Add basic_streambuf::alloc_size

fix #133

CHANGELOG.md

@@ -3,6 +3,7 @@
 * Change implicit to default value in example
 * Tidy up some declarations
 * Fix basic_streambuf::capacity
+* Add basic_streambuf::alloc_size
 
 --------------------------------------------------------------------------------
 

include/beast/core/basic_streambuf.hpp

@@ -25,7 +25,7 @@ namespace beast {
     the sequence to accommodate changes in the size of the character
     sequence.
 
-    @note Meets the requirements of @b `DynamicBuffer`.
+    @note Meets the requirements of @b DynamicBuffer.
 
     @tparam Allocator The allocator to use for managing memory.
 */
@@ -209,6 +209,36 @@ public:
         return this->member();
     }
 
+    /** Returns the default allocation size.
+
+        This is the smallest size that the stream buffer will allocate.
+        The size of the allocation can influence capacity, which will
+        affect algorithms that use capacity to efficiently read from
+        streams.
+    */
+    std::size_t
+    alloc_size() const
+    {
+        return alloc_size_;
+    }
+
+    /** Set the default allocation size.
+
+        This is the smallest size that the stream buffer will allocate.
+        The size of the allocation can influence capacity, which will
+        affect algorithms that use capacity to efficiently read from
+        streams.
+
+        @note This will not affect any already-existing allocations.
+
+        @param n The number of bytes.
+    */
+    void
+    alloc_size(std::size_t n)
+    {
+        alloc_size_ = n;
+    }
+
     /// Returns the size of the input sequence.
     size_type
     size() const

test/core/basic_streambuf.cpp

@@ -397,11 +397,12 @@ public:
         BEAST_EXPECT(to_string(sb.data()) == "x");
     }
 
-    void testReadSizeHelper()
+    void testCapacity()
     {
         using boost::asio::buffer_size;
         {
-            streambuf sb(10);
+            streambuf sb{10};
+            BEAST_EXPECT(sb.alloc_size() == 10);
             BEAST_EXPECT(read_size_helper(sb, 0) == 0);
             BEAST_EXPECT(read_size_helper(sb, 1) == 1);
             BEAST_EXPECT(read_size_helper(sb, 10) == 10);
@@ -414,6 +415,7 @@ public:
         }
         {
             streambuf sb(1000);
+            BEAST_EXPECT(sb.alloc_size() == 1000);
             BEAST_EXPECT(read_size_helper(sb, 0) == 0);
             BEAST_EXPECT(read_size_helper(sb, 1) == 1);
             BEAST_EXPECT(read_size_helper(sb, 1000) == 1000);
@@ -435,12 +437,33 @@ public:
             BEAST_EXPECT(read_size_helper(sb, 2000) == 997);
         }
         {
-            streambuf sb(2);
+            streambuf sb{2};
+            BEAST_EXPECT(sb.alloc_size() == 2);
             BEAST_EXPECT(test::buffer_count(sb.prepare(2)) == 1);
             BEAST_EXPECT(test::buffer_count(sb.prepare(3)) == 2);
             BEAST_EXPECT(buffer_size(sb.prepare(5)) == 5);
             BEAST_EXPECT(read_size_helper(sb, 10) == 6);
         }
+        {
+            auto avail =
+                [](streambuf const& sb)
+                {
+                    return sb.capacity() - sb.size();
+                };
+            streambuf sb{100};
+            BEAST_EXPECT(sb.alloc_size() == 100);
+            BEAST_EXPECT(avail(sb) == 0);
+            sb.prepare(100);
+            BEAST_EXPECT(avail(sb) == 100);
+            sb.commit(100);
+            BEAST_EXPECT(avail(sb) == 0);
+            sb.consume(100);
+            BEAST_EXPECT(avail(sb) == 0);
+            sb.alloc_size(200);
+            BEAST_EXPECT(sb.alloc_size() == 200);
+            sb.prepare(1);
+            BEAST_EXPECT(avail(sb) == 200);
+        }
     }
 
     void run() override
@@ -453,7 +476,7 @@ public:
         testMatrix();
         testIterators();
         testOutputStream();
-        testReadSizeHelper();
+        testCapacity();
     }
 };