Implement url en/decoding

src/get_handler.c

@@ -1,7 +1,7 @@
 static enum MHD_Result handle_get(struct MHD_Connection *connection, SV url, Settings settings, SV username) {
     noh_arena_save(&temp);
     Noh_String fs_path = build_path(false, false, &settings.base_path, &username, &url);
-    noh_string_replace(&fs_path, '+', ' ');
+    url_decode(&fs_path);
 
     noh_log(NOH_INFO, "Physical path: "Nsv_Fmt, Nsv_Arg(fs_path));
 

src/opds_handler.c

@@ -49,7 +49,7 @@ static Noh_String create_feed_response(Library_Entry self_path, SV url, Library_
 static enum MHD_Result handle_opds(struct MHD_Connection *connection, SV url, Settings settings, SV username) {
     noh_arena_save(&temp);
     Noh_String fs_path = build_path(false, false, &settings.base_path, &username, &url);
-    noh_string_replace(&fs_path, '+', ' ');
+    url_decode(&fs_path);
     Noh_String fs_path_cstr = fs_path;
     noh_string_append_null(&fs_path_cstr);
 

src/path.c

@@ -1,3 +1,103 @@
+static inline bool byte_is_url_safe(char c) {
+    return (c >= 'A' && c <= 'Z')
+        || (c >= 'a' && c <= 'z')
+        || (c >= '0' && c <+ '9')
+        || (c >= '(' && c <= '*')
+        || c == '!' || c == '-'
+        || c == '.' || c == '_';
+}
+
+// Determines if a string needs to be URL encoded.
+// Sets the number of unsafe characters that need to be replaced by a hexadecimal format.
+static bool needs_encoding(Noh_String string, int *unsafe_count) {
+    *unsafe_count = 0;
+    bool safe = true ;
+    for (size_t i = 0; i < string.count; i++) {
+        bool needs_encode = byte_is_url_safe(string.elems[i]);
+        if (needs_encode || string.elems[i] == ' ') safe = false;
+        if (needs_encode) (*unsafe_count)++;
+    }
+
+    return safe;
+}
+
+static inline char to_char_lower(int value) {
+    value &= 0XF;
+    value += '0';
+    if (value > '9') value += ('a'  - ('9' + 1));
+
+    return (char)value;
+}
+
+static inline int from_char(char c) {
+    if (c >= '0' && c <= '9') return c - '0';
+    if (c >= 'a' && c <= 'z') return c - 'a';
+    if (c >= 'A' && c <= 'Z') return c - 'A';
+
+    return 0xFF;
+}
+
+void url_encode(Noh_String *string) {
+    int unsafe_count = 0;
+    if (!needs_encoding(*string, &unsafe_count)) return;
+
+    // TODO: Use the calculated size to allocate exactly enough memory?
+    // size_t new_string_size = string->count + unsafe_count * 2 + 1;
+    Noh_String result = {0};
+
+    for (size_t i = 0; i < string->count; i++) {
+        char cur = string->elems[i];
+        if (cur  == ' ') noh_da_append(&result, '+');
+
+        if (!byte_is_url_safe(cur)) {
+            noh_da_append(&result, '%');
+            noh_da_append(&result, to_char_lower(cur >> 4));
+            noh_da_append(&result, to_char_lower(cur));
+        }
+    }
+
+    noh_string_free(string);
+    string->elems = result.elems;
+    string->count = result.count;
+    string->capacity = result.capacity;
+}
+
+void url_decode(Noh_String *string) {
+    size_t read = 0;
+    size_t write = 0;
+
+    while (read < string->count) {
+        char c = string->elems[read++];
+        if (c == '+') {
+             string->elems[write++] = ' ';
+            continue;
+        }
+
+        if (c == '%') {
+            int h1 = string->elems[read];
+            int h2 = string->elems[read + 1];
+
+            // If valid hex chars, add it.
+            if ((h1 | h2) != 0xFF) {
+                string->elems[write] = (char)((h1 << 4) | h2);
+                read += 2;
+                continue;
+            }
+
+            // Fallback to just adding the '%'.
+        }
+
+        // Just copy the character.
+        string->elems[write++] = c;
+    }
+
+    // Zero-out the rest.
+    string->count = read;
+    for (size_t i = read; i < string->count; i++) {
+        string->elems[i] = 0;
+    }
+}
+
 #define build_path(url, first, ...) build_path_((url), (first), __VA_ARGS__, NULL)
 static Noh_String build_path_(bool url, bool go_up, Noh_String_View *first, ...) {
     va_list args;
@@ -23,7 +123,7 @@ static Noh_String build_path_(bool url, bool go_up, Noh_String_View *first, ...)
     }
     va_end(args);
 
-    if (url) noh_string_replace(&result, ' ', '+');
+    if (url) url_encode(&result);
 
     return result;
 }