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/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
 }