Update StringBuffer to support partial reads test case.

Per #115, `ContentReader::match` must block until the whole pattern is
read or the underlying `Reader` is closed. The previous commit reverted
the change from #50 to ensure this behavior is still implemented.

This commit re-adds the unit test from #50 with an update to the
behavior of `StringBuffer` to correct implement `Reader` so that
the partial read test case is still covered by the unit tests.

src/content_stream_test.cpp

@@ -81,3 +81,16 @@ TEST(ContentStreamTest, ShortRead) {
   ASSERT_EQ(cs.read(), "Content payload number three");
   ASSERT_EQ(cs.read(), "");
 }
+
+TEST(ContentStreamTest, PartialReadAndParse) {
+  auto sb = std::make_shared<dap::StringBuffer>();
+  sb->write("Content");
+  sb->write("-Length: ");
+  sb->write("26");
+  sb->write("\r\n\r\n");
+  sb->write("Content payload number one");
+
+  dap::ContentReader cs(sb);
+  ASSERT_EQ(cs.read(), "Content payload number one");
+  ASSERT_EQ(cs.read(), "");
+}

src/string_buffer.h

@@ -19,6 +19,7 @@
 
 #include <algorithm>  // std::min
 #include <cstring>    // memcpy
+#include <deque>
 #include <memory>  // std::unique_ptr
 #include <string>
 
@@ -39,6 +40,7 @@ class StringBuffer : public virtual Reader, public virtual Writer {
 
  private:
   std::string str;
+  std::deque<size_t> chunk_lengths;
   bool closed = false;
 };
 
@@ -62,12 +64,19 @@ std::string StringBuffer::string() const {
 }
 
 size_t StringBuffer::read(void* buffer, size_t bytes) {
-  if (closed || bytes == 0 || str.size() == 0) {
+  if (closed || bytes == 0 || str.size() == 0 || chunk_lengths.size() == 0) {
     return 0;
   }
-  auto len = std::min(bytes, str.size());
+  size_t& chunk_length = chunk_lengths.front();
+
+  auto len = std::min(bytes, chunk_length);
   memcpy(buffer, str.data(), len);
   str = std::string(str.begin() + len, str.end());
+  if (bytes < chunk_length) {
+    chunk_length -= bytes;
+  } else {
+    chunk_lengths.pop_front();
+  }
   return len;
 }
 
@@ -77,6 +86,7 @@ bool StringBuffer::write(const void* buffer, size_t bytes) {
   }
   auto chars = reinterpret_cast<const char*>(buffer);
   str.append(chars, chars + bytes);
+  chunk_lengths.push_back(bytes);
   return true;
 }