server/internal: copy bmizerany/ollama-go to internal package (#9294)

This commit copies (without history) the bmizerany/ollama-go repository
with the intention of integrating it into the ollama as a replacement
for the pushing, and pulling of models, and management of the cache they
are pushed and pulled from.

New homes for these packages will be determined as they are integrated
and we have a better understanding of proper package boundaries.

server/internal/cache/blob/digest.go

@@ -0,0 +1,95 @@
+package blob
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"slices"
+	"strings"
+)
+
+var ErrInvalidDigest = errors.New("invalid digest")
+
+// Digest is a blob identifier that is the SHA-256 hash of a blob's content.
+//
+// It is comparable and can be used as a map key.
+type Digest struct {
+	sum [32]byte
+}
+
+// ParseDigest parses a digest from a string. If the string is not a valid
+// digest, a call to the returned digest's IsValid method will return false.
+//
+// The input string may be in one of two forms:
+//
+//   - ("sha256-<hex>"), where <hex> is a 64-character hexadecimal string.
+//   - ("sha256:<hex>"), where <hex> is a 64-character hexadecimal string.
+//
+// The [Digest.String] method will return the canonical form of the
+// digest, "sha256:<hex>".
+func ParseDigest[S ~[]byte | ~string](v S) (Digest, error) {
+	s := string(v)
+	i := strings.IndexAny(s, ":-")
+	var zero Digest
+	if i < 0 {
+		return zero, ErrInvalidDigest
+	}
+
+	prefix, sum := s[:i], s[i+1:]
+	if prefix != "sha256" || len(sum) != 64 {
+		return zero, ErrInvalidDigest
+	}
+
+	var d Digest
+	_, err := hex.Decode(d.sum[:], []byte(sum))
+	if err != nil {
+		return zero, ErrInvalidDigest
+	}
+	return d, nil
+}
+
+func DigestFromBytes[S ~[]byte | ~string](v S) Digest {
+	return Digest{sha256.Sum256([]byte(v))}
+}
+
+// String returns the string representation of the digest in the conventional
+// form "sha256:<hex>".
+func (d Digest) String() string {
+	return fmt.Sprintf("sha256:%x", d.sum[:])
+}
+
+func (d Digest) Short() string {
+	return fmt.Sprintf("%x", d.sum[:4])
+}
+
+func (d Digest) Compare(other Digest) int {
+	return slices.Compare(d.sum[:], other.sum[:])
+}
+
+// IsValid returns true if the digest is valid, i.e. if it is the SHA-256 hash
+// of some content.
+func (d Digest) IsValid() bool {
+	return d != (Digest{})
+}
+
+// MarshalText implements the encoding.TextMarshaler interface. It returns an
+// error if [Digest.IsValid] returns false.
+func (d Digest) MarshalText() ([]byte, error) {
+	return []byte(d.String()), nil
+}
+
+// UnmarshalText implements the encoding.TextUnmarshaler interface, and only
+// works for a zero digest. If [Digest.IsValid] returns true, it returns an
+// error.
+func (d *Digest) UnmarshalText(text []byte) error {
+	if *d != (Digest{}) {
+		return errors.New("digest: illegal UnmarshalText on valid digest")
+	}
+	v, err := ParseDigest(string(text))
+	if err != nil {
+		return err
+	}
+	*d = v
+	return nil
+}