Update readme and docstrings, minor refactors.

presigned.go

@@ -16,6 +16,7 @@ const (
 	defaultPresignedURLFormat = "%s.s3.amazonaws.com" // <bucket>
 )
 
+// PresignedInput is passed to GeneratePresignedURL as a parameter.
 type PresignedInput struct {
 	Bucket        string
 	ObjectKey     string
@@ -25,10 +26,13 @@ type PresignedInput struct {
 	ExpirySeconds int
 }
 
+// GeneratePresignedURL creates a Presigned URL that can be used
+// for Authentication using Query Parameters.
+// (https://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-query-string-auth.html)
 func (s3 *S3) GeneratePresignedURL(in PresignedInput) string {
 	var (
 		nowTime = in.Timestamp.UTC()
-		cred    = s3.buildCredential(nowTime)
+		cred    = fmt.Sprintf("%s/"+s3.buildCredentialWithoutKey(nowTime), s3.AccessKey)
 		amzdate = nowTime.Format(amzDateISO8601TimeFormat)
 		expiry  = strconv.Itoa(in.ExpirySeconds)
 	)
@@ -41,7 +45,7 @@ func (s3 *S3) GeneratePresignedURL(in PresignedInput) string {
 	signedHeaders["host"] = fmt.Sprintf(defaultPresignedURLFormat, in.Bucket)
 
 	// Start Canonical Request Formation
-	h := sha256.New()
+	h := sha256.New()                     // We write the canonical request directly to the SHA256 hash.
 	fmt.Fprintf(h, "%s\n", in.Method)     // HTTP Verb
 	fmt.Fprintf(h, "/%s\n", in.ObjectKey) // CanonicalURL
 
@@ -54,44 +58,53 @@ func (s3 *S3) GeneratePresignedURL(in PresignedInput) string {
 	}
 
 	// We need to have a sorted order,
-	keysQS := make([]string, 0, len(queryString))
+	// for QueryStrings and SignedHeaders
+	sortedQS := make([]string, 0, len(queryString))
 	for name := range queryString {
-		keysQS = append(keysQS, name)
+		sortedQS = append(sortedQS, name)
 	}
-	sort.Strings(keysQS) //sort by key
-	for _, k := range keysQS {
+	sort.Strings(sortedQS) //sort by key
+
+	sortedSH := make([]string, 0, len(signedHeaders))
+	for name := range signedHeaders {
+		sortedSH = append(sortedSH, name)
+	}
+	sort.Strings(sortedSH) //sort by key
+
+	// Proceed to write canonical query params
+	for _, k := range sortedQS {
 		fmt.Fprintf(h, "%s=%s&", url.QueryEscape(k), url.QueryEscape(queryString[k])) // HTTP Verb
 	}
 
 	fmt.Fprintf(h, "X-Amz-SignedHeaders=")
 	// Add Signed Headers to Query String
 	first := true
-	for k := range signedHeaders {
+	for k := range sortedSH {
 		if first {
-			fmt.Fprintf(h, "%s", url.QueryEscape(k))
+			fmt.Fprintf(h, "%s", url.QueryEscape(sortedSH[k]))
 			first = false
 		} else {
-			fmt.Fprintf(h, "%s", url.QueryEscape(";"+k))
+			fmt.Fprintf(h, "%s", url.QueryEscape(";"+sortedSH[k]))
 		}
 	}
 	fmt.Fprintf(h, "\n")
 	// End QueryString Params
 
 	// Start Canonical Headers
-	for k, v := range signedHeaders {
-		fmt.Fprintf(h, "%s:%s\n", strings.ToLower(k), strings.TrimSpace(v))
+	for _, k := range sortedSH {
+		fmt.Fprintf(h, "%s:%s\n", strings.ToLower(k), strings.TrimSpace(signedHeaders[k]))
 	}
 	fmt.Fprintf(h, "\n")
 	// End Canonical Headers
 
 	// Start Signed Headers
 	first = true
-	for k := range signedHeaders {
+	for k := range sortedSH {
 		if first {
-			fmt.Fprintf(h, "%s", url.QueryEscape(k))
+			fmt.Fprintf(h, "%s", url.QueryEscape(sortedSH[k]))
 			first = false
 		} else {
-			fmt.Fprintf(h, "%s", url.QueryEscape(";"+k))
+			fmt.Fprintf(h, "%s", url.QueryEscape(";"+sortedSH[k]))
 		}
 	}
 	fmt.Fprintf(h, "\n")
@@ -126,7 +139,8 @@ func (s3 *S3) GeneratePresignedURL(in PresignedInput) string {
 		[]byte("s3")),
 		[]byte("aws4_request"),
 	)
-	// sigKey gen verified using https://docs.aws.amazon.com/general/latest/gr/signature-v4-examples.html#signature-v4-examples-other
+	// sigKey gen verified using
+	// https://docs.aws.amazon.com/general/latest/gr/signature-v4-examples.html#signature-v4-examples-other
 	// (TODO: add a test using the same, consolidate with signKeys())
 
 	signedStrToSign := makeHMac(sigKey, stringToSign)
@@ -142,21 +156,20 @@ func (s3 *S3) GeneratePresignedURL(in PresignedInput) string {
 
 	// We don't need to have a sorted order here,
 	// but just to preserve tests.
-	for _, k := range keysQS {
+	for _, k := range sortedQS {
 		fmt.Fprintf(&b, "%s=%s&", url.QueryEscape(k), url.QueryEscape(queryString[k])) // HTTP Verb
 	}
 	fmt.Fprintf(&b, "%s=", "X-Amz-SignedHeaders")
 	first = true
-	for k := range signedHeaders {
+	for k := range sortedSH {
 		if first {
-			fmt.Fprintf(&b, "%s", url.QueryEscape(k))
+			fmt.Fprintf(&b, "%s", url.QueryEscape(sortedSH[k]))
 			first = false
 		} else {
-			fmt.Fprintf(&b, "%s", url.QueryEscape(";"+k))
+			fmt.Fprintf(&b, "%s", url.QueryEscape(";"+sortedSH[k]))
 		}
 	}
 	fmt.Fprintf(&b, "&X-Amz-Signature=%s", signature)
-	resultURL := b.String()
 
-	return resultURL
+	return b.String()
 }