ensureReaderClosed was designed to be usable regardless if a response
was nil (error) or non-nil (success). Some code-paths were optimized to
avoid using a defer (which used to have an overhead), but the overhead
of defer is neglectable in current versions of Go, and some of these
optimizations made the logic more complicated (and err-prone).
This patch switches to use a defer for all places.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
These comments were added to enforce using the correct import path for
our packages ("github.com/docker/docker", not "github.com/moby/moby").
However, when working in go module mode (not GOPATH / vendor), they have
no effect, so their impact is limited.
Remove these imports in preparation of migrating our code to become an
actual go module.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
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]: 5dd6452d4d
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
Since Go 1.7, context is a standard package. Since Go 1.9, everything
that is provided by "x/net/context" is a couple of type aliases to
types in "context".
Many vendored packages still use x/net/context, so vendor entry remains
for now.
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
