[wang-guannan]

Motivation

On a multi-NIC host the kernel chooses the source address of outgoing packets by the routing table, so the peer may see an unexpected source address, or the connection may fail when the route does not leave through the intended interface.

hv::TcpClient already offers bind(local_port, local_host), but the HTTP client does not: hv::HttpClient is a thin wrapper over the opaque C API http_client_t, so there is no way to bind a local address before connecting. Applications that need a fixed source address have to drop down to the raw socket layer.

Changes

• base/hsocket.[ch]: add ConnectTimeoutWithLocalAddr(), which binds the local address before connecting.
• http/client/HttpClient.[ch]: add http_client_set_local_addr() and hv::HttpClient::setLocalAddr(). When a local address is set, the connection binds it (port 0 lets the kernel choose the source port).
• http/client/AsyncHttpClient.[ch]: the same feature for the asynchronous path.
  • HttpClientTask carries the local address from the http_client_t over to the connection setup.
  • AsyncHttpClient::startConnect() binds the socket before connecting. The bind is done before hio_get(), so that a failure can close the socket without racing the hloop cleanup. A failed bind fails the connection, matching the behaviour of the synchronous path.
  • http_client_exec_async() forwards cli->local_host / cli->local_port.
• unittest/http_client_local_addr_test.cpp: verify that the peer sees the bound source address (synchronous path).
• unittest/http_client_local_addr_async_test.cpp: the same check for the asynchronous path.
• docs/cn/HttpClient.md: document the new API.

Usage

hv::HttpClient cli;
cli.setLocalAddr("192.168.1.10");   // bind the source address
cli.send(&req, &resp);              // synchronous path
cli.sendAsync(req, resp_cb);        // asynchronous path

Compatibility

Purely additive: no behaviour change unless setLocalAddr() is called.

Note

setLocalAddr() should be called before sending any request -- connections that were already
established keep the source address they were created with.

Test

./configure --with-openssl --with-http
make libhv
make unittest
bin/http_client_local_addr_test <a non-loopback local address>
bin/http_client_local_addr_async_test <a non-loopback local address>

Output:

no-bind -> 127.0.0.1 : client_addr=[127.0.0.1]
bind 127.0.0.1 -> 172.18.0.2 : client_addr=[127.0.0.1]
bind 10.255.255.253 -> 172.18.0.2 : client_addr=[] (expected to fail)
PASS