Final clean-up of byte_range.{h,cpp}

src/server/byte_range.cpp

@@ -22,6 +22,8 @@
 
 #include "tools/stringTools.h"
 
+#include <cassert>
+
 namespace kiwix {
 
 namespace {
@@ -34,7 +36,7 @@ ByteRange parseByteRange(const std::string& rangeStr)
   if (iss >> start) {
     if ( start < 0 ) {
       if ( iss.eof() )
-        return ByteRange(ByteRange::PARSED, start, end);
+        return ByteRange(-start);
     } else {
       char c;
       if (iss >> c && c=='-') {
@@ -60,7 +62,37 @@ ByteRange::ByteRange(Kind kind, int64_t first, int64_t last)
   : kind_(kind)
   , first_(first)
   , last_(last)
-{}
+{
+  assert(kind != NONE);
+  assert(first >= 0);
+  assert(last >= first);
+}
+
+ByteRange::ByteRange(int64_t suffix_length)
+  : kind_(PARSED)
+  , first_(-suffix_length)
+  , last_(INT64_MAX)
+{
+  assert(suffix_length > 0);
+}
+
+int64_t ByteRange::first() const
+{
+  assert(kind_ > PARSED);
+  return first_;
+}
+
+int64_t ByteRange::last() const
+{
+  assert(kind_ > PARSED);
+  return last_;
+}
+
+int64_t ByteRange::length() const
+{
+  assert(kind_ > PARSED);
+  return last_ + 1 - first_;
+}
 
 ByteRange ByteRange::parse(const std::string& rangeStr)
 {
@@ -77,16 +109,16 @@ ByteRange ByteRange::resolve(int64_t contentSize) const
     return ByteRange(RESOLVED_FULL_CONTENT, 0, contentSize-1);
 
   if ( kind() == INVALID )
-    return ByteRange(INVALID, 0, contentSize-1);
+    return ByteRange(RESOLVED_UNSATISFIABLE, 0, contentSize-1);
 
-  const int64_t resolved_first = first() < 0
-                               ? std::max(int64_t(0), contentSize + first())
-                               : first();
+  const int64_t resolved_first = first_ < 0
+                               ? std::max(int64_t(0), contentSize + first_)
+                               : first_;
 
-  const int64_t resolved_last = std::min(contentSize-1, last());
+  const int64_t resolved_last = std::min(contentSize-1, last_);
 
   if ( resolved_first > resolved_last )
-    return ByteRange(INVALID, 0, contentSize-1);
+    return ByteRange(RESOLVED_UNSATISFIABLE, 0, contentSize-1);
 
   return ByteRange(RESOLVED_PARTIAL_CONTENT, resolved_first, resolved_last);
 }

src/server/byte_range.h

@@ -29,33 +29,49 @@ namespace kiwix {
 class ByteRange
 {
   public: // types
+
+    // ByteRange is parsed in a request, then it must be resolved (taking
+    // into account the actual size of the requested resource) before
+    // being applied in the response.
+    // The Kind enum represents possible states in such a lifecycle.
     enum Kind {
-      // No byte-range was present in the request
+      // The request is not a range request (no Range header)
       NONE,
 
-      // The value of the Range header is not a valid continuous range.
-      // Note that a valid (according to RFC7233) sequence of byte ranges is
-      // considered invalid in this context.
+      // The value of the Range header is not a valid continuous
+      // range. Note that a valid (according to RFC7233) sequence of multiple
+      // byte ranges is considered invalid in the current implementation
+      // (i.e. only single-range partial requests are supported).
       INVALID,
 
-      // This byte-range has been parsed from request
+      // This byte-range has been successfully parsed from the request
       PARSED,
 
-      // This is a response to a regular request
+      // This is a response to a regular (non-range) request
       RESOLVED_FULL_CONTENT,
 
-      // This is a response to a range request
-      RESOLVED_PARTIAL_CONTENT
+      // The range request is valid but unsatisfiable
+      RESOLVED_UNSATISFIABLE,
+
+      // This is a response to a (satisfiable) range request
+      RESOLVED_PARTIAL_CONTENT,
     };
 
   public: // functions
+    // Constructs a ByteRange object of NONE kind
     ByteRange();
+
+    // Constructs a ByteRange object of the given kind (except NONE)
     ByteRange(Kind kind, int64_t first, int64_t last);
 
+    // Constructs a ByteRange object of PARSED kind corresponding to a
+    // range request of the form "Range: bytes=-suffix_length"
+    explicit ByteRange(int64_t suffix_length);
+
     Kind kind() const { return kind_; }
-    int64_t first() const { return first_; }
-    int64_t last() const { return last_; }
-    int64_t length() const { return last_ + 1 - first_; }
+    int64_t first() const;
+    int64_t last() const;
+    int64_t length() const;
 
     static ByteRange parse(const std::string& rangeStr);
     ByteRange resolve(int64_t contentSize) const;

src/server/response.cpp

@@ -342,7 +342,7 @@ void Response::set_entry(const Entry& entry, const RequestContext& request) {
 
     set_content(content);
     set_compress(true);
-  } else if ( m_byteRange.kind() == ByteRange::INVALID ) {
+  } else if ( m_byteRange.kind() == ByteRange::RESOLVED_UNSATISFIABLE ) {
     set_code(416);
     set_content("");
     m_mode = ResponseMode::ERROR_RESPONSE;