Access http:h2

Learn how to access Http2.

Example

example/http_c++

About h2

brpc names the HTTP/2 protocol to “h2”, no matter encrypted or not. However HTTP/2 connections without SSL are shown on /connections with the official name “h2c”, and the ones with SSL are shown as “h2”.

The APIs for http and h2 in brpc are basically same. Without explicit statement, mentioned http features work for h2 as well.

Create Channel

In order to use brpc::Channel to access http/h2 services, ChannelOptions.protocol must be set to PROTOCOL_HTTP or PROTOCOL_H2.

Once the protocol is set, the first parameter of Channel::Init can be any valid URL. Note: Only host and port inside the URL are used by Init(), other parts are discarded. Allowing full URL simply saves the user from additional parsing code.

brpc::ChannelOptions options;
options.protocol = brpc::PROTOCOL_HTTP;  // or brpc::PROTOCOL_H2
if (channel.Init("www.baidu.com" /*any url*/, &options) != 0) {
     LOG(ERROR) << "Fail to initialize channel";
     return -1;
}

http/h2 channel also support BNS address or other naming services.

GET

brpc::Controller cntl;
cntl.http_request().uri() = "www.baidu.com/index.html";  // Request URL
channel.CallMethod(NULL, &cntl, NULL, NULL, NULL/*done*/);

http/h2 does not relate to protobuf much, thus all parameters of CallMethod are NULL except Controller and done. Issue asynchronous RPC with non-NULL done.

cntl.response_attachment() is body of the http/h2 response and typed butil::IOBuf. IOBuf can be converted to std::string by to_string(), which needs to allocate memory and copy all data. If performance is important, the code should consider supporting IOBuf directly rather than requiring continuous memory.

POST

The default HTTP Method is GET, which can be changed to POST or other http methods. The data to POST should be put into request_attachment(), which is typed butil::IOBuf and able to append std :: string or char * directly.

brpc::Controller cntl;
cntl.http_request().uri() = "...";  // Request URL
cntl.http_request().set_method(brpc::HTTP_METHOD_POST);
cntl.request_attachment().append("{\"message\":\"hello world!\"}");
channel.CallMethod(NULL, &cntl, NULL, NULL, NULL/*done*/);

If the body needs a lot of printing to build, consider using butil::IOBufBuilder, which has same interfaces as std::ostringstream, probably simpler and more efficient than c-style printf when lots of objects need to be printed.

brpc::Controller cntl;
cntl.http_request().uri() = "...";  // Request URL
cntl.http_request().set_method(brpc::HTTP_METHOD_POST);
butil::IOBufBuilder os;
os << "A lot of printing" << printable_objects << ...;
os.move_to(cntl.request_attachment());
channel.CallMethod(NULL, &cntl, NULL, NULL, NULL/*done*/);

Change HTTP version

brpc behaves as http/1.1 by default.

Comparing to http/1.1, http/1.0 lacks of long connections(KeepAlive). To communicate brpc client with some legacy http servers, the client may be configured as follows:

cntl.http_request().set_version(1, 0);

Setting http version does not work for h2, but the versions in h2 responses received by client and h2 requests received by server are set to (2, 0).

brpc server recognizes http versions automically and responds accordingly without users’ aid.

URL

Genaral form of an URL:

// URI scheme : http://en.wikipedia.org/wiki/URI_scheme
//
//  foo://username:password@example.com:8042/over/there/index.dtb?type=animal&name=narwhal#nose
//  \_/   \_______________/ \_________/ \__/            \___/ \_/ \______________________/ \__/
//   |           |               |       |                |    |            |                |
//   |       userinfo           host    port              |    |          query          fragment
//   |    \________________________________/\_____________|____|/ \__/        \__/
// scheme                 |                          |    |    |    |          |
//                    authority                      |    |    |    |          |
//                                                 path   |    |    interpretable as keys
//                                                        |    |
//        \_______________________________________________|____|/       \____/     \_____/
//                             |                          |    |          |           |
//                     hierarchical part                  |    |    interpretable as values
//                                                        |    |
//                                   interpretable as filename |
//                                                             |
//                                                             |
//                                               interpretable as extension

As we saw in examples above, Channel.Init() and cntl.http_request().uri() both need the URL. Why does uri() need to be set additionally rather than using the URL to Init() directly?

Indeed, the settings are repeated in simple cases. But they are different in more complex scenes:

  • Access multiple servers under a NamingService (for example BNS), in which case Channel::Init accepts a name meaningful to the NamingService(for example node names in BNS), while uri() is assigned with the URL.
  • Access servers via http/h2 proxy, in which case Channel::Init takes the address of the proxy server, while uri() is still assigned with the URL.

Host header

If user already sets Host header(case insensitive), framework makes no change.

If user does not set Host header and the URL has host, for example http://www.foo.com/path, the http request contains “Host: www.foo.com”.

If user does not set host header and the URL does not have host as well, for example “/index.html?name=value”, but if the address initialized by the channel contains domain name. framework sets Host header with domain name of the target server. if this address is “http://www.foo.com”, this http server should see Host: www.foo.com, if this address is “http://www.foo.com:8989”, this http server should be see Host: www.foo.com:8989.

If user does not set host header and the URL does not have host as well, for example “/index.html?name=value”, and the address initialized by the channel doesn’t contain domain name. framework sets Host header with IP and port of the target server. A http server at 10.46.188.39:8989 should see Host: 10.46.188.39:8989.

The header is named “:authority” in h2.

Common usages

Take http request as an example (similar with http response), common operations are listed as follows:

Access an HTTP header named Foo

const std::string* value = cntl->http_request().GetHeader("Foo"); // NULL when not exist

Set an HTTP header named Foo

cntl->http_request().SetHeader("Foo", "value");

Access a query named Foo

const std::string* value = cntl->http_request().uri().GetQuery("Foo"); // NULL when not exist

Set a query named Foo

cntl->http_request().uri().SetQuery("Foo", "value");

Set HTTP method

cntl->http_request().set_method(brpc::HTTP_METHOD_POST);

Set the URL

cntl->http_request().uri() = "http://www.baidu.com";

Set the content-type

cntl->http_request().set_content_type("text/plain");

Get HTTP body

butil::IOBuf& buf = cntl->request_attachment();
std::string str = cntl->request_attachment().to_string(); // trigger copy underlying

Set HTTP body

cntl->request_attachment().append("....");
butil::IOBufBuilder os; os << "....";
os.move_to(cntl->request_attachment());

Notes on http header:

  • field_name of the header is case-insensitive according to rfc2616. brpc supports case-insensitive field names and keeps same cases at printing as users set.
  • If multiple headers have same field names, according to rfc2616, values should be merged and separated by comma (,). Users figure out how to use this kind of values by their own.
  • Queries are separated by “&” and key/value in a query are separated by “=”. Values can be omitted. For example, key1=value1&key2&key3=value3 is a valid query string, in which the value for key2 is an empty string.

Debug HTTP messages

Turn on -http_verbose so that the framework prints each http request and response. Note that this should only be used in tests or debuggings rather than online services.

HTTP errors

When server returns a non-2xx HTTP status code, the HTTP RPC is considered to be failed and cntl->ErrorCode() at client-side is set to EHTTP, users can check cntl-> http_response().status_code() for more specific HTTP error. In addition, server can put html or json describing the error into cntl->response_attachment() which is sent back to the client as http body.

Compress Request Body

Controller::set_request_compress_type(brpc::COMPRESS_TYPE_GZIP) makes framework try to gzip the HTTP body. “try to” means the compression may not happen, because:

  • Size of body is smaller than bytes specified by -http_body_compress_threshold, which is 512 by default. The reason is that gzip is not a very fast compression algorithm, when body is small, the delay caused by compression may even larger than the latency saved by faster transportation.

Decompress Response Body

brpc does not decompress bodies of responses automatically due to universality. The decompression code is not complicated and users can do it by themselves. The code is as follows:

#include <brpc/policy/gzip_compress.h>
...
const std::string* encoding = cntl->http_response().GetHeader("Content-Encoding");
if (encoding != NULL && *encoding == "gzip") {
    butil::IOBuf uncompressed;
    if (!brpc::policy::GzipDecompress(cntl->response_attachment(), &uncompressed)) {
        LOG(ERROR) << "Fail to un-gzip response body";
        return;
    }
    cntl->response_attachment().swap(uncompressed);
}
// Now cntl->response_attachment() contains the decompressed data

Progressively Download

http client normally does not complete the RPC until http body has been fully downloaded. During the process http body is stored in memory. If the body is very large or infinitely large(a FLV file for live streaming), memory grows continuously until the RPC is timedout. Such http clients are not suitable for downloading very large files.

brpc client supports completing RPC before reading the full body, so that users can read http bodies progressively after RPC. Note that this feature does not mean “support for http chunked mode”, actually the http implementation in brpc supports chunked mode from the very beginning. The real issue is how to let users handle very or infinitely large http bodies, which does not imply the chunked mode.

How to use:

  1. Implement ProgressiveReader below:

    #include <brpc/progressive_reader.h>
...
class ProgressiveReader {
public:
    // Called when one part was read.
    // Error returned is treated as *permenant* and the socket where the
    // data was read will be closed.
    // A temporary error may be handled by blocking this function, which
    // may block the HTTP parsing on the socket.
    virtual butil::Status OnReadOnePart(const void* data, size_t length) = 0;

    // Called when there's nothing to read anymore. The `status' is a hint for
    // why this method is called.
    // - status.ok(): the message is complete and successfully consumed.
    // - otherwise: socket was broken or OnReadOnePart() failed.
    // This method will be called once and only once. No other methods will
    // be called after. User can release the memory of this object inside.
    virtual void OnEndOfMessage(const butil::Status& status) = 0;
};

    OnReadOnePart is called each time a piece of data is read. OnEndOfMessage is called at the end of data or the connection is broken. Read comments carefully before implementing.

  2. Set cntl.response_will_be_read_progressively(); before RPC to make brpc end RPC just after reading all headers.

  3. Call cntl.ReadProgressiveAttachmentBy(new MyProgressiveReader); after RPC. MyProgressiveReader is an instance of user-implemented ProgressiveReader. User may delete the object inside OnEndOfMessage.

Progressively Upload

Currently the POST data should be intact before launching the http call, thus brpc http client is still not suitable for uploading very large bodies.

Access Servers with authentications

Generate auth_data according to authenticating method of the server and set it into Authorization header. If you’re using curl, add option -H "Authorization : <auth_data>".

Send https requests

https is short for “http over SSL”, SSL is not exclusive for http, but effective for all protocols. The generic method for turning on client-side SSL is here. brpc enables SSL automatically for URIs starting with https:// to make the usage more handy.

Last modified May 17, 2022: update brpc users page (#71) (a31ce10d3)