- Added attributions for ported code

- Added config validations for tripper
- Added comment for aps
- Removed noEscape to signer internal state

pkg/sigv4/const.go

@@ -1,7 +1,9 @@
 package sigv4
 
 const (
-	awsServiceName   = "aps"
+	// Amazon Managed Service for Prometheus
+	awsServiceName = "aps"
+
 	signingAlgorithm = "AWS4-HMAC-SHA256"
 
 	authorizationHeaderKey = "Authorization"

pkg/sigv4/sigv4.go

@@ -21,13 +21,20 @@ type Signer interface {
 
 type DefaultSigner struct {
 	config *Config
+
+	// noEscape represents the characters that AWS doesn't escape
+	noEscape [256]bool
 }
 
 func NewDefaultSigner(config *Config) Signer {
-	// initialize noEscape array. This way we can avoid using init() functions
-	for i := 0; i < len(noEscape); i++ {
+	ds := &DefaultSigner{
+		config:   config,
+		noEscape: [256]bool{},
+	}
+
+	for i := 0; i < len(ds.noEscape); i++ {
 		// AWS expects every character except these to be escaped
-		noEscape[i] = (i >= 'A' && i <= 'Z') ||
+		ds.noEscape[i] = (i >= 'A' && i <= 'Z') ||
 			(i >= 'a' && i <= 'z') ||
 			(i >= '0' && i <= '9') ||
 			i == '-' ||
@@ -36,7 +43,7 @@ func NewDefaultSigner(config *Config) Signer {
 			i == '~'
 	}
 
-	return &DefaultSigner{config: config}
+	return ds
 }
 
 func (d *DefaultSigner) Sign(req *http.Request) error {
@@ -59,7 +66,7 @@ func (d *DefaultSigner) Sign(req *http.Request) error {
 	canonicalQueryString := getCanonicalQueryString(req.URL)
 	canonicalReq := buildCanonicalString(
 		req.Method,
-		getCanonicalURI(req.URL),
+		getCanonicalURI(req.URL, d.noEscape),
 		canonicalQueryString,
 		canonicalHeaderStr,
 		signedHeadersStr,
@@ -136,6 +143,7 @@ var ignoredHeaders = map[string]struct{}{
 	"Expect":          struct{}{},
 }
 
+// buildCanonicalHeaders is mostly ported from https://github.com/aws/aws-sdk-go-v2/aws/signer/v4 buildCanonicalHeaders
 func buildCanonicalHeaders(req *http.Request) (signed http.Header, signedHeaders, canonicalHeadersStr string) {
 	host, header, length := req.Host, req.Header, req.ContentLength
 
@@ -203,8 +211,8 @@ func buildCanonicalHeaders(req *http.Request) (signed http.Header, signedHeaders
 	return signed, signedHeaders, canonicalHeadersStr
 }
 
-func getCanonicalURI(u *url.URL) string {
-	return escapePath(getURIPath(u), false)
+func getCanonicalURI(u *url.URL, noEscape [256]bool) string {
+	return escapePath(getURIPath(u), false, noEscape)
 }
 
 func getCanonicalQueryString(u *url.URL) string {

pkg/sigv4/tripper.go

@@ -3,6 +3,7 @@ package sigv4
 import (
 	"errors"
 	"net/http"
+	"strings"
 )
 
 type Tripper struct {
@@ -22,10 +23,22 @@ func NewRoundTripper(config *Config, next http.RoundTripper) (*Tripper, error) {
 		return nil, errors.New("can't initialize a sigv4 round tripper with nil config")
 	}
 
+	if len(strings.TrimSpace(config.Region)) == 0 {
+		return nil, errors.New("sigV4 config `Region` must be set")
+	}
+
+	if len(strings.TrimSpace(config.AwsSecretAccessKey)) == 0 {
+		return nil, errors.New("sigV4 config `AwsSecretAccessKey` must be set")
+	}
+
+	if len(strings.TrimSpace(config.AwsAccessKeyID)) == 0 {
+		return nil, errors.New("sigV4 config `AwsAccessKeyID` must be set")
+	}
+
 	if next == nil {
 		next = http.DefaultTransport
 	}
-
+	
 	tripper := &Tripper{
 		config: config,
 		next:   next,

pkg/sigv4/utils.go

@@ -7,10 +7,9 @@ import (
 	"strings"
 )
 
-var noEscape [256]bool
-
 // escapePath escapes part of a URL path in Amazon style.
-func escapePath(path string, encodeSep bool) string {
+// inspired by github.com/aws/smithy-go/encoding/httpbinding EscapePath method
+func escapePath(path string, encodeSep bool, noEscape [256]bool) string {
 	var buf bytes.Buffer
 	for i := 0; i < len(path); i++ {
 		c := path[i]
@@ -25,6 +24,7 @@ func escapePath(path string, encodeSep bool) string {
 
 // stripExcessSpaces will rewrite the passed in slice's string values to not
 // contain multiple side-by-side spaces.
+// Ported from github.com/aws/aws-sdk-go-v2/aws/signer/internal/v4 StripExcessSpaces
 func stripExcessSpaces(str string) string {
 	const doubleSpace = "  "
 
@@ -65,6 +65,7 @@ func stripExcessSpaces(str string) string {
 }
 
 // getURIPath returns the escaped URI component from the provided URL.
+// Ported from github.com/aws/aws-sdk-go-v2/aws/signer/internal/v4 GetURIPath
 func getURIPath(u *url.URL) string {
 	var uriPath string