Add sbuffer::read_from() to read data from std::istream.

include/msgpack/v1/sbuffer.hpp

@@ -16,6 +16,7 @@
 
 #include <stdexcept>
 #include <cstring>
+#include <istream>
 
 namespace msgpack {
 
@@ -81,6 +82,22 @@ class sbuffer {
         m_size += len;
     }
 
+    size_t read_from(std::istream& is, size_t len)
+    {
+        if (len == 0) return 0;
+
+        if(m_alloc - m_size < len) {
+            expand_buffer(len);
+        }
+
+        is.read(m_data + m_size, static_cast<std::streamsize>(len));
+        const std::streamsize n = is.gcount();
+        if (n <= 0) return 0;
+
+        m_size += static_cast<size_t>(n);
+        return static_cast<size_t>(n);
+    }
+
     char* data()
     {
         return m_data;

test/buffer.cpp

@@ -5,6 +5,8 @@
 #define BOOST_TEST_MODULE buffer
 #include <boost/test/unit_test.hpp>
 
+#include <sstream>
+#include <string>
 #include <string.h>
 
 BOOST_AUTO_TEST_CASE(sbuffer)
@@ -27,6 +29,41 @@ BOOST_AUTO_TEST_CASE(sbuffer)
 }
 
 
+BOOST_AUTO_TEST_CASE(sbuffer_read_from)
+{
+    const std::string src = "abcdefghij";
+
+    std::istringstream is(src);
+    msgpack::sbuffer sbuf;
+
+    // A part of the stream is appended to the buffer.
+    BOOST_CHECK_EQUAL(4ul, sbuf.read_from(is, 4));
+    BOOST_CHECK_EQUAL(4ul, sbuf.size());
+    BOOST_CHECK( memcmp(sbuf.data(), "abcd", 4) == 0 );
+
+    // A request larger than the remaining data reads up to the end of the stream.
+    BOOST_CHECK_EQUAL(6ul, sbuf.read_from(is, 100));
+    BOOST_CHECK_EQUAL(10ul, sbuf.size());
+    BOOST_CHECK( memcmp(sbuf.data(), "abcdefghij", 10) == 0 );
+
+    // len == 0 reads nothing.
+    BOOST_CHECK_EQUAL(0ul, sbuf.read_from(is, 0));
+    BOOST_CHECK_EQUAL(10ul, sbuf.size());
+
+    // Reading at the end of the stream reads nothing.
+    is.clear();
+    BOOST_CHECK_EQUAL(0ul, sbuf.read_from(is, 1));
+    BOOST_CHECK_EQUAL(10ul, sbuf.size());
+
+    // The buffer grows as needed.
+    msgpack::sbuffer small(1);
+    std::istringstream is2(src);
+    BOOST_CHECK_EQUAL(10ul, small.read_from(is2, 10));
+    BOOST_CHECK_EQUAL(10ul, small.size());
+    BOOST_CHECK( memcmp(small.data(), "abcdefghij", 10) == 0 );
+}
+
+
 BOOST_AUTO_TEST_CASE(vrefbuffer)
 {
     msgpack::vrefbuffer vbuf;