dotcloud/docker

package client // import "github.com/docker/docker/client"

import (
    "context"
    "net/http"
    "path"
    "strings"

    "github.com/docker/docker/api/types"
    "github.com/docker/docker/api/types/swarm"
    "github.com/docker/docker/errdefs"
)

// Ping pings the server and returns the value of the "Docker-Experimental",
// "Builder-Version", "OS-Type" & "API-Version" headers. It attempts to use
// a HEAD request on the endpoint, but falls back to GET if HEAD is not supported
// by the daemon. It ignores internal server errors returned by the API, which
// may be returned if the daemon is in an unhealthy state, but returns errors
// for other non-success status codes, failing to connect to the API, or failing
// to parse the API response.
func (cli *Client) Ping(ctx context.Context) (types.Ping, error) {
    var ping types.Ping

    // Using cli.buildRequest() + cli.doRequest() instead of cli.sendRequest()
    // because ping requests are used during API version negotiation, so we want
    // to hit the non-versioned /_ping endpoint, not /v1.xx/_ping
    req, err := cli.buildRequest(ctx, http.MethodHead, path.Join(cli.basePath, "/_ping"), nil, nil)
    if err != nil {
        return ping, err
    }
    serverResp, err := cli.doRequest(req)
    if err == nil {
        defer ensureReaderClosed(serverResp)
        switch serverResp.statusCode {
        case http.StatusOK, http.StatusInternalServerError:
            // Server handled the request, so parse the response
            return parsePingResponse(cli, serverResp)
        }
    } else if IsErrConnectionFailed(err) {
        return ping, err
    }

    // HEAD failed; fallback to GET.
    req.Method = http.MethodGet
    serverResp, err = cli.doRequest(req)
    defer ensureReaderClosed(serverResp)
    if err != nil {
        return ping, err
    }
    return parsePingResponse(cli, serverResp)
}

func parsePingResponse(cli *Client, resp serverResponse) (types.Ping, error) {
    var ping types.Ping
    if resp.header == nil {
        err := cli.checkResponseErr(resp)
        return ping, errdefs.FromStatusCode(err, resp.statusCode)
    }
    ping.APIVersion = resp.header.Get("API-Version")
    ping.OSType = resp.header.Get("OSType")
    if resp.header.Get("Docker-Experimental") == "true" {
        ping.Experimental = true
    }
    if bv := resp.header.Get("Builder-Version"); bv != "" {
        ping.BuilderVersion = types.BuilderVersion(bv)
    }
    if si := resp.header.Get("Swarm"); si != "" {
        state, role, _ := strings.Cut(si, "/")
        ping.SwarmStatus = &swarm.Status{
            NodeState:        swarm.LocalNodeState(state),
            ControlAvailable: role == "manager",
        }
    }
    err := cli.checkResponseErr(resp)
    return ping, errdefs.FromStatusCode(err, resp.statusCode)
}