[libc] Add a simple StringStream class.

[sivachandra]

Summary

This class will be used in future changes to construct simple strings.

[sivachandra]

Add more tests.

[michaelrj]

libc/src/__support/CPP/stringstream.h

16

it would probably be better to include StringView explicitly instead of through integer_to_string.

27

why is this separate from write_size? It seems like they're tracking the same data.

[sivachandra]

Address comments.

[sivachandra]

libc/src/__support/CPP/stringstream.h

27

Ah, I had a seek method which I removed as I don't need it anymore. Forgot to clean this up. Done now.

[michaelrj]

LGTM

libc/src/__support/CPP/CMakeLists.txt

 
 add_header_library(
   string_view
   HDRS
     StringView.h
 )
 
 add_header_library(
+  stringstream
+  HDRS
+    stringstream.h
+  DEPENDS
+    .array_ref
+    .string_view
+    libc.src.__support.integer_to_string
+)
+
+add_header_library(
   type_traits
   HDRS
     TypeTraits.h
   DEPENDS
     .uint
 )
 
 add_header_library(

libc/src/__support/CPP/stringstream.h

+//===-- A simple implementation of string stream class ----------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SUPPORT_CPP_STRINGSTREAM_H
+#define LLVM_LIBC_SRC_SUPPORT_CPP_STRINGSTREAM_H
+
+#include "ArrayRef.h"
+#include "StringView.h"
+#include "TypeTraits.h"
+
+#include "src/__support/integer_to_string.h"
+
+namespace __llvm_libc {
+namespace cpp {
+
+// This class is to be used to write simple strings into a user provided buffer
+// without any dynamic memory allocation. There is no requirement to mimic the
+// C++ standard library class std::stringstream.
+class StringStream {
+  MutableArrayRef<char> data;
+  size_t write_ptr = 0; // The current write pointer
+  bool err = false;     // If an error occurs while writing
+
+  void write(const char *bytes, size_t size) {
+    size_t i = 0;
+    const size_t data_size = data.size();
+    for (; write_ptr < data_size && i < size; ++i, ++write_ptr)
+      data[write_ptr] = bytes[i];
+    if (i < size) {
+      // If some of the characters couldn't be written, set error.
+      err = true;
+    }
+  }
+
+public:
+  static constexpr char ENDS = '\0';
+
+  // Create a string stream which will write into |buf|.
+  constexpr StringStream(const MutableArrayRef<char> &buf) : data(buf) {}
+
+  // Return a StringView to the current characters in the stream. If a
+  // null terminator was not explicitly written, then the return value
+  // will not include one. In order to produce a StringView to a null
+  // terminated string, write ENDS explicitly.
+  StringView str() const { return StringView(data.data(), write_ptr); }
+
+  // Write the characters from |str| to the stream.
+  StringStream &operator<<(StringView str) {
+    write(str.data(), str.size());
+    return *this;
+  }
+
+  // Write the |val| as string.
+  template <typename T, EnableIfType<IsIntegral<T>::Value, int> = 0>
+  StringStream &operator<<(T val) {
+    const auto int_to_str = integer_to_string(val);
+    return operator<<(int_to_str.str());
+  }
+
+  template <typename T, EnableIfType<IsFloatingPointType<T>::Value, int> = 0>
+  StringStream &operator<<(T val) {
+    // If this specialization gets activated, then the static_assert will
+    // trigger a compile error about missing floating point number support.
+    static_assert(!IsFloatingPointType<T>::Value,
+                  "Writing floating point numbers is not yet supported");
+    return *this;
+  }
+
+  // Write a null-terminated string. The terminating null character is not
+  // written to allow stremaing to continue.
+  StringStream &operator<<(const char *str) {
+    return operator<<(StringView(str));
+  }
+
+  // Write a single character.
+  StringStream &operator<<(char a) {
+    write(&a, 1);
+    return *this;
+  }
+
+  // Return true if any write operation(s) failed due to insufficient size.
+  bool overflow() const { return err; }
+};
+
+} // namespace cpp
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_SUPPORT_CPP_STRINGSTREAM_H

libc/test/src/__support/CPP/CMakeLists.txt

add_libc_unittest(
   blockstore_test
   SUITE
     libc_cpp_utils_unittests
   SRCS
     blockstore_test.cpp
   DEPENDS
     libc.src.__support.CPP.blockstore
 )
+
+add_libc_unittest(
+  stringstream_test
+  SUITE
+    libc_cpp_utils_unittests
+  SRCS
+    stringstream_test.cpp
+  DEPENDS
+    libc.src.__support.CPP.array_ref
+    libc.src.__support.CPP.stringstream
+)

libc/test/src/__support/CPP/stringstream_test.cpp

+//===-- Unittests for StringStream ----------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/CPP/ArrayRef.h"
+#include "src/__support/CPP/stringstream.h"
+#include "utils/UnitTest/Test.h"
+
+using __llvm_libc::cpp::MutableArrayRef;
+using __llvm_libc::cpp::StringStream;
+
+TEST(LlvmLibcStringStreamTest, Simple) {
+  char buf[256];
+  MutableArrayRef<char> bufref(reinterpret_cast<void *>(buf), 256);
+
+  StringStream ss1(bufref);
+  ss1 << "Hello, Stream - " << int(123) << StringStream::ENDS;
+  ASSERT_FALSE(ss1.overflow());
+  ASSERT_STREQ(ss1.str().data(), "Hello, Stream - 123");
+
+  StringStream ss2(bufref);
+  ss2 << 'a' << 'b' << 'c' << StringStream::ENDS;
+  ASSERT_FALSE(ss2.overflow());
+  ASSERT_STREQ(ss2.str().data(), "abc");
+}
+
+TEST(LlvmLibcStringStreamTest, Overflow) {
+  constexpr size_t BUFSIZE = 8;
+  char buf[BUFSIZE];
+  MutableArrayRef<char> bufref(reinterpret_cast<void *>(buf), BUFSIZE);
+
+  StringStream ss1(bufref);
+  ss1 << "Hello, Stream - " << int(123) << StringStream::ENDS;
+  ASSERT_TRUE(ss1.overflow());
+  ASSERT_EQ(ss1.str().size(), BUFSIZE);
+
+  StringStream ss2(bufref);
+  ss2 << "7777777";
+  ASSERT_FALSE(ss2.overflow());
+  ASSERT_EQ(ss2.str().size(), size_t(7));
+  ss2 << "8";
+  ASSERT_FALSE(ss2.overflow());
+  ASSERT_EQ(ss2.str().size(), size_t(8));
+  ss2 << StringStream::ENDS;
+  ASSERT_TRUE(ss2.overflow());
+  ASSERT_EQ(ss2.str().size(), BUFSIZE);
+}