Implementation of protobuf service based on http

 

Usually webapi implementations return textual json, xml and other strings through http get/post requests. This article uses Tomcat8 as the web server and responds to binary data with the help of the protobuf framework.

Since the protobuf protocol can be cross-language, we can use java servlet to implement the server, and C/C++ to implement the client to achieve the purpose of decoupling each module. Both parties need to set the ContentType to application/x-protobuf.

 

1. Prepare the proto file

 

package qwd.kettas;

// request structure
message CTestReq
{
        optional uint32 ShopId = 1; // Shop ID
}

message CProduct
{
        optional uint32 Id = 1; // item ID
        optional bytes Name = 2; // product name
        optional double price = 3; // item price
}

// response structure
message CTestResp
{
        optional int32 Total = 1; // total number of items
        repeated CProduct Product = 2; // array of products
}

 

2. Java Servlet Service

 

/**
 * Servlet service implementation, receiving post requests, responding to protocol buffer binary data
 */
protected void service( HttpServletRequest req, HttpServletResponse resp )
	throws ServletException, IOException {
	/*	
	 * Note: Filling 0 with no data in in.read() will cause parseFrom() to fail, which is not feasible.
	byte[] postBuf = new byte[128];
	InputStream in = req.getInputStream();
	int len ​​= in.read( postBuf );
	 */
	
	// protobuf parsing parameters
	CTestReq tReq = CTestReq.parseFrom( req.getInputStream() ); // InputStream as parameter
	int shopid = tReq.getShopId();
	
	// prepare data
	CTestResp.Builder pBuilder = CTestResp.newBuilder();
	pBuilder.setTotal(2);
	
	// product one
	CProduct.Builder pProBuild1 = CProduct.newBuilder();
	pProBuild1.setId( shopid + 1001 );
	pProBuild1.setName( ByteString.copyFrom("Xiao Ming","UTF-8") ); // String needs to be converted by ByteString, it is best to define string
	pProBuild1.setPrice(15.8);
	pBuilder.addProduct( pProBuild1 );
	
	// product two
	pProBuild1 = CProduct.newBuilder();
	pProBuild1.setId( shopid + 1002 );
	pProBuild1.setName( ByteString.copyFrom("小王","UTF-8") );
	pProBuild1.setPrice(29.8);
	pBuilder.addProduct( pProBuild1 );
	
	// reply
	CTestResp pResp = pBuilder.build();
	System.out.println( "Data: " + pResp.toString() );
	
	// Serialization
	byte[] buff = pResp.toByteArray();
	
	// Response, set the HTTP header to: application/x-protobuf
	resp.setContentType("application/x-protobuf");
	resp.getOutputStream().write( buff );	// 发送
}

 

 

3. Client Test

 

// data callback function
size_t OnWriteData( void* buffer, size_t size, size_t nmemb, void *lpVoid )
{
        std::string* str = dynamic_cast<std::string*>((std::string *)lpVoid);
        if ( NULL == str || NULL == buffer )
        {   
                return -1;
        }   

        char* pData = (char*)buffer;
        str->append(pData, size * nmemb);
        return nmemb;
}


// curl simulates post request
void TestCurl()
{
        printf( "\n****************TestCurl*******************\n" );
        const char *url = "http://10.14.230.7:8080/protoweb/proto";
        CTestReq req;
        CTestResp resp;
        string sReq;
        string sResp;

        req.set_shopid( 1500 );

        // serialize the request
        if ( !req.SerializeToString(&sReq) )
                return;

        curl_slist *m_header = NULL;
        m_header = curl_slist_append( m_header, "Content-Type: application/x-protobuf" ); // set message header

        CURL *curl = curl_easy_init();
        curl_easy_setopt( curl, CURLOPT_HTTPHEADER, m_header ); // Header
        curl_easy_setopt( curl, CURLOPT_REFERER, "nginx" );
        curl_easy_setopt( curl, CURLOPT_VERBOSE, 1L );
        curl_easy_setopt( curl, CURLOPT_URL, url );
        curl_easy_setopt( curl, CURLOPT_NOSIGNAL, 1);
                                          
        curl_easy_setopt( curl, CURLOPT_POSTFIELDS, sReq.c_str() );             // Post
        curl_easy_setopt( curl, CURLOPT_POSTFIELDSIZE, sReq.length() );
        curl_easy_setopt( curl, CURLOPT_WRITEFUNCTION, OnWriteData );
        curl_easy_setopt( curl, CURLOPT_WRITEDATA, (void*)&sResp );     // Accept data

        CURLcode ret = curl_easy_perform( curl );
        assert (ret == CURLE_OK);
        curl_easy_cleanup( curl );
        curl_slist_free_all( m_header );

        // deserialize data
        if ( !resp.ParseFromString(sResp) )
                return;

        printf( "Response: %s\n", resp.DebugString().c_str() );
}

 

As a result of the execution, curl initiates a post request and returns 46 bytes of content: