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72c91e378d
Looking in history to learn why this struct existed, shows that this type was mostly the result of tech-debt accumulating over time; - originally ([moby@1aa7f13]) most of the request handling was internal; the [`call()` function][1] would make a request, read the `response.Body`, and return it as a `[]byte` (or an error if one happened). - some features needed the statuscode, so [moby@a4bcf7e] added an extra output variable to return the `response.StatusCode`. - some new features required streaming, so [moby@fdd8d4b] changed the function to return the `response.Body` as a `io.ReadCloser`, instead of a `[]byte`. - some features needed access to the content-type header, so a new `clientRequest` method was introduced in [moby@6b2eeaf] to read the `Content-Type` header from `response.Headers` and return it as a string. - of course, `Content-Type` may not be the only header needed, so [moby@0cdc3b7] changed the signature to return `response.Headers` as a whole as a `http.Header` - things became a bit unwieldy now, with the function having four (4) output variables, so [moby@126529c] chose to refactor this code, introducing a `serverResponse` struct to wrap them all, not realizing that all these values were effectively deconstructed from the `url.Response`, so now re-assembling them into our own "URL response", only preserving a subset of the information available. - now that we had a custom struct, it was possible to add more information to it without changing the signature. When there was a need to know the URL of the request that initiated the response, [moby@27ef09a] introduced a `reqURL` field to hold the `request.URL` which notably also is available in `response.Request.URL`. In short; - The original implementation tried to (pre-maturely) abstract the underlying response to provide a simplified interface. - While initially not needed, abstracting caused relevant information from the response (and request) to be unavailable to callers. - As a result, we ended up in a situation where we are deconstructing the original `url.Response`, only to re-assemble it into our own, custom struct (`serverResponsee`) with only a subset of the information preserved. This patch removes the `serverResponse` struct, instead returning the `url.Response` as-is, so that all information is preserved, allowing callers to use the information they need. There is one follow-up change to consider; commit [moby@589df17] introduced a `ensureReaderClosed` utility. Before that commit, the response body would be closed in a more idiomatic way through a [`defer serverResp.body.Close()`][2]. A later change in [docker/engine-api@5dd6452] added an optimization to that utility, draining the response to allow connections to be reused. While skipping that utility (and not draining the response) would not be a critical issue, it may be easy to overlook that utility, and to close the response body in the "idiomatic" way, resulting in a possible performance regression. We need to check if that optimization is still relevant or if later changes in Go itself already take care of this; we should also look if context cancellation is handled correctly for these. If it's still relevant, we could - Wrap the the `url.Response` in a custom struct ("drainCloser") to provide a `Close()` function handling the draining and closing; this would re- introduce a custom type to be returned, so perhaps not what we want. - Wrap the `url.Response.Body` in the response returned (so, calling) `response.Body.Close()` would call the wrapped closer. - Change the signature of `Client.sendRequest()` (and related) to return a `close()` func to handle this; doing so would more strongly encourage callers to close the response body. [1]:1aa7f1392d/commands.go (L1008-L1027)[2]:589df17a1a/api/client/ps.go (L84-L89)[moby@1aa7f13]:1aa7f1392d[moby@a4bcf7e]:a4bcf7e1ac[moby@fdd8d4b]:fdd8d4b7d9[moby@6b2eeaf]:6b2eeaf896[moby@0cdc3b7]:0cdc3b7539[moby@126529c]:126529c6d0[moby@27ef09a]:27ef09a46f[moby@589df17]:589df17a1a[docker/engine-api@5dd6452]:5dd6452d4dSigned-off-by: Sebastiaan van Stijn <github@gone.nl>
81 lines
2.5 KiB
Go
81 lines
2.5 KiB
Go
package client // import "github.com/docker/docker/client"
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import (
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"context"
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"net/http"
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"path"
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"strings"
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"github.com/docker/docker/api/types"
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"github.com/docker/docker/api/types/swarm"
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)
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// Ping pings the server and returns the value of the "Docker-Experimental",
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// "Builder-Version", "OS-Type" & "API-Version" headers. It attempts to use
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// a HEAD request on the endpoint, but falls back to GET if HEAD is not supported
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// by the daemon. It ignores internal server errors returned by the API, which
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// may be returned if the daemon is in an unhealthy state, but returns errors
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// for other non-success status codes, failing to connect to the API, or failing
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// to parse the API response.
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func (cli *Client) Ping(ctx context.Context) (types.Ping, error) {
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var ping types.Ping
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// Using cli.buildRequest() + cli.doRequest() instead of cli.sendRequest()
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// because ping requests are used during API version negotiation, so we want
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// to hit the non-versioned /_ping endpoint, not /v1.xx/_ping
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req, err := cli.buildRequest(ctx, http.MethodHead, path.Join(cli.basePath, "/_ping"), nil, nil)
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if err != nil {
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return ping, err
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}
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resp, err := cli.doRequest(req)
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if err != nil {
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if IsErrConnectionFailed(err) {
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return ping, err
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}
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// We managed to connect, but got some error; continue and try GET request.
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} else {
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defer ensureReaderClosed(resp)
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switch resp.StatusCode {
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case http.StatusOK, http.StatusInternalServerError:
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// Server handled the request, so parse the response
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return parsePingResponse(cli, resp)
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}
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}
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// HEAD failed; fallback to GET.
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req.Method = http.MethodGet
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resp, err = cli.doRequest(req)
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defer ensureReaderClosed(resp)
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if err != nil {
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return ping, err
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}
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return parsePingResponse(cli, resp)
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}
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func parsePingResponse(cli *Client, resp *http.Response) (types.Ping, error) {
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if resp == nil {
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return types.Ping{}, nil
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}
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var ping types.Ping
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if resp.Header == nil {
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return ping, cli.checkResponseErr(resp)
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}
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ping.APIVersion = resp.Header.Get("Api-Version")
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ping.OSType = resp.Header.Get("Ostype")
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if resp.Header.Get("Docker-Experimental") == "true" {
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ping.Experimental = true
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}
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if bv := resp.Header.Get("Builder-Version"); bv != "" {
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ping.BuilderVersion = types.BuilderVersion(bv)
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}
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if si := resp.Header.Get("Swarm"); si != "" {
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state, role, _ := strings.Cut(si, "/")
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ping.SwarmStatus = &swarm.Status{
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NodeState: swarm.LocalNodeState(state),
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ControlAvailable: role == "manager",
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}
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}
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return ping, cli.checkResponseErr(resp)
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}
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