move httpsig

vendor/code.superseriousbusiness.org/httpsig/digest.go

@@ -0,0 +1,120 @@
+package httpsig
+
+import (
+	"bytes"
+	"crypto"
+	"encoding/base64"
+	"fmt"
+	"hash"
+	"net/http"
+	"strings"
+)
+
+type DigestAlgorithm string
+
+const (
+	DigestSha256 DigestAlgorithm = "SHA-256"
+	DigestSha512                 = "SHA-512"
+)
+
+var digestToDef = map[DigestAlgorithm]crypto.Hash{
+	DigestSha256: crypto.SHA256,
+	DigestSha512: crypto.SHA512,
+}
+
+// IsSupportedDigestAlgorithm returns true if hte string is supported by this
+// library, is not a hash known to be weak, and is supported by the hardware.
+func IsSupportedDigestAlgorithm(algo string) bool {
+	uc := DigestAlgorithm(strings.ToUpper(algo))
+	c, ok := digestToDef[uc]
+	return ok && c.Available()
+}
+
+func getHash(alg DigestAlgorithm) (h hash.Hash, toUse DigestAlgorithm, err error) {
+	upper := DigestAlgorithm(strings.ToUpper(string(alg)))
+	c, ok := digestToDef[upper]
+	if !ok {
+		err = fmt.Errorf("unknown or unsupported Digest algorithm: %s", alg)
+	} else if !c.Available() {
+		err = fmt.Errorf("unavailable Digest algorithm: %s", alg)
+	} else {
+		h = c.New()
+		toUse = upper
+	}
+	return
+}
+
+const (
+	digestHeader = "Digest"
+	digestDelim  = "="
+)
+
+func addDigest(r *http.Request, algo DigestAlgorithm, b []byte) (err error) {
+	_, ok := r.Header[digestHeader]
+	if ok {
+		err = fmt.Errorf("cannot add Digest: Digest is already set")
+		return
+	}
+	var h hash.Hash
+	var a DigestAlgorithm
+	h, a, err = getHash(algo)
+	if err != nil {
+		return
+	}
+	h.Write(b)
+	sum := h.Sum(nil)
+	r.Header.Add(digestHeader,
+		fmt.Sprintf("%s%s%s",
+			a,
+			digestDelim,
+			base64.StdEncoding.EncodeToString(sum[:])))
+	return
+}
+
+func addDigestResponse(r http.ResponseWriter, algo DigestAlgorithm, b []byte) (err error) {
+	_, ok := r.Header()[digestHeader]
+	if ok {
+		err = fmt.Errorf("cannot add Digest: Digest is already set")
+		return
+	}
+	var h hash.Hash
+	var a DigestAlgorithm
+	h, a, err = getHash(algo)
+	if err != nil {
+		return
+	}
+	h.Write(b)
+	sum := h.Sum(nil)
+	r.Header().Add(digestHeader,
+		fmt.Sprintf("%s%s%s",
+			a,
+			digestDelim,
+			base64.StdEncoding.EncodeToString(sum[:])))
+	return
+}
+
+func verifyDigest(r *http.Request, body *bytes.Buffer) (err error) {
+	d := r.Header.Get(digestHeader)
+	if len(d) == 0 {
+		err = fmt.Errorf("cannot verify Digest: request has no Digest header")
+		return
+	}
+	elem := strings.SplitN(d, digestDelim, 2)
+	if len(elem) != 2 {
+		err = fmt.Errorf("cannot verify Digest: malformed Digest: %s", d)
+		return
+	}
+	var h hash.Hash
+	h, _, err = getHash(DigestAlgorithm(elem[0]))
+	if err != nil {
+		return
+	}
+	h.Write(body.Bytes())
+	sum := h.Sum(nil)
+	encSum := base64.StdEncoding.EncodeToString(sum[:])
+	if encSum != elem[1] {
+		err = fmt.Errorf("cannot verify Digest: header Digest does not match the digest of the request body")
+		return
+	}
+	return
+}