Add ReadFileOrDie test util function.

This fixes a compilation error; I'd left it out of the previous commit adding
a sqlite-test.cc method which depends on it.

src/filesystem.cc

@@ -79,6 +79,19 @@ class RealFile : public File {
     return 0;
   }
 
+  int Read(void *buf, size_t size, size_t *bytes_read) final {
+    ssize_t ret;
+    while ((ret = read(fd_, buf, size)) == -1 && errno == EINTR)
+      ;
+    if (ret < 0) {
+      return errno;
+    }
+    *bytes_read = static_cast<size_t>(ret);
+    return 0;
+  }
+
+  int Stat(struct stat *buf) final { return (fstat(fd_, buf) < 0) ? errno : 0; }
+
   int Sync() final { return (fsync(fd_) < 0) ? errno : 0; }
 
   int Truncate(off_t length) final {
@@ -86,9 +99,6 @@ class RealFile : public File {
   }
 
   int Write(re2::StringPiece data, size_t *bytes_written) final {
-    if (fd_ < 0) {
-      return EBADF;
-    }
     ssize_t ret;
     while ((ret = write(fd_, data.data(), data.size())) == -1 && errno == EINTR)
       ;

src/filesystem.h

@@ -71,6 +71,13 @@ class File {
   // ftruncate(), returning 0 on success or errno>0 on failure.
   virtual int Truncate(off_t length) = 0;
 
+  // read(), returning 0 on success or errno>0 on failure.
+  // On success, |bytes_read| will be updated.
+  virtual int Read(void *buf, size_t count, size_t *bytes_read) = 0;
+
+  // fstat(), returning 0 on success or errno>0 on failure.
+  virtual int Stat(struct stat *buf) = 0;
+
   // Write to the file, returning 0 on success or errno>0 on failure.
   // On success, |bytes_written| will be updated.
   virtual int Write(re2::StringPiece data, size_t *bytes_written) = 0;

src/testutil.cc

@@ -118,4 +118,24 @@ void WriteFileOrDie(const std::string &path, re2::StringPiece contents) {
   CHECK_EQ(ret, 0) << "close " << path << ": " << strerror(ret);
 }
 
+std::string ReadFileOrDie(const std::string &path) {
+  std::unique_ptr<File> f;
+  int ret = GetRealFilesystem()->Open(path.c_str(), O_RDONLY, &f);
+  CHECK_EQ(ret, 0) << "open " << path << ": " << strerror(ret);
+  struct stat statbuf;
+  ret = f->Stat(&statbuf);
+  CHECK_EQ(ret, 0) << "fstat " << path << ": " << strerror(ret);
+  std::string out(statbuf.st_size, '0');
+  off_t bytes_read_total = 0;
+  size_t bytes_read;
+  while (bytes_read_total < statbuf.st_size) {
+    ret = f->Read(&out[bytes_read_total], statbuf.st_size - bytes_read_total,
+                  &bytes_read);
+    CHECK_EQ(ret, 0) << "read " << path << ": " << strerror(ret);
+    CHECK_GT(bytes_read, 0);
+    bytes_read_total += bytes_read;
+  }
+  return out;
+}
+
 }  // namespace moonfire_nvr

src/testutil.h

@@ -46,6 +46,9 @@ std::string PrepareTempDirOrDie(const std::string &test_name);
 // Write the given file contents to the given path, or die.
 void WriteFileOrDie(const std::string &path, re2::StringPiece contents);
 
+// Read the contents of the given path, or die.
+std::string ReadFileOrDie(const std::string &path);
+
 // A scoped log sink for testing that the right log messages are sent.
 // Modelled after glog's "mock-log.h", which is not exported.
 // Use as follows: