Add InputStream::ReadExactly

Read() can return fewer bytes than requested.
ReadExactly() will call Read() repeatedly until we
have read as many bytes as we need.

PiperOrigin-RevId: 518719418

internal/platform/BUILD

@@ -232,6 +232,7 @@ cc_test(
         "bluetooth_utils_test.cc",
         "byte_array_test.cc",
         "feature_flags_test.cc",
+        "input_stream_test.cc",
         "prng_test.cc",
     ],
     deps = [

internal/platform/exception.h

@@ -107,6 +107,15 @@ class ExceptionOr {
   Exception exception_{Exception::kFailed};
 };
 
+template <typename T>
+constexpr inline bool operator==(const ExceptionOr<T>& a,
+                                 const ExceptionOr<T>& b) {
+  if (a.ok() && b.ok()) {
+    return a.result() == b.result();
+  }
+  return a.exception() == b.exception();
+}
+
 }  // namespace nearby
 
 #endif  // PLATFORM_BASE_EXCEPTION_H_

internal/platform/input_stream.cc

@@ -17,6 +17,7 @@
 #include <algorithm>
 #include <cstddef>
 #include <cstdint>
+#include <utility>
 
 #include "internal/platform/byte_array.h"
 #include "internal/platform/exception.h"
@@ -43,4 +44,34 @@ ExceptionOr<size_t> InputStream::Skip(size_t offset) {
   return ExceptionOr<size_t>(offset);
 }
 
+ExceptionOr<ByteArray> InputStream::ReadExactly(std::size_t size) {
+  ByteArray buffer;
+  std::size_t current_pos = 0;
+
+  while (current_pos < size) {
+    ExceptionOr<ByteArray> read_bytes = Read(size - current_pos);
+    if (!read_bytes.ok()) {
+      return read_bytes;
+    }
+    const ByteArray& result = read_bytes.result();
+
+    if (result.Empty()) {
+      return ExceptionOr<ByteArray>(Exception::kIo);
+    }
+    if (current_pos == 0) {
+      if (result.size() == size) {
+        // We have read the requested `size` bytes in one chunk. We can return
+        // it directly.
+        return read_bytes;
+      } else {
+        // Reserve space for in the buffer.
+        buffer.SetData(size);
+      }
+    }
+    buffer.CopyAt(current_pos, result);
+    current_pos += result.size();
+  }
+
+  return ExceptionOr<ByteArray>(std::move(buffer));
+}
 }  // namespace nearby

internal/platform/input_stream.h

@@ -38,6 +38,11 @@ class InputStream {
   // or Exception::kIo on error.
   virtual ExceptionOr<size_t> Skip(size_t offset);
 
+  // Reads exactly `size` bytes from the input stream.
+  // Return Exception::kIo on error, or if end of file is reached before reading
+  // `size` bytes.
+  ExceptionOr<ByteArray> ReadExactly(std::size_t size);
+
   // throws Exception::kIo
   virtual Exception Close() = 0;
 };

internal/platform/input_stream_test.cc

@@ -0,0 +1,119 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "internal/platform/input_stream.h"
+
+#include <string>
+
+#include "gmock/gmock.h"
+#include "protobuf-matchers/protocol-buffer-matchers.h"
+#include "gtest/gtest.h"
+#include "internal/platform/byte_array.h"
+#include "internal/platform/exception.h"
+
+namespace nearby {
+namespace {
+
+using ::testing::_;
+using ::testing::InSequence;
+using ::testing::NiceMock;
+using ::testing::Return;
+
+class TestInputStream : public InputStream {
+ public:
+  MOCK_METHOD(ExceptionOr<ByteArray>, Read, (std::int64_t), (override));
+  MOCK_METHOD(Exception, Close, (), (override));
+};
+
+// Returns a ByteArray with values: a, a + 1, a + 2, ..., b - 1.
+ExceptionOr<ByteArray> Range(char a, char b) {
+  std::string s;
+  for (char c = a; c < b; c++) {
+    s.push_back(c);
+  }
+  return ExceptionOr<ByteArray>(ByteArray(s));
+}
+
+TEST(InputStreamTest, Skip) {
+  NiceMock<TestInputStream> stream;
+  InSequence seq;
+  EXPECT_CALL(stream, Read(50)).WillOnce(Return(Range(0, 10)));
+  EXPECT_CALL(stream, Read(40)).WillOnce(Return(Range(0, 10)));
+  EXPECT_CALL(stream, Read(30)).WillOnce(Return(Range(0, 30)));
+
+  ExceptionOr<std::size_t> skipped = stream.Skip(50);
+
+  EXPECT_EQ(skipped.result(), 50);
+}
+
+TEST(InputStreamTest, SkipsLessOnEof) {
+  NiceMock<TestInputStream> stream;
+  InSequence seq;
+  EXPECT_CALL(stream, Read(50)).WillOnce(Return(Range(0, 10)));
+  EXPECT_CALL(stream, Read(40)).WillOnce(Return(Range(0, 10)));
+  // Returns EOF
+  EXPECT_CALL(stream, Read(30)).WillOnce(Return(Range(0, 0)));
+
+  ExceptionOr<std::size_t> skipped = stream.Skip(50);
+
+  EXPECT_EQ(skipped.result(), 20);
+}
+
+TEST(InputStreamTest, SkipFailsOnError) {
+  NiceMock<TestInputStream> stream;
+  InSequence seq;
+  EXPECT_CALL(stream, Read(50)).WillOnce(Return(Range(0, 10)));
+  EXPECT_CALL(stream, Read(40))
+      .WillOnce(Return(ExceptionOr<ByteArray>(Exception::kIo)));
+
+  ExceptionOr<std::size_t> skipped = stream.Skip(50);
+
+  EXPECT_EQ(skipped.exception(), Exception::kIo);
+}
+
+TEST(InputStreamTest, ReadExactlyOneChunk) {
+  NiceMock<TestInputStream> stream;
+  EXPECT_CALL(stream, Read(10)).WillOnce(Return(Range(0, 10)));
+
+  ExceptionOr<ByteArray> result = stream.ReadExactly(10);
+
+  EXPECT_EQ(result, Range(0, 10));
+}
+
+TEST(InputStreamTest, ReadExactlyMultipleChunks) {
+  NiceMock<TestInputStream> stream;
+  InSequence seq;
+  EXPECT_CALL(stream, Read(30)).WillOnce(Return(Range(0, 10)));
+  EXPECT_CALL(stream, Read(20)).WillOnce(Return(Range(10, 20)));
+  EXPECT_CALL(stream, Read(10)).WillOnce(Return(Range(20, 30)));
+
+  ExceptionOr<ByteArray> result = stream.ReadExactly(30);
+
+  EXPECT_EQ(result, Range(0, 30));
+}
+
+TEST(InputStreamTest, ReadExactlyFailsOnError) {
+  NiceMock<TestInputStream> stream;
+  InSequence seq;
+  EXPECT_CALL(stream, Read(30)).WillOnce(Return(Range(0, 10)));
+  EXPECT_CALL(stream, Read(20))
+      .WillOnce(Return(ExceptionOr<ByteArray>(Exception::kIo)));
+
+  ExceptionOr<ByteArray> result = stream.ReadExactly(30);
+
+  EXPECT_EQ(result.exception(), Exception::kIo);
+}
+
+}  // namespace
+}  // namespace nearby