dotcloud/docker

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

import (
    "bytes"
    "context"
    "encoding/json"
    "errors"
    "io"
    "net/url"

    "github.com/docker/docker/api/types/container"
    "github.com/docker/docker/api/types/versions"
)

const containerWaitErrorMsgLimit = 2 * 1024 /* Max: 2KiB */

// ContainerWait waits until the specified container is in a certain state
// indicated by the given condition, either "not-running" (default),
// "next-exit", or "removed".
//
// If this client's API version is before 1.30, condition is ignored and
// ContainerWait will return immediately with the two channels, as the server
// will wait as if the condition were "not-running".
//
// If this client's API version is at least 1.30, ContainerWait blocks until
// the request has been acknowledged by the server (with a response header),
// then returns two channels on which the caller can wait for the exit status
// of the container or an error if there was a problem either beginning the
// wait request or in getting the response. This allows the caller to
// synchronize ContainerWait with other calls, such as specifying a
// "next-exit" condition before issuing a ContainerStart request.
func (cli *Client) ContainerWait(ctx context.Context, containerID string, condition container.WaitCondition) (<-chan container.WaitResponse, <-chan error) {
    resultC := make(chan container.WaitResponse)
    errC := make(chan error, 1)

    // Make sure we negotiated (if the client is configured to do so),
    // as code below contains API-version specific handling of options.
    //
    // Normally, version-negotiation (if enabled) would not happen until
    // the API request is made.
    if err := cli.checkVersion(ctx); err != nil {
        errC <- err
        return resultC, errC
    }
    if versions.LessThan(cli.ClientVersion(), "1.30") {
        return cli.legacyContainerWait(ctx, containerID)
    }

    query := url.Values{}
    if condition != "" {
        query.Set("condition", string(condition))
    }

    resp, err := cli.post(ctx, "/containers/"+containerID+"/wait", query, nil, nil)
    if err != nil {
        defer ensureReaderClosed(resp)
        errC <- err
        return resultC, errC
    }

    go func() {
        defer ensureReaderClosed(resp)

        body := resp.body
        responseText := bytes.NewBuffer(nil)
        stream := io.TeeReader(body, responseText)

        var res container.WaitResponse
        if err := json.NewDecoder(stream).Decode(&res); err != nil {
            // NOTE(nicks): The /wait API does not work well with HTTP proxies.
            // At any time, the proxy could cut off the response stream.
            //
            // But because the HTTP status has already been written, the proxy's
            // only option is to write a plaintext error message.
            //
            // If there's a JSON parsing error, read the real error message
            // off the body and send it to the client.
            if errors.As(err, new(*json.SyntaxError)) {
                _, _ = io.ReadAll(io.LimitReader(stream, containerWaitErrorMsgLimit))
                errC <- errors.New(responseText.String())
            } else {
                errC <- err
            }
            return
        }

        resultC <- res
    }()

    return resultC, errC
}

// legacyContainerWait returns immediately and doesn't have an option to wait
// until the container is removed.
func (cli *Client) legacyContainerWait(ctx context.Context, containerID string) (<-chan container.WaitResponse, <-chan error) {
    resultC := make(chan container.WaitResponse)
    errC := make(chan error)

    go func() {
        resp, err := cli.post(ctx, "/containers/"+containerID+"/wait", nil, nil, nil)
        if err != nil {
            errC <- err
            return
        }
        defer ensureReaderClosed(resp)

        var res container.WaitResponse
        if err := json.NewDecoder(resp.body).Decode(&res); err != nil {
            errC <- err
            return
        }

        resultC <- res
    }()

    return resultC, errC
}