buffer: add cbegin() methods

Signed-off-by: Kefu Chai <kchai@redhat.com>

diff --git a/src/include/buffer.h b/src/include/buffer.h
index 41b69508675410eb8556294ad00e8c633111c57a..606025005b0d47720ec197c69b487bdb7ed18bee 100644 (file)
--- a/src/include/buffer.h
+++ b/src/include/buffer.h
@@ -181,51 +181,41 @@ namespace buffer CEPH_BUFFER_API {
 
     void release();
 
-  public:
-    class iterator {
+    template<bool is_const>
+    class iterator_impl {
       const ptr *bp;     ///< parent ptr
       const char *start; ///< starting pointer into bp->c_str()
       const char *pos;   ///< pointer into bp->c_str()
       const char *end_ptr;   ///< pointer to bp->end_c_str()
-      bool deep;         ///< if true, do not allow shallow ptr copies
+      const bool deep;   ///< if true, do not allow shallow ptr copies
 
-      iterator(const ptr *p, size_t offset, bool d)
+      iterator_impl(std::conditional_t<is_const, const ptr*, ptr*> p,
+                   size_t offset, bool d)
        : bp(p),
          start(p->c_str() + offset),
          pos(start),
          end_ptr(p->end_c_str()),
-         deep(d) {}
+         deep(d)
+      {}
 
       friend class ptr;
 
     public:
-      const char *get_pos_add(size_t n) {
-       const char *r = pos;
-       pos += n;
-       if (pos > end_ptr)
-         throw end_of_buffer();
+      using pointer = std::conditional_t<is_const, const char*, char *>;
+      pointer get_pos_add(size_t n) {
+       auto r = pos;
+       advance(n);
        return r;
       }
-
       ptr get_ptr(size_t len) {
        if (deep) {
          return buffer::copy(get_pos_add(len), len);
        } else {
          size_t off = pos - bp->c_str();
-         pos += len;
-         if (pos > end_ptr)
-           throw end_of_buffer();
+         advance(len);
          return ptr(*bp, off, len);
        }
       }
-      ptr get_preceding_ptr(size_t len) {
-       if (deep) {
-         return buffer::copy(get_pos() - len, len);
-       } else {
-         size_t off = pos - bp->c_str();
-         return ptr(*bp, off - len, len);
-       }
-      }
 
       void advance(size_t len) {
        pos += len;
@@ -249,6 +239,10 @@ namespace buffer CEPH_BUFFER_API {
       }
     };
 
+  public:
+    using const_iterator = iterator_impl<true>;
+    using iterator = iterator_impl<false>;
+
     ptr() : _raw(0), _off(0), _len(0) {}
     // cppcheck-suppress noExplicitConstructor
     ptr(raw *r);
@@ -270,11 +264,17 @@ namespace buffer CEPH_BUFFER_API {
     void swap(ptr& other) noexcept;
     ptr& make_shareable();
 
-    iterator begin(size_t offset=0) const {
+    iterator begin(size_t offset=0) {
       return iterator(this, offset, false);
     }
-    iterator begin_deep(size_t offset=0) const {
-      return iterator(this, offset, true);
+    const_iterator begin(size_t offset=0) const {
+      return const_iterator(this, offset, false);
+    }
+    const_iterator cbegin() const {
+      return begin();
+    }
+    const_iterator begin_deep(size_t offset=0) const {
+      return const_iterator(this, 0, true);
     }
 
     // misc
@@ -822,6 +822,9 @@ namespace buffer CEPH_BUFFER_API {
     const_iterator begin() const {
       return const_iterator(this, 0);
     }
+    const_iterator cbegin() const {
+      return begin();
+    }
     const_iterator end() const {
       return const_iterator(this, _len, _buffers.end(), 0);
     }