internal/pkg: expose response body

This uses the new measured reader provided by Cache. This should make httpArtifact zero-copy.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/file.go

@@ -2,7 +2,6 @@ package pkg
 
 import (
 	"bytes"
-	"context"
 	"crypto/sha512"
 	"fmt"
 	"io"
@@ -54,6 +53,6 @@ func (a *fileArtifact) Checksum() Checksum {
 }
 
 // Cure returns the caller-supplied data.
-func (a *fileArtifact) Cure(context.Context) (io.ReadCloser, error) {
+func (a *fileArtifact) Cure(*RContext) (io.ReadCloser, error) {
 	return io.NopCloser(bytes.NewReader(*a)), nil
 }

internal/pkg/net.go

@@ -1,14 +1,11 @@
 package pkg
 
 import (
-	"bytes"
-	"context"
-	"crypto/sha512"
 	"fmt"
 	"io"
 	"net/http"
 	"path"
-	"sync"
+	"unique"
 )
 
 // An httpArtifact is an [Artifact] backed by a [http] url string. The method is
@@ -18,18 +15,12 @@ type httpArtifact struct {
 	// Caller-supplied url string.
 	url string
 
-	// Caller-supplied checksum of the response body. This is validated during
-	// curing and the first call to Data.
-	checksum Checksum
+	// Caller-supplied checksum of the response body. This is validated when
+	// closing the [io.ReadCloser] returned by Cure.
+	checksum unique.Handle[Checksum]
 
 	// doFunc is the Do method of [http.Client] supplied by the caller.
 	doFunc func(req *http.Request) (*http.Response, error)
-
-	// Response body read to EOF.
-	data []byte
-
-	// Synchronises access to data.
-	mu sync.Mutex
 }
 
 var _ KnownChecksum = new(httpArtifact)
@@ -45,7 +36,7 @@ func NewHTTPGet(
 	if c == nil {
 		c = http.DefaultClient
 	}
-	return &httpArtifact{url: url, checksum: checksum, doFunc: c.Do}
+	return &httpArtifact{url: url, checksum: unique.Make(checksum), doFunc: c.Do}
 }
 
 // Kind returns the hardcoded [Kind] constant.
@@ -61,7 +52,7 @@ func (a *httpArtifact) Params(ctx *IContext) {
 func (a *httpArtifact) Dependencies() []Artifact { return nil }
 
 // Checksum returns the caller-supplied checksum.
-func (a *httpArtifact) Checksum() Checksum { return a.checksum }
+func (a *httpArtifact) Checksum() Checksum { return a.checksum.Value() }
 
 // String returns [path.Base] over the backing url.
 func (a *httpArtifact) String() string { return path.Base(a.url) }
@@ -74,11 +65,13 @@ func (e ResponseStatusError) Error() string {
 	return "the requested URL returned non-OK status: " + http.StatusText(int(e))
 }
 
-// do sends the caller-supplied request on the caller-supplied [http.Client]
-// and reads its response body to EOF and returns the resulting bytes.
-func (a *httpArtifact) do(ctx context.Context) (data []byte, err error) {
+// Cure sends the http request and returns the resulting response body reader
+// wrapped to perform checksum validation. It is valid but not encouraged to
+// close the resulting [io.ReadCloser] before it is read to EOF, as that causes
+// Close to block until all remaining data is consumed and validated.
+func (a *httpArtifact) Cure(r *RContext) (rc io.ReadCloser, err error) {
 	var req *http.Request
-	req, err = http.NewRequestWithContext(ctx, http.MethodGet, a.url, nil)
+	req, err = http.NewRequestWithContext(r.Unwrap(), http.MethodGet, a.url, nil)
 	if err != nil {
 		return
 	}
@@ -93,37 +86,6 @@ func (a *httpArtifact) do(ctx context.Context) (data []byte, err error) {
 		return nil, ResponseStatusError(resp.StatusCode)
 	}
 
-	if data, err = io.ReadAll(resp.Body); err != nil {
-		_ = resp.Body.Close()
-		return
-	}
-
-	err = resp.Body.Close()
-	return
-}
-
-// Cure completes the http request and returns the resulting response body read
-// to EOF. Data does not interact with the filesystem.
-func (a *httpArtifact) Cure(ctx context.Context) (r io.ReadCloser, err error) {
-	a.mu.Lock()
-	defer a.mu.Unlock()
-
-	if a.data != nil {
-		// validated by cache or a previous call to Cure
-		return io.NopCloser(bytes.NewReader(a.data)), nil
-	}
-
-	var data []byte
-	if data, err = a.do(ctx); err != nil {
-		return
-	}
-
-	h := sha512.New384()
-	h.Write(data)
-	if got := (Checksum)(h.Sum(nil)); got != a.checksum {
-		return nil, &ChecksumMismatchError{got, a.checksum}
-	}
-	a.data = data
-	r = io.NopCloser(bytes.NewReader(data))
+	rc = r.NewMeasuredReader(resp.Body, a.checksum)
 	return
 }

internal/pkg/net_test.go

@@ -8,6 +8,7 @@ import (
 	"testing"
 	"testing/fstest"
 	"unique"
+	"unsafe"
 
 	"hakurei.app/container/check"
 	"hakurei.app/internal/pkg"
@@ -32,6 +33,12 @@ func TestHTTPGet(t *testing.T) {
 
 	checkWithCache(t, []cacheTestCase{
 		{"direct", nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
+			var r pkg.RContext
+			rCacheVal := reflect.ValueOf(&r).Elem().FieldByName("cache")
+			reflect.NewAt(
+				rCacheVal.Type(),
+				unsafe.Pointer(rCacheVal.UnsafeAddr()),
+			).Elem().Set(reflect.ValueOf(c))
 
 			f := pkg.NewHTTPGet(
 				&client,
@@ -39,12 +46,14 @@ func TestHTTPGet(t *testing.T) {
 				testdataChecksum.Value(),
 			)
 			var got []byte
-			if r, err := f.Cure(t.Context()); err != nil {
+			if rc, err := f.Cure(&r); err != nil {
 				t.Fatalf("Cure: error = %v", err)
-			} else if got, err = io.ReadAll(r); err != nil {
+			} else if got, err = io.ReadAll(rc); err != nil {
 				t.Fatalf("ReadAll: error = %v", err)
 			} else if string(got) != testdata {
 				t.Fatalf("Cure: %x, want %x", got, testdata)
+			} else if err = rc.Close(); err != nil {
+				t.Fatalf("Close: error = %v", err)
 			}
 
 			// check direct validation
@@ -56,8 +65,21 @@ func TestHTTPGet(t *testing.T) {
 			wantErrMismatch := &pkg.ChecksumMismatchError{
 				Got: testdataChecksum.Value(),
 			}
-			if _, err := f.Cure(t.Context()); !reflect.DeepEqual(err, wantErrMismatch) {
-				t.Fatalf("Cure: error = %#v, want %#v", err, wantErrMismatch)
+			if rc, err := f.Cure(&r); err != nil {
+				t.Fatalf("Cure: error = %v", err)
+			} else if got, err = io.ReadAll(rc); err != nil {
+				t.Fatalf("ReadAll: error = %v", err)
+			} else if string(got) != testdata {
+				t.Fatalf("Cure: %x, want %x", got, testdata)
+			} else if err = rc.Close(); !reflect.DeepEqual(err, wantErrMismatch) {
+				t.Fatalf("Close: error = %#v, want %#v", err, wantErrMismatch)
+			}
+
+			// check fallback validation
+			if rc, err := f.Cure(&r); err != nil {
+				t.Fatalf("Cure: error = %v", err)
+			} else if err = rc.Close(); !reflect.DeepEqual(err, wantErrMismatch) {
+				t.Fatalf("Close: error = %#v, want %#v", err, wantErrMismatch)
 			}
 
 			// check direct response error
@@ -67,12 +89,19 @@ func TestHTTPGet(t *testing.T) {
 				pkg.Checksum{},
 			)
 			wantErrNotFound := pkg.ResponseStatusError(http.StatusNotFound)
-			if _, err := f.Cure(t.Context()); !reflect.DeepEqual(err, wantErrNotFound) {
+			if _, err := f.Cure(&r); !reflect.DeepEqual(err, wantErrNotFound) {
 				t.Fatalf("Cure: error = %#v, want %#v", err, wantErrNotFound)
 			}
 		}, pkg.MustDecode("E4vEZKhCcL2gPZ2Tt59FS3lDng-d_2SKa2i5G_RbDfwGn6EemptFaGLPUDiOa94C")},
 
 		{"cure", nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
+			var r pkg.RContext
+			rCacheVal := reflect.ValueOf(&r).Elem().FieldByName("cache")
+			reflect.NewAt(
+				rCacheVal.Type(),
+				unsafe.Pointer(rCacheVal.UnsafeAddr()),
+			).Elem().Set(reflect.ValueOf(c))
+
 			f := pkg.NewHTTPGet(
 				&client,
 				"file:///testdata",
@@ -91,12 +120,14 @@ func TestHTTPGet(t *testing.T) {
 			}
 
 			var got []byte
-			if r, err := f.Cure(t.Context()); err != nil {
+			if rc, err := f.Cure(&r); err != nil {
 				t.Fatalf("Cure: error = %v", err)
-			} else if got, err = io.ReadAll(r); err != nil {
+			} else if got, err = io.ReadAll(rc); err != nil {
 				t.Fatalf("ReadAll: error = %v", err)
 			} else if string(got) != testdata {
 				t.Fatalf("Cure: %x, want %x", got, testdata)
+			} else if err = rc.Close(); err != nil {
+				t.Fatalf("Close: error = %v", err)
 			}
 
 			// check load from cache
@@ -105,12 +136,14 @@ func TestHTTPGet(t *testing.T) {
 				"file:///testdata",
 				testdataChecksum.Value(),
 			)
-			if r, err := f.Cure(t.Context()); err != nil {
+			if rc, err := f.Cure(&r); err != nil {
 				t.Fatalf("Cure: error = %v", err)
-			} else if got, err = io.ReadAll(r); err != nil {
+			} else if got, err = io.ReadAll(rc); err != nil {
 				t.Fatalf("ReadAll: error = %v", err)
 			} else if string(got) != testdata {
 				t.Fatalf("Cure: %x, want %x", got, testdata)
+			} else if err = rc.Close(); err != nil {
+				t.Fatalf("Close: error = %v", err)
 			}
 
 			// check error passthrough

internal/pkg/pkg.go

@@ -215,6 +215,20 @@ func (f *FContext) GetArtifact(a Artifact) (
 	panic(InvalidLookupError(f.cache.Ident(a).Value()))
 }
 
+// RContext is passed to [FileArtifact.Cure] and provides helper methods useful
+// for curing the [FileArtifact].
+//
+// Methods of RContext are safe for concurrent use. RContext is valid
+// until [FileArtifact.Cure] returns.
+type RContext struct {
+	// Address of underlying [Cache], should be zeroed or made unusable after
+	// [FileArtifact.Cure] returns and must not be exposed directly.
+	cache *Cache
+}
+
+// Unwrap returns the underlying [context.Context].
+func (r *RContext) Unwrap() context.Context { return r.cache.ctx }
+
 // An Artifact is a read-only reference to a piece of data that may be created
 // deterministically but might not currently be available in memory or on the
 // filesystem.
@@ -323,7 +337,7 @@ type FileArtifact interface {
 	// Callers are responsible for closing the resulting [io.ReadCloser].
 	//
 	// Result must remain identical across multiple invocations.
-	Cure(ctx context.Context) (io.ReadCloser, error)
+	Cure(r *RContext) (io.ReadCloser, error)
 
 	Artifact
 }
@@ -952,7 +966,7 @@ func (c *Cache) openFile(f FileArtifact) (r io.ReadCloser, err error) {
 				}
 			}()
 		}
-		return f.Cure(c.ctx)
+		return f.Cure(&RContext{c})
 	}
 	return
 }
@@ -1229,6 +1243,88 @@ func (c *Cache) getWriter(w io.Writer) *bufio.Writer {
 	return bw
 }
 
+// measuredReader implements [io.ReadCloser] and measures the checksum during
+// Close. If the underlying reader is not read to EOF, Close blocks until all
+// remaining data is consumed and validated.
+type measuredReader struct {
+	// Underlying reader. Never exposed directly.
+	r io.ReadCloser
+	// For validating checksum. Never exposed directly.
+	h hash.Hash
+	// Buffers writes to h, initialised by [Cache]. Never exposed directly.
+	hbw *bufio.Writer
+	// Expected checksum, compared during Close.
+	want unique.Handle[Checksum]
+
+	// For accessing free lists.
+	c *Cache
+
+	// Set up via [io.TeeReader] by [Cache].
+	io.Reader
+}
+
+// Close reads the underlying [io.ReadCloser] to EOF, closes it and measures its
+// outcome. It returns a [ChecksumMismatchError] for an unexpected checksum.
+func (mr *measuredReader) Close() (err error) {
+	if mr.hbw == nil || mr.Reader == nil {
+		return os.ErrInvalid
+	}
+	err = mr.hbw.Flush()
+	mr.c.putWriter(mr.hbw)
+	mr.hbw, mr.Reader = nil, nil
+	if err != nil {
+		_ = mr.r.Close()
+		return
+	}
+	var n int64
+	if n, err = io.Copy(mr.h, mr.r); err != nil {
+		_ = mr.r.Close()
+		return
+	}
+
+	if n > 0 {
+		mr.c.msg.Verbosef("missed %d bytes on measured reader", n)
+	}
+
+	if err = mr.r.Close(); err != nil {
+		return
+	}
+
+	buf := mr.c.getIdentBuf()
+	mr.h.Sum(buf[:0])
+
+	if got := Checksum(buf[:]); got != mr.want.Value() {
+		err = &ChecksumMismatchError{
+			Got:  got,
+			Want: mr.want.Value(),
+		}
+	}
+
+	mr.c.putIdentBuf(buf)
+	return
+}
+
+// newMeasuredReader implements [RContext.NewMeasuredReader].
+func (c *Cache) newMeasuredReader(
+	r io.ReadCloser,
+	checksum unique.Handle[Checksum],
+) io.ReadCloser {
+	mr := measuredReader{r: r, h: sha512.New384(), want: checksum, c: c}
+	mr.hbw = c.getWriter(mr.h)
+	mr.Reader = io.TeeReader(r, mr.hbw)
+	return &mr
+}
+
+// NewMeasuredReader returns an [io.ReadCloser] implementing behaviour required
+// by [FileArtifact]. The resulting [io.ReadCloser] holds a buffer originating
+// from [Cache] and must be closed to return this buffer.
+func (r *RContext) NewMeasuredReader(
+	rc io.ReadCloser,
+	checksum unique.Handle[Checksum],
+) io.ReadCloser {
+	return r.cache.newMeasuredReader(rc, checksum)
+}
+
 // putWriter adds bw to bufioPool.
 func (c *Cache) putWriter(bw *bufio.Writer) { c.bufioPool.Put(bw) }
 
@@ -1363,7 +1459,7 @@ func (c *Cache) cure(a Artifact, curesExempt bool) (
 		if err = c.enterCure(curesExempt); err != nil {
 			return
 		}
-		r, err = f.Cure(c.ctx)
+		r, err = f.Cure(&RContext{c})
 		if err == nil {
 			if checksumPathname == nil || c.IsStrict() {
 				h := sha512.New384()

internal/pkg/pkg_test.go

@@ -119,7 +119,7 @@ type stubFile struct {
 	stubArtifact
 }
 
-func (a *stubFile) Cure(context.Context) (io.ReadCloser, error) {
+func (a *stubFile) Cure(*pkg.RContext) (io.ReadCloser, error) {
 	return io.NopCloser(bytes.NewReader(a.data)), a.err
 }