for #742, refine the file reader and writer interface.

@@ -156,7 +156,7 @@ ModuleLibIncs=(${SRS_OBJS_DIR})
 MODULE_FILES=("srs_kernel_error" "srs_kernel_log" "srs_kernel_buffer"
         "srs_kernel_utility" "srs_kernel_flv" "srs_kernel_codec" "srs_kernel_file" 
         "srs_kernel_consts" "srs_kernel_aac" "srs_kernel_mp3" "srs_kernel_ts"
-        "srs_kernel_stream" "srs_kernel_balance" "srs_kernel_mp4")
+        "srs_kernel_stream" "srs_kernel_balance" "srs_kernel_mp4" "srs_kernel_io")
 KERNEL_INCS="src/kernel"; MODULE_DIR=${KERNEL_INCS} . auto/modules.sh
 KERNEL_OBJS="${MODULE_OBJS[@]}"
 #

@@ -115,6 +115,7 @@
 		3C7175B91E1DEA8000E8C49F /* sync.c in Sources */ = {isa = PBXBuildFile; fileRef = 3C7175B11E1DEA8000E8C49F /* sync.c */; };
 		3C82802C1BAFF8CC004A1794 /* srs_kafka_stack.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 3C82802A1BAFF8CC004A1794 /* srs_kafka_stack.cpp */; };
 		3C8CE01E1C3F482100548CC6 /* srs_app_hourglass.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 3C8CE01D1C3F482100548CC6 /* srs_app_hourglass.cpp */; };
+		3CA432A81E3F46DD001DA0C6 /* srs_kernel_io.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 3CA432A61E3F46DD001DA0C6 /* srs_kernel_io.cpp */; };
 		3CB25C2A1BB269FD00C97A63 /* jmp_sp.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 3CB25C291BB269FD00C97A63 /* jmp_sp.cpp */; };
 		3CC52DD81ACE4023006FEB01 /* srs_utest_amf0.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 3CC52DCA1ACE4023006FEB01 /* srs_utest_amf0.cpp */; };
 		3CC52DD91ACE4023006FEB01 /* srs_utest_config.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 3CC52DCC1ACE4023006FEB01 /* srs_utest_config.cpp */; };
@@ -403,6 +404,8 @@
 		3C82802B1BAFF8CC004A1794 /* srs_kafka_stack.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; name = srs_kafka_stack.hpp; path = ../../../src/protocol/srs_kafka_stack.hpp; sourceTree = "<group>"; };
 		3C8CE01C1C3F482100548CC6 /* srs_app_hourglass.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; name = srs_app_hourglass.hpp; path = ../../../src/app/srs_app_hourglass.hpp; sourceTree = "<group>"; };
 		3C8CE01D1C3F482100548CC6 /* srs_app_hourglass.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = srs_app_hourglass.cpp; path = ../../../src/app/srs_app_hourglass.cpp; sourceTree = "<group>"; };
+		3CA432A61E3F46DD001DA0C6 /* srs_kernel_io.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = srs_kernel_io.cpp; path = ../../../src/kernel/srs_kernel_io.cpp; sourceTree = "<group>"; };
+		3CA432A71E3F46DD001DA0C6 /* srs_kernel_io.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; name = srs_kernel_io.hpp; path = ../../../src/kernel/srs_kernel_io.hpp; sourceTree = "<group>"; };
 		3CB25C281BB2596300C97A63 /* setup_variables.sh */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.script.sh; name = setup_variables.sh; path = ../../../auto/setup_variables.sh; sourceTree = "<group>"; };
 		3CB25C291BB269FD00C97A63 /* jmp_sp.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = jmp_sp.cpp; path = ../../../research/arm/jmp_sp.cpp; sourceTree = "<group>"; };
 		3CC52DCA1ACE4023006FEB01 /* srs_utest_amf0.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = srs_utest_amf0.cpp; path = ../../src/utest/srs_utest_amf0.cpp; sourceTree = "<group>"; };
@@ -534,6 +537,8 @@
 				3C1232131AAE814D00CE8F6C /* srs_kernel_file.hpp */,
 				3C1232141AAE814D00CE8F6C /* srs_kernel_flv.cpp */,
 				3C1232151AAE814D00CE8F6C /* srs_kernel_flv.hpp */,
+				3CA432A61E3F46DD001DA0C6 /* srs_kernel_io.cpp */,
+				3CA432A71E3F46DD001DA0C6 /* srs_kernel_io.hpp */,
 				3C1232161AAE814D00CE8F6C /* srs_kernel_log.cpp */,
 				3C1232171AAE814D00CE8F6C /* srs_kernel_log.hpp */,
 				3C1232181AAE814D00CE8F6C /* srs_kernel_mp3.cpp */,
@@ -1074,6 +1079,7 @@
 				3C12329D1AAE81D900CE8F6C /* srs_app_heartbeat.cpp in Sources */,
 				3C1232231AAE814D00CE8F6C /* srs_kernel_consts.cpp in Sources */,
 				3C1232AF1AAE81D900CE8F6C /* srs_app_rtsp.cpp in Sources */,
+				3CA432A81E3F46DD001DA0C6 /* srs_kernel_io.cpp in Sources */,
 				3CC52DDD1ACE4023006FEB01 /* srs_utest_reload.cpp in Sources */,
 				3C689FA11AB6AAC800C9CEEE /* sync.c in Sources */,
 				3C068D6A1B10149F00AA722C /* srs_protocol_kbps.cpp in Sources */,

@@ -155,7 +155,7 @@ int SrsHttpResponseWriter::write(char* data, int size)
     return ret;
 }
 
-int SrsHttpResponseWriter::writev(iovec* iov, int iovcnt, ssize_t* pnwrite)
+int SrsHttpResponseWriter::writev(const iovec* iov, int iovcnt, ssize_t* pnwrite)
 {
     int ret = ERROR_SUCCESS;
     
@@ -163,7 +163,7 @@ int SrsHttpResponseWriter::writev(iovec* iov, int iovcnt, ssize_t* pnwrite)
     if (!header_wrote || content_length != -1) {
         ssize_t nwrite = 0;
         for (int i = 0; i < iovcnt; i++) {
-            iovec* piovc = iov + i;
+            const iovec* piovc = iov + i;
             nwrite += piovc->iov_len;
             if ((ret = write((char*)piovc->iov_base, (int)piovc->iov_len)) != ERROR_SUCCESS) {
                 return ret;
@@ -196,7 +196,7 @@ int SrsHttpResponseWriter::writev(iovec* iov, int iovcnt, ssize_t* pnwrite)
     // chunk size.
     int size = 0;
     for (int i = 0; i < iovcnt; i++) {
-        iovec* data_iov = iov + i;
+        const iovec* data_iov = iov + i;
         size += data_iov->iov_len;
     }
     written += size;
@@ -215,7 +215,7 @@ int SrsHttpResponseWriter::writev(iovec* iov, int iovcnt, ssize_t* pnwrite)
     
     // chunk body.
     for (int i = 0; i < iovcnt; i++) {
-        iovec* data_iov = iov + i;
+        const iovec* data_iov = iov + i;
         iovs[0].iov_base = (char*)data_iov->iov_base;
         iovs[0].iov_len = (int)data_iov->iov_len;
         iovs++;

@@ -103,7 +103,7 @@ public:
     virtual int final_request();
     virtual SrsHttpHeader* header();
     virtual int write(char* data, int size);
-    virtual int writev(iovec* iov, int iovcnt, ssize_t* pnwrite);
+    virtual int writev(const iovec* iov, int iovcnt, ssize_t* pnwrite);
     virtual void write_header(int code);
     virtual int send_header(char* data, int size);
 };

@@ -440,7 +440,7 @@ int SrsBufferWriter::write(void* buf, size_t count, ssize_t* pnwrite)
     return writer->write((char*)buf, (int)count);
 }
 
-int SrsBufferWriter::writev(iovec* iov, int iovcnt, ssize_t* pnwrite)
+int SrsBufferWriter::writev(const iovec* iov, int iovcnt, ssize_t* pnwrite)
 {
     return writer->writev(iov, iovcnt, pnwrite);
 }

@@ -210,7 +210,7 @@ public:
     virtual int64_t tellg();
 public:
     virtual int write(void* buf, size_t count, ssize_t* pnwrite);
-    virtual int writev(iovec* iov, int iovcnt, ssize_t* pnwrite);
+    virtual int writev(const iovec* iov, int iovcnt, ssize_t* pnwrite);
 };
 
 /**

@@ -146,13 +146,13 @@ int SrsFileWriter::write(void* buf, size_t count, ssize_t* pnwrite)
     return ret;
 }
 
-int SrsFileWriter::writev(iovec* iov, int iovcnt, ssize_t* pnwrite)
+int SrsFileWriter::writev(const iovec* iov, int iovcnt, ssize_t* pnwrite)
 {
     int ret = ERROR_SUCCESS;
     
     ssize_t nwrite = 0;
     for (int i = 0; i < iovcnt; i++) {
-        iovec* piov = iov + i;
+        const iovec* piov = iov + i;
         ssize_t this_nwrite = 0;
         if ((ret = write(piov->iov_base, piov->iov_len, &this_nwrite)) != ERROR_SUCCESS) {
             return ret;

@@ -29,6 +29,8 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
 #include <srs_core.hpp>
 
+#include <srs_kernel_io.hpp>
+
 #include <string>
 
 // for srs-librtmp, @see https://github.com/ossrs/srs/issues/213
@@ -39,7 +41,7 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 /**
 * file writer, to write to file.
 */
-class SrsFileWriter
+class SrsFileWriter : public ISrsBufferWriter
 {
 private:
     std::string path;
@@ -77,13 +79,13 @@ public:
      * for the HTTP FLV, to writev to improve performance.
      * @see https://github.com/ossrs/srs/issues/405
      */
-    virtual int writev(iovec* iov, int iovcnt, ssize_t* pnwrite);
+    virtual int writev(const iovec* iov, int iovcnt, ssize_t* pnwrite);
 };
 
 /**
 * file reader, to read from file.
 */
-class SrsFileReader
+class SrsFileReader : public ISrsBufferReader
 {
 private:
     std::string path;

+/*
+The MIT License (MIT)
+
+Copyright (c) 2013-2017 SRS(ossrs)
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software is furnished to do so,
+subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+*/
+
+#include <srs_kernel_io.hpp>
+
+ISrsBufferReader::ISrsBufferReader()
+{
+}
+
+ISrsBufferReader::~ISrsBufferReader()
+{
+}
+
+ISrsBufferWriter::ISrsBufferWriter()
+{
+}
+
+ISrsBufferWriter::~ISrsBufferWriter()
+{
+}
+

+/*
+The MIT License (MIT)
+
+Copyright (c) 2013-2017 SRS(ossrs)
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software is furnished to do so,
+subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+*/
+
+#ifndef SRS_KERNEL_IO_HPP
+#define SRS_KERNEL_IO_HPP
+
+/*
+#include <srs_kernel_io.hpp>
+*/
+
+#include <srs_core.hpp>
+
+// for srs-librtmp, @see https://github.com/ossrs/srs/issues/213
+#ifndef _WIN32
+#include <sys/uio.h>
+#endif
+
+/**
+ * the reader for the buffer to read from whatever channel.
+ */
+class ISrsBufferReader
+{
+public:
+    ISrsBufferReader();
+    virtual ~ISrsBufferReader();
+    // for protocol/amf0/msg-codec
+public:
+    virtual int read(void* buf, size_t size, ssize_t* nread) = 0;
+};
+
+/**
+ * the writer for the buffer to write to whatever channel.
+ */
+class ISrsBufferWriter
+{
+public:
+    ISrsBufferWriter();
+    virtual ~ISrsBufferWriter();
+    // for protocol
+public:
+    /**
+     * write bytes over writer.
+     * @nwrite the actual written bytes. NULL to ignore.
+     */
+    virtual int write(void* buf, size_t size, ssize_t* nwrite) = 0;
+    /**
+     * write iov over writer.
+     * @nwrite the actual written bytes. NULL to ignore.
+     */
+    virtual int writev(const iovec *iov, int iov_size, ssize_t* nwrite) = 0;
+};
+
+#endif
+

@@ -201,7 +201,7 @@ public:
      * for the HTTP FLV, to writev to improve performance.
      * @see https://github.com/ossrs/srs/issues/405
      */
-    virtual int writev(iovec* iov, int iovcnt, ssize_t* pnwrite) = 0;
+    virtual int writev(const iovec* iov, int iovcnt, ssize_t* pnwrite) = 0;
     
     // WriteHeader sends an HTTP response header with status code.
     // If WriteHeader is not called explicitly, the first call to Write

@@ -23,22 +23,6 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 #include <srs_protocol_io.hpp>
 
-ISrsBufferReader::ISrsBufferReader()
-{
-}
-
-ISrsBufferReader::~ISrsBufferReader()
-{
-}
-
-ISrsBufferWriter::ISrsBufferWriter()
-{
-}
-
-ISrsBufferWriter::~ISrsBufferWriter()
-{
-}
-
 ISrsProtocolStatistic::ISrsProtocolStatistic()
 {
 }

@@ -30,10 +30,7 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 #include <srs_core.hpp>
 
-// for srs-librtmp, @see https://github.com/ossrs/srs/issues/213
-#ifndef _WIN32
-#include <sys/uio.h>
-#endif
+#include <srs_kernel_io.hpp>
 
 /**
 * the system io reader/writer architecture:
@@ -61,41 +58,6 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
 
 /**
-* the reader for the buffer to read from whatever channel.
-*/
-class ISrsBufferReader
-{
-public:
-    ISrsBufferReader();
-    virtual ~ISrsBufferReader();
-// for protocol/amf0/msg-codec
-public:
-    virtual int read(void* buf, size_t size, ssize_t* nread) = 0;
-};
-
-/**
-* the writer for the buffer to write to whatever channel.
-*/
-class ISrsBufferWriter
-{
-public:
-    ISrsBufferWriter();
-    virtual ~ISrsBufferWriter();
-// for protocol
-public:
-    /**
-    * write bytes over writer.
-    * @nwrite the actual written bytes. NULL to ignore.
-    */
-    virtual int write(void* buf, size_t size, ssize_t* nwrite) = 0;
-    /**
-    * write iov over writer.
-    * @nwrite the actual written bytes. NULL to ignore.
-    */
-    virtual int writev(const iovec *iov, int iov_size, ssize_t* nwrite) = 0;
-};
-
-/**
 * get the statistic of channel.
 */
 class ISrsProtocolStatistic