl/curl.h"
 
+#include "mozilla/Unused.h"
+
 namespace PingSender {
 
 using std::string;
 
+using mozilla::Unused;
+
 /**
  * A simple wrapper around libcurl "easy" functions. Provides RAII opening
  * and initialization of the curl library
@@ -135,11 +139,23 @@ CurlWrapper::Init()
   return true;
 }
 
+static size_t
+DummyWriteCallback(char *ptr, size_t size, size_t nmemb, void *userdata)
+{
+  Unused << ptr;
+  Unused << size;
+  Unused << nmemb;
+  Unused << userdata;
+
+  return size * nmemb;
+}
+
 bool
 CurlWrapper::Post(const string& url, const string& payload)
 {
   easy_setopt(mCurl, CURLOPT_URL, url.c_str());
   easy_setopt(mCurl, CURLOPT_USERAGENT, kUserAgent);
+  easy_setopt(mCurl, CURLOPT_WRITEFUNCTION, DummyWriteCallback);
 
   // Build the date header.
   std::string dateHeader = GenerateDateHeader();