internal/pkg: improve artifact interface

This moves all cache I/O code to Cache. Artifact now only contains methods for constructing their actual contents.

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

internal/pkg/net.go

@@ -3,11 +3,10 @@ package pkg
 import (
 	"context"
 	"crypto/sha512"
-	"errors"
 	"io"
 	"net/http"
-	"os"
 	"sync"
+	"syscall"
 
 	"hakurei.app/container/check"
 )
@@ -17,38 +16,34 @@ type httpArtifact struct {
 	// Caller-supplied request.
 	req *http.Request
 
-	// Caller-supplied checksum of the response body, also used as the
-	// identifier. This is validated during curing.
-	id ID
+	// Caller-supplied checksum of the response body. This is validated during
+	// curing and the first call to Data.
+	checksum Checksum
 
 	// doFunc is the Do method of [http.Client] supplied by the caller.
 	doFunc func(req *http.Request) (*http.Response, error)
 
-	// Instance of [Cache] to submit the cured artifact to.
-	c *Cache
 	// Response body read to EOF.
 	data []byte
-	// Populated when submitting to or loading from [Cache].
-	pathname *check.Absolute
 
-	// Synchronises access to pathname and data.
+	// Synchronises access to data.
 	mu sync.Mutex
 }
 
 // NewHTTP returns a new [File] backed by the supplied client and request. If
 // c is nil, [http.DefaultClient] is used instead.
-func (c *Cache) NewHTTP(hc *http.Client, req *http.Request, checksum Checksum) File {
-	if hc == nil {
-		hc = http.DefaultClient
+func NewHTTP(c *http.Client, req *http.Request, checksum Checksum) File {
+	if c == nil {
+		c = http.DefaultClient
 	}
-	return &httpArtifact{req: req, id: checksum, doFunc: hc.Do, c: c}
+	return &httpArtifact{req: req, checksum: checksum, doFunc: c.Do}
 }
 
 // NewHTTPGet returns a new [File] backed by the supplied client. A GET request
 // is set up for url. If c is nil, [http.DefaultClient] is used instead.
-func (c *Cache) NewHTTPGet(
+func NewHTTPGet(
 	ctx context.Context,
-	hc *http.Client,
+	c *http.Client,
 	url string,
 	checksum Checksum,
 ) (File, error) {
@@ -56,14 +51,25 @@ func (c *Cache) NewHTTPGet(
 	if err != nil {
 		return nil, err
 	}
-	return c.NewHTTP(hc, req, checksum), nil
+	return NewHTTP(c, req, checksum), nil
 }
 
 // Kind returns the hardcoded [Kind] constant.
 func (a *httpArtifact) Kind() Kind { return KindHTTP }
 
 // ID returns the caller-supplied hash of the response body.
-func (a *httpArtifact) ID() ID { return a.id }
+func (a *httpArtifact) ID() ID { return a.checksum }
+
+// Params is unreachable.
+func (a *httpArtifact) Params() []byte {
+	panic("not implemented")
+}
+
+// Dependencies returns a nil slice.
+func (a *httpArtifact) Dependencies() []Artifact { return nil }
+
+// Checksum returns the address to the caller-supplied checksum.
+func (a *httpArtifact) Checksum() *Checksum { return &a.checksum }
 
 // ResponseStatusError is returned for a response returned by an [http.Client]
 // with a status code other than [http.StatusOK].
@@ -95,44 +101,13 @@ func (a *httpArtifact) do() (data []byte, err error) {
 	return
 }
 
-// Hash cures the [Artifact] and returns its hash. The return value is always
-// identical to that of the ID method.
-func (a *httpArtifact) Hash() (Checksum, error) { _, err := a.Pathname(); return a.id, err }
-
-// Pathname cures the [Artifact] and returns its pathname in the [Cache].
-func (a *httpArtifact) Pathname() (pathname *check.Absolute, err error) {
-	a.mu.Lock()
-	defer a.mu.Unlock()
-
-	if a.pathname != nil {
-		return a.pathname, nil
-	}
-
-	if a.data != nil {
-		pathname, err = a.c.StoreFile(
-			a.id, a.data,
-			(*Checksum)(&a.id),
-			true,
-		)
-		if err == nil {
-			a.pathname = pathname
-		}
-		return
-	} else {
-		a.pathname, a.data, _, err = a.c.LoadOrStoreFile(
-			a.id, a.do,
-			(*Checksum)(&a.id),
-			true,
-		)
-		if err != nil {
-			a.pathname, a.data = nil, nil
-		}
-		return a.pathname, err
-	}
+// Cure returns syscall.ENOTSUP. Callers should use Data instead.
+func (a *httpArtifact) Cure(*check.Absolute, CacheDataFunc) error {
+	return syscall.ENOTSUP
 }
 
 // Data completes the http request and returns the resulting response body read
-// to EOF. Data does not write to the underlying [Cache].
+// to EOF. Data does not interact with the filesystem.
 func (a *httpArtifact) Data() (data []byte, err error) {
 	a.mu.Lock()
 	defer a.mu.Unlock()
@@ -142,23 +117,14 @@ func (a *httpArtifact) Data() (data []byte, err error) {
 		return a.data, nil
 	}
 
-	if a.pathname, a.data, err = a.c.LoadFile(a.id); err == nil {
-		return a.data, nil
-	} else {
-		a.pathname, a.data = nil, nil
-		if !errors.Is(err, os.ErrNotExist) {
-			return
-		}
-	}
-
 	if data, err = a.do(); err != nil {
 		return
 	}
 
 	h := sha512.New384()
 	h.Write(data)
-	if got := (Checksum)(h.Sum(nil)); got != a.id {
-		return nil, &ChecksumMismatchError{got, a.id}
+	if got := (Checksum)(h.Sum(nil)); got != a.checksum {
+		return nil, &ChecksumMismatchError{got, a.checksum}
 	}
 	a.data = data
 	return