Incorporate @jen20 code comments (errors, errwrap, TODO’s)

Implement content_md5, content_type, extension_headers support.

builtin/providers/google/data_source_storage_object_signed_url.go

@@ -9,6 +9,7 @@ import (
 	"crypto/x509"
 	"encoding/base64"
 	"encoding/pem"
+	"errors"
 	"fmt"
 	"log"
 	"net/url"
@@ -17,11 +18,15 @@ import (
 	"strings"
 	"time"
 
+	"sort"
+
+	"regexp"
+
+	"github.com/hashicorp/errwrap"
 	"github.com/hashicorp/terraform/helper/pathorcontents"
 	"github.com/hashicorp/terraform/helper/schema"
 	"golang.org/x/oauth2/google"
 	"golang.org/x/oauth2/jwt"
-	"sort"
 )
 
 const gcsBaseUrl = "https://storage.googleapis.com"
@@ -36,6 +41,11 @@ func dataSourceGoogleSignedUrl() *schema.Resource {
 				Type:     schema.TypeString,
 				Required: true,
 			},
+			"content_md5": &schema.Schema{
+				Type:     schema.TypeString,
+				Optional: true,
+				Default:  "",
+			},
 			"content_type": &schema.Schema{
 				Type:     schema.TypeString,
 				Optional: true,
@@ -50,20 +60,17 @@ func dataSourceGoogleSignedUrl() *schema.Resource {
 				Optional: true,
 				Default:  "1h",
 			},
+			"extension_headers": &schema.Schema{
+				Type:         schema.TypeMap,
+				Optional:     true,
+				Elem:         schema.TypeString,
+				ValidateFunc: validateExtensionHeaders,
+			},
 			"http_method": &schema.Schema{
-				Type:     schema.TypeString,
+				Type:         schema.TypeString,
-				Optional: true,
+				Optional:     true,
-				Default:  "GET",
+				Default:      "GET",
-			},
+				ValidateFunc: validateHttpMethod,
-			"http_headers": &schema.Schema{
-				Type:     schema.TypeMap,
-				Optional: true,
-				Elem:     schema.TypeString,
-			},
-			"md5_digest": &schema.Schema{
-				Type:     schema.TypeString,
-				Optional: true,
-				Default:  "",
 			},
 			"path": &schema.Schema{
 				Type:     schema.TypeString,
@@ -77,6 +84,26 @@ func dataSourceGoogleSignedUrl() *schema.Resource {
 	}
 }
 
+func validateExtensionHeaders(v interface{}, k string) (ws []string, errors []error) {
+	hdrMap := v.(map[string]interface{})
+	for k, _ := range hdrMap {
+		if !strings.HasPrefix(strings.ToLower(k), "x-goog") {
+			errors = append(errors, fmt.Errorf(
+				"extension_header (%s) not valid, header name must begin with 'x-goog-'", k))
+		}
+	}
+	return
+}
+
+func validateHttpMethod(v interface{}, k string) (ws []string, errs []error) {
+	value := v.(string)
+	value = strings.ToUpper(value)
+	if !regexp.MustCompile(`^(GET|HEAD|PUT|DELETE)$`).MatchString(value) {
+		errs = append(errs, errors.New("HTTP method must be one of [GET|HEAD|PUT|DELETE]"))
+	}
+	return
+}
+
 func dataSourceGoogleSignedUrlRead(d *schema.ResourceData, meta interface{}) error {
 	config := meta.(*Config)
 
@@ -87,7 +114,7 @@ func dataSourceGoogleSignedUrlRead(d *schema.ResourceData, meta interface{}) err
 	if method, ok := d.GetOk("http_method"); ok && len(method.(string)) >= 3 {
 		urlData.HttpMethod = method.(string)
 	} else {
-		return fmt.Errorf("not a valid http method")
+		return errors.New("not a valid http method")
 	}
 
 	// convert duration to an expiration datetime (unix time in seconds)
@@ -97,16 +124,23 @@ func dataSourceGoogleSignedUrlRead(d *schema.ResourceData, meta interface{}) err
 	}
 	duration, err := time.ParseDuration(durationString)
 	if err != nil {
-		return fmt.Errorf("could not parse duration")
+		return errwrap.Wrapf("could not parse duration: {{err}}", err)
 	}
 	expires := time.Now().Unix() + int64(duration.Seconds())
 	urlData.Expires = int(expires)
 
+	// content_md5 is optional
+	if v, ok := d.GetOk("content_md5"); ok {
+		urlData.ContentMd5 = v.(string)
+	}
+
+	// content_type is optional
 	if v, ok := d.GetOk("content_type"); ok {
 		urlData.ContentType = v.(string)
 	}
 
-	if v, ok := d.GetOk("http_headers"); ok {
+	// extension_headers (x-goog-* HTTP headers) are optional
+	if v, ok := d.GetOk("extension_headers"); ok {
 		hdrMap := v.(map[string]interface{})
 
 		if len(hdrMap) > 0 {
@@ -117,10 +151,6 @@ func dataSourceGoogleSignedUrlRead(d *schema.ResourceData, meta interface{}) err
 		}
 	}
 
-	if v, ok := d.GetOk("md5_digest"); ok {
-		urlData.Md5Digest = v.(string)
-	}
-
 	// object path
 	path := []string{
 		"",
@@ -137,26 +167,28 @@ func dataSourceGoogleSignedUrlRead(d *schema.ResourceData, meta interface{}) err
 	}
 	urlData.JwtConfig = jwtConfig
 
-	// Sign url object data
-	signature, err := SignString(urlData.CreateSigningString(), jwtConfig)
-	if err != nil {
-		return fmt.Errorf("could not sign data: %v", err)
-	}
-	urlData.Signature = signature
-
 	// Construct URL
-	finalUrl := urlData.BuildUrl()
+	signedUrl, err := urlData.SignedUrl()
-	d.SetId(urlData.EncodedSignature())
+	if err != nil {
-	d.Set("signed_url", finalUrl)
+		return err
+	}
+
+	// Success
+	d.Set("signed_url", signedUrl)
+
+	encodedSig, err := urlData.EncodedSignature()
+	if err != nil {
+		return err
+	}
+	d.SetId(encodedSig)
 
 	return nil
 }
 
-// This looks for credentials json in the following places,
+// loadJwtConfig looks for credentials json in the following places,
 // in order of preference:
-//
+//   1. `credentials` attribute of the datasource
-//   1. Credentials provided in data source `credentials` attribute.
+//   2. `credentials` attribute in the provider definition.
-//   2. Credentials provided in the provider definition.
 //   3. A JSON file whose path is specified by the
 //      GOOGLE_APPLICATION_CREDENTIALS environment variable.
 func loadJwtConfig(d *schema.ResourceData, meta interface{}) (*jwt.Config, error) {
@@ -180,17 +212,17 @@ func loadJwtConfig(d *schema.ResourceData, meta interface{}) (*jwt.Config, error
 	if strings.TrimSpace(credentials) != "" {
 		contents, _, err := pathorcontents.Read(credentials)
 		if err != nil {
-			return nil, fmt.Errorf("Error loading credentials: %s", err)
+			return nil, errwrap.Wrapf("Error loading credentials: {{err}}", err)
 		}
 
 		cfg, err := google.JWTConfigFromJSON([]byte(contents), "")
 		if err != nil {
-			return nil, fmt.Errorf("Error parsing credentials: \n %s \n Error: %s", contents, err)
+			return nil, errwrap.Wrapf("Error parsing credentials: {{err}}", err)
 		}
 		return cfg, nil
 	}
 
-	return nil, fmt.Errorf("Credentials not found in datasource, provider configuration or GOOGLE_APPLICATION_CREDENTIALS environment variable.")
+	return nil, errors.New("Credentials not found in datasource, provider configuration or GOOGLE_APPLICATION_CREDENTIALS environment variable.")
 }
 
 // parsePrivateKey converts the binary contents of a private key file
@@ -208,29 +240,29 @@ func parsePrivateKey(key []byte) (*rsa.PrivateKey, error) {
 	if err != nil {
 		parsedKey, err = x509.ParsePKCS1PrivateKey(key)
 		if err != nil {
-			return nil, fmt.Errorf("private key should be a PEM or plain PKSC1 or PKCS8; parse error: %v", err)
+			return nil, errwrap.Wrapf("private key should be a PEM or plain PKSC1 or PKCS8; parse error: {{err}}", err)
 		}
 	}
 	parsed, ok := parsedKey.(*rsa.PrivateKey)
 	if !ok {
-		return nil, fmt.Errorf("private key is invalid")
+		return nil, errors.New("private key is invalid")
 	}
 	return parsed, nil
 }
 
+// UrlData stores the values required to create a Signed Url
 type UrlData struct {
 	JwtConfig   *jwt.Config
+	ContentMd5  string
 	ContentType string
 	HttpMethod  string
 	Expires     int
-	Md5Digest   string
 	HttpHeaders map[string]string
 	Path        string
-	Signature   []byte
 }
 
-// Creates a string in the form ready for signing:
+// SigningString creates a string representation of the UrlData in a form ready for signing:
-// https://cloud.google.com/storage/docs/access-control/create-signed-urls-program
+// see https://cloud.google.com/storage/docs/access-control/create-signed-urls-program
 // Example output:
 // -------------------
 // GET
@@ -239,59 +271,78 @@ type UrlData struct {
 // 1388534400
 // bucket/objectname
 // -------------------
-func (u *UrlData) CreateSigningString() []byte {
+func (u *UrlData) SigningString() []byte {
 	var buf bytes.Buffer
 
-	// HTTP VERB
+	// HTTP Verb
 	buf.WriteString(u.HttpMethod)
 	buf.WriteString("\n")
 
-	// MD5 digest (optional)
+	// Content MD5 (optional, always add new line)
-	buf.WriteString(u.Md5Digest)
+	buf.WriteString(u.ContentMd5)
 	buf.WriteString("\n")
 
-	// request content-type (optional)
+	// Content Type (optional, always add new line)
 	buf.WriteString(u.ContentType)
 	buf.WriteString("\n")
 
-	// signed url expiration
+	// Expiration
 	buf.WriteString(strconv.Itoa(u.Expires))
 	buf.WriteString("\n")
 
-	// additional request headers (optional)
+	// Extra HTTP headers (optional)
 	// Must be sorted in lexigraphical order
 	var keys []string
 	for k := range u.HttpHeaders {
 		keys = append(keys, strings.ToLower(k))
 	}
 	sort.Strings(keys)
-
+	// Write sorted headers to signing string buffer
-	// To perform the opertion you want
 	for _, k := range keys {
 		buf.WriteString(fmt.Sprintf("%s:%s\n", k, u.HttpHeaders[k]))
 	}
 
-	// object path
+	// Storate Object path (includes bucketname)
 	buf.WriteString(u.Path)
 
-	fmt.Printf("SIGNING STRING: \n%s\n", buf.String())
-
 	return buf.Bytes()
 }
 
-func (u *UrlData) EncodedSignature() string {
+func (u *UrlData) Signature() ([]byte, error) {
+	// Sign url data
+	signature, err := SignString(u.SigningString(), u.JwtConfig)
+	if err != nil {
+		return nil, err
+
+	}
+
+	return signature, nil
+}
+
+// EncodedSignature returns the Signature() after base64 encoding and url escaping
+func (u *UrlData) EncodedSignature() (string, error) {
+	signature, err := u.Signature()
+	if err != nil {
+		return "", err
+	}
+
 	// base64 encode signature
-	encoded := base64.StdEncoding.EncodeToString(u.Signature)
+	encoded := base64.StdEncoding.EncodeToString(signature)
 	// encoded signature may include /, = characters that need escaping
 	encoded = url.QueryEscape(encoded)
 
-	return encoded
+	return encoded, nil
 }
 
-// Builds the final signed URL a client can use to retrieve storage object
+// SignedUrl constructs the final signed URL a client can use to retrieve storage object
-func (u *UrlData) BuildUrl() string {
+func (u *UrlData) SignedUrl() (string, error) {
 
-	// set url
+	encodedSig, err := u.EncodedSignature()
+	if err != nil {
+		return "", err
+	}
+
+	// build url
 	// https://cloud.google.com/storage/docs/access-control/create-signed-urls-program
 	var urlBuffer bytes.Buffer
 	urlBuffer.WriteString(gcsBaseUrl)
@@ -301,16 +352,17 @@ func (u *UrlData) BuildUrl() string {
 	urlBuffer.WriteString("&Expires=")
 	urlBuffer.WriteString(strconv.Itoa(u.Expires))
 	urlBuffer.WriteString("&Signature=")
-	urlBuffer.WriteString(u.EncodedSignature())
+	urlBuffer.WriteString(encodedSig)
 
-	return urlBuffer.String()
+	return urlBuffer.String(), nil
 }
 
+// SignString calculates the SHA256 signature of the input string
 func SignString(toSign []byte, cfg *jwt.Config) ([]byte, error) {
 	// Parse private key
 	pk, err := parsePrivateKey(cfg.PrivateKey)
 	if err != nil {
-		return nil, fmt.Errorf("could not parse key: %v\nKey:%s", err, string(cfg.PrivateKey))
+		return nil, errwrap.Wrapf("failed to sign string, could not parse key: {{err}}", err)
 	}
 
 	// Hash string
@@ -320,7 +372,7 @@ func SignString(toSign []byte, cfg *jwt.Config) ([]byte, error) {
 	// Sign string
 	signed, err := rsa.SignPKCS1v15(rand.Reader, pk, crypto.SHA256, hasher.Sum(nil))
 	if err != nil {
-		return nil, fmt.Errorf("error signing string: %s\n", err)
+		return nil, errwrap.Wrapf("failed to sign string, an error occurred: {{err}}", err)
 	}
 
 	return signed, nil

builtin/providers/google/data_source_storage_object_signed_url_test.go

@@ -6,15 +6,15 @@ import (
 	"bytes"
 	"encoding/base64"
 	"fmt"
+	"io/ioutil"
+	"net/http"
+	"net/url"
+
 	"github.com/hashicorp/go-cleanhttp"
 	"github.com/hashicorp/terraform/helper/acctest"
 	"github.com/hashicorp/terraform/helper/resource"
 	"github.com/hashicorp/terraform/terraform"
 	"golang.org/x/oauth2/google"
-	"io/ioutil"
-	"net/http"
-	"net/url"
-	"strings"
 )
 
 const fakeCredentials = `{
@@ -64,7 +64,7 @@ func TestUrlData_Signing(t *testing.T) {
 	}
 
 	// create url data signature
-	toSign := urlData.CreateSigningString()
+	toSign := urlData.SigningString()
 	result, err := SignString(toSign, cfg)
 	if err != nil {
 		t.Error(err)
@@ -77,17 +77,7 @@ func TestUrlData_Signing(t *testing.T) {
 
 }
 
-func TestUrlData_BuildUrl(t *testing.T) {
+func TestUrlData_SignedUrl(t *testing.T) {
-	// unescape and decode the expected signature
-	encodedSig, err := url.QueryUnescape(testUrlExpectedSignatureBase64Encoded)
-	if err != nil {
-		t.Error(err)
-	}
-	sig, err := base64.StdEncoding.DecodeString(encodedSig)
-	if err != nil {
-		t.Error(err)
-	}
-
 	// load fake service account credentials
 	cfg, err := google.JWTConfigFromJSON([]byte(fakeCredentials), "")
 	if err != nil {
@@ -98,10 +88,12 @@ func TestUrlData_BuildUrl(t *testing.T) {
 		HttpMethod: "GET",
 		Expires:    testUrlExpires,
 		Path:       testUrlPath,
-		Signature:  sig,
 		JwtConfig:  cfg,
 	}
-	result := urlData.BuildUrl()
+	result, err := urlData.SignedUrl()
+	if err != nil {
+		t.Errorf("Could not generated signed url: %+v", err)
+	}
 	if result != testUrlExpectedUrl {
 		t.Errorf("URL does not match expected value:\n%s\n%s", testUrlExpectedUrl, result)
 	}
@@ -125,6 +117,11 @@ func TestDatasourceSignedUrl_basic(t *testing.T) {
 func TestDatasourceSignedUrl_accTest(t *testing.T) {
 	bucketName := fmt.Sprintf("tf-test-bucket-%d", acctest.RandInt())
 
+	headers := map[string]string{
+		"x-goog-test":                "foo",
+		"x-goog-if-generation-match": "1",
+	}
+
 	resource.Test(t, resource.TestCase{
 		PreCheck:  func() { testAccPreCheck(t) },
 		Providers: testAccProviders,
@@ -133,55 +130,8 @@ func TestDatasourceSignedUrl_accTest(t *testing.T) {
 				Config: testAccTestGoogleStorageObjectSingedUrl(bucketName),
 				Check: resource.ComposeTestCheckFunc(
 					testAccGoogleSignedUrlRetrieval("data.google_storage_object_signed_url.story_url", nil),
-				),
-			},
-		},
-	})
-}
-
-func TestDatasourceSignedUrl_wHeaders(t *testing.T) {
-
-	headers := map[string]string{
-		"x-goog-test": "foo",
-	}
-
-	resource.Test(t, resource.TestCase{
-		PreCheck:  func() { testAccPreCheck(t) },
-		Providers: testAccProviders,
-		Steps: []resource.TestStep{
-			resource.TestStep{
-				Config: testAccTestGoogleStorageObjectSingedUrl_wHeader(),
-				Check: resource.ComposeTestCheckFunc(
 					testAccGoogleSignedUrlRetrieval("data.google_storage_object_signed_url.story_url_w_headers", headers),
-				),
-			},
-		},
-	})
-}
-
-func TestDatasourceSignedUrl_wContentType(t *testing.T) {
-	resource.Test(t, resource.TestCase{
-		PreCheck:  func() { testAccPreCheck(t) },
-		Providers: testAccProviders,
-		Steps: []resource.TestStep{
-			resource.TestStep{
-				Config: testAccTestGoogleStorageObjectSingedUrl_wContentType(),
-				Check: resource.ComposeTestCheckFunc(
 					testAccGoogleSignedUrlRetrieval("data.google_storage_object_signed_url.story_url_w_content_type", nil),
-				),
-			},
-		},
-	})
-}
-
-func TestDatasourceSignedUrl_wMD5(t *testing.T) {
-	resource.Test(t, resource.TestCase{
-		PreCheck:  func() { testAccPreCheck(t) },
-		Providers: testAccProviders,
-		Steps: []resource.TestStep{
-			resource.TestStep{
-				Config: testAccTestGoogleStorageObjectSingedUrl_wMD5(),
-				Check: resource.ComposeTestCheckFunc(
 					testAccGoogleSignedUrlRetrieval("data.google_storage_object_signed_url.story_url_w_md5", nil),
 				),
 			},
@@ -189,35 +139,6 @@ func TestDatasourceSignedUrl_wMD5(t *testing.T) {
 	})
 }
 
-// formatRequest generates ascii representation of a request
-func formatRequest(r *http.Request) string {
-	// Create return string
-	var request []string
-	request = append(request, "--------")
-	// Add the request string
-	url := fmt.Sprintf("%v %v %v", r.Method, r.URL, r.Proto)
-	request = append(request, url)
-	// Add the host
-	request = append(request, fmt.Sprintf("Host: %v", r.Host))
-	// Loop through headers
-	for name, headers := range r.Header {
-		//name = strings.ToLower(name)
-		for _, h := range headers {
-			request = append(request, fmt.Sprintf("%v: %v", name, h))
-		}
-	}
-
-	// If this is a POST, add post data
-	if r.Method == "POST" {
-		r.ParseForm()
-		request = append(request, "\n")
-		request = append(request, r.Form.Encode())
-	}
-	request = append(request, "--------")
-	// Return the request as a string
-	return strings.Join(request, "\n")
-}
-
 func testAccGoogleSignedUrlExists(n string) resource.TestCheckFunc {
 	return func(s *terraform.State) error {
 
@@ -244,43 +165,37 @@ func testAccGoogleSignedUrlRetrieval(n string, headers map[string]string) resour
 			return fmt.Errorf("signed_url is empty: %v", a)
 		}
 
+		// create HTTP request
 		url := a["signed_url"]
-		fmt.Printf("URL: %s\n", url)
 		method := a["http_method"]
-
 		req, _ := http.NewRequest(method, url, nil)
 
-		// Apply custom headers to request
+		// Add extension headers to request, if provided
 		for k, v := range headers {
-			fmt.Printf("Adding Header (%s: %s)\n", k, v)
 			req.Header.Set(k, v)
 		}
 
+		// content_type is optional, add to test query if provided in datasource config
 		contentType := a["content_type"]
 		if contentType != "" {
-			fmt.Printf("Adding Content-Type: %s\n", contentType)
 			req.Header.Add("Content-Type", contentType)
 		}
 
-		md5Digest := a["md5_digest"]
+		// content_md5 is optional, add to test query if provided in datasource config
-		if md5Digest != "" {
+		contentMd5 := a["content_md5"]
-			fmt.Printf("Adding Content-MD5: %s\n", md5Digest)
+		if contentMd5 != "" {
-			req.Header.Add("Content-MD5", md5Digest)
+			req.Header.Add("Content-MD5", contentMd5)
 		}
 
-		// send request to GET object using signed url
+		// send request using signed url
 		client := cleanhttp.DefaultClient()
-
-		// Print request
-		//dump, _ := httputil.DumpRequest(req, true)
-		//fmt.Printf("%+q\n", strings.Replace(string(dump), "\\n", "\n", 99))
-		fmt.Printf("%s\n", formatRequest(req))
-
 		response, err := client.Do(req)
 		if err != nil {
 			return err
 		}
 		defer response.Body.Close()
+
+		// check content in response, should be our test string or XML with error
 		body, err := ioutil.ReadAll(response.Body)
 		if err != nil {
 			return err
@@ -318,42 +233,15 @@ data "google_storage_object_signed_url" "story_url" {
   bucket = "${google_storage_bucket.bucket.name}"
   path   = "${google_storage_bucket_object.story.name}"
 
-}`, bucketName)
-}
-
-func testAccTestGoogleStorageObjectSingedUrl_wHeader() string {
-	return fmt.Sprintf(`
-resource "google_storage_bucket" "bucket" {
-	name = "tf-signurltest-%s"
-}
-
-resource "google_storage_bucket_object" "story" {
-  name   = "path/to/file"
-  bucket = "${google_storage_bucket.bucket.name}"
-
-  content = "once upon a time..."
 }
 
 data "google_storage_object_signed_url" "story_url_w_headers" {
   bucket = "${google_storage_bucket.bucket.name}"
   path   = "${google_storage_bucket_object.story.name}"
-  http_headers {
+  extension_headers {
   	x-goog-test = "foo"
+  	x-goog-if-generation-match = 1
   }
-}`, acctest.RandString(6))
-}
-
-func testAccTestGoogleStorageObjectSingedUrl_wContentType() string {
-	return fmt.Sprintf(`
-resource "google_storage_bucket" "bucket" {
-	name = "tf-signurltest-%s"
-}
-
-resource "google_storage_bucket_object" "story" {
-  name   = "path/to/file"
-  bucket = "${google_storage_bucket.bucket.name}"
-
-  content = "once upon a time..."
 }
 
 data "google_storage_object_signed_url" "story_url_w_content_type" {
@@ -361,26 +249,12 @@ data "google_storage_object_signed_url" "story_url_w_content_type" {
   path   = "${google_storage_bucket_object.story.name}"
 
   content_type = "text/plain"
-}`, acctest.RandString(6))
-}
-
-func testAccTestGoogleStorageObjectSingedUrl_wMD5() string {
-	return fmt.Sprintf(`
-resource "google_storage_bucket" "bucket" {
-	name = "tf-signurltest-%s"
-}
-
-resource "google_storage_bucket_object" "story" {
-  name   = "path/to/file"
-  bucket = "${google_storage_bucket.bucket.name}"
-
-  content = "once upon a time..."
 }
 
 data "google_storage_object_signed_url" "story_url_w_md5" {
   bucket = "${google_storage_bucket.bucket.name}"
   path   = "${google_storage_bucket_object.story.name}"
 
-  md5_digest = "${google_storage_bucket_object.story.md5hash}"
+  content_md5 = "${google_storage_bucket_object.story.md5hash}"
-}`, acctest.RandString(6))
+}`, bucketName)
 }

website/source/docs/providers/google/d/signed_url.html.markdown

@@ -14,7 +14,7 @@ For more info about signed URL's is available [here](https://cloud.google.com/st
 
 ## Example Usage
 
-```
+```hcl
 data "google_storage_object_signed_url" "artifact" {
   bucket = "install_binaries"
   path   = "path/to/install_file.bin"
@@ -27,7 +27,7 @@ resource "google_compute_instance" "vm" {
     
     provisioner "remote-exec" {
         inline = [
-                "wget ${data.google_storage_object_signed_url.artifact.signed_url}",
+                "wget '${data.google_storage_object_signed_url.artifact.signed_url}' -O install_file.bin",
                 "chmod +x install_file.bin",
                 "./install_file.bin"
                 ]
@@ -35,6 +35,23 @@ resource "google_compute_instance" "vm" {
 }
 ```
 
+## Full Example
+
+```hcl
+data "google_storage_object_signed_url" "get_url" {
+  bucket       = "fried_chicken"
+  path         = "path/to/file"
+  content_md5  = "pRviqwS4c4OTJRTe03FD1w=="
+  content_type = "text/plain"
+  duration     = "2d"
+  credentials  = "${file("path/to/credentials.json")}"
+  
+  extension_headers {
+    x-goog-if-generation-match = 1
+  }
+}
+```
+
 ## Argument Reference
 
 The following arguments are supported:
@@ -42,10 +59,20 @@ The following arguments are supported:
 * `bucket` - (Required) The name of the bucket to read the object from
 * `path` - (Required) The full path to the object inside the bucket
 * `http_method` - (Optional) What HTTP Method will the signed URL allow (defaults to `GET`)
-* `duration` - (Optional) For how long shall the signed URL be valid (defaults to 1 hour `1h`). See [here](https://golang.org/pkg/time/#ParseDuration) for info on valid duration formats.
+* `duration` - (Optional) For how long shall the signed URL be valid (defaults to 1 hour - i.e. `1h`). 
-* `credentials` - (Optional) What Google service account credentials json should be used to sign the URL. This data source checks the following locations for credentials, in order of preference: data source `credentials` attribute, provider `credentials` attribute and finally the GOOGLE_APPLICATION_CREDENTIALS environment variable.
+     See [here](https://golang.org/pkg/time/#ParseDuration) for info on valid duration formats.
-    
+* `credentials` - (Optional) What Google service account credentials json should be used to sign the URL. 
+     This data source checks the following locations for credentials, in order of preference: data source `credentials` attribute, provider `credentials` attribute and finally the GOOGLE_APPLICATION_CREDENTIALS environment variable.
+     
 > **NOTE** the default google credentials configured by `gcloud` sdk or the service account associated with a compute instance cannot be used, because these do not include the private key required to sign the URL. A valid `json` service account credentials key file must be used, as generated via Google cloud console. 
+     
+* `content_type` - (Optional) If you specify this in the datasource, the client must provide the `Content-Type` HTTP header with the same value in its request.
+* `content_md5` - (Optional) The [MD5 digest](https://cloud.google.com/storage/docs/hashes-etags#_MD5) value in Base64.
+     Typically retrieved from `google_storage_bucket_object.object.md5hash` attribute.
+     If you provide this in the datasource, the client (e.g. browser, curl) must provide the `Content-MD5` HTTP header with this same value in its request.
+* `extension_headers` - (Optional) As needed. The server checks to make sure that the client provides matching values in requests using the signed URL. 
+     Any header starting with `x-goog-` is accepted but see the [Google Docs](https://cloud.google.com/storage/docs/xml-api/reference-headers) for list of headers that are supported by Google.
+    
 
 ## Attributes Reference