Remove allocs in Headers.getAll()

Provide `Headers.getAllIterator()` to iterate over matching headers, use
this to iterate through `Accept-Encoding` headers in
CompressionMiddleware.

src/jetzig/http/Headers.zig

@@ -59,6 +59,10 @@ pub fn getFirstValue(self: *const Headers, name: []const u8) ?[]const u8 {
     return self.get(name);
 }
 
+pub fn count(self: Headers) usize {
+    return self.httpz_headers.len;
+}
+
 /// Add `name` and `value` to headers.
 pub fn append(self: *Headers, name: []const u8, value: []const u8) !void {
     if (self.httpz_headers.len >= self.httpz_headers.keys.len) return error.JetzigTooManyHeaders;
@@ -75,6 +79,46 @@ pub fn append(self: *Headers, name: []const u8, value: []const u8) !void {
     self.httpz_headers.add(header.name, header.value);
 }
 
+const Iterator = struct {
+    position: usize = 0,
+    headers: Headers,
+    filter_name: ?[]const u8 = null,
+
+    pub fn next(self: *Iterator) ?Header {
+        const header_count = self.headers.count();
+        if (self.position >= header_count) {
+            return null;
+        }
+        const start = self.position;
+
+        var buf: [jetzig.config.get(u16, "max_bytes_header_name")]u8 = undefined;
+        const filter_name = if (self.filter_name) |name| std.ascii.lowerString(&buf, name) else null;
+
+        for (start..header_count) |index| {
+            const key = self.headers.httpz_headers.keys[start + index];
+            const value = self.headers.httpz_headers.values[start + index];
+            self.position += 1;
+            if (filter_name) |name| {
+                if (std.mem.eql(u8, name, key)) {
+                    return .{ .name = key, .value = value };
+                }
+            } else {
+                return .{ .name = key, .value = value };
+            }
+        }
+
+        return null;
+    }
+};
+
+pub fn getAllIterator(self: Headers, name: []const u8) Iterator {
+    return .{ .headers = self, .filter_name = name };
+}
+
+pub fn iterator(self: Headers) Iterator {
+    return .{ .headers = self };
+}
+
 test "append (deprecated)" {
     const allocator = std.testing.allocator;
     var httpz_headers = try httpz.key_value.KeyValue.init(allocator, 10);

src/jetzig/middleware/CompressionMiddleware.zig

@@ -44,8 +44,9 @@ pub fn beforeResponse(request: *jetzig.http.Request, response: *jetzig.http.Resp
 }
 
 fn detectEncoding(request: *const jetzig.http.Request) ?Encoding {
-    for (request.headers.getAll("Accept-Encoding")) |encodings| {
-        var it = std.mem.tokenizeScalar(u8, encodings, ',');
+    var headers_it = request.headers.getAllIterator("Accept-Encoding");
+    while (headers_it.next()) |header| {
+        var it = std.mem.tokenizeScalar(u8, header.value, ',');
         while (it.next()) |param| {
             inline for (@typeInfo(Encoding).Enum.fields) |field| {
                 if (std.mem.eql(u8, field.name, jetzig.util.strip(param))) {