. /include/boost/corosio /tls_context.hpp
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1   // 1   //
2   // Copyright (c) 2025 Vinnie Falco (vinnie.falco@gmail.com) 2   // Copyright (c) 2025 Vinnie Falco (vinnie.falco@gmail.com)
3   // Copyright (c) 2026 Michael Vandeberg 3   // Copyright (c) 2026 Michael Vandeberg
4   // 4   //
5   // Distributed under the Boost Software License, Version 1.0. (See accompanying 5   // Distributed under the Boost Software License, Version 1.0. (See accompanying
6   // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) 6   // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
7   // 7   //
8   // Official repository: https://github.com/cppalliance/corosio 8   // Official repository: https://github.com/cppalliance/corosio
9   // 9   //
10   10  
11   #ifndef BOOST_COROSIO_TLS_CONTEXT_HPP 11   #ifndef BOOST_COROSIO_TLS_CONTEXT_HPP
12   #define BOOST_COROSIO_TLS_CONTEXT_HPP 12   #define BOOST_COROSIO_TLS_CONTEXT_HPP
13   13  
14   #include <boost/corosio/detail/config.hpp> 14   #include <boost/corosio/detail/config.hpp>
15   15  
16   #include <cstddef> 16   #include <cstddef>
17   #include <functional> 17   #include <functional>
18   #include <span> 18   #include <span>
19   #include <system_error> 19   #include <system_error>
20   #include <memory> 20   #include <memory>
21   #include <string_view> 21   #include <string_view>
22   22  
23   namespace boost::corosio { 23   namespace boost::corosio {
24   24  
25   // 25   //
26   // Enumerations 26   // Enumerations
27   // 27   //
28   28  
29   /** TLS protocol version. 29   /** TLS protocol version.
30   30  
31   Specifies the minimum or maximum TLS protocol version to use 31   Specifies the minimum or maximum TLS protocol version to use
32   for connections. Only modern, secure versions are supported. 32   for connections. Only modern, secure versions are supported.
33   33  
34   @see tls_context::set_min_protocol_version 34   @see tls_context::set_min_protocol_version
35   @see tls_context::set_max_protocol_version 35   @see tls_context::set_max_protocol_version
36   */ 36   */
37   enum class tls_version 37   enum class tls_version
38   { 38   {
39   /// TLS 1.2 (RFC 5246). 39   /// TLS 1.2 (RFC 5246).
40   tls_1_2, 40   tls_1_2,
41   41  
42   /// TLS 1.3 (RFC 8446). 42   /// TLS 1.3 (RFC 8446).
43   tls_1_3 43   tls_1_3
44   }; 44   };
45   45  
46   /** Certificate and key file format. 46   /** Certificate and key file format.
47   47  
48   Specifies the encoding format for certificate and key data. 48   Specifies the encoding format for certificate and key data.
49   49  
50   @see tls_context::use_certificate 50   @see tls_context::use_certificate
51   @see tls_context::use_private_key 51   @see tls_context::use_private_key
52   */ 52   */
53   enum class tls_file_format 53   enum class tls_file_format
54   { 54   {
55   /// PEM format (Base64-encoded with header/footer lines). 55   /// PEM format (Base64-encoded with header/footer lines).
56   pem, 56   pem,
57   57  
58   /// DER format (raw ASN.1 binary encoding). 58   /// DER format (raw ASN.1 binary encoding).
59   der 59   der
60   }; 60   };
61   61  
62   /** Peer certificate verification mode. 62   /** Peer certificate verification mode.
63   63  
64   Controls how the TLS implementation verifies the peer's 64   Controls how the TLS implementation verifies the peer's
65   certificate during the handshake. 65   certificate during the handshake.
66   66  
67   @see tls_context::set_verify_mode 67   @see tls_context::set_verify_mode
68   */ 68   */
69   enum class tls_verify_mode 69   enum class tls_verify_mode
70   { 70   {
71   /// Do not request or verify the peer certificate. 71   /// Do not request or verify the peer certificate.
72   none, 72   none,
73   73  
74   /// Request and verify the peer certificate if presented. 74   /// Request and verify the peer certificate if presented.
75   peer, 75   peer,
76   76  
77   /// Require and verify the peer certificate (fail if not presented). 77   /// Require and verify the peer certificate (fail if not presented).
78   require_peer 78   require_peer
79   }; 79   };
80   80  
81   /** Certificate revocation checking policy. 81   /** Certificate revocation checking policy.
82   82  
83   Controls how certificate revocation status is checked during 83   Controls how certificate revocation status is checked during
84   verification. 84   verification.
85   85  
86   @see tls_context::set_revocation_policy 86   @see tls_context::set_revocation_policy
87   */ 87   */
88   enum class tls_revocation_policy 88   enum class tls_revocation_policy
89   { 89   {
90   /// Do not check revocation status. 90   /// Do not check revocation status.
91   disabled, 91   disabled,
92   92  
93   /// Check revocation but allow connection if status is unknown. 93   /// Check revocation but allow connection if status is unknown.
94   soft_fail, 94   soft_fail,
95   95  
96   /// Require successful revocation check (fail if status is unknown). 96   /// Require successful revocation check (fail if status is unknown).
97   hard_fail 97   hard_fail
98   }; 98   };
99   99  
100   /** Purpose for password callback invocation. 100   /** Purpose for password callback invocation.
101   101  
102   Indicates whether the password is needed for reading (decrypting) 102   Indicates whether the password is needed for reading (decrypting)
103   or writing (encrypting) key material. 103   or writing (encrypting) key material.
104   104  
105   @see tls_context::set_password_callback 105   @see tls_context::set_password_callback
106   */ 106   */
107   enum class tls_password_purpose 107   enum class tls_password_purpose
108   { 108   {
109   /// Password needed to decrypt/read protected key material. 109   /// Password needed to decrypt/read protected key material.
110   for_reading, 110   for_reading,
111   111  
112   /// Password needed to encrypt/write protected key material. 112   /// Password needed to encrypt/write protected key material.
113   for_writing 113   for_writing
114   }; 114   };
115   115  
116   class tls_context; 116   class tls_context;
117   117  
118   /** A non-owning view of certificate verification state. 118   /** A non-owning view of certificate verification state.
119   119  
120   An instance is passed to the callback installed via 120   An instance is passed to the callback installed via
121   tls_context::set_verify_callback during the TLS handshake. It 121   tls_context::set_verify_callback during the TLS handshake. It
122   exposes the backend's native verification handle so the callback 122   exposes the backend's native verification handle so the callback
123   can inspect the certificate and chain currently being verified. 123   can inspect the certificate and chain currently being verified.
124   124  
125   The value returned by native_handle() is, for the OpenSSL and 125   The value returned by native_handle() is, for the OpenSSL and
126   WolfSSL backends, an `X509_STORE_CTX*`. For portable inspection that 126   WolfSSL backends, an `X509_STORE_CTX*`. For portable inspection that
127   works across backends (for example certificate pinning), prefer 127   works across backends (for example certificate pinning), prefer
128   certificate(), which returns the DER encoding of the certificate 128   certificate(), which returns the DER encoding of the certificate
129   currently being verified. 129   currently being verified.
130   130  
131   @par Lifetime 131   @par Lifetime
132   132  
133   The wrapped handle and the certificate() bytes are owned by the TLS 133   The wrapped handle and the certificate() bytes are owned by the TLS
134   backend and are valid only for the duration of a single callback 134   backend and are valid only for the duration of a single callback
135   invocation. Do not retain them beyond the call. 135   invocation. Do not retain them beyond the call.
136   136  
137   @see tls_context::set_verify_callback 137   @see tls_context::set_verify_callback
138   */ 138   */
139   class verify_context 139   class verify_context
140   { 140   {
141   void* handle_; 141   void* handle_;
142   unsigned char const* der_; 142   unsigned char const* der_;
143   std::size_t der_len_; 143   std::size_t der_len_;
144   144  
145   public: 145   public:
146   /** Construct from a native handle and the current certificate. 146   /** Construct from a native handle and the current certificate.
147   147  
148   @param handle The backend verification handle (for OpenSSL and 148   @param handle The backend verification handle (for OpenSSL and
149   WolfSSL, an `X509_STORE_CTX*`). 149   WolfSSL, an `X509_STORE_CTX*`).
150   @param der Pointer to the DER encoding of the certificate under 150   @param der Pointer to the DER encoding of the certificate under
151   verification, or `nullptr` if unavailable. 151   verification, or `nullptr` if unavailable.
152   @param der_len Length of the DER encoding in bytes. 152   @param der_len Length of the DER encoding in bytes.
153   */ 153   */
154   verify_context( 154   verify_context(
155   void* handle, unsigned char const* der, std::size_t der_len) noexcept 155   void* handle, unsigned char const* der, std::size_t der_len) noexcept
156   : handle_(handle), der_(der), der_len_(der_len) 156   : handle_(handle), der_(der), der_len_(der_len)
157   { 157   {
158   } 158   }
159   159  
160   /** Return the native verification handle. 160   /** Return the native verification handle.
161   161  
162   Cast the result to the backend's verification context type 162   Cast the result to the backend's verification context type
163   (e.g. `X509_STORE_CTX*`) to inspect the certificate chain using 163   (e.g. `X509_STORE_CTX*`) to inspect the certificate chain using
164   backend-specific APIs. 164   backend-specific APIs.
165   165  
166   @return The native handle, or `nullptr` if none is available. 166   @return The native handle, or `nullptr` if none is available.
167   */ 167   */
168   void* native_handle() const noexcept { return handle_; } 168   void* native_handle() const noexcept { return handle_; }
169   169  
170   /** Return the DER encoding of the certificate being verified. 170   /** Return the DER encoding of the certificate being verified.
171   171  
172   This is the portable way to inspect the peer certificate from a 172   This is the portable way to inspect the peer certificate from a
173   verification callback: it works identically on every backend, 173   verification callback: it works identically on every backend,
174   without depending on backend-specific build options. A DER 174   without depending on backend-specific build options. A DER
175   certificate is an ASN.1 `SEQUENCE`, so the first byte is `0x30`. 175   certificate is an ASN.1 `SEQUENCE`, so the first byte is `0x30`.
176   176  
177   @return A view of the certificate's DER bytes, valid only for the 177   @return A view of the certificate's DER bytes, valid only for the
178   duration of the callback. Empty if the certificate is not 178   duration of the callback. Empty if the certificate is not
179   available. 179   available.
180   */ 180   */
MISUBC 181   ✗ std::span<unsigned char const> certificate() const noexcept 181   ✗ std::span<unsigned char const> certificate() const noexcept
182   { 182   {
MISUBC 183   ✗ return {der_, der_len_}; 183   ✗ return {der_, der_len_};
184   } 184   }
185   }; 185   };
186   186  
187   namespace detail { 187   namespace detail {
188   struct tls_context_data; 188   struct tls_context_data;
189   tls_context_data const& get_tls_context_data(tls_context const&) noexcept; 189   tls_context_data const& get_tls_context_data(tls_context const&) noexcept;
190   } // namespace detail 190   } // namespace detail
191   191  
192   /** A portable TLS context for certificate and settings storage. 192   /** A portable TLS context for certificate and settings storage.
193   193  
194   The `tls_context` class provides a backend-agnostic interface for 194   The `tls_context` class provides a backend-agnostic interface for
195   configuring TLS connections. It stores credentials (certificates and 195   configuring TLS connections. It stores credentials (certificates and
196   private keys), trust anchors, protocol settings, and verification 196   private keys), trust anchors, protocol settings, and verification
197   options that are used when establishing TLS connections. 197   options that are used when establishing TLS connections.
198   198  
199   This class is a shared handle to an opaque implementation. Copies 199   This class is a shared handle to an opaque implementation. Copies
200   share the same underlying state. This allows contexts to be passed 200   share the same underlying state. This allows contexts to be passed
201   by value and shared across multiple TLS streams. 201   by value and shared across multiple TLS streams.
202   202  
203   This class abstracts the configuration phase of TLS across multiple 203   This class abstracts the configuration phase of TLS across multiple
204   backend implementations (OpenSSL, WolfSSL, mbedTLS, Schannel, etc.), 204   backend implementations (OpenSSL, WolfSSL, mbedTLS, Schannel, etc.),
205   allowing portable code that works regardless of which TLS library 205   allowing portable code that works regardless of which TLS library
206   is linked. 206   is linked.
207   207  
208   @par Modification After Stream Creation 208   @par Modification After Stream Creation
209   209  
210   Modifying a context after a TLS stream has been created from it 210   Modifying a context after a TLS stream has been created from it
211   results in undefined behavior. The context's configuration is 211   results in undefined behavior. The context's configuration is
212   captured when the first stream is constructed, and subsequent 212   captured when the first stream is constructed, and subsequent
213   modifications are not reflected in existing or new streams 213   modifications are not reflected in existing or new streams
214   sharing the context. 214   sharing the context.
215   215  
216   If different configurations are needed, create separate context 216   If different configurations are needed, create separate context
217   objects. 217   objects.
218   218  
219   @par Thread Safety 219   @par Thread Safety
220   220  
221   Distinct objects: Safe. 221   Distinct objects: Safe.
222   222  
223   Shared objects: Unsafe. A context must not be modified while 223   Shared objects: Unsafe. A context must not be modified while
224   any thread is creating streams from it. 224   any thread is creating streams from it.
225   225  
226   @par Example 226   @par Example
227   @code 227   @code
228   // Create a client context with system trust anchors 228   // Create a client context with system trust anchors
229   corosio::tls_context ctx; 229   corosio::tls_context ctx;
230 - ctx.set_default_verify_paths(); 230 + if (auto ec = ctx.set_default_verify_paths())
231 - ctx.set_verify_mode( corosio::tls_verify_mode::peer ); 231 + co_return;
  232 + if (auto ec = ctx.set_verify_mode( corosio::tls_verify_mode::peer ))
  233 + co_return;
232   234  
233   // Use with a TLS stream 235   // Use with a TLS stream
234   corosio::openssl_stream secure( &sock, ctx ); 236   corosio::openssl_stream secure( &sock, ctx );
235   secure.set_hostname( "example.com" ); 237   secure.set_hostname( "example.com" );
236 - co_await secure.handshake( corosio::tls_role::client ); 238 + if (auto [ec] = co_await secure.handshake( corosio::tls_role::client ); ec)
  239 + co_return;
237   @endcode 240   @endcode
238   241  
239   @see tls_role 242   @see tls_role
240   */ 243   */
241   #ifdef _MSC_VER 244   #ifdef _MSC_VER
242   #pragma warning(push) 245   #pragma warning(push)
243   #pragma warning(disable : 4251) // shared_ptr needs dll-interface 246   #pragma warning(disable : 4251) // shared_ptr needs dll-interface
244   #endif 247   #endif
245   class BOOST_COROSIO_DECL tls_context 248   class BOOST_COROSIO_DECL tls_context
246   { 249   {
247   struct implementation; 250   struct implementation;
248   std::shared_ptr<implementation> impl_; 251   std::shared_ptr<implementation> impl_;
249   252  
250   friend detail::tls_context_data const& 253   friend detail::tls_context_data const&
251   detail::get_tls_context_data(tls_context const&) noexcept; 254   detail::get_tls_context_data(tls_context const&) noexcept;
252   255  
253   public: 256   public:
254   /** Construct a default TLS context. 257   /** Construct a default TLS context.
255   258  
256   Creates a context with default settings suitable for TLS 1.2 259   Creates a context with default settings suitable for TLS 1.2
257   and TLS 1.3 connections. No certificates or trust anchors are 260   and TLS 1.3 connections. No certificates or trust anchors are
258   loaded; call the appropriate methods to configure credentials 261   loaded; call the appropriate methods to configure credentials
259   and verification. 262   and verification.
260   263  
261   @par Example 264   @par Example
262   @code 265   @code
263   corosio::tls_context ctx; 266   corosio::tls_context ctx;
264   @endcode 267   @endcode
265   */ 268   */
266   tls_context(); 269   tls_context();
267   270  
268   /** Copy constructor. 271   /** Copy constructor.
269   272  
270   Creates a new handle that shares ownership of the underlying 273   Creates a new handle that shares ownership of the underlying
271   TLS context state with `other`. 274   TLS context state with `other`.
272   275  
273   @param other The context to copy from. 276   @param other The context to copy from.
274   */ 277   */
HITCBC 275   2 tls_context(tls_context const& other) = default; 278   2 tls_context(tls_context const& other) = default;
276   279  
277   /** Copy assignment operator. 280   /** Copy assignment operator.
278   281  
279   Releases the current context's shared ownership and acquires 282   Releases the current context's shared ownership and acquires
280   shared ownership of `other`'s underlying state. 283   shared ownership of `other`'s underlying state.
281   284  
282   @param other The context to copy from. 285   @param other The context to copy from.
283   286  
284   @return Reference to this context. 287   @return Reference to this context.
285   */ 288   */
HITCBC 286   1 tls_context& operator=(tls_context const& other) = default; 289   1 tls_context& operator=(tls_context const& other) = default;
287   290  
288   /** Move constructor. 291   /** Move constructor.
289   292  
290   Transfers ownership of the TLS context from another instance. 293   Transfers ownership of the TLS context from another instance.
291   After the move, `other` is in a valid but empty state. 294   After the move, `other` is in a valid but empty state.
292   295  
293   @param other The context to move from. 296   @param other The context to move from.
294   */ 297   */
HITCBC 295   2 tls_context(tls_context&& other) noexcept = default; 298   2 tls_context(tls_context&& other) noexcept = default;
296   299  
297   /** Move assignment operator. 300   /** Move assignment operator.
298   301  
299   Releases the current context's shared ownership and transfers 302   Releases the current context's shared ownership and transfers
300   ownership from another instance. After the move, `other` is 303   ownership from another instance. After the move, `other` is
301   in a valid but empty state. 304   in a valid but empty state.
302   305  
303   @param other The context to move from. 306   @param other The context to move from.
304   307  
305   @return Reference to this context. 308   @return Reference to this context.
306   */ 309   */
HITCBC 307   1 tls_context& operator=(tls_context&& other) noexcept = default; 310   1 tls_context& operator=(tls_context&& other) noexcept = default;
308   311  
309   /** Destructor. 312   /** Destructor.
310   313  
311   Releases this handle's shared ownership of the underlying 314   Releases this handle's shared ownership of the underlying
312   context. The context state is destroyed when the last handle 315   context. The context state is destroyed when the last handle
313   is released. 316   is released.
314   */ 317   */
HITCBC 315   55 ~tls_context() = default; 318   55 ~tls_context() = default;
316   319  
317   // 320   //
318   // Credential Loading 321   // Credential Loading
319   // 322   //
320   323  
321   /** Load the entity certificate from a memory buffer. 324   /** Load the entity certificate from a memory buffer.
322   325  
323   Sets the certificate that identifies this endpoint to the peer. 326   Sets the certificate that identifies this endpoint to the peer.
324   For servers, this is the server certificate. For clients using 327   For servers, this is the server certificate. For clients using
325   mutual TLS, this is the client certificate. 328   mutual TLS, this is the client certificate.
326   329  
327   The certificate must match the private key loaded via 330   The certificate must match the private key loaded via
328   `use_private_key()` or `use_private_key_file()`. 331   `use_private_key()` or `use_private_key_file()`.
329   332  
330   @param certificate The certificate data. 333   @param certificate The certificate data.
331   334  
332   @param format The encoding format of the certificate data. 335   @param format The encoding format of the certificate data.
333   336  
334 - @return Success, or an error if the certificate could not be parsed 337 + @return Success. The certificate is recorded and decoded when the
335 - or is invalid. 338 + native context is first built; a malformed certificate surfaces
  339 + as a handshake failure.
336   340  
337   @see use_certificate_file 341   @see use_certificate_file
338   @see use_private_key 342   @see use_private_key
339   */ 343   */
340 - std::error_code 344 + [[nodiscard]] std::error_code
341   use_certificate(std::string_view certificate, tls_file_format format); 345   use_certificate(std::string_view certificate, tls_file_format format);
342   346  
343   /** Load the entity certificate from a file. 347   /** Load the entity certificate from a file.
344   348  
345   Sets the certificate that identifies this endpoint to the peer. 349   Sets the certificate that identifies this endpoint to the peer.
346   For servers, this is the server certificate. For clients using 350   For servers, this is the server certificate. For clients using
347   mutual TLS, this is the client certificate. 351   mutual TLS, this is the client certificate.
348   352  
349   @param filename Path to the certificate file. 353   @param filename Path to the certificate file.
350   354  
351   @param format The encoding format of the file. 355   @param format The encoding format of the file.
352   356  
353 - @return Success, or an error if the file could not be read or the 357 + @return Success, or an error if the file could not be read. The
354 - certificate is invalid. 358 + certificate is decoded when the native context is first built;
  359 + a malformed certificate surfaces as a handshake failure.
355   360  
356   @par Example 361   @par Example
357   @code 362   @code
358 - ctx.use_certificate_file( "server.crt", tls_file_format::pem ); 363 + if (auto ec = ctx.use_certificate_file(
  364 + "server.crt", tls_file_format::pem ))
  365 + return;
359   @endcode 366   @endcode
360   367  
361   @see use_certificate 368   @see use_certificate
362   @see use_private_key_file 369   @see use_private_key_file
363   */ 370   */
364 - std::error_code 371 + [[nodiscard]] std::error_code
365   use_certificate_file(std::string_view filename, tls_file_format format); 372   use_certificate_file(std::string_view filename, tls_file_format format);
366   373  
367   /** Load a certificate chain from a memory buffer. 374   /** Load a certificate chain from a memory buffer.
368   375  
369   Loads the entity certificate followed by intermediate CA certificates. 376   Loads the entity certificate followed by intermediate CA certificates.
370   The chain should be ordered from leaf to root (excluding the root). 377   The chain should be ordered from leaf to root (excluding the root).
371   This is the typical format for PEM certificate bundles. 378   This is the typical format for PEM certificate bundles.
372   379  
373   @param chain The certificate chain data in PEM format (concatenated 380   @param chain The certificate chain data in PEM format (concatenated
374   certificates). 381   certificates).
375   382  
376 - @return Success, or an error if the chain could not be parsed. 383 + @return Success. The chain is recorded and decoded when the native
  384 + context is first built; a malformed chain surfaces as a
  385 + handshake failure.
377   386  
378   @see use_certificate_chain_file 387   @see use_certificate_chain_file
379   */ 388   */
380 - std::error_code use_certificate_chain(std::string_view chain); 389 + [[nodiscard]] std::error_code use_certificate_chain(std::string_view chain);
381   390  
382   /** Load a certificate chain from a file. 391   /** Load a certificate chain from a file.
383   392  
384   Loads the entity certificate followed by intermediate CA certificates 393   Loads the entity certificate followed by intermediate CA certificates
385   from a PEM file. The file should contain concatenated PEM certificates 394   from a PEM file. The file should contain concatenated PEM certificates
386   ordered from leaf to root (excluding the root). 395   ordered from leaf to root (excluding the root).
387   396  
388   @param filename Path to the certificate chain file. 397   @param filename Path to the certificate chain file.
389   398  
390 - @return Success, or an error if the file could not be read or parsed. 399 + @return Success, or an error if the file could not be read. The
  400 + chain is decoded when the native context is first built; a
  401 + malformed chain surfaces as a handshake failure.
391   402  
392   @par Example 403   @par Example
393   @code 404   @code
394 - // Load certificate chain (cert + intermediates) 405 + if (auto ec = ctx.use_certificate_chain_file( "fullchain.pem" ))
395 - ctx.use_certificate_chain_file( "fullchain.pem" ); 406 + return;
396   @endcode 407   @endcode
397   408  
398   @see use_certificate_chain 409   @see use_certificate_chain
399   */ 410   */
400 - std::error_code use_certificate_chain_file(std::string_view filename); 411 + [[nodiscard]] std::error_code use_certificate_chain_file(std::string_view filename);
401   412  
402   /** Load the private key from a memory buffer. 413   /** Load the private key from a memory buffer.
403   414  
404   Sets the private key corresponding to the entity certificate. 415   Sets the private key corresponding to the entity certificate.
405   The key must match the certificate loaded via `use_certificate()` 416   The key must match the certificate loaded via `use_certificate()`
406   or `use_certificate_chain()`. 417   or `use_certificate_chain()`.
407   418  
408   If the key is encrypted, set a password callback via 419   If the key is encrypted, set a password callback via
409   `set_password_callback()` before calling this function. 420   `set_password_callback()` before calling this function.
410   421  
411   @param private_key The private key data. 422   @param private_key The private key data.
412   423  
413   @param format The encoding format of the key data. 424   @param format The encoding format of the key data.
414   425  
415 - @return Success, or an error if the key could not be parsed, 426 + @return Success. The key is recorded and decoded when the native
416 - is encrypted without a password callback, or doesn't match 427 + context is first built; a malformed key, a missing password
417 - the certificate. 428 + callback for an encrypted key, or a certificate mismatch
  429 + surfaces as a handshake failure.
418   430  
419   @see use_private_key_file 431   @see use_private_key_file
420   @see set_password_callback 432   @see set_password_callback
421   */ 433   */
422 - std::error_code 434 + [[nodiscard]] std::error_code
423   use_private_key(std::string_view private_key, tls_file_format format); 435   use_private_key(std::string_view private_key, tls_file_format format);
424   436  
425   /** Load the private key from a file. 437   /** Load the private key from a file.
426   438  
427   Sets the private key corresponding to the entity certificate. 439   Sets the private key corresponding to the entity certificate.
428   The key must match the certificate loaded via `use_certificate_file()` 440   The key must match the certificate loaded via `use_certificate_file()`
429   or `use_certificate_chain_file()`. 441   or `use_certificate_chain_file()`.
430   442  
431   If the key file is encrypted, set a password callback via 443   If the key file is encrypted, set a password callback via
432   `set_password_callback()` before calling this function. 444   `set_password_callback()` before calling this function.
433   445  
434   @param filename Path to the private key file. 446   @param filename Path to the private key file.
435   447  
436   @param format The encoding format of the file. 448   @param format The encoding format of the file.
437   449  
438 - @return Success, or an error if the file could not be read, 450 + @return Success, or an error if the file could not be read. The
439 - the key is invalid, or it doesn't match the certificate. 451 + key is decoded when the native context is first built; a
  452 + malformed key or a certificate mismatch surfaces as a
  453 + handshake failure.
440   454  
441   @par Example 455   @par Example
442   @code 456   @code
443 - ctx.use_private_key_file( "server.key", tls_file_format::pem ); 457 + if (auto ec = ctx.use_private_key_file(
  458 + "server.key", tls_file_format::pem ))
  459 + return;
444   @endcode 460   @endcode
445   461  
446   @see use_private_key 462   @see use_private_key
447   @see set_password_callback 463   @see set_password_callback
448   */ 464   */
449 - std::error_code 465 + [[nodiscard]] std::error_code
450   use_private_key_file(std::string_view filename, tls_file_format format); 466   use_private_key_file(std::string_view filename, tls_file_format format);
451   467  
452   /** Load credentials from a PKCS#12 bundle in memory. 468   /** Load credentials from a PKCS#12 bundle in memory.
453   469  
454   PKCS#12 (also known as PFX) is a binary format that bundles a 470   PKCS#12 (also known as PFX) is a binary format that bundles a
455   certificate, private key, and optionally intermediate certificates 471   certificate, private key, and optionally intermediate certificates
456   into a single password-protected file. 472   into a single password-protected file.
457   473  
458   @param data The PKCS#12 bundle data. 474   @param data The PKCS#12 bundle data.
459   475  
460   @param passphrase The password protecting the bundle. 476   @param passphrase The password protecting the bundle.
461   477  
462   @return Success. The bundle is recorded and decoded into the 478   @return Success. The bundle is recorded and decoded into the
463   certificate, private key, and chain when the native context is 479   certificate, private key, and chain when the native context is
464   first built; a malformed bundle or wrong passphrase surfaces as 480   first built; a malformed bundle or wrong passphrase surfaces as
465   a handshake failure. 481   a handshake failure.
466   482  
467   @note Intermediate certificates inside the bundle are loaded and 483   @note Intermediate certificates inside the bundle are loaded and
468   sent during the handshake on both backends. 484   sent during the handshake on both backends.
469   485  
470   @see use_pkcs12_file 486   @see use_pkcs12_file
471   */ 487   */
472 - std::error_code 488 + [[nodiscard]] std::error_code
473   use_pkcs12(std::string_view data, std::string_view passphrase); 489   use_pkcs12(std::string_view data, std::string_view passphrase);
474   490  
475   /** Load credentials from a PKCS#12 file. 491   /** Load credentials from a PKCS#12 file.
476   492  
477   PKCS#12 (also known as PFX) is a binary format that bundles a 493   PKCS#12 (also known as PFX) is a binary format that bundles a
478   certificate, private key, and optionally intermediate certificates 494   certificate, private key, and optionally intermediate certificates
479   into a single password-protected file. This is common on Windows 495   into a single password-protected file. This is common on Windows
480   and for certificates exported from browsers. 496   and for certificates exported from browsers.
481   497  
482   @param filename Path to the PKCS#12 file. 498   @param filename Path to the PKCS#12 file.
483   499  
484   @param passphrase The password protecting the file. 500   @param passphrase The password protecting the file.
485   501  
486   @return Success, or an error if the file could not be read. The 502   @return Success, or an error if the file could not be read. The
487   bundle is decoded when the native context is first built; a 503   bundle is decoded when the native context is first built; a
488   malformed bundle or wrong passphrase surfaces as a handshake 504   malformed bundle or wrong passphrase surfaces as a handshake
489   failure. 505   failure.
490   506  
491   @note Intermediate certificates inside the bundle are loaded and 507   @note Intermediate certificates inside the bundle are loaded and
492   sent during the handshake on both backends. 508   sent during the handshake on both backends.
493   509  
494   @par Example 510   @par Example
495   @code 511   @code
496 - ctx.use_pkcs12_file( "credentials.pfx", "secret" ); 512 + if (auto ec = ctx.use_pkcs12_file( "credentials.pfx", "secret" ))
  513 + return;
497   @endcode 514   @endcode
498   515  
499   @see use_pkcs12 516   @see use_pkcs12
500   */ 517   */
501 - std::error_code 518 + [[nodiscard]] std::error_code
502   use_pkcs12_file(std::string_view filename, std::string_view passphrase); 519   use_pkcs12_file(std::string_view filename, std::string_view passphrase);
503   520  
504   // 521   //
505   // Trust Anchors 522   // Trust Anchors
506   // 523   //
507   524  
508   /** Add a certificate authority for peer verification. 525   /** Add a certificate authority for peer verification.
509   526  
510   Adds a single CA certificate to the trust store used for verifying 527   Adds a single CA certificate to the trust store used for verifying
511   peer certificates. Call this multiple times to add multiple CAs, 528   peer certificates. Call this multiple times to add multiple CAs,
512   or use `load_verify_file()` for a bundle. 529   or use `load_verify_file()` for a bundle.
513   530  
514   @param ca The CA certificate data in PEM format. 531   @param ca The CA certificate data in PEM format.
515   532  
516 - @return Success, or an error if the certificate could not be parsed. 533 + @return Success. The certificate is recorded and decoded when the
  534 + native context is first built; a malformed certificate
  535 + surfaces as a handshake failure.
517   536  
518   @see load_verify_file 537   @see load_verify_file
519   @see set_default_verify_paths 538   @see set_default_verify_paths
520   */ 539   */
521 - std::error_code add_certificate_authority(std::string_view ca); 540 + [[nodiscard]] std::error_code add_certificate_authority(std::string_view ca);
522   541  
523   /** Load CA certificates from a file. 542   /** Load CA certificates from a file.
524   543  
525   Loads one or more CA certificates from a PEM file. The file may 544   Loads one or more CA certificates from a PEM file. The file may
526   contain multiple concatenated PEM certificates. 545   contain multiple concatenated PEM certificates.
527   546  
528   @param filename Path to a PEM file containing CA certificates. 547   @param filename Path to a PEM file containing CA certificates.
529   548  
530 - @return Success, or an error if the file could not be read or parsed. 549 + @return Success, or an error if the file could not be read. The
  550 + certificates are decoded when the native context is first
  551 + built; malformed certificates surface as a handshake failure.
531   552  
532   @par Example 553   @par Example
533   @code 554   @code
534 - // Load a custom CA bundle 555 + if (auto ec = ctx.load_verify_file(
535 - ctx.load_verify_file( "/etc/ssl/certs/ca-certificates.crt" ); 556 + "/etc/ssl/certs/ca-certificates.crt" ))
  557 + return;
536   @endcode 558   @endcode
537   559  
538   @see add_certificate_authority 560   @see add_certificate_authority
539   @see add_verify_path 561   @see add_verify_path
540   */ 562   */
541 - std::error_code load_verify_file(std::string_view filename); 563 + [[nodiscard]] std::error_code load_verify_file(std::string_view filename);
542   564  
543   /** Add a directory of CA certificates for verification. 565   /** Add a directory of CA certificates for verification.
544   566  
545   Adds a directory of CA certificates to the trust store. The 567   Adds a directory of CA certificates to the trust store. The
546   directory is applied when the native context is first built from 568   directory is applied when the native context is first built from
547   this context. 569   this context.
548   570  
549   The expected directory layout depends on the backend. OpenSSL 571   The expected directory layout depends on the backend. OpenSSL
550   performs on-demand lookups and requires each certificate file to 572   performs on-demand lookups and requires each certificate file to
551   be named by its subject-name hash (as generated by 573   be named by its subject-name hash (as generated by
552   `openssl rehash` or `c_rehash`); WolfSSL loads every certificate 574   `openssl rehash` or `c_rehash`); WolfSSL loads every certificate
553   file in the directory. 575   file in the directory.
554   576  
555   @param path Path to the directory of CA certificates. 577   @param path Path to the directory of CA certificates.
556   578  
557   @return Success. The path is recorded and applied when the native 579   @return Success. The path is recorded and applied when the native
558   context is built; a directory that cannot be read at that time 580   context is built; a directory that cannot be read at that time
559   is skipped rather than reported here. 581   is skipped rather than reported here.
560   582  
561   @par Example 583   @par Example
562   @code 584   @code
563 - ctx.add_verify_path( "/etc/ssl/certs" ); 585 + if (auto ec = ctx.add_verify_path( "/etc/ssl/certs" ))
  586 + return;
564   @endcode 587   @endcode
565   588  
566   @see load_verify_file 589   @see load_verify_file
567   @see set_default_verify_paths 590   @see set_default_verify_paths
568   */ 591   */
569 - std::error_code add_verify_path(std::string_view path); 592 + [[nodiscard]] std::error_code add_verify_path(std::string_view path);
570   593  
571   /** Use the system default CA certificate store. 594   /** Use the system default CA certificate store.
572   595  
573   Configures the context to use the operating system's default 596   Configures the context to use the operating system's default
574   trust store for peer certificate verification. This is the 597   trust store for peer certificate verification. This is the
575   recommended approach for HTTPS clients connecting to public 598   recommended approach for HTTPS clients connecting to public
576   servers. 599   servers.
577   600  
578   The system store is loaded when the native context is first built 601   The system store is loaded when the native context is first built
579   from this context. For a verified-safe client, combine this with 602   from this context. For a verified-safe client, combine this with
580   `set_verify_mode( tls_verify_mode::peer )` and, when connecting by 603   `set_verify_mode( tls_verify_mode::peer )` and, when connecting by
581   name, `tls_stream::set_hostname()`. 604   name, `tls_stream::set_hostname()`.
582   605  
583   @return Success. The request is recorded and applied when the 606   @return Success. The request is recorded and applied when the
584   native context is built; if the system store cannot be loaded 607   native context is built; if the system store cannot be loaded
585   at that time it is skipped rather than reported here, so a 608   at that time it is skipped rather than reported here, so a
586   context that must reject unverified peers should also use 609   context that must reject unverified peers should also use
587   `set_verify_mode( tls_verify_mode::peer )`. 610   `set_verify_mode( tls_verify_mode::peer )`.
588   611  
589   @note The OpenSSL backend honors the `SSL_CERT_FILE` and 612   @note The OpenSSL backend honors the `SSL_CERT_FILE` and
590   `SSL_CERT_DIR` environment variables. The WolfSSL backend 613   `SSL_CERT_DIR` environment variables. The WolfSSL backend
591   requires a build with `WOLFSSL_SYS_CA_CERTS`; without it the 614   requires a build with `WOLFSSL_SYS_CA_CERTS`; without it the
592   system store is unavailable and this call has no effect. 615   system store is unavailable and this call has no effect.
593   616  
594   @par Example 617   @par Example
595   @code 618   @code
596   // Trust the same CAs as the system 619   // Trust the same CAs as the system
597 - ctx.set_default_verify_paths(); 620 + if (auto ec = ctx.set_default_verify_paths())
598 - ctx.set_verify_mode( tls_verify_mode::peer ); 621 + return;
  622 + if (auto ec = ctx.set_verify_mode( tls_verify_mode::peer ))
  623 + return;
599   @endcode 624   @endcode
600   625  
601   @see load_verify_file 626   @see load_verify_file
602   @see add_verify_path 627   @see add_verify_path
603   @see set_verify_mode 628   @see set_verify_mode
604   */ 629   */
605 - std::error_code set_default_verify_paths(); 630 + [[nodiscard]] std::error_code set_default_verify_paths();
606   631  
607   // 632   //
608   // Protocol Configuration 633   // Protocol Configuration
609   // 634   //
610   635  
611   /** Set the minimum TLS protocol version. 636   /** Set the minimum TLS protocol version.
612   637  
613   Connections will reject protocol versions older than this. 638   Connections will reject protocol versions older than this.
614   The default allows TLS 1.2 and newer. 639   The default allows TLS 1.2 and newer.
615   640  
616   @param v The minimum protocol version to accept. 641   @param v The minimum protocol version to accept.
617   642  
618 - @return Success, or an error if the version is not supported 643 + @return Success. The version is recorded and applied when the
619 - by the backend. 644 + native context is first built.
620   645  
621   @par Example 646   @par Example
622   @code 647   @code
623   // Require TLS 1.3 minimum 648   // Require TLS 1.3 minimum
624 - ctx.set_min_protocol_version( tls_version::tls_1_3 ); 649 + if (auto ec = ctx.set_min_protocol_version( tls_version::tls_1_3 ))
  650 + return;
625   @endcode 651   @endcode
626   652  
627   @see set_max_protocol_version 653   @see set_max_protocol_version
628   */ 654   */
629 - std::error_code set_min_protocol_version(tls_version v); 655 + [[nodiscard]] std::error_code set_min_protocol_version(tls_version v);
630   656  
631   /** Set the maximum TLS protocol version. 657   /** Set the maximum TLS protocol version.
632   658  
633   Connections will not negotiate protocol versions newer than this. 659   Connections will not negotiate protocol versions newer than this.
634   The default allows the newest supported version. 660   The default allows the newest supported version.
635   661  
636   @param v The maximum protocol version to accept. 662   @param v The maximum protocol version to accept.
637   663  
638 - @return Success, or an error if the version is not supported 664 + @return Success. The version is recorded and applied when the
639 - by the backend. 665 + native context is first built.
640   666  
641   @note On WolfSSL the ceiling is applied by selecting a 667   @note On WolfSSL the ceiling is applied by selecting a
642   version-specific method (no native set-max API exists); an 668   version-specific method (no native set-max API exists); an
643   invalid window where the minimum exceeds the maximum yields a 669   invalid window where the minimum exceeds the maximum yields a
644   context that fails the handshake. 670   context that fails the handshake.
645   671  
646   @see set_min_protocol_version 672   @see set_min_protocol_version
647   */ 673   */
648 - std::error_code set_max_protocol_version(tls_version v); 674 + [[nodiscard]] std::error_code set_max_protocol_version(tls_version v);
649   675  
650   /** Set the allowed cipher suites. 676   /** Set the allowed cipher suites.
651   677  
652   Configures which cipher suites may be used for connections. 678   Configures which cipher suites may be used for connections.
653   The format is backend-specific but typically follows OpenSSL 679   The format is backend-specific but typically follows OpenSSL
654   cipher list syntax. 680   cipher list syntax.
655   681  
656   @param ciphers The cipher suite specification string. 682   @param ciphers The cipher suite specification string.
657   683  
658 - @return Success, or an error if the cipher string is invalid. 684 + @return Success. The string is recorded and applied when the
  685 + native context is first built; an invalid cipher string
  686 + surfaces as a handshake failure.
659   687  
660   @par Example 688   @par Example
661   @code 689   @code
662   // TLS 1.2 cipher suites (OpenSSL format) 690   // TLS 1.2 cipher suites (OpenSSL format)
663 - ctx.set_ciphersuites( "ECDHE+AESGCM:ECDHE+CHACHA20" ); 691 + if (auto ec = ctx.set_ciphersuites( "ECDHE+AESGCM:ECDHE+CHACHA20" ))
  692 + return;
664   @endcode 693   @endcode
665   694  
666   @note This configures cipher suites for TLS 1.2 and below. For 695   @note This configures cipher suites for TLS 1.2 and below. For
667   TLS 1.3, use @ref set_ciphersuites_tls13. 696   TLS 1.3, use @ref set_ciphersuites_tls13.
668   */ 697   */
669 - std::error_code set_ciphersuites(std::string_view ciphers); 698 + [[nodiscard]] std::error_code set_ciphersuites(std::string_view ciphers);
670   699  
671   /** Set the allowed TLS 1.3 cipher suites. 700   /** Set the allowed TLS 1.3 cipher suites.
672   701  
673   TLS 1.3 uses a distinct, fixed set of cipher suites configured 702   TLS 1.3 uses a distinct, fixed set of cipher suites configured
674   separately from earlier versions. The format is a colon-separated 703   separately from earlier versions. The format is a colon-separated
675   list of TLS 1.3 suite names. 704   list of TLS 1.3 suite names.
676   705  
677   @param ciphers The TLS 1.3 cipher suite list. 706   @param ciphers The TLS 1.3 cipher suite list.
678   707  
679 - @return Success, or an error if the cipher string is invalid. 708 + @return Success. The string is recorded and applied when the
  709 + native context is first built; an invalid cipher string
  710 + surfaces as a handshake failure.
680   711  
681   @par Example 712   @par Example
682   @code 713   @code
683 - ctx.set_ciphersuites_tls13( 714 + if (auto ec = ctx.set_ciphersuites_tls13(
684 - "TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256" ); 715 + "TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256" ))
  716 + return;
685   @endcode 717   @endcode
686   718  
687   @note On the WolfSSL backend, TLS 1.2 and TLS 1.3 suites share a 719   @note On the WolfSSL backend, TLS 1.2 and TLS 1.3 suites share a
688   single cipher list; this call and @ref set_ciphersuites are 720   single cipher list; this call and @ref set_ciphersuites are
689   merged into one list. 721   merged into one list.
690   722  
691   @see set_ciphersuites 723   @see set_ciphersuites
692   */ 724   */
693 - std::error_code set_ciphersuites_tls13(std::string_view ciphers); 725 + [[nodiscard]] std::error_code set_ciphersuites_tls13(std::string_view ciphers);
694   726  
695   /** Set the ALPN protocol list. 727   /** Set the ALPN protocol list.
696   728  
697   Configures Application-Layer Protocol Negotiation (ALPN) for 729   Configures Application-Layer Protocol Negotiation (ALPN) for
698   the connection. ALPN is used to negotiate which application 730   the connection. ALPN is used to negotiate which application
699   protocol to use over the TLS connection (e.g., "h2" for HTTP/2, 731   protocol to use over the TLS connection (e.g., "h2" for HTTP/2,
700   "http/1.1" for HTTP/1.1). 732   "http/1.1" for HTTP/1.1).
701   733  
702   The protocols are tried in preference order (first = highest). 734   The protocols are tried in preference order (first = highest).
703   735  
704   @param protocols Ordered list of protocol identifiers. 736   @param protocols Ordered list of protocol identifiers.
705   737  
706   @return Success, or an error if ALPN configuration fails. 738   @return Success, or an error if ALPN configuration fails.
707   739  
708   @note Read the negotiated protocol after the handshake via 740   @note Read the negotiated protocol after the handshake via
709   @ref tls_stream::alpn_protocol. On WolfSSL, ALPN requires a 741   @ref tls_stream::alpn_protocol. On WolfSSL, ALPN requires a
710   build with `HAVE_ALPN`; without it, offering protocols fails 742   build with `HAVE_ALPN`; without it, offering protocols fails
711   the handshake with `std::errc::function_not_supported` rather 743   the handshake with `std::errc::function_not_supported` rather
712   than negotiate nothing silently. 744   than negotiate nothing silently.
713   745  
714   @par Example 746   @par Example
715   @code 747   @code
716   // Prefer HTTP/2, fall back to HTTP/1.1 748   // Prefer HTTP/2, fall back to HTTP/1.1
717 - ctx.set_alpn( { "h2", "http/1.1" } ); 749 + if (auto ec = ctx.set_alpn( { "h2", "http/1.1" } ))
  750 + return;
718   @endcode 751   @endcode
719   */ 752   */
720 - std::error_code set_alpn(std::initializer_list<std::string_view> protocols); 753 + [[nodiscard]] std::error_code set_alpn(std::initializer_list<std::string_view> protocols);
721   754  
722   // 755   //
723   // Certificate Verification 756   // Certificate Verification
724   // 757   //
725   758  
726   /** Set the peer certificate verification mode. 759   /** Set the peer certificate verification mode.
727   760  
728   Controls whether and how peer certificates are verified during 761   Controls whether and how peer certificates are verified during
729   the TLS handshake. 762   the TLS handshake.
730   763  
731   @param mode The verification mode to use. 764   @param mode The verification mode to use.
732   765  
733 - @return Success, or an error if the mode could not be set. 766 + @return Success. The mode is recorded and applied when the native
  767 + context is first built.
734   768  
735   @par Example 769   @par Example
736   @code 770   @code
737 - // Verify peer certificate (typical for clients) 771 + // Verify peer certificate (typical for clients; servers doing
738 - ctx.set_verify_mode( tls_verify_mode::peer ); 772 + // mTLS use tls_verify_mode::require_peer instead)
739 - 773 + if (auto ec = ctx.set_verify_mode( tls_verify_mode::peer ))
740 - // Require client certificate (server-side mTLS) 774 + return;
741 - ctx.set_verify_mode( tls_verify_mode::require_peer );  
742   @endcode 775   @endcode
743   776  
744   @see tls_verify_mode 777   @see tls_verify_mode
745   */ 778   */
746 - std::error_code set_verify_mode(tls_verify_mode mode); 779 + [[nodiscard]] std::error_code set_verify_mode(tls_verify_mode mode);
747   780  
748   /** Set the maximum certificate chain verification depth. 781   /** Set the maximum certificate chain verification depth.
749   782  
750   Limits how many intermediate certificates can appear between 783   Limits how many intermediate certificates can appear between
751   the peer certificate and a trusted root. The default is 784   the peer certificate and a trusted root. The default is
752   typically 100, which is sufficient for most certificate chains. 785   typically 100, which is sufficient for most certificate chains.
753   786  
754   @param depth Maximum number of intermediate certificates allowed. 787   @param depth Maximum number of intermediate certificates allowed.
755   788  
756 - @return Success, or an error if the depth is invalid. 789 + @return Success. The depth is recorded and applied when the native
  790 + context is first built.
757   */ 791   */
758 - std::error_code set_verify_depth(int depth); 792 + [[nodiscard]] std::error_code set_verify_depth(int depth);
759   793  
760   /** Set a custom certificate verification callback. 794   /** Set a custom certificate verification callback.
761   795  
762   Installs a callback that is invoked during certificate chain 796   Installs a callback that is invoked during certificate chain
763   verification. The callback can perform additional validation 797   verification. The callback can perform additional validation
764   beyond the standard checks and can override verification 798   beyond the standard checks and can override verification
765   results. 799   results.
766   800  
767   The callback receives the built-in verification result so far and 801   The callback receives the built-in verification result so far and
768   a verify_context describing the certificate being verified. Return 802   a verify_context describing the certificate being verified. Return
769   `true` to accept the certificate, `false` to reject. Inspect the 803   `true` to accept the certificate, `false` to reject. Inspect the
770   certificate portably via `verify_context::certificate()` (its DER 804   certificate portably via `verify_context::certificate()` (its DER
771   encoding) — for example to pin a specific certificate. 805   encoding) — for example to pin a specific certificate.
772   806  
773   @par Backend Support 807   @par Backend Support
774   808  
775   The exact set of certificates the callback sees differs by backend: 809   The exact set of certificates the callback sees differs by backend:
776   810  
777   - OpenSSL: the callback runs once per certificate in the chain, 811   - OpenSSL: the callback runs once per certificate in the chain,
778   including certificates that passed the built-in checks. It can 812   including certificates that passed the built-in checks. It can
779   therefore both relax verification (return `true` for a 813   therefore both relax verification (return `true` for a
780   certificate the library rejected) and tighten it (return `false` 814   certificate the library rejected) and tighten it (return `false`
781   for a certificate the library accepted, e.g. pinning). 815   for a certificate the library accepted, e.g. pinning).
782   - WolfSSL built with `WOLFSSL_ALWAYS_VERIFY_CB` (implied by 816   - WolfSSL built with `WOLFSSL_ALWAYS_VERIFY_CB` (implied by
783   `--enable-opensslextra`): same as OpenSSL. 817   `--enable-opensslextra`): same as OpenSSL.
784   - WolfSSL without that option: the library invokes the callback 818   - WolfSSL without that option: the library invokes the callback
785   only on verification *failure*, so it cannot be honored on a 819   only on verification *failure*, so it cannot be honored on a
786   successful handshake. To avoid silently ignoring a 820   successful handshake. To avoid silently ignoring a
787   verification-tightening callback (which would fail open), a 821   verification-tightening callback (which would fail open), a
788   context that carries a callback instead **fails the handshake** 822   context that carries a callback instead **fails the handshake**
789   with `std::errc::function_not_supported` on such a build. Rebuild 823   with `std::errc::function_not_supported` on such a build. Rebuild
790   WolfSSL with `WOLFSSL_ALWAYS_VERIFY_CB`, or omit the callback. 824   WolfSSL with `WOLFSSL_ALWAYS_VERIFY_CB`, or omit the callback.
791   825  
792   @tparam Callback A callable with signature 826   @tparam Callback A callable with signature
793   `bool( bool preverified, verify_context& ctx )`. 827   `bool( bool preverified, verify_context& ctx )`.
794   828  
795 - @param callback The verification callback. 829 + @param callback The verification callback. Recorded here and
796 - 830 + applied during the handshake; on a WolfSSL build that
797 - @return Success. The callback is recorded here and applied during the 831 + cannot honor it, the handshake fails with
798 - handshake. On a WolfSSL build that cannot honor it, the handshake 832 + `std::errc::function_not_supported` (see Backend Support).
799 - fails with `std::errc::function_not_supported` (see Backend  
800 - Support).  
801   833  
802   @par Example 834   @par Example
803   @code 835   @code
804 - ctx.set_verify_mode( tls_verify_mode::peer ); 836 + if (auto ec = ctx.set_verify_mode( tls_verify_mode::peer ))
  837 + return;
805   ctx.set_verify_callback( 838   ctx.set_verify_callback(
806   []( bool preverified, verify_context& ctx ) -> bool 839   []( bool preverified, verify_context& ctx ) -> bool
807   { 840   {
808   if( ! preverified ) 841   if( ! preverified )
809   return false; 842   return false;
810   // Pin: accept only a certificate whose DER matches. 843   // Pin: accept only a certificate whose DER matches.
811   auto der = ctx.certificate(); 844   auto der = ctx.certificate();
812   return der.size() == expected_pin.size() && 845   return der.size() == expected_pin.size() &&
813   std::equal( der.begin(), der.end(), expected_pin.begin() ); 846   std::equal( der.begin(), der.end(), expected_pin.begin() );
814   }); 847   });
815   @endcode 848   @endcode
816   849  
817   @see verify_context 850   @see verify_context
818   @see set_verify_mode 851   @see set_verify_mode
819   */ 852   */
820   template<typename Callback> 853   template<typename Callback>
821 - std::error_code set_verify_callback(Callback callback); 854 + void set_verify_callback(Callback callback);
822   855  
823   /** Set a callback for Server Name Indication (SNI). 856   /** Set a callback for Server Name Indication (SNI).
824   857  
825   For server connections, this callback is invoked during the TLS 858   For server connections, this callback is invoked during the TLS
826   handshake when a client sends an SNI extension. The callback 859   handshake when a client sends an SNI extension. The callback
827   receives the requested hostname and can accept or reject the 860   receives the requested hostname and can accept or reject the
828   connection. 861   connection.
829   862  
830   @tparam Callback A callable with signature 863   @tparam Callback A callable with signature
831   `bool( std::string_view hostname )`. 864   `bool( std::string_view hostname )`.
832   865  
833   @param callback The SNI callback. Return `true` to accept the 866   @param callback The SNI callback. Return `true` to accept the
834   connection or `false` to reject it with an alert. 867   connection or `false` to reject it with an alert.
835   868  
836   @par Example 869   @par Example
837   @code 870   @code
838   // Accept connections for specific domains only 871   // Accept connections for specific domains only
839   ctx.set_servername_callback( 872   ctx.set_servername_callback(
840   []( std::string_view hostname ) -> bool 873   []( std::string_view hostname ) -> bool
841   { 874   {
842   return hostname == "api.example.com" || 875   return hostname == "api.example.com" ||
843   hostname == "www.example.com"; 876   hostname == "www.example.com";
844   }); 877   });
845   @endcode 878   @endcode
846   879  
847   @note For virtual hosting with different certificates per hostname, 880   @note For virtual hosting with different certificates per hostname,
848   create separate contexts and select the appropriate one before 881   create separate contexts and select the appropriate one before
849   creating the TLS stream. 882   creating the TLS stream.
850   883  
851   @see tls_stream::set_hostname 884   @see tls_stream::set_hostname
852   */ 885   */
853   template<typename Callback> 886   template<typename Callback>
854   void set_servername_callback(Callback callback); 887   void set_servername_callback(Callback callback);
855   888  
856   private: 889   private:
857   void set_servername_callback_impl( 890   void set_servername_callback_impl(
858   std::function<bool(std::string_view)> callback); 891   std::function<bool(std::string_view)> callback);
859   892  
860   void set_password_callback_impl( 893   void set_password_callback_impl(
861   std::function<std::string(std::size_t, tls_password_purpose)> callback); 894   std::function<std::string(std::size_t, tls_password_purpose)> callback);
862   895  
863   void set_verify_callback_impl( 896   void set_verify_callback_impl(
864   std::function<bool(bool, verify_context&)> callback); 897   std::function<bool(bool, verify_context&)> callback);
865   898  
866   public: 899   public:
867   // 900   //
868   // Revocation Checking 901   // Revocation Checking
869   // 902   //
870   903  
871   /** Add a Certificate Revocation List from memory. 904   /** Add a Certificate Revocation List from memory.
872   905  
873   Adds a CRL to the verification store for checking whether 906   Adds a CRL to the verification store for checking whether
874   certificates have been revoked. CRLs are typically fetched 907   certificates have been revoked. CRLs are typically fetched
875   from the URLs in a certificate's CRL Distribution Points 908   from the URLs in a certificate's CRL Distribution Points
876   extension. 909   extension.
877   910  
878   @param crl The CRL data in DER or PEM format. 911   @param crl The CRL data in DER or PEM format.
879   912  
880 - @return Success, or an error if the CRL could not be parsed. 913 + @return Success. The CRL is recorded and decoded when the native
  914 + context is first built; a malformed CRL surfaces as a
  915 + handshake failure.
881   916  
882   @note CRLs are consulted only when a revocation policy is set via 917   @note CRLs are consulted only when a revocation policy is set via
883   @ref set_revocation_policy. On WolfSSL, CRL checking requires a 918   @ref set_revocation_policy. On WolfSSL, CRL checking requires a
884   build with `HAVE_CRL`; without it, supplying a CRL or a 919   build with `HAVE_CRL`; without it, supplying a CRL or a
885   revocation policy fails the handshake with 920   revocation policy fails the handshake with
886   `std::errc::function_not_supported`. 921   `std::errc::function_not_supported`.
887   922  
888   @see add_crl_file 923   @see add_crl_file
889   @see set_revocation_policy 924   @see set_revocation_policy
890   */ 925   */
891 - std::error_code add_crl(std::string_view crl); 926 + [[nodiscard]] std::error_code add_crl(std::string_view crl);
892   927  
893   /** Add a Certificate Revocation List from a file. 928   /** Add a Certificate Revocation List from a file.
894   929  
895   Adds a CRL to the verification store for checking whether 930   Adds a CRL to the verification store for checking whether
896   certificates have been revoked. 931   certificates have been revoked.
897   932  
898   @param filename Path to a CRL file (DER or PEM format). 933   @param filename Path to a CRL file (DER or PEM format).
899   934  
900 - @return Success, or an error if the file could not be read 935 + @return Success, or an error if the file could not be read. The
901 - or the CRL is invalid. 936 + CRL is decoded when the native context is first built; a
  937 + malformed CRL surfaces as a handshake failure.
902   938  
903   @note CRLs are consulted only when a revocation policy is set via 939   @note CRLs are consulted only when a revocation policy is set via
904   @ref set_revocation_policy (WolfSSL requires a `HAVE_CRL` 940   @ref set_revocation_policy (WolfSSL requires a `HAVE_CRL`
905   build). 941   build).
906   942  
907   @par Example 943   @par Example
908   @code 944   @code
909 - ctx.add_crl_file( "issuer.crl" ); 945 + if (auto ec = ctx.add_crl_file( "issuer.crl" ))
  946 + return;
910   @endcode 947   @endcode
911   948  
912   @see add_crl 949   @see add_crl
913   @see set_revocation_policy 950   @see set_revocation_policy
914   */ 951   */
915 - std::error_code add_crl_file(std::string_view filename); 952 + [[nodiscard]] std::error_code add_crl_file(std::string_view filename);
916   953  
917   /** Set the certificate revocation checking policy. 954   /** Set the certificate revocation checking policy.
918   955  
919   Controls how certificate revocation status is checked during 956   Controls how certificate revocation status is checked during
920   verification via CRLs. 957   verification via CRLs.
921   958  
922   @param policy The revocation checking policy. 959   @param policy The revocation checking policy.
923   960  
924   @par Example 961   @par Example
925   @code 962   @code
926   // Require successful revocation check 963   // Require successful revocation check
927   ctx.set_revocation_policy( tls_revocation_policy::hard_fail ); 964   ctx.set_revocation_policy( tls_revocation_policy::hard_fail );
928   965  
929   // Check but allow unknown status 966   // Check but allow unknown status
930   ctx.set_revocation_policy( tls_revocation_policy::soft_fail ); 967   ctx.set_revocation_policy( tls_revocation_policy::soft_fail );
931   @endcode 968   @endcode
932   969  
933   @note Revocation is checked via CRLs supplied with @ref add_crl / 970   @note Revocation is checked via CRLs supplied with @ref add_crl /
934   @ref add_crl_file. `soft_fail` accepts a certificate whose 971   @ref add_crl_file. `soft_fail` accepts a certificate whose
935   status cannot be determined (missing/expired CRL) but rejects 972   status cannot be determined (missing/expired CRL) but rejects
936   one that is actually revoked; `hard_fail` also rejects unknown 973   one that is actually revoked; `hard_fail` also rejects unknown
937   status. OCSP-based revocation is not available (see the TLS 974   status. OCSP-based revocation is not available (see the TLS
938   guide). On WolfSSL a non-disabled policy requires a `HAVE_CRL` 975   guide). On WolfSSL a non-disabled policy requires a `HAVE_CRL`
939   build, else the handshake fails with 976   build, else the handshake fails with
940   `std::errc::function_not_supported`. 977   `std::errc::function_not_supported`.
941   978  
942   @see tls_revocation_policy 979   @see tls_revocation_policy
943   @see add_crl 980   @see add_crl
944   */ 981   */
945   void set_revocation_policy(tls_revocation_policy policy); 982   void set_revocation_policy(tls_revocation_policy policy);
946   983  
947   // 984   //
948   // Password Handling 985   // Password Handling
949   // 986   //
950   987  
951   /** Set the password callback for encrypted keys. 988   /** Set the password callback for encrypted keys.
952   989  
953   Installs a callback that provides passwords for encrypted 990   Installs a callback that provides passwords for encrypted
954   private keys and PKCS#12 files. The callback is invoked when 991   private keys and PKCS#12 files. The callback is invoked when
955   loading encrypted key material. 992   loading encrypted key material.
956   993  
957   @tparam Callback A callable with signature 994   @tparam Callback A callable with signature
958   `std::string( std::size_t max_length, password_purpose purpose )`. 995   `std::string( std::size_t max_length, password_purpose purpose )`.
959   996  
960   @param callback The password callback. It receives the maximum 997   @param callback The password callback. It receives the maximum
961   password length and the purpose (reading or writing), and 998   password length and the purpose (reading or writing), and
962   returns the password string. 999   returns the password string.
963   1000  
964   @par Example 1001   @par Example
965   @code 1002   @code
966   ctx.set_password_callback( 1003   ctx.set_password_callback(
967   []( std::size_t max_len, tls_password_purpose purpose ) 1004   []( std::size_t max_len, tls_password_purpose purpose )
968   { 1005   {
969   // In practice, prompt user or read from secure storage 1006   // In practice, prompt user or read from secure storage
970   return std::string( "my-key-password" ); 1007   return std::string( "my-key-password" );
971   }); 1008   });
972   1009  
973   // Now load encrypted key 1010   // Now load encrypted key
974 - ctx.use_private_key_file( "encrypted.key", tls_file_format::pem ); 1011 + if (auto ec = ctx.use_private_key_file(
  1012 + "encrypted.key", tls_file_format::pem ))
  1013 + return;
975   @endcode 1014   @endcode
976   1015  
977   @see tls_password_purpose 1016   @see tls_password_purpose
978   */ 1017   */
979   template<typename Callback> 1018   template<typename Callback>
980   void set_password_callback(Callback callback); 1019   void set_password_callback(Callback callback);
981   }; 1020   };
982   #ifdef _MSC_VER 1021   #ifdef _MSC_VER
983   #pragma warning(pop) 1022   #pragma warning(pop)
984   #endif 1023   #endif
985   1024  
986   template<typename Callback> 1025   template<typename Callback>
987   void 1026   void
HITCBC 988   1 tls_context::set_servername_callback(Callback callback) 1027   1 tls_context::set_servername_callback(Callback callback)
989   { 1028   {
HITCBC 990   1 set_servername_callback_impl(std::move(callback)); 1029   1 set_servername_callback_impl(std::move(callback));
HITCBC 991   1 } 1030   1 }
992   1031  
993   template<typename Callback> 1032   template<typename Callback>
994   void 1033   void
HITCBC 995   4 tls_context::set_password_callback(Callback callback) 1034   4 tls_context::set_password_callback(Callback callback)
996   { 1035   {
HITCBC 997   4 set_password_callback_impl(std::move(callback)); 1036   4 set_password_callback_impl(std::move(callback));
HITCBC 998   4 } 1037   4 }
999   1038  
1000   template<typename Callback> 1039   template<typename Callback>
1001 - std::error_code 1040 + void
HITCBC 1002   2 tls_context::set_verify_callback(Callback callback) 1041   2 tls_context::set_verify_callback(Callback callback)
1003   { 1042   {
DCB 1004 - 2 return {};  
HITCBC 1005   2 set_verify_callback_impl(std::move(callback)); 1043   2 set_verify_callback_impl(std::move(callback));
HITGIC 1006   } 1044   2 }
1007   1045  
1008   } // namespace boost::corosio 1046   } // namespace boost::corosio
1009   1047  
1010   #endif 1048   #endif