5 files changed, 255 insertions, 0 deletions
diff --git a/src/server/helper/clean.go b/src/server/helper/clean.go
new file mode 100644
index 0000000..35937de
--- /dev/null
+++ b/src/server/helper/clean.go
@@ -0,0 +1,37 @@
+package helper
+
+import (
+	"regexp"
+)
+
+func removeTrailingWhitespace(str string) string {
+	re := regexp.MustCompile(`(^\s+)|(\s+$)`)
+	return re.ReplaceAllString(str, "")
+}
+
+func removeDuplicateWhitespace(str string) string {
+	re := regexp.MustCompile(`\s{2,}`)
+	return re.ReplaceAllString(str, " ")
+}
+
+func removeNewlines(str string) string {
+	re := regexp.MustCompile(`\n+`)
+	return re.ReplaceAllString(str, "")
+}
+
+func removeDuplicateNewlines(str string) string {
+	re := regexp.MustCompile(`\n{2,}`)
+	return re.ReplaceAllString(str, "\n")
+}
+
+func CleanTitle(title string) string {
+	title = removeDuplicateWhitespace(title)
+	title = removeNewlines(title)
+	return removeTrailingWhitespace(title)
+}
+
+func CleanContents(contents string) string {
+	contents = removeDuplicateWhitespace(contents)
+	contents = removeDuplicateNewlines(contents)
+	return removeTrailingWhitespace(contents)
+}
diff --git a/src/server/helper/crypto.go b/src/server/helper/crypto.go
new file mode 100644
index 0000000..d676fba
--- /dev/null
+++ b/src/server/helper/crypto.go
@@ -0,0 +1,46 @@
+package helper
+
+import (
+	"crypto/rand"
+	"encoding/base64"
+
+	"golang.org/x/crypto/scrypt"
+)
+
+// Recommended https://pkg.go.dev/golang.org/x/crypto/scrypt
+const SCRYPT_N = 32768
+const SCRYPT_R = 8
+const SCRYPT_P = 1
+const SCRYPT_L = 64
+
+const SALT_LENGTH = SCRYPT_L
+
+func getEncoding() *base64.Encoding {
+	return base64.StdEncoding.WithPadding(base64.NoPadding)
+}
+
+// Generates truly random bytes.
+func generateRandomBytes(len int) ([]byte, error) {
+	salt := make([]byte, len)
+	_, err := rand.Read(salt)
+	if err != nil {
+		return nil, err
+	}
+	return salt, nil
+}
+
+func GenerateSalt() (string, error) {
+	salt, err := generateRandomBytes(SALT_LENGTH)
+	if err != nil {
+		return "", err
+	}
+	return getEncoding().EncodeToString(salt), nil
+}
+
+func GenerateHash(password string, salt string) (string, error) {
+	hash, err := scrypt.Key([]byte(password), []byte(salt), SCRYPT_N, SCRYPT_R, SCRYPT_P, SCRYPT_L)
+	if err != nil {
+		return "", err
+	}
+	return getEncoding().EncodeToString(hash), nil
+}
diff --git a/src/server/helper/error.go b/src/server/helper/error.go
new file mode 100644
index 0000000..8c76304
--- /dev/null
+++ b/src/server/helper/error.go
@@ -0,0 +1,36 @@
+package helper
+
+import (
+	"encoding/json"
+	"log"
+	"net/http"
+)
+
+type jsonError struct {
+	Message string `json:"error"`
+}
+
+func WriteInternalError(err error, writer http.ResponseWriter) {
+	log.Printf("internal server error: %s\n", err)
+	http.Error(writer, "internal server error", http.StatusInternalServerError)
+}
+
+func WriteErrorJson(message string, writer http.ResponseWriter, code int) {
+	json_error := &jsonError{
+		Message: message,
+	}
+
+	marshal, err := json.Marshal(json_error)
+	if err != nil {
+		http.Error(writer, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+	http.Error(writer, string(marshal), code)
+}
+
+// Logs the error and responds with a generic server error.
+func WriteInternalErrorJson(err error, writer http.ResponseWriter) {
+	log.Printf("internal server error: %s\n", err)
+	WriteErrorJson("internal server error", writer, http.StatusInternalServerError)
+}
diff --git a/src/server/helper/jwt.go b/src/server/helper/jwt.go
new file mode 100644
index 0000000..ae127bd
--- /dev/null
+++ b/src/server/helper/jwt.go
@@ -0,0 +1,66 @@
+package helper
+
+import (
+	"net/http"
+	"strconv"
+	"time"
+
+	"github.com/golang-jwt/jwt/v4"
+)
+
+// WARNING this key should be secret and constant between deployments.
+// If you use this software in the wild, at the very least change this value!
+// https://www.sohamkamani.com/golang/jwt-authentication/
+var jwt_key = []byte("iph7noo1ohQuam5sou5wa2aeChixo7")
+
+func IssueToken(uid int, writer http.ResponseWriter) error {
+	expiration := time.Now().Add(60 * time.Minute)
+	token := jwt.NewWithClaims(jwt.SigningMethodHS256, jwt.RegisteredClaims{
+		Subject:   strconv.Itoa(uid),
+		ExpiresAt: jwt.NewNumericDate(expiration),
+		Issuer:    "react-go-forum",
+	})
+	token_string, err := token.SignedString(jwt_key)
+	if err != nil {
+		return err
+	}
+
+	http.SetCookie(writer, &http.Cookie{
+		Name:     "token",
+		Value:    token_string,
+		Expires:  expiration,
+		SameSite: http.SameSiteStrictMode,
+		Path:     "/",
+	})
+	return nil
+}
+
+// Returns a non-nil RegisteredClaims if valid, nil otherwise. Handles responding to bad tokens.
+func GetValidClaims(writer http.ResponseWriter, request *http.Request) *jwt.RegisteredClaims {
+	cookie, err := request.Cookie("token")
+	if err != nil {
+		if err == http.ErrNoCookie {
+			WriteErrorJson("access denied", writer, http.StatusUnauthorized)
+			return nil
+		}
+
+		WriteInternalErrorJson(err, writer)
+		return nil
+	}
+
+	claims := &jwt.RegisteredClaims{}
+	token, err := jwt.ParseWithClaims(cookie.Value, claims, func(token *jwt.Token) (interface{}, error) {
+		return jwt_key, nil
+	})
+	if err != nil {
+		WriteInternalErrorJson(err, writer)
+		return nil
+	}
+
+	if !token.Valid {
+		WriteErrorJson("access denied", writer, http.StatusUnauthorized)
+		return nil
+	}
+
+	return claims
+}
diff --git a/src/server/helper/valid.go b/src/server/helper/valid.go
new file mode 100644
index 0000000..9363747
--- /dev/null
+++ b/src/server/helper/valid.go
@@ -0,0 +1,70 @@
+package helper
+
+import (
+	"image"
+	"net/http"
+)
+
+// Checks if the subreact exists, responds with a bad status when false.
+func IsValidSubreact(subreact string, writer http.ResponseWriter) bool {
+	switch subreact {
+	case "":
+		fallthrough
+	case "t":
+		fallthrough
+	case "g":
+		fallthrough
+	case "k":
+		fallthrough
+	case "p":
+		fallthrough
+	case "a":
+		fallthrough
+	case "pr":
+		fallthrough
+	case "m":
+		break
+	default:
+		WriteErrorJson("invalid subreact", writer, http.StatusBadRequest)
+		return false
+	}
+	return true
+}
+
+// Range checks the length of the argument, responds with a bad status when false.
+func IsValidRange(str string, name string, min int, max int, writer http.ResponseWriter) bool {
+	if len(str) < min {
+		WriteErrorJson(name+" too short", writer, http.StatusBadRequest)
+		return false
+	}
+	if len(str) > max {
+		WriteErrorJson(name+" too long", writer, http.StatusBadRequest)
+		return false
+	}
+	return true
+}
+
+// Checks that the image has supported properties, responds with a bad status when false.
+func IsImageSupported(image image.Image, format string, writer http.ResponseWriter) bool {
+	if bounds := image.Bounds(); bounds.Dx() > 4096 || bounds.Dy() > 4096 {
+		WriteErrorJson("image dimensions too large", writer, http.StatusBadRequest)
+		return false
+	} else if bounds.Dx() < 256 || bounds.Dy() < 256 {
+		WriteErrorJson("image dimensions too small", writer, http.StatusBadRequest)
+		return false
+	}
+
+	switch format {
+	case "png":
+		fallthrough
+	case "jpeg":
+		fallthrough
+	case "gif":
+		break
+	default:
+		WriteErrorJson("image format no recognised", writer, http.StatusBadRequest)
+		return false
+	}
+
+	return true
+}