Fix content reader for partial input

When there is partial message in reader, popping out the
characters lead to parse errors on the subsequent attempt
to parse. To avoid this, the last matched characters'
index is stored during parsing and reset on error.

src/content_stream.cpp

@@ -44,13 +44,17 @@ void ContentReader::close() {
 }
 
 std::string ContentReader::read() {
+  matched_idx = 0;
+
   // Find Content-Length header prefix
   if (!scan("Content-Length:")) {
     return "";
   }
+
   // Skip whitespace and tabs
   while (matchAny(" \t")) {
   }
+
   // Parse length
   size_t len = 0;
   while (true) {
@@ -68,10 +72,16 @@ std::string ContentReader::read() {
   if (!match("\r\n\r\n")) {
     return "";
   }
+
   // Read message
-  if (!buffer(len)) {
+  if (!buffer(len + matched_idx)) {
     return "";
   }
+
+  for (size_t i = 0; i < matched_idx; i++) {
+    buf.pop_front();
+  }
+
   std::string out;
   out.reserve(len);
   for (size_t i = 0; i < len; i++) {
@@ -97,18 +107,17 @@ bool ContentReader::scan(const char* str) {
 }
 
 bool ContentReader::match(const uint8_t* seq, size_t len) {
-  if (!buffer(len)) {
+  if (!buffer(len + matched_idx)) {
     return false;
   }
-  auto it = buf.begin();
+  auto it = matched_idx;
   for (size_t i = 0; i < len; i++, it++) {
-    if (*it != seq[i]) {
+    if (buf[it] != seq[i]) {
       return false;
     }
   }
-  for (size_t i = 0; i < len; i++) {
-    buf.pop_front();
-  }
+
+  matched_idx += len;
   return true;
 }
 
@@ -118,12 +127,12 @@ bool ContentReader::match(const char* str) {
 }
 
 char ContentReader::matchAny(const char* chars) {
-  if (!buffer(1)) {
+  if (!buffer(1 + matched_idx)) {
     return false;
   }
-  int c = buf.front();
+  int c = buf[matched_idx];
   if (auto p = strchr(chars, c)) {
-    buf.pop_front();
+    matched_idx++;
     return *p;
   }
   return 0;

src/content_stream.h

@@ -47,6 +47,7 @@ class ContentReader {
 
   std::shared_ptr<Reader> reader;
   std::deque<uint8_t> buf;
+  uint32_t matched_idx = 0;
 };
 
 class ContentWriter {

src/content_stream_test.cpp

@@ -81,3 +81,19 @@ 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>();
+  dap::ContentReader cs(sb);
+  sb->write("Content");
+  ASSERT_EQ(cs.read(), "");
+  sb->write("-Length: ");
+  ASSERT_EQ(cs.read(), "");
+  sb->write("26");
+  ASSERT_EQ(cs.read(), "");
+  sb->write("\r\n\r\n");
+  ASSERT_EQ(cs.read(), "");
+  sb->write("Content payload number one");
+  ASSERT_EQ(cs.read(), "Content payload number one");
+  ASSERT_EQ(cs.read(), "");
+}