Add FileReaderInterface. Move StringFileWriter to StringFile and

util/file/string_file.cc

Index: util/file/string_file.cc
diff --git a/util/file/string_file_writer.cc b/util/file/string_file.cc
similarity index 77%
rename from util/file/string_file_writer.cc
rename to util/file/string_file.cc
index e2669b3264c8a011cc127e4e8eb0a412106fca28..3e4362e60c64ef412a4af0d2038cb3644eb62597 100644
--- a/util/file/string_file_writer.cc
+++ b/util/file/string_file.cc
@@ -12,28 +12,58 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-#include "util/file/string_file_writer.h"
+#include "util/file/string_file.h"
 
 #include <string.h>
 
+#include <algorithm>
+
 #include "base/logging.h"
 #include "base/numerics/safe_math.h"
 #include "util/numeric/safe_assignment.h"
 
 namespace crashpad {
 
-StringFileWriter::StringFileWriter() : string_(), offset_(0) {
+StringFile::StringFile() : string_(), offset_(0) {
 }
 
-StringFileWriter::~StringFileWriter() {
+StringFile::~StringFile() {
 }
 
-void StringFileWriter::Reset() {
+void StringFile::SetString(const std::string& string) {
+  string_ = string;
+  offset_ = 0;
+}
+
+void StringFile::Reset() {
   string_.clear();
   offset_ = 0;
 }
 
-bool StringFileWriter::Write(const void* data, size_t size) {
+ssize_t StringFile::Read(void* data, size_t size) {
+  DCHECK(offset_.IsValid());
+
+  const size_t offset = offset_.ValueOrDie();
+  if (offset >= string_.size()) {
+    return 0;
+  }
+
+  const size_t nread = std::min(size, string_.size() - offset);
+
+  base::CheckedNumeric<ssize_t> new_offset = offset_;
+  new_offset += nread;
+  if (!new_offset.IsValid()) {
+    LOG(ERROR) << "Read(): file too large";
+    return -1;
+  }
+
+  memcpy(data, &string_[offset], nread);
+  offset_ = new_offset;
+
+  return nread;
+}
+
+bool StringFile::Write(const void* data, size_t size) {
   DCHECK(offset_.IsValid());
 
   const size_t offset = offset_.ValueOrDie();
@@ -54,7 +84,7 @@ bool StringFileWriter::Write(const void* data, size_t size) {
   return true;
 }
 
-bool StringFileWriter::WriteIoVec(std::vector<WritableIoVec>* iovecs) {
+bool StringFile::WriteIoVec(std::vector<WritableIoVec>* iovecs) {
   DCHECK(offset_.IsValid());
 
   if (iovecs->empty()) {
@@ -87,7 +117,7 @@ bool StringFileWriter::WriteIoVec(std::vector<WritableIoVec>* iovecs) {
   return true;
 }
 
-FileOffset StringFileWriter::Seek(FileOffset offset, int whence) {
+FileOffset StringFile::Seek(FileOffset offset, int whence) {
   DCHECK(offset_.IsValid());
 
   size_t base_offset;