std::string_view support #275

sjanel · 2023-01-15T10:34:21Z

If the json library supports std::string_view, allow jwt-cpp take builder parameters as std::string_view and algorithm constructors as well.

Also small optimizations in some methods of jwt.h to make sure only one object is returned so that RVO can be used.

PR is ready for review. Only the coverage is failing, I will check why.

prince-chrismc

I generally understand the motivation behind this contribution but I would generally suggest opening an issue to discuss ideas this large, tip for the future :)

There are a handful of changes which are a little unclear what the motivation so I left some comments during an initial pass.

Overall the code looks really good, my comments are for existing users who might want to update as well as some performance consideration :)

prince-chrismc · 2023-03-25T04:14:31Z

include/picojson/picojson.h

 #define SNPRINTF snprintf
 #endif

 namespace picojson {


This is a thirdparty library and I am not sure changing the source code here is going to help us move away from it since it's no longer maintained

But the modifications are necessary for the tests to compile. What do you suggest ?

If you need to modify the json library for it to work with jwt-cpp then we can't do so much string_view. jwt-cpp aims to be as agnostic as possible to json/ssl libraries.

If it's no longer maintained, why is it a problem anyway as it should be removed from this repo ?

prince-chrismc · 2023-03-25T04:15:12Z

tests/BaseTest.cpp

-	ASSERT_EQ("MTIz", jwt::base::trim<jwt::alphabet::base64url>("MTIz"));
-	ASSERT_EQ("MTIzNA", jwt::base::trim<jwt::alphabet::base64url>("MTIzNA%3d%3d"));
-}
+namespace jwt {


Would you mind removing these namespaces it introduces a lot of change and it more difficult to see whats different

I placed using namespace jwt; instead and opened another PR.

prince-chrismc · 2023-03-25T04:17:16Z

include/jwt-cpp/traits/boost-json/traits.h

 			}

-			static bool parse(value_type& val, string_type str) {
+			template<class string_t>


should this not be specialized based on what the library supports?

json::parse (from nlohmann) accepts a templated type. IMHO it's safe to also take any string type.

prince-chrismc · 2023-03-25T04:18:45Z

include/jwt-cpp/traits/nlohmann-json/traits.h

+			template<class string_t>
+			static bool parse(json& val, const string_t& str) {


Would it not be more ideal to specialize these so users do not make mistakes

https://github.com/nlohmann/json/blob/6af826d0bdb55e4b69e3ad817576745335f243ca/README.md?plain=1#L1640

There could be one for both types?

Template function solves two problems:

Ambiguity issues, for instance if you provide a function for std::string_view and const std::string & and you call the function with a const char * you will have a compile error

It allows usage of custom string. For instance, fbstring is a good drop-in replacement for std::string.

prince-chrismc · 2023-03-25T04:20:43Z

include/jwt-cpp/jwt.h

+			std::string res;
 			if (!certbio || !keybio) {
 				ec = error::rsa_error::create_mem_bio_failed;
-				return {};
+				return res;


Have you checked how this impacts compiler optimizations? Last I checked the compilers are better at implementing copy elision with r-values

Having only one returned variable enables use of RVO (in the modified code). I believe that new code may be slightly more efficient, although I did not check. The impacts should be minor though, it's more a matter of code style in the end. If it's an issue for you, I can revert these modifications.

I'd prefer to keep the current one because it makes it obvious that an empty result is returned.

include/jwt-cpp/jwt.h

include/jwt-cpp/string_types.h

prince-chrismc · 2023-03-25T04:22:49Z

tests/BaseTest.cpp

+namespace jwt {
+
+	namespace {
+		base::details::padding count_padding(string_view base, std::initializer_list<std::string> fills) {


Should this not be in base details with the other implementation since users would need it?

Normally base details are only for internal usage, when do you think users would need them ?

prince-chrismc · 2023-03-25T04:23:56Z

include/jwt-cpp/base.h


 		inline uint32_t index(const std::array<char, 64>& alphabet, char symbol) {
-			auto itr = std::find_if(alphabet.cbegin(), alphabet.cend(), [symbol](char c) { return c == symbol; });
+			if (symbol >= 'A' && symbol <= 'Z') { return static_cast<uint32_t>(symbol - 'A'); }


Have you checked the performance hit for all these branches?

Here it is: https://quick-bench.com/q/8u7o4DL5yBu256Rzgu_KLi2Z4JA

There are a lot less branches as in the original code you check all elements one by one linearly. New code is smarter.

prince-chrismc · 2023-03-25T04:24:28Z

include/jwt-cpp/base.h

-				for (const auto& fill : fills) {
-					if (base.size() < fill.size()) continue;
+			template<class StrInputIt>
+			padding count_padding(string_view base, StrInputIt fillStart, StrInputIt fillEnd) {


Could you please change these to snake_case to match the rest of the code base?

sjanel · 2023-08-11T17:13:46Z

I generally understand the motivation behind this contribution but I would generally suggest opening an issue to discuss ideas this large, tip for the future :)

There are a handful of changes which are a little unclear what the motivation so I left some comments during an initial pass.

Overall the code looks really good, my comments are for existing users who might want to update as well as some performance consideration :)

Thanks for the comments, I was quite busy these days, but I will try to come back on my PR, I did not forget it ;)
I will try to split it as well. I think I can extract some stuff in base.h first.

Thalhammer · 2023-08-21T12:21:26Z

include/jwt-cpp/base.h

 		 */
 		struct base64 {
+
+#define JWT_BASE_ALPHABET                                                                                              \


Not really a fan of new macros.

I introduced conditional compiling and I thought it was a good idea to factorize some code and avoid several definitions of the same alphabet

Thalhammer · 2023-08-21T12:22:01Z

include/jwt-cpp/base.h

-			if (itr == alphabet.cend()) { throw std::runtime_error("Invalid input: not within alphabet"); }
+		template<class char_it>
+		inline uint32_t index(char_it alphabetBeg, char_it alphabetEnd, char symbol) {
+			if (symbol >= 'A' && symbol <= 'Z') { return static_cast<uint32_t>(symbol - 'A'); }


Keep in mind, that the new code is not a direct equivalent to the original though. It relies on the fact that the first 62 chars of the alphabet are "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789" which effectively demotes the alphabet type to a 2 char field. I am not sure if this is a smart thing to do, it doesn't feel right to provide a user hook to change the whole alphabet just to ignore 96% of it. In the best case this leads to inconvenience, in the worst to bugs.

It's at least equivalent considering the alphabets it receives. Do we expect the alphabets to change ? As this file is meant to be internal the risk is close to 0 to introduce a bug here (and it's unit tested anyway).

include/jwt-cpp/base.h

Thalhammer · 2023-08-21T12:36:25Z

include/jwt-cpp/base.h

+			return details::trim(base, T::kFill[0]);
 		}
+
+#else


Whats the point of checking for JWT_HAS_STRING_VIEW if the else branch uses string_view as well ?

In C++ v >= 17, there are no functions, only static constexpr arrays which makes the code simpler. This will allow easier code update when jwt-cpp will require a C++17 compiler as minimum version.

include/jwt-cpp/jwt.h

Thalhammer · 2023-08-21T12:53:57Z

include/jwt-cpp/jwt.h

 			 * \param siglen The bit length of the signature
 			 */
-			ecdsa(const std::string& public_key, const std::string& private_key, const std::string& public_key_password,
-				  const std::string& private_key_password, const EVP_MD* (*md)(), std::string name, size_t siglen)


Consider keeping the algorithm name as a std string to avoid allocating if a string is passed in. Otherwise we convert string to string_view to string instead of directly moving the first string.

Thalhammer · 2023-08-21T12:55:40Z

include/jwt-cpp/jwt.h

 			const EVP_MD* (*md)();
 			/// algorithm's name
-			const std::string alg_name;
+			std::string alg_name;


Why remove the const ?

Already answered about that above

Thalhammer · 2023-08-21T12:56:24Z

include/jwt-cpp/jwt.h

 			 * \param name Name of the algorithm
 			 */
-			eddsa(const std::string& public_key, const std::string& private_key, const std::string& public_key_password,
-				  const std::string& private_key_password, std::string name)


See the comment above regarding move

Thalhammer · 2023-08-21T14:02:33Z

include/picojson/picojson.h

 #define SNPRINTF snprintf
 #endif

 namespace picojson {


If you need to modify the json library for it to work with jwt-cpp then we can't do so much string_view. jwt-cpp aims to be as agnostic as possible to json/ssl libraries.

sjanel

Reverted changes based on std::string res as suggested in code review comments
alg name as std::string passed by copy then std::move

sjanel · 2023-08-18T13:50:04Z

tests/BaseTest.cpp

+namespace jwt {
+
+	namespace {
+		base::details::padding count_padding(string_view base, std::initializer_list<std::string> fills) {


Normally base details are only for internal usage, when do you think users would need them ?

sjanel · 2023-08-18T16:29:05Z

include/jwt-cpp/traits/nlohmann-json/traits.h

+			template<class string_t>
+			static bool parse(json& val, const string_t& str) {


Template function solves two problems:

Ambiguity issues, for instance if you provide a function for std::string_view and const std::string & and you call the function with a const char * you will have a compile error

It allows usage of custom string. For instance, fbstring is a good drop-in replacement for std::string.

include/jwt-cpp/jwt.h

sjanel · 2023-08-21T18:02:46Z

include/jwt-cpp/base.h

 		 */
 		struct base64 {
+
+#define JWT_BASE_ALPHABET                                                                                              \


I introduced conditional compiling and I thought it was a good idea to factorize some code and avoid several definitions of the same alphabet

sjanel · 2023-08-21T18:05:50Z

include/jwt-cpp/base.h

-			if (itr == alphabet.cend()) { throw std::runtime_error("Invalid input: not within alphabet"); }
+		template<class char_it>
+		inline uint32_t index(char_it alphabetBeg, char_it alphabetEnd, char symbol) {
+			if (symbol >= 'A' && symbol <= 'Z') { return static_cast<uint32_t>(symbol - 'A'); }


It's at least equivalent considering the alphabets it receives. Do we expect the alphabets to change ? As this file is meant to be internal the risk is close to 0 to introduce a bug here (and it's unit tested anyway).

sjanel · 2023-08-21T18:14:01Z

include/picojson/picojson.h

 #define SNPRINTF snprintf
 #endif

 namespace picojson {


If it's no longer maintained, why is it a problem anyway as it should be removed from this repo ?

sjanel · 2023-08-21T18:15:55Z

include/jwt-cpp/base.h

+			return details::trim(base, T::kFill[0]);
 		}
+
+#else


In C++ v >= 17, there are no functions, only static constexpr arrays which makes the code simpler. This will allow easier code update when jwt-cpp will require a C++17 compiler as minimum version.

sjanel · 2023-08-21T18:21:59Z

include/jwt-cpp/jwt.h

 			ec.clear();

-			auto c_str = reinterpret_cast<const unsigned char*>(cert_der_str.c_str());
+			auto c_str = reinterpret_cast<const unsigned char*>(cert_der_str.data());


Fine for me.

include/jwt-cpp/jwt.h

sjanel · 2023-08-21T18:27:54Z

include/jwt-cpp/jwt.h

 			const EVP_MD* (*md)();
 			/// algorithm's name
-			const std::string alg_name;
+			std::string alg_name;


Already answered about that above

… late std::string res return objects

Thalhammer · 2023-08-24T09:06:43Z

For some reason I could not reply to a bunch of your comments, so here we go.

It's at least equivalent considering the alphabets it receives. Do we expect the alphabets to change ? As this file is meant to be internal the risk is close to 0 to introduce a bug here (and it's unit tested anyway).

Likely not, but its exposed to the public and someone might use it with a different alphabet. Its a user visible header and the base64 stuff is not in a details namespace which makes it kinda public api (even if its not advertised as one). If we potentially break peoples code, we should at least break it at the compile stage (I.e. change the types inside the alphabets and remove the - no superficial - first 62 chars) instead of silently changing behavior in edge cases.

If it's no longer maintained, why is it a problem anyway as it should be removed from this repo ?

Mostly because it being there didn't hurt so far and removing it would likely break a lot of users codebase because its the default library. Also having one in there that does not rely on a third party json library makes it way easier to use (no extra dependencies).

sjanel · 2023-10-27T08:21:55Z

Hello @Thalhammer @prince-chrismc

I answered your comments, not sure what is preventing the PR to be merged currently.

Also, it fixes following gcc 12 compiling error:

[build] include/jwt-cpp/base.h: In static member function ‘static const std::initializer_list<std::__cxx11::basic_string<char> >& jwt::alphabet::helper::base64url_percent_encoding::fill()’:
[build] include/jwt-cpp/base.h:86:100: error: ‘(((const std::__cxx11::basic_string<char>*)(& <temporary>)) != 0)’ is not a constant expression
[build]    86 |                                         static std::initializer_list<std::string> fill{"%3D", "%3d"};

and an attempt to fix it 'easily' is more complicated than expected.

Here with this PR and string_view it's much easier.

EDIT: sorry I did not catch your last global comment. I can revert the changes in the alphabet if needed. However I don't see how to avoid picojson code changes (see my below comment)

sjanel · 2023-10-27T08:27:05Z

Mostly because it being there didn't hurt so far and removing it would likely break a lot of users codebase because its the default library. Also having one in there that does not rely on a third party json library makes it way easier to use (no extra dependencies).

That's the reason why I fixed it instead of removing it. They are not complicated changes, and backward compatible with ancient compilers. If we cannot remove it, and cannot change it, how can we move on ?

prince-chrismc · 2023-11-10T17:25:15Z

I am sincerely sorry, I've been meaning to follow up but I am currently between jobs and trying to move countries. It might be several more weeks before I have a chance to work from my computer so I'd really appreciate your patients.

ambiennt · 2025-04-17T00:19:56Z

Is there any way this could get merged in soon? I find that supporting a string view interface is very important in order to avoid large allocation overheads for string-like types that the jwt-cpp API doesn't need to take ownership of (like passing the public/private key pairs when constructing a jwt::algorithm type), especially since they can get pretty long.

sjanel marked this pull request as draft January 15, 2023 10:36

sjanel force-pushed the feature/string-view-support branch 4 times, most recently from cd66010 to a73ec5c Compare January 20, 2023 22:16

sjanel marked this pull request as ready for review January 20, 2023 22:21

prince-chrismc reviewed Mar 25, 2023

View reviewed changes

Add basic support of string_view to picojson for the tests to compile

f3f091b

sjanel force-pushed the feature/string-view-support branch 6 times, most recently from 3570344 to 478a743 Compare August 18, 2023 12:50

Addition of string_view support

5b418af

sjanel force-pushed the feature/string-view-support branch from 478a743 to 5b418af Compare August 18, 2023 13:16

Thalhammer requested changes Aug 21, 2023

View reviewed changes

sjanel force-pushed the feature/string-view-support branch from bcda1ae to 3e77901 Compare August 23, 2023 10:34

sjanel commented Aug 23, 2023

View reviewed changes

sjanel force-pushed the feature/string-view-support branch from 3e77901 to 1fc6924 Compare August 23, 2023 10:47

Code review updates - Pass algo name with std::move from std::string,…

8262bb8

… late std::string res return objects

sjanel force-pushed the feature/string-view-support branch from 1fc6924 to 8262bb8 Compare August 23, 2023 10:55

sjanel mentioned this pull request Oct 27, 2023

Fix gcc 12 compiling error #312

Merged

		template<class string_t>
		static bool parse(json& val, const string_t& str) {

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std::string_view support #275

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std::string_view support #275

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sjanel commented Jan 15, 2023 •

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